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TRAINING REPORT ON
OIL AND NATURAL GAS CORPORATION
GAS PROCESSING PLANT HAZlRA,
SURAT (GUJARAT)
Duration: 17/05/2018-18/06/2018
Submitted to: Submitted by:
I/C Training Department, Lalit
Hazira Plant, Electrical Engineering
Oil & Natural Gas Corporation, SVNIT,
Surat, Gujarat. Surat, Gujarat

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TRAINING REPORT ON
SURAT (GUJARAT)
Duration: 17/05/2018-18/06/2018
Submitted by: Submitted To:
Patil Parth Shashikant I/C Training Department,
Chitroda Rutvij Ashokhai Hazira Plant,
Mistry Nikhilkumar Sureshbhai Oil & Natural Gas Corp. Surat,
Modi Viral Pareshkumar Gujarat.
Patel Parthkumar Arunkumar
Patel Smit Satishkumar
Vaiwala Rahul Jignesh
Electrical Engineering,
SCET,
Surat, Gujarat.

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TRAINING REPORT ON
SURAT (GUJARAT)
Duration: 17/05/2018-18/06/2018
Submitted by: Submitted To:
Naik Zeel Hemantkumar I/C Training Department
Patel Prachi Dineshbhai Hazira Plant,
Thakor Bhavya Bharatsingh Oil & Natural Gas Corp. Surat,
Gujarat.
Electrical Engineering,
C. K. Pithawalla College of
Engg. & Tech.,
Surat, Gujarat.

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ACKNOWLEDGEMENT
Industrial Training is an integral part of engineering curriculum providing
engineers with first hand and practical aspects of their studies. It gives them the
knowledge about the work and circumstances existing in the company. The
preparation of this report would not have been possible without the valuable
contribution of the ONGC family comprising of several experienced engineers
in their respective field of work. It gives me great pleasure in completing my
training at Gas Processing Plant of ONGC at Hazira and submitting the training
report for the same.
1 express my deepest gratitude to Mr. SANJAY PRAKASH SHARAN, DGM
(Mechanical) for giving us the permission for orientation in operational area
of plant. I am also thankful to Mr. A. KRISHNAN, CE(E) - CO-GEN
who supported us constantly and channelize our work toward more positive
manner.
Our sincere thanks to Mr. EKRAMUL WAHAB, Chief Engineer
(production) for continuously guiding throughout various aspect, functioning,
and processes of the plant and their effective coordination and allotting us
the appropriate schedule to undertake the training.
Also thanks to Mr.ROHIT BELWAL, Mr.RUCHIR AGRAWAL, Mr.VIJAY
AZMEERA & Mr. DEEPAK UPADHYAY for all having support , guidance at
ground level and sharing valuable technical knowledge .
A major contribution of this work would definitely be my parents who have
constantly supported me for my training in here and my friends who have
always been there as a pillar of strength.
And at last but not least we are also thankful to all the staff members of plant
for their kind cooperation and valuable guidance throughout the process of
work.

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PREFACE
In any organization success or failure of the company depend upon 4 M's i.e.
Materials, Men, Machine and Method. Today is the age of competition and an
organization cannot survive without satisfaction of its customers. Quality of
material is to be maintained in order to stand in the competitive market.
To be a perfect engineer one must be familiar with individual experience in
industrial environment. He must be aware of basic industrial problems and their
remedies.
While undergoing this type of industrial training at ONGC, Hazira, Surat
(Gujarat). I learned a lot of practical aspect. My theoretical knowledge was
exposed here practically. In this report 1 have tried to summarize what I have
learned in the ONGC plant. For preparing this report I visited the plant, referred
to the process and cleared related doubts to the responsible personal & inferred
to manuals and process reports.
This study has been primarily undertaken by me with a view to evaluate proper
working process in the organization. Born as the modest corporate house in
1956 as a commission ONGC has grown today into a full fledges integrated
upstream petroleum company with in house service capabilities and
infrastructure in the entire range of oil and gas exploration and production
activities achieving excellence over the years on the path of further growth.

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Table of contents:
1 .Overview & Basic Knowledge Of ONGC
2. Places Visited During Training
3.Production Process
4. Process Unit
5. CO-Generation Unit:
5.1 What is Co-Generation?
5.2 overview of COGEN Unit
5.3 Objectives of COGEN
5.4 Advantages of GT Based CPP
5.5 COGEN Power Efficiency
5.6 Major Systems of COGEN Plant
5.7 Gas Turbine
5.7.1 Theory of operation
5.7.2 Gas Turbine Construction Details
5.7.3 GT System & Components
5.7.4 GT Protection
5.7.5 GT Generator System
5.8 Boilers
5.8.1 Working Principle
5.8.2 Basic details of Boiler
5.9 Switchyard Rating
5.10 Two 11kV bus as SS-I
5.11 Power & Steam Demand
5.12 HRSG (Heat Recovery Steam Generator)
5.13 Power Generation
5.14 Modes of operation
5.15 Generator Protection
5.16 Benefits of COGEN

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6. Electrical Repair Workshop
6.1 UPS (Uninterrupted Power Supply)
6.1.1 UPS Applications
6.1.2 UPS Components
6.1.3 Operation Mode
6.1.4 Working Principle
6.1.5 UPS Attributes
6.1.6 UPS Topology
6.1.7 UPS Protection
6.2 Air Conditioning
6.2.1 Principle of AC
6.2.2 Process of AC Systems
6.2.3 Types of AC Systems
6.3 Lighting
6.3.1 Types of lights
6.3.2 Different Uses
6.3.3 Advantage & Disadvantage
7. Basic Knowledge at SS-4
7.1 Transformers
7.1.1 Construction of Transformers
7.1.2 Principle of Transformers
7.1.3 Protection Component of Transformer
7.1.4 Maintenances of Transformers
7.1.5 Various Testing of Transformers
7.2 Reactors
7.3 Capacitors Bank
7.4 Earthing Of Transformers
7.5 DOL
8.Safety Measures & Fire Extinguishers
9.Conclusion

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Overview & Basic knowledge of ONGC HAZIRA Plant:-
oil and gas company headquartered in Dehradun,India. It is a Public Sector
Undertaking (PSU) of the Government of India, under the administrative control
of the Ministry of Petroleum and Natural Gas.
largest oil and gas exploration and production company. It
produces around 69% of India’s crude oil (equivalent to around 30% of country’s
total demand) and around 62% of its natural gas.
(NGL), Aromatic Rich Naphtha(ARN) and Kerosene. Internationally its wholly
owned subsidiary ONGC Videsh Limited has number of existing and up-coming
interest in selected Oil patches including development of large gas field in
Vietnam offshore.
ts kind in India
and Asia’s largest gas processing facility.It is situated near Bhatpore Village ,on
Surat-Dumas Road, 18 km to the western side from Surat Railway Station.
Tapti River connecting Kuchchh track pipeline originating from the South Basin
in off shore Vasai gas fields of ONGC Mumbai and Panna,Mukta &Tapti fields
operating under joint venture.
working inside the Plant. The Plant was set up in September 1985.
and Fractionation Units. Liquefied Petroleum Gas Plant, Gas Sweetening Unit,
Unit for Gas Dehydration, Dew Point Depression. Sulphur Recovery Unit,
Kerosene recovery unit and Co-Generation Unit

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including Phase-III (A). In view
of ageing of Phase-I & Phase-II facilities (commissioned in 1988 & 1990 respectively) and likely to increase
of gas production from ONGC’s Western Offshore fields, as part of Phase-IV of expansion of Hazira Complex, ONGC
has installed Additional Gas Processing Facilities (AGPF Project).
from the Vasai, South Bassein, Heera, Panna, Mukta and other fields of the
Bombay Offshore region
.
time it was seen that there were
concentrations of sour gas coming in the line. Hence the plant was converted into a sour gas plant.
containing poisonous Hydrogen
Sulfide Gas (also known as acid gas/sour gas) in varying amount. Sour natural gas containing H2S require
special treatment for removal of the poisonous gas.
rise to production of sour LPG which requires additional treatment for making it sweet,
marketable and safe for use.
azira Gas processing complex is receiving sour natural gas from South Basin
Gas Fields which is subsea reservoir. The gas is transported from South Basin field to
HGPC through subsea pipelines.
gas and slug containing HC condensate,
moisture and chemicals (like corrosion inhibitors) are separated. Gas and associated
Condensates are sent further in separate system for processing.

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Places visited during training
• COGEN Control Room
• Gas Turbine
• Boilers , HRSG
• DM Plant
• Breakers
• Capacitor Bank in SS-4
• Electrical Repair Workshop
• UPS(Uninterruted Power Supply) Control Room
• SS-1 , SS-4, SS-7 , SS-14
• Gas Terminal Unit
• Air -Conditioning Unit
• Lighting Unit
• Battery Charging
• Transformers in SS-1 ,SS-4
• Reactors

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THE PRODUCTION PROCESS
• Theplant receives gas in 36”and42”pipelines through217kmlong submarine pipes from South Bassein to
Umbrhatand then14km long lines from Umbrhat totheGasTerminal.
• Here gas and any condensates formed are seperated. The gas goes to Gas Sweetening Unit or GSU and the
condensateissenttoCondensateFractionationUnitorCFU.
• InGSU the feed gasisfreed of hydrogensulphideandis hence“sweetened”.
• The hydrogen sulphide recovered is sent to Sulphur Recovery Unit or SRU, where it is converted into
elemental sulphur and dried into bricks.
• Commercialproductionofthesameisnotdone.Sweetgasissent toGas DehydrationUnit or GDU for removal of
any moisture.
• Productof GDUis sent to the DewPointDepressionUnit or DPDU,where the sweet and dry fuelgas is freed
anycondensates,andthen is sent for packaging and dispatch.
• Apartof sweet gas from GSU is taken within the plant and sent to the LPG recovery unitto obtain LPG and
Propane,latterbeing required to refrigeration within theplant.
• The condensate sent to the CFU is separated into Naphtha and Natural Gasoline Liquid or NGL. The former is
packedand dispatched.
• The latter is sent to Kerosene Recovery Unit or KRU where value added products like Superior Kerosene
Oil(SKO), AviationTurbineFuel(ATF) and HightSpeedDiesel(HSD)are formed.
• The LPG, SKO and ATF from CFU and KRU are passed through a Caustic Wash Unit to remove hydrogen
sulphide. Additives are added to the same beforetheir packaging anddispatch.
• A COGEN unit is also in function to fulfill plant powerrequirements.Systemsofeffluentdisposalsalongwith air,
inertgasandwatersupplyarealsosetup.
• Theoutput of the plant sustains the HBJ or Hazira-Bijapur-Jagdispur bysupplying fuel gas toGAIL.
• Other customers include IOCL,BPCL,HPCL,RIL,KRIBHCO,NTPC,ESSAR etc.

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Process units
➢ GAS TERMINALS
Itreceives&separatesourgas&associatedcondensatefrom offshore.
➢ GAS SWEETENING UNIT
RemovalofH2SfromsourgasbyselectiveabsorptioninMethylDi- Ethanol Amine.
➢ GAS DEHYDRATION UNIT
Removal of Moisture by Absorption in Tri-Ethylene Glycol.
➢ DEW POINT DEPRESSION
Removal of liquid hydocarbon by chilling to make it suitable for transportation through 2300 km long HBJ pipe
lineanyformation of hydrates
➢ CONDENSATE FRACTIONATION UNIT
FractionaldistillationofassociatedSourcondensatetoproduceLPG & NGL.
➢ L.P.G RECOVERY UNIT
Production of LPG & ARN from sweet Gas by Cryogenic Process.
➢ KEROSENE RECOVERY UNIT
Fractionation of NGL to produce Naphtha, SKO/AFT &HSD.

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DISTRIBUTION NETWORK DIAGRAM

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HGPC ELECTRICAL POWER SYSTEM:-
To feed the electricity to the entire Hazira Gas Processing Complex and the
residential townships for the employees ONGC Nagar-1, ONGC Nagar-2 and
Bachelor’s Colony at Magdalla, Surat with cumulative requirement to feed
approximate 31MW of Electrical load, ONGC HGPC is capable of generating 19.2
x 3 approx. 61.5 MW.
MW of power at full capacity from the Co-Generation Plant. This power is fed to
the various processing units by the network of the total 17 substations
consisting of more than 60 transformers throughout the palnt.
The HGPC consist various electrical devices, machines and apparatuses at
various process and utility units. These includes electrical machines like HT
motors, LT motors, EOT Cranes, Illumination and Air-conditioning utilities,
Circuit breakers(VCB), numerical relays and other minor apparatuses in large
number of amounts. The regular preventive maintenance and breakdown
maintenance is handled by Field Maintenance Group throughout the year.
Thus, Electrical Power System of HGPC is divided into three units.
1.COGEN Unit
2.Substations
3.Field Maintenance Group
Cogeneration Unit:-
What is Cogen Plant?.
The generation of Power and Steam is done simultaneously at the same time
is known as cogeneration. COGEN unit fulfills the Steam and Electricity
requirement of ONGC,HGPC. Thus is called Cogeneration Plant. And the use of
exhaust gas from gas turbine to produce steam increases its efficacy.
PRINCIPLE OF COGENERATION
Cogeneration or combined heat and power (CHP) is the use of a heat engine or
power station to simultaneously generate electricity and useful heat. Tri-
generation or Combined cooling heat and power (CCHP) refers to the
simultaneous generation of electricity and useful heating and cooling from the
combustion of a fuel or a solar heat collector.
• Cogeneration is a thermodynamically efficient use of fuel. In separate
production of electricity some energy must be discarded as waste heat
but in cogeneration this thermal energy is put to use.
Objective Of COGEN
To to the process ensure uninterrupted power supply and HP , LP & MP Steam
Maximise revenue through export of sulplus power in the form of wheeling to Mehsana
Asset & sale to state Electricity board
The COGEN unit can generate maximum of 61.5 MW of power from the 3 Generator units
coupled with the GasTurbines.

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IMPORTANT MOTORS USED IN CO-GEN PLANT
Mehsana Asset & Sale to State Electricity Board.
The COGEN unit can generate maximum of 61.5 MW of Power from the 3
Generator units coupled with the Gas Turbines. Out of all the Power generated,
approximately 28-31 MW Power is utilised within the HGPC itself. 11.2 MW of
Power is exported to Mehsana Asset through wheeling with State Electricity
Board and the rest of the surplus power is exported to the State Electricity Board
for Sale.
OVERVIEW OF COGENERATION,HGPC
In cogeneration unit we have 3 GTs
GT1 and GT2 are BRUSH make while GT3 is BHEL make
All GTs have rating as : 19.25 KW,11KV
Incoming power of GT1,2 is on 11KV Bus from there it is transmitted 11KV SS1.
After power is transferred to 11KV Bus of S/S-1 via 3 incomers eachof GT1,GT2
AND GT3(either section A or section B of 11KV S/S-1).Power is distributed to all
over the plant for process requirement ,exported to State grid after being stepped
up to 66kv,residential complex of ongc and wheeled to other ongc installations
via state grid network.
Four incomers from 11KV Bus bring power to phase 1 and 3. In phase 3 we have
415 V bus which gets power from 11 KV Bus through 2 transformers.
415 V Bus of phase 3 is called PMCC Bus and supplies power to HP pumps of
HRSG 3 Boiler and also two various local loads like station Battery Charger and
various Boilers auxiliaries.
Two incomers from SS-1 to phase1 supplies power to 11KV Cogen Bus from
where it is distributed to 2 other Buses of 6.6KV and 415V.
Two 750 KVA transformers step-down the voltage from 11KV to 6.6 KV.
Now this 6.6KV Bus is source to FD fan motors of HRSG 1 and 2.

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Load Shed Scheme of HAZIRA PLANT:-
Purpose of load shed scheme is to minimise total power blackout probability by shedding pre-defined load. This is
done under following four condition:
(1) NO GEB Condition + system frequency less than 47.55 HZ
(2) NO GT Condition : this is met when breakers of all the GTs are in off condition
(3) GEB available with only one GT condition
(4) NO GEB condition + only one GT available
Operation of GTs:
(a) Solo operation of GT:- Single GT should run in either of the two modes
1.isochronous mode
2.droop mode :part load
(b) Parallel operation of GTs without Grid
When two generators are operating in parallel one should be in
‘ISO’ mode (i.e. it will take care of load variation and will maintain the frequency at 50 Hz).
And the other GT should be in ‘droop mode’
(c) Operation of GTs with Grid
When GTs are operated in parallel with grid they have to be in
‘Droop Mode’(preselect or base load).In this mode frequency will not change.
o Most reliable & trouble free.
o Quick starting & loading time. o More compact.
o Cheaper overhauling cost.
o Quality power within minimal tolerance limit. o Flexibility in use of fuel.
o Waste heat of gas turbines used for steam generation in HRSGs. o Open cycle efficiency: 30-35%
o Combined cycle efficiency: 75-80%
o Cogeneration cycle efficiency: 50-60%.

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DEMINERALIZATION PLANT(DM WATER PLANT):-
This plant is used to remove dissolved salts from the water. When salts dissolve in water, the molecular constituents of
the salt form ions which have either positive(+) electrical charge or negative(-) electrical charge.
Ion exchange De-mineralisation is accomplished using resins that exchange one ion for another.
:
o Cat-ion exchanger: 3 numbers(80m³/hr. each)
o Weak base anion exchanger:3 numbers(80m³/hr. each)
o Strong base anion exchanger:3 numbers(80m³/hr. each)
o Degasser tower, blowers & pumps.
o Mix bed exchanger:3 numbers(80m³/hr. each)
o DM transfer pumps: 4 numbers(135m³/hr. each)
o DM water consumption:1500m³/day

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GAS TURBINE
A Gas Turbine also called a combustion turbine is a type of internal combustion engine. It has an upstream rotating
compressor coupled to a downstream turbine and a combustion chamber in between.
The basic operation of the Gas Turbine is similar to that of the steam power plant except that air is used instead of
water. Fresh atmospheric air flows through a compressor that brings it to higher pressure. Energy is added by
spraying fuel into the air and lighting it so the combustion generates a high-temperature flow. This high-temperature,
high-pressure gas enters turbine where it expands down to the exhaust pressure, producing a shaft work output in the
process. The turbine shaft work is used to drive the compressor and other devices such as electrical generator that
may be coupled to the shaft. The energy that is not used for shaft work comes out in the exhaust gases, so these have
either a high temperature or high velocity. The purpose of the gas turbine determines the design so that the most
desirable energy is maximized.
Compressor section:
-17 stage axial-flow compressor
-It consists of rotor and casing along with the inlet guide vanes and three rows of exit guide vanes.
FUNCTION -
It develops a highly compressed air with PRESSURE 8.1 Kg/cm2 and temperature of 343 Degree.
COMPRESSOR STATOR ASSEMBLY CASINGS :
-It directs the flow of outside air into the compressor.
-It consists of the inlet guide vanes, journal bearing no.1 and sealing surface to prevent bearing oil ingress.
-Inlet section of the compressor is connected to the air inlet duct to convey air into compressor zero stage.
-It consists of the compressor stages blades 0 to 3aft casing -It contains of compressor stages blades from 4 to 9.
-It contains stator blading from 10th to 16th stage and the exit guide vanes.
Bleed air from the 4th and 10th stages of the rotor is extracted for various uses like sealing, cooling
and preventing start -up surges through bleed valve.

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The Baryton cycle has more recently been give to the gas turbine engine.
PROBLEM OF START UP SURGES:
startup, the air density changes through the machine to a lesser degree than it does at full speed and
causes stalling of the compressor with reduction or virtual break down of the flow lending to start up trouble.
THEORY OF OPERATION
are described thermodynamically by the Brayton cycle in which air is compressed isentropic ally
combustion occurs at constant pressure, and expansion over the turbine occurs isentropic ally back to the starting
pressure.
In practice, friction and turbulence cause:
1. Non-isentropic compression: for a given overall pressure ratio, the compressor delivery temperature is higher than
ideal.
2. Non-isentropic expansion: although the turbine temperature drop necessary to drive the compressor is unaffected
the associated pressure ratio is greater, which decreased the expansion available to provide useful work.
3. Pressure losses in the air intake, combustor and exhaust: reduces the expansion available to provide useful
work.
efficiency. The limiting factor is the ability of the steel, nickel, ceramic or other materials that make up the engine to
withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Some turbines also
try to recover exhaust heat, which otherwise is wasted energy. Recurpertators are heat exchangers that pass exhaust
heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems and
combined heat and power (co-generation) uses waste heat for hot water production.
Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple
turbines might have one moving part: the shaft/ compressor/ turbine/ alternative-rotor assembly not counting the
fuel system. However, the required precision manufacturing for components and temperature resistant alloys
necessary for high efficiency often makes the construction of a simple turbine more complicated than piston engines.
engines) may have multiple shafts (spools),
hundreds of turbines blade top speed determines the maximum power possible independent of the size of the engine.
they have been hydrodynamic oil bearings or oil-cooled ball bearings. These bearings are being surpassed by foil
bearings, which have been successfully used in micro turbines and auxiliary power units.
This also has three components:
-A Gas compressor
-A burner (or combustion chamber) --An
expansion turbine
chamber-pressure process since the chamber is open to flow in and out.

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expanding through a turbine (or series of turbines). Some of the work
extracted by the turbine is used to drive the compressor.
Actual Brayton cycle:
– Compression
– Heat addition
– Expansion
– Heat rejection
Gas turbine construction details:
o Compressor stages :17
o Turbine stages:2
o Number of combustors:10
o Pressure ratio:10:3
o Firing temperature:963˚C
o Load gear box rating:31500KW
o Load gear design: Single helical
Gas turbine system & components:
o Starting system:
o Compressor- (17 stage, axial flow)
o Fuel gas system
o Air inlet system
-cleaning air filters
o Combustion chamber: 10 nos.
o Turbine-2 stages
o Lube oil & hydraulic oil system
o Temperature & Vibration monitoring system
o Gas/ fire detection & control system
o Accessory gear & auxiliaries
o Load gear & generator
o Water wash & line cleaning system
SPEEDTRONIK CONTROL (MK V & VI) FOR TURBINE CONTROL:
o Pre start-up checks & sequencing
o Start-up acceleration & shutdown
o Synchronising & loading of turbine
o Load & speed control
o Temperature control
o High vibration
o Over speed
o Fire detection
o High temperature

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o Loss of flame
:
o The 31.25 MVA generators have Brushless excitation system.
o Winding temperature monitoring system.
o Generator protection system.
o Rotor earth fault monitoring system.
o Synchronising circuits
o GTG 1&2 –Forced open air cooling system
o GTG 3-closed air- water cooling system
TRANSFORMER DETAILS:-
GRID TRANSFORMER 1/2
Make : VOLTAMP
MVA RATING : 25/31
HV VOLT : 66 KV
LV VOLT : 11 KV
HV AMP. : 218.69/271.8 AMP.
LV AMP. : 1312.16/1627.08 AMP.
IMP % Voltage : 10.54(ONAF)/13.02(ONAN)
COOLING : ONAN/ONAF
FREQUENCY : 50 Hz
WEIGHT OF OIL : 11500 Kg
WEIGHT OF CORE & WINDING : 21000 Kg
TOTAL WEIGHT : 49000 Kg
RATED CURRENT AT NO LOAD : 0.75 % FLRC
NO LOAD LOSS : 17.1 KW
INSULATION LEVEL : HV – 325 KVP HVN – 95 KVP
LV & LVN --75KVP
UNIT AUXILLARY TRANSFORME (3 No.)
Make : BHEL ( DRY TYPE )
RATING : 400 KVA
HV VOLT : 11 KV
LV VOLT : 433 V
HV AMP. : 21 A
LV AMP. : 533 A
COOLING : AN
FREQUENCY : 50 Hz
INSULATION CLASS : F
WEIGHT : 3600 Kg
INSULATION LEVEL : 75 KNP
IMPEDANCE % VOLTAGE : 4.5 V

24# In ONGC Hazira Plant:
-Approximate 1500 LT Motors
-Approximate 105 HT Motors
o 66 kV switchyard with:
-4 number of MOCBs
-2 number of 25/31.5 MVA, 66/11kV transformers with OLTC
-Bus PTs
-CTs
-Lightning Arrestors
-GEB Metering System
o Two GEB grid feeders with contract demand of 8MVA

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V bus at Substation-1 with:
o A Bus Coupler
o A reactor connecting both Buses
o Numerous feeders supplying the total load of HGPC through VCB
Pipes Color-Code in Plant
Grey :- Water
Yellow :- Gas
Red :- Fire water
Blue :- Instrumented Air
Green :- DM Water
DURATION OF MAINTAINENCE OF VARIOUS ELECTRICAL MACHINES:
1.LT MOTORS:ONCE IN EVERY 3 MONTHS
2.HT MOTORS:ONCE IN EVERY 6 MONTHS
3.GTS:ONCE IN EVERY 5 YEARS
4.TRANSFORMER: ONCE IN EVERY 6 MONTHS

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ELECTRICAL SYSTEM:-
11 KV cubicle of Generator is provided at the Cogen switchgear room for
Generator’s power input and consists of:
• 11 KV minimum Oil-circuit Breaker(Master Breaker)
• Fused tee-off connection suitable for connection to the unit auxiliary transformer and a parallel connection
to 11 KV Bus PT.
• Unit auxiliary transformer incomer.
• Terminating and connection of generator outgoing feeder cables.
• Bus PT for live bus incoming voltage sensing.
For supplying power to unit auxiliaries at 415V, one no. 315KVA, 11/.415KV, Delta/Star transformer has been
provided. The transformer is oil immersed type. The power tapping is taken from the 11KV system by a tee-off provision
inside the line side cubicle.
GT MCC:
This provides control of electrical auxiliaries through motor controllers. Each motor controller includes
OFF/HAND/AUTO Switch Control, Power Transformer, Control Circuit, Power Contactor, ON/STANDBY Duty Selector
Switch and Indicating Lights. Each turbine has various auxiliary motors and other auxiliary supply modules housed in
MCC. In Cogen plant each GT has a MCC module of its own. MCC receives power from two sources:
(1) UAT breaker and
(2) Section C of PCC(415 V) bus
In case if supply from UAT breaker fails or if UAT is under maintenance then, power could be harnessed from Section
C of PCC panel.GT-MCC module boxes supply of 125V DC, 110V AC, 230V AC used for various auxiliaries . 125V DC is
used for Emergency oil pump, Ratchet motor and aux. supply for GCP panel of Generator and TCP panel of turbine.
All the auxiliaries of GT have their power supply from MCC panel. E.g.-vent fans of turbine, Auxiliary Lube oil pump,
Auxiliary Hydraulic oil pump, Emergency Lube oil pump, Battery Charger supply etc.
415V PCC:
In one way or the other PCC is called the heart of the distribution system of
Cogen Plant as, it boxes all important
LT loads of the Cogen. All the pumps of Boilers (HP & LP), AC and Ventilation,
415V supply to UPS of mother substation S/S-1 etc. are all fed by PCC panel of
Cogen plant. PCC gets its incoming supply as 415V from two incoming 2 MVA Transformer each fed by 11KV from
Cogen 11KV Bus.

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Human Machine Interface (HMI)
(Human Machine Interface) The user interface in a manufacturing or process
control system. It provides a graphics-based visualization of an industrial control
and monitoring system. Previously called an "MMI" (man machine interface), an
HMI typically resides in an office-based Windows computer that communicates
with a specialized computer in the plant such as a programmable automation
controller (PAC), programmable logic controller (PLC) or distributed control
system (DCS).
Boilers
not necessarily boil (Furnace is normally used if the purpose is not actually to
boil the fluid). The heated or vaporized fluid exits the boilers for use in various
processes or heating applications.
(which are relatively new and of more capacity) and fire tube boilers (which are
relatively older and of less capacity and efficiency). Working principle of water
tube boiler is hence mentioned.
The working principle of water tube boiler: It consists of mainly 2 drums, one is
upper drum called Stream Drum other is lower drum called Mud drum. These
upper drum and lower drum are connected with two tubes namely down-comer
and riser tubes as shown in picture.
Water in the lower drum is the riser connected to it, is heated and steam is
produced in them which comes to the upper drums naturally. In the upper drum
the stream is separated from water naturally and stored above the water surface.
The colder water is fed from feed water inlet at upper drum as this water is
heavier than the other water of lower drum and that in the riser. So there is one

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conventional flow of water in the boiler system.
More and more steam is produced the pressure of the closed system increases
which obstructs this conventional flow of water and hence rate production of
steam becomes slower proportionately. Again if the steam is taken through steam
outlet, the pressure inside the system falls and consequently the conventional
flow of water becomes faster which result in faster steam production rate. In
this way the water tube boiler can control its own pressure. Hence this type of
boiler is referred as self-controlled machine.
he boiler produces steam which is used further for heating purpose in
COGEN plant.In general, As both steam and power is produced in this unit so
the name COGENERATION is given.
having high latent heat vaporization is the best medium to generate heat as it
maintains its temperature as constant till all the steam is cooled to water. This
is the main advantage of using steam for heating purposes in plant.
bine boilers and three old fire tube boilers in
plant. approximately 20MW.
pressure), and HP (High
pressure).
BASIC DETAILS OFTHE BOILER
o HRSG 1,2& KTI
boilers o HP
18.5T/Hr,37kg/cm² o
LP 105T/Hr,9kg/cm²
o HRSG-3(HP)
50T/Hr,37kg/cm² o Dumping
facility
o 04 Gas Fired Boilers(MP)
32T/Hr.
o Average power demand of 30 to
31MW
o HP Steam demand of 45-65 Ton/Hr. at 26
kg/cm²
o MP Steam demand of 60-85 Ton/Hr. at 18kg/cm²
o LP Steam demand of 140-180 Ton/Hr. at 6kg/cm²

29
Heat recovery steam generator (HRSG):-
The form and size depends on the application: mobile steam engines such as
steam locomotives, portable engines and steam powered road vehicles typically
use a smaller boiler that form an integral part of the vehicle; stationary steam
engines, industrial installations and power station will usually have a larger
separate steam generating facility connected to the point-of-use by piping. A
notable exception is the steam-powered fireless locomotive, where separately-
generated steams are transferred to a receiver (tank) on the locomotive.
heat recovery steam generator (HRSG) is an energy recovery heat exchanger
that recovers heat from a hot gas steam. It produces steam that can be used in
a process or used to drive a steam turbine. A common application for an HRSG
is in a combined-cycle power station where hot exhaust from a gasturbine is
fed to an HSRG to generate steam which in turn drives a steam turbine. This
combination produces electricity more efficiently than either the gas turbine
alone. Another application for an HRSG is in diesel engine combined cycle
power plants, where hot exhaust from a diesel engine, as primary source of
energy, is fed to an HSRG to generate steam which in turn drives a steam
turbine.
Combined cycle plant typically has a higher overall efficiency in comparison to
a Cogeneration plant. This is due to loss of energy associated with the steam
turbine.
categorized by a number of ways such as direction of
exhaust gases flow or number of pressure level. Based on the flow exhaust
gases, HRSGs are categorized into single pressure and level. Based on the flow
exhaust gases, HRSGs are categorized into vertical and horizontal types. In
horizontal type HRSGs exhaust gas flows horizontally over vertical tubes
whereas in vertical types HRSGs exhaust gas flow vertically over horizontal
tubes. Based on pressure levels, HRSGs can be categorized into single
pressure and multi pressure. Single pressure HRSGs have only steam drum
and steam is generated at single pressure level whereas multi pressure HRSGs
employ two (double pressure) or triple pressure steam drums. As such triple
pressure HRSGs consist of three sections LP section, a reheat/IP (intermediate
pressure) section. Each section has a steam drum and an evaporator section
where water is converted to steam. This steam then passes through super
heaters to raise the temperature and pressure past the saturation point.

30
POWER GENERATION:-
Grid Feeders .
.
normally GTs are synchronised with Grid. With this arrangement, following
advantages are obtained:-
1.To draw power from GEB, incase of disturbance of power from GTs.It shall
prevent / reduce possibility of blackout at the Process Complex.
2.Wheeling required power(if available at our plant) to other installations (other
assets of ONGC).
3. selling of excess power to GEB.
to some Abnormality.
tageMonit
oring
of Sudden Shortfall in Generation due

31
:
o The synchronising of all generators and the grid feeders is done at 11kV level
only.
o The generators synchronising can be done either in Auto or Manually.
o Load Shedding is done whenever there is load-generation mismatch.
o This scheme is operated by frequency sensing and no. of power source
available at a time.
o Winding Temperature Protection through RTDs.
o Overcurrent Protection.
o Voltage Restrained Overcurrent Protection
o Reverse Power Protection Stage 1 & Stage 2
o Negative Sequence Current Protection
o Under Voltage Protection
o Over Voltage Protection
o Differential Protection
o Pole slipping protection
o Loss of Field
o Under Frequency
o Turbine under speed trip.
OBJECTIVE OF PROTECTION:
The objective of power system protection is to isolate a faulty section of electrical
power system from rest of the live system so that the rest portion can function
satisfactorily without any severer damage due to fault current.
COMPONENTS OF POWER SYSTEM PROTECTION:
1.SWITCHGEAR
2.STATION BATTERY
1.SWITCH GEAR
A switchgear or electrical switchgear is a generic term which includes all the
switching devices associated with mainly power system protection. It also
includes all devices associated with control, metering and regulating of electrical
power system. Assembly of such devices in a logical manner forms switchgear.
The switchgear has to perform the function of carrying, making and breaking the
normal load current like a switch and it has to perform the function of clearing
the fault in addition to that it also has provision of metering and regulating
the various parameters of electrical power system. Thus the switchgear
includes circuit breaker, current transformer, voltage transformer, protection
relay, measuring instrument, electrical switch, electrical fuse, miniature
circuit breaker, lightning arrester or surge arrester, electrical isolator and
other associated equipment.

32
PARTS OF SWITCH GEAR
(A) CIRCUIT BREAKER
The modern power system deals with huge power network and huge numbers of
associated electrical equipments. During short circuit fault or any other types of
electrical fault these equipment as well as the power network suffer a high stress
of fault current in them which may damage the equipment and networks
permanently.
For saving these equipment and the power networks the fault current should be
cleared from the system as quickly as possible. Again after the fault is cleared,
the system must come to its normal working condition as soon as possible for
supplying reliable quality power to the receiving ends. In addition to that for
proper controlling of power system, different switching operations are required
to be performed.
So for timely disconnecting and reconnecting different parts of power system
network for protection and control, there must be some special type of switching
devices which can be operated safely under huge current carrying condition.
During interruption of huge current, there would be large arcing in between
switching contacts, so care should be taken to quench these arcs in circuit
breaker in safe manner. The circuit breaker is the special device which does all
the required switching operations during current carrying condition. This was
the basic introduction to circuit breaker.
There are different types of breaker depending upon handling of power:
(a) Oil Breaker : 1-60 KW
(b) Air Circuit Breaker : 60-160 KW
(c) Vacuum/SF6 Breaker : above 160 KW
(B) ELECTRICAL ISOLATOR
Circuit breaker always trip the circuit but open contacts of breaker cannot be
visible physically from outside of the breaker and that is why it is recommended
not to touch any electrical circuit just by switching off the circuit breaker. So for
better safety there must be some arrangement so that one can see open condition of
the section of the circuit before touching it. Isolator is a mechanical switch which
isolates a part of circuit from system as when required. Electrical isolators separate
a part of the system from rest for safe maintenance works.
(C)PROTECTION RELAY
A relay is automatic device which senses an abnormal condition of electrical
circuit and closes or opens its utility. These contacts in turns close and complete
the circuit breaker trip coil circuit hence make the circuit breaker tripped for
disconnecting the faulty portion of the electrical circuit from rest of the healthy
circuit

33
(D)LIGHTNING ARRESTOR OR SURGE ARRESTER
A surge arrester is a device to protect electrical equipment from over-voltage
transients caused by external (lightning) or internal (switching) events.
2.BATTERY STATION
All the circuit breakers of electrical power system are DC (Direct Current)
operated. Because DC power can be stored in battery and if situation comes when
total failure of incoming power occurs, still the circuit breakers can be operated
for restoring the situation by the power of storage station battery.
Hence, the battery is another essential item of the power system. Some time it is
referred as the heart of the electrical substation. An electrical substation battery or
simply a station battery containing a number of cells accumulate energy during
the period of availability of AC supply and discharge at the time when relays
operate so that relevant circuit breaker is tripped at the time failure of incoming
AC power.
Benefits of cogeneration
Provide the cogeneration is optimized in the way described above( i.e. sized
according to the heat demand), the following benefits can be obtained:
-Increased efficiency of energy conversion and use.
-Lower emissions to the environment, in particular of CO₂, the main
greenhouse gas.
process or agricultural wastes (either anaerobically digested or gratified) are
used.
the cost effectiveness and reduces the need for waste disposal. Large cost
savings, providing additional competitiveness for industrial and commercial
users while offering affordable heat for domestics’ users also.
forms of electricity
generation where plants are designed to meet the needs of local consumers,
providing high efficiency, avoiding transmission losses and increasing flexibility
in system use.
nergy carrier. An
opportunity to increase the diversity of generation plant, and provide competition
in generation. Cogeneration provides one of the most important vehicles for
promoting liberalization in energy markets.

38
UPS(uninterrupted power supply):-
n uninterruptible power supply, also uninterruptible power source, UPS or
battery/flywheel backup, is an electrical apparatus that provides emergency
power to a load when the input power source or mains power fails. A UPS differs
from an auxiliary or emergency power system or standby generator in that it will
provide near-instantaneous protection from input power interruptions, by
supplying energy stored in batteries, super capacitors, or flywheels. The on-
battery runtime of most uninterruptible power sources is relatively short (only a
few minutes) but sufficient to start a standby power source or properly shut
down the protected equipment.
telecommunication equipment or other electrical equipment where an
unexpected power disruption could cause injuries, fatalities, serious business
disruption or data loss. UPS units range in size from units designed to protect a
single computer without a video monitor (around 200 voltampere rating) to large
units powering entire data centres or buildings. The world's largest UPS, the 46-
megawatt Battery Electric Storage System (BESS), in Fairbanks, Alaska, powers
the entire city and nearby rural communities during outages.
An Uninterrupted Power Supply is employed for critical loads which cannot be
powered by utility supply (mains) directly. An UPS system protects the critical
loads from utility supply problems such as the following:
ystem:-
This unit is already a part of our installation. It distributes the Mains (utility)
and/or Generator power to your facility and will also supply input to your UPS
system. The safety “earth” connection for the UPS system is also considered to be
a part of the Mains distribution unit.

39
An Auxiliary module generally comprises a Voltage Stabilizer (static type or servo
type) to provide a stable Alternate supply to the UPS.
Consists of the UPS (without Battery).Depending upon the configuration selected,
one or more UPS modules can be employed.
This module comprises the battery pack for supplying power to the UPS module
in the event of a mains failure. There are various types of batteries- SMFB (Sealed
Maintenance Free Battery), LATB, NI-CD etc. Battery module may either be in the
form of an enclosure or may be supplied as a rack. Vented batteries such as
LATB can emit acidic fumes & requires a special room
.
odule
Output of the UPS system needs to be distributed to various loads. Such a
module generally comprises switches, fuses, etc. The coordination of fuses is
important to avoid faults from affecting the other loads supported by the UPS.
OPERATION MODE
The Modular UPS is an on-line, double-conversion UPS that permits operation in
the following mode
• Normal mode
• Battery mode
• Bypass mode
• Maintenance mode (manual bypass)
The inverter of power modules continuously supply the critical AC load. The
rectifier/charger derives power from the AC mains input source and supplies DC
power to the inverter while simultaneously FLOAT or BOOST charging its
associated backup battery.
:
Upon failure of the AC mains input power, the inverter of power modules, which
obtain power from the battery, supply the critical AC load. There is no
interruption in power to the critical load upon failure. After restoration of the AC
mains input power, the” Normal mode” operation will continue automatically
without the necessity of user intervention.
:
If the inverter overload capacity is exceeded under Normal mode, or if the inverter
becomes unavailable for any reason, the static transfer switch will perform a
transfer of the load from the inverter to the bypass source, with no interruption
in power to the critical AC load. Should the inverter be asynchronous with the
bypass, the static switch will perform a transfer of the load from the inverter to
the bypass with power interruption to the load. This is to avoid large cross
currents due to the paralleling of unsynchronized AC sources. This interruption
is programmable but typically set to be less than 3/4 of an electrical cycle, e.g.,
less than 15ms (50Hz) or less than 12.5ms (60Hz). The action of transfer/re-
transfer can also be done by the command through monitor.

40
A manual bypass switch is available to ensure continuity of supply to the critical
load when the UPS becomes unavailable e.g. during a maintenance procedure.
Working principles of ups:
The UPS consisting of four major sections:
#UPS Front panel:
Rectifier/chargersection:
phase controlled rectifiers.
The rectifiers operate according to the constant voltage current limiting principle
and shall incorporate a “Soft Start” feature to gradually accept load on initial
energizing.
prevent damage to the battery.
able of precise regulation to

41
of single phase inverter having 4 switches
Static switch:-
inverter failure the supply of power to the load will maintained automatically and
without break by connecting it to the incoming Bypass supply.
switch employs a pair of back-to-back thyristors. One set is in series
with the inverter output and another in series with Bypass supply.

42
BATTERY:
When mains fail the battery takes over the DC supply of the inverter without any
interruption. The voltage of the battery is supervised by the control card. Right
before the battery voltage reaches its end an alarm (LOW BATT) is generated.
When the battery voltage reaches its end the UPS is switched-off automatically,
to prevent an abnormal discharging of the battery. Battery is supporting the
charger in case of transient surge and dip at the inverter.
Role of battery in ups
• To provide reliable emergency DC power to the inverter when the normal power
fails or degrades.
UPS Attributes:-
• Excellent Transient Response
• High Crest Factor Load Handling Capability
• High Fuse clearing Capability
• Low Noise
• Wide Frequency Synchronization Window
• Connectivity
Ups topology:-
• Static UPS
– Single Conversion
– Double Conversion
– Delta Conversion
• Rotary UPS

43
Double conversion-
Basic element of static ups:-
UPS are available in following configuration:
- Single alone system
- Cascaded Reductant System
- Parallel Reductant System
- Split Reductant System
• RFI/EMI filter protection
• Input voltage surge protection using GMOV
• Input current spikes protection through Line chokes and Semiconductor fuses.
• Input under voltage & over voltage protection.
• Soft start feature for Charger and Inverter.
• Battery protection through current limit
• Battery reverses polarity protection.
• DC over-voltage and under voltage protection.
• Inverter Short circuit and over temperature Protection.
• Di/dt and dv/dt protection for power devices.

44
AIR CONDITIONING
The principle behind working of A.C. is same as that of refrigerator. A.C. works on the mechanism of refrigerant liquid.
Any A.C. will comprise of three parts i.e. a compressor, a condenser and an evaporator. Compressor and condenser are
usually kept outside the house where as an evaporator is kept inside the house.
Types of Air-Conditioner
There are different types of air conditioners available. Which type of the AC should be used depends upon the size of
the area which has to be cooled. The following are few types of AC used:
1. Window Air-Conditioning System
2. Split Air-Conditioning System
3. Central Air-Conditioning System
4. Package Air-Conditioning System
As there are large buildings in ONGC Hazira Plant so the most efficient cooling system which can be used for cooling
purposes are Central Air-Conditioning System as they are used for cooling of large building areas and are efficient also
as only single system have to be installed in it as compared to Split AC.
CENTRAL AIR-CONDITIONING UNIT:-
Central air conditioner unit is an energy moving or converted machines that are designed to cool or heat the entire
house. It does not create heat or cool. It just removes heat from one area, where it is undesirable, to an area where it
is less significant.
Central air conditions has a centralize duct system. The duct system (air distribution system) has an air
handler, air supply system, air return duct and the grilles and register that circulates warm air from a furnace or
cooled air from central air conditioning units to our room. It returns that air back to the system and starts again.
It uses Ac refrigerant (we may know it as Freon) as a substance to absorb the heat from indoor evaporator coils and
rejects that heat to outdoor condenser coils or vice versa.
Central air conditioner units a blower, which is mounted indoor to circulate that cold air to the entire house through air
distribution system (duct). It uses the same duct system for heating and cooling.
THE OPERATION PRINCIPLE OF CENTRAL AC:
Central air conditioner unit is simply a matter of removing heat from indoor (evaporator coil) to outdoor (condenser
unit) by using the four basic mechanical components:
The compressor, the condenser, the expansion device, the evaporator and the refrigerant copper tube that connects
these components.
If we understand how the basic refrigeration cycle works, we understand how any air conditioner units work. Since all
air conditioner units have the same basic components, refrigeration cycle and air conditioning theory.

45
BASIC MECHANICAL COMPONENTS OF CENTRAL AC:
1. COMPRESSOR:
The air conditioner compressors, located outdoor within the condenser unit is responsible for providing the pressure
difference in an air conditioner system.
The compressor pulls in low-pressure, temperature from the evaporator and compresses that gas to high-pressure,
high temperature superheats to the condenser.
2. CONDENSER:
Air conditioner condenser, it’s a square (or round) metal box located outdoor. It receives the high-pressure,
temperature vapour refrigerant from the compressor and rejects that heat to the surrounding air (medium).
As a result of condensing the hot vapour heat, the refrigerant turns to liquid.
3. EVAPORATOR:
The air conditioner evaporator, located indoor within the air handler or furnace is responsible for absorbing heat from
whatever places that needs to be cool.
4. REFRIGRANT:
Air Conditioner Refrigerant copper tube- Its copper tube that connects the compressor, the condenser, the metering
device, and the evaporator.
Once the refrigerant’s tube connects to these components, and we add refrigerant in it. It is now known as refrigeration
cycle (close- loop air conditioner units).The copper tube comes in many differences sizes, purpose and comes with an
insulator.
5. EXPANSION VALVE:
The air conditioner expansion valve (meter devices) is located indoor in the air handler or furnace. The meter devices
are near the evaporator coil which is within the air handler. It acts as a restriction. It’s responsible for providing the
correct amount of refrigerant to the evaporator coil.

46
LIGHTING
An electric lamp is a conventional light emitting component used in different circuits, mainly for lighting and
indicating purposes. The construction of lamp is quite simple, it has one filament surrounding which, a transparent
glass made spherical cover is provided. The filament of the lamp is mainly made of tungsten as it has high melting
point temperature. A lamp emits light energy as the thin small tungsten filament of lamp glows without being melted,
while current flows through it.
Types of Electric Lamps
1.incandescent lamp
2.fluorescent lamp
3.tungsten halogen lamp
4.high pressure sodium lamp
1.Incandescent lamp:
The electrical light source which works on the principle of incandescent phenomenon is called Incandescent Lamp. In
other words, the lamp works due to glowing of the filament caused by electric current through it, is called
incandescent lamp.
WORKING:
When an object is made hot, the atoms inside the object become thermally excited. If the object is not melt the outer
orbit electrons of the atoms jump to higher energy level due to the supplied energy. The electrons on these higher
energy levels are not stable they again fall back to lower energy levels. During falling from higher to lower energy levels,
the electrons release their extra energy in a form of photons. These photons then emitted from the surface of the object
in the form of electromagnetic radiation.This radiation will have different wavelengths. A portion of the wavelengths is
in the visible range of wavelengths, and a significant portion of wavelengths are in inferred range. The electromagnetic
wave with wavelengths within the range of inferred is heat energy and the electromagnetic wave with wavelengths
within visible range is light energy. Incandescent means producing visible light by heating an object. An incandescent
lamp works in the same principle. The simplest form of the artificial source of light using electricity is an incandescent
lamp. Here we use electric current to flow through a thin and fine filament to produce visible light. The current rises
the temperature of the filament to such extent that it becomes luminous.
2.FLUORESCENT LAMP:
A fluorescent lamp or a fluorescent tube is a low weight mercury vapour lamp that uses fluorescence to deliver visible
light. An electric current in the gas energizes mercury vapor which delivers ultraviolet radiation through discharge
process which causes a phosphor coating of the lamp inner wall to radiate visible light. A fluorescent lamp changes over
electrical vitality into useful light a great deal more proficiently than incandescent lamps. The normal luminous
viability of fluorescent lighting frameworks is 50-100 lumens for every watt, a few times the adequacy of incandescent
lamps with equivalent light yield.

47
WORKING:
When the switch is ON, full voltage will come across the tube light through ballast and fluorescent lamp starter. No
discharge happens initially i.e. no lumen output from the lamp.
At that full voltage first the glow discharge is established in the starter. This is because the electrodes gap in the neon
bulb of starter is much lesser than that of inside the fluorescent lamp.
Then gas inside the starter gets ionized due to this full voltage and heats the bimetallic strip that is caused to be bent
to connect to the fixed contact. Current starts flowing through the starter. Although the ionization potential of the neon
is little bit more than that of the argon but still due to small electrode gap high voltage gradient is appeared in the neon
bulb and hence glow discharge is started first in starter.
As voltage gets reduced due to the current causes a voltage drop across the inductor, the strip cools and breaks away
from the fixed contact. At that moment a large L di/dt voltage surge comes across the inductor at the time of breaking.
This high valued surge comes across the tube light electrodes and strike penning mixture (mixture argon gas and
mercury vapor).
Gas discharge process continues and current gets path to flow through the tube light gas only due to low resistance as
compared to resistance of starter.
The discharge of mercury atoms produces ultraviolet radiation which in turn excites the phosphor powder coating to
radiate visible light.
Starter gets inactive during operation of tube light.
3. TUNGSTEN HALOGEN LAMP:
a halogen gas (basically Iodine) inside the incandescent lamp. Basically, without halogen gas, incandescent lamp
filament gradually losses its performance because of its filament evaporation at higher temperature of operation.
The evaporated tungsten from the filament of normal incandescent lamp gets deposited inside the bulb surface
gradually. Thus lumens get obstructed from its way to come out from the bulb. So the efficacy i.e. lumen/watt of the
incandescent lamp goes down gradually.But the insertion of halogen gas into the incandescent lamp overcomes this
difficulty in addition to different advantages. Because this inserted halogen gas helps the evaporated tungsten to form
tungsten halide which never gets deposited on the inner bulb surface at bulb surface temperature between 500oK and
1500oK.So the lumens never face obstruction. So Lumen per watt of the lamp does not deteriorate. Again due to
insertion of pressurized halogen gas, the rate of evaporation of the filament goes down.
4. HIGH PRESSURE SODIUM LAMP:
It has an inner PCA arc tube that is filled with xenon gas. This xenon gas is used for starting purpose of the lamp as
ionization potential of xenon gas is lowest among all other inert gases used for this purpose. In addition to xenon gas
sodium mercury amalgam is present in this arc tube, too. In each end, back
wound and coated tungsten electrodes are mounted. To seal the tube monolithic seal is used instead of niobium end
cap.
The arc tube is inserted into a heat resistant outer bulb. It is supported by an end clamp that is floating. This end clamp
permits the entire structure to expand contract without distorting. The space between the tube and the bulb is a
vacuum space. This vacuum space is needed to insulate heat from the arc tube. Because it is necessary to keep the arc

48
tube at required temperature to sustain arc during normal operation.
High pressure sodium lamp has very small diameter (3/8 inch). So there is no enough space to provide any starting
electrode in the arc tube. So higher voltage is required to initiate arc. A ballast with igniter is used for this purpose.
High voltage is fed to the lamp from the ballast by using the phenomenon of superimposing a low energy high voltage
pulse. Generally a typical pulse has a peak voltage of 2500V and it has durability for only 1 microsecond only. This
high voltage pulse makes the xenon gas ionized sufficiently. Then it initiates and maintains the xenon arc. The initial
arc has sky blue color. Amalgam used in the reservoir formed inside the arc tube. It is in the back of one of the
electrodes. It is normally vaporized during lamp operation. As the xenon arc has started temperature of arc tube is
increased which first vaporizes mercury and the lamp start glowing with bluish white color. This color represents the
effect of the xenon and mercury mixture at excitation. Gradually the temperature again rises, and sodium becomes
vaporized lastly and becomes excited, a low pressure monochromatic yellow sodium spectrum results. During the
period of sodium spectral line becomes at 589 nm. With temperature the sodium pressure increases from 0.02 atm in
the monochromatic discharge to over 1 atm in the final steady state, broad spectrum condition. Also presence of
excited mercury and xenon gives bluish effect to the lamp radiation and finally pleasant golden bright light comes out.
LED:-
The pn junction diode, which is specially doped and made of special type of semiconductor, emits light when it is
forward biased is called light emitting diode.
Advantages of LED or Light Emitting Diode:
If anybody compares LEDs to other illumination methods present in the market now days it will be found that LED
lighting in by far the most saving solution. In modern era of technology, there is an up gradation from analog to digital.
You can say LED is digital light which has huge advantages over conventional analog lights. The main advantages are
briefly described below.
1.Size :-
Sizes of Light Emitting Diodes are from 3 mm to 8 mm long. The small size allows them to be used in small spaces where
tube lights cannot be used. Because of its small size, various designs can be made very simply.
2.Larger lifetime :-
This is the number one benefit of LEDs lights. As an example a high power white LEDs life time is projected to be
35,000 to 50,000 hours. Where as an incandescent bulbs life time is 750 to 2,000 hours. For compact fluorescent
bulbs, the life time is 8,000 to 10,000 hours. Actually unlike standard lighting LEDs do not burn out. They just
gradually fade.
3.Lower Temperature :-
LED's mechanism does not consists of any step to produce heat. In conventional lights, the production of heat are very
common fact. They waste most of their energy as heat. They remain cool. LED drivers are Constant Current LED drivers that
have been finely tuned to provide a precise current to the LED module that is less than what the driver is rated for. This is done as a
way to adjust light levels while minimizing heat loss.
4.Energy Efficiency :-
Light Emitting Diode is today’s most energy efficient way of lighting its energy efficiency is nearly 80% to 90% whereas
traditional lights have 20% energy efficiency, 80% is lost, as heat. More over the quality of lighting is very good.
5.Design Flexibility :-
LEDs can be merged in any shape or combination. They can be used in singly as an irony. Single LED can be operated,
resulting in a dynamic control of light. Superb lighting effects of different colors can be achieved by well designed LED
illumination system.
6.Ecologically Friendly:-
LED lights do not contain any toxic chemical. They do not leave any toxic material and 100% recyclable. Their
illuminations are close to no UV emission. The solid package of it can be designed to focus its light also.
7.Color:-
LEDs can be emit light of intended color this is done by charging the compositions of the solid state materials doping
without using any color filter.
8.On/Off Time:-
Light Emitting Diodes can be operated very quickly. They can be used in frequent on/off operation in communicate on
devices.

49
BASIC KNOWLEDGE AT SS-4:-
7.1 Transformer :-
Electrical power transformer is a static device which transforms electrical energy from one circuit to another without any direct electrical
connection and with the help of mutual induction between two windings.It transforms power from one circuit to another without changing its
frequency but may be in different voltage level.
7.1.1 Construction of Transformer :-
Basically a transformer consists of two inductive windings and a laminated steel core. The coils are insulated from each other as well as from the
steel core. A transformer may also consist of a container for winding and core assembly (called as tank), suitable bushings to take our the
terminals, oil conservator to provide oil in the transformer tank for cooling purposes etc. The figure at left illustrates the basic construction of a
transformer.
In all types of transformers, core is constructed by assembling (stacking) laminated sheets of steel, with minimum air-gap between them (to
achieve continuous magnetic path). The steel used is having high silicon content and sometimes heat treated, to provide high permeability and low
hysteresis loss. Laminated sheets of steel are used to reduce eddy current loss. The sheets are cut in the shape as E,I and L. To avoid high
reluctance at joints, laminations are stacked by alternating the sides of joint. That is, if joints of first sheet assembly are at front face, the joints of
following assemble are kept at back face.
Types Of Transformers:-
Transformers can be classified on different basis, like types of construction, types of cooling etc.
(A)On the basis of construction, transformers can be classified into two types as;
(i) Core type transformer
(ii) Shell type transformer
(I) Core Type Transformer
In core type transformer, windings are cylindrical former wound, mounted on the core limbs as shown in the figure above. The cylindrical coils
have different layers and each layer is insulated from each other. Materials like paper, cloth or mica can be used for insulation. Low voltage
windings are placed nearer to the core, as they are easier to insulate.

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(II) Shell Type Transformer
The coils are former wound and mounted in layers stacked with insulation between them. A shell type transformer may have simple rectangular
form (as shown in above fig), or it may have a distributed form.
(B) On the basis of their purpose
1. Step up transformer: Voltage increases (with subsequent decrease in current) at secondary.
2. Step down transformer: Voltage decreases (with subsequent increase in current) at secondary.
(C) On the basis of type of supply
1. Single phase transformer
2. Three phase transformer
(D) On the basis of their use
1. Power transformer: Used in transmission network, high rating
2. Distribution transformer: Used in distribution network, comparatively lower rating than that of power transformers.
3. Instrument transformer: Used in relay and protection purpose in different instruments in industries
o Current transformer (CT)
o Potential transformer (PT)
(E) On the basis of cooling employed
1. Oil-filled self cooled type
2. Oil-filled water cooled type
3. Air blast type (air cooled)
7.1.2Working Principle of Transformer:-
The working principle of transformer is very simple. It depends upon Faraday's law of electromagnetic induction. Mutual induction between two or
more winding is responsible for transformation action in an electrical transformer.
Faraday's Laws of Electromagnetic Induction
According to these Faraday's laws, "Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor
or coil".
Basic Theory of Transformer
X’mer have one winding which is supplied by an alternating electrical source. The alternating current through the winding produces a continually
changing flux or alternating flux that surrounds the winding. If any other winding is brought nearer to the previous one, obviously some portion of
this flux will link with the second. As this flux is continually changing in its amplitude and direction, there must be a change in flux linkage in the
second winding or coil. According to Faraday's law of electromagnetic induction, there must be an EMF induced in the second. If the circuit of the
later winding is closed, there must be a current flowing through it. This is the simplest form of an electrical power transformer, and this is the most
basic of working principle of transformer.
Whenever we apply alternating current to an electric coil, there will be an alternating flux surrounding that coil. Now if we bring another coil near
the first one, there will be an alternating flux linkage with that second coil. As the flux is alternating, there will be obviously a rate of change in
flux linkage with respect to time in the second coil. Naturally emf will be induced in it as per Faraday's law of electromagnetic induction. This is
the most basic concept of the theory of transformer.

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The winding which takes electrical power from the source, is known as the primary winding of a transformer. Here in our above example, it is first
winding.
The winding which gives the desired output voltage due to mutual induction in the transformer is commonly known as the secondary winding of
the transformer. Here in our example, it is second winding.
The form mentioned above of a transformer is theoretically possible but not practically, because in open air very tiny portion of the flux of the first
winding will link with second; so the current that flows through the closed circuit of later, will be so small in amount that it will be difficult to
measure.
The rate of change of flux linkage depends upon the amount of linked flux with the second winding. So, almost all flux of primary winding should
link to the secondary winding. This is effectively and efficiently done by placing one low reluctance path common to both of the winding. This low
reluctance path is core of transformer, through which the maximum number of flux produced by the primary is passed through and linked with the
secondary winding. This is the most basic theory of transformer.
7.1.3 Protection components of Transformer:-
Oil Transformer protection
The power transformer protection is realized with two different kinds of devices, namely the devices that are measuring the electrical
quantities affecting the transformer through instrument transformers and the devices that are indicating the status of the physical quantities at
the transformer itself.An example of the former could be current-based differential protection and of the latter oil temperature monitoring.
Protection Devices:-
The following discusses protection devices typically delivered as a part of the power transformer delivery.
1. Buchholz (Gas) Relay
2. Pressure Relay
3. Oil Level Monitor Device
4. Winding Thermometer
The power transformer protection as a whole and the utilization of the below presented protection devices are not discussed here.
1. Buchholz (Gas) Relay:-

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The Buchholz protection is a mechanical fault detector for electrical faults in oil-immersed transformers. The Buchholz (gas) relay is placed
in the piping between the transformer main tank and the oil conservator. The conservator pipe must be inclined slightly for reliable
operation.Often there is a bypass pipe that makes it possible to take the Buchholz relay out of service.
The Buchholz protection is a fast and sensitive fault detector. It works independent of the number of transformer windings, tap changer
position and instrument transformers. If the tap changer is of the on-tank (container) type, having its own oil enclosure with oil conservator,
there is a dedicated Buchholz relay for the tap changer.A typical Buchholz protection comprises a pivoted float (F) and a pivoted vane (V) as
shown in Figure 1. The float carries one mercury switch and the vane also carries another mercury switch. Normally, the casing is filled with oil
and the mercury switches are open.
When minor fault occurs…
Here is assumed that a minor fault occurs within the transformer. Gases produced by minor faults rise from the fault location to the top of
the transformer. Then the gas bubbles pass up the piping to the conservator. The gas bubbles will be tapped in the casing of the Buchholz
protection.This means that the gas replaces the oil in the casing. As the oil level falls, the float (F) will follow and the mercury switch tilts and
closes an alarm circuit.
When major fault occurs…
It is also assumed that a major fault, either to earth of between phases or windings, occurs within the transformer. Such faults rapidly
produce large volumes of gas (more than 50 cm3/(kWs) and oil vapor which cannot escape.They therefore produce a steep buildup of pressure
and displace oil. This sets up a rapid flow from the transformer towards the conservator. The vane (V) responds to high oil and gas flow in the
pipe to the conservator. In this case, the mercury switch closes a trip circuit. The operating time of the trip contact depends on the location of
the fault and the magnitude of the fault current.The gas accumulator relay also provides a long-term accumulation of gasses associated with
overheating of various parts of the transformer conductor and insulation systems. This will detect fault sources in their early stages and prevent
significant damage.When the transformer is first put into service, the air trapped in the windings may give unnecessary alarm signals. It is
customary to remove the air in the power transformers by vacuum treatment during the filling of the transformer tank with oil.The gas
accumulated without this treatment will, of course, be air, which can be confirmed by seeing that it is not inflammable.
2. Pressure Relay
Many power transformers with an on-tank-type tap changer have a pressure protection for the separate tap changer oil
compartment. This protection detects a sudden rate-of-increase of pressure inside the tap changer oil enclosure.
Figure shows the principle of a pressure relay.

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When the pressure in front of the piston exceeds the counter force of the spring, the piston will move operating the switching contacts. The
micro switch inside the switching unit is hermetically sealed and pressurized with nitrogen gas.The simplest form of pressure relief device is the
widely used frangible disk. The surge of oil caused by a heavy internal fault bursts the disk and allows the oil to discharge rapidly. Relieving
and limiting the pressure rise prevent explosive rupture of the tank and consequent fire.Also, if used, the separate tap changer oil enclosure can
be fitted with a pressure relief device. The pressure relief device can be fitted with contact unit(s) to provide a signal for circuit breaker(s)
tripping circuits. A drawback of the frangible disk is that the oil remaining in the tank is left exposed to the atmosphere after a rupture.
This is avoided in a more effective device, the pressure relief valve, which opens to allow the discharge of oil if the pressure exceeds the pre-
adjusted limit. If the abnormal pressure is relatively high, this spring-controlled valve can operate within a few milliseconds and provide fast
tripping when suitable contacts are fitted. The valve closes automatically as the internal pressure falls below a critical level.
3. Oil Level Monitor Device
Transformers with oil conservator(s) (expansion tank) often have an oil level monitor. Usually, the monitor has two contacts for alarm. One
contact is for maximum oil level alarm and the other contact is for minimum oil level alarm.
The top-oil thermometer has a liquid thermometer bulb in a pocket at the top of the transformer. The thermometer measures the top-oil
temperature of the transformer. The top-oil thermometer can have one to four contacts, which sequentially close at successively higher
temperature.
The figure below shows the construction of a capillary-type top-oil thermometer, where the bulb is situated in a “pocket” surrounded by oil
on top of the transformer. The bulb is connected to the measuring bellow inside the main unit via a capillary tube. The bellow moves the
indicator through mechanical linkages, resulting in the operation of the contacts at set temperatures.
The top-oil temperature may be considerably lower than the winding temperature, especially shortly after a sudden load increase. This means
that the top-oil thermometer is not an effective overheating protection.
However, where the policy towards transformers’ loss of life permits, tripping on top-oil temperature may be satisfactory. This has the
added advantage of directly monitoring the oil temperature to ensure that it does not reach the flash temperature.

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4. Winding Thermometer
The winding thermometer, shown in the figure below, responds to both the top-oil temperature and the heating effect of the load current.
The winding thermometer creates an image of the hottest part of the winding. The top-oil temperature is measured with a similar method as
introduced earlier. The measurement is further expanded with a current signal proportional to the loading current in the winding.
This current signal is taken from a current transformer located inside the bushing of that particular winding. This current is lead to a resistor
element in the main unit. This resistor heats up, and as a result of the current flowing through it, it will in its turn heat up the measurement
bellow, resulting in an increased indicator movement.
The temperature bias is proportional to the resistance of the electric heating (resistor) element.The result of the heat run provides data to
adjust the resistance and thereby the temperature bias. The bias should correspond to the difference between the hot-spot temperature and
the top-oil temperature. The time constant of the heating of the pocket should match the time constant of the heating of the winding.The
temperature sensor then measures a temperature that is equal to the winding temperature if the bias is equal to the temperature difference and
the time constants are equal.With four contacts fitted, the two lowest levels are commonly used to start fans or pumps for forced cooling, the
third level to initiate an alarm and the fourth step to trip load breakers or de-energize the transformer or both.In case a power transformer
is fitted with top-oil thermometer and winding thermometer, the latter one normally takes care of the forced cooling control.
7.1.4 Maintenance of Transformer:-
A power transformer is most costly and essential equipment of an electrical transformer. So for getting high performance and long functional life
of the transformer, it is desired to perform various maintenance activities. Not only that, a power transformer also requires various maintenance
actions including measurement and testing of different parameters of the transformer. There are mainly two types of maintenance of transformer.
We perform one group is in routine basis, and second group is as when required.
That means for getting smooth performance from a transformer we have to perform some maintenance actions in regular basis.
Some other type of maintenance of transformer we perform as when they are required. But if one performs regular maintenance properly, he
may not have any provision of performing emergency maintenance. The regular checking and maintenance of transformer is also known as
condition maintenance. Hence by proper condition maintenance one can avoid emergency and breakdown maintenance. That is why one technical
personnel should mainly concentrate on condition maintenance. As 100% condition maintenance causes 0% breakdown of an equipment. There are
many different maintenance action, to be performed on a power transformer. Some of them in yearly basis, some of them are monthly basis, some
other are quarterly, some are half-yearly basis. These are mainly transformer maintenance action, which to be performed in 3 to 4 years interval.

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Monthly Basis Maintenance of Transformer
Let us first discuss about the action to be taken on power transformer in monthly basis.
1. The oil level in oil cap under silica gel breather must be checked in one month interval. If it is found the transformer oil inside the cup
comes below the specified level, oil to be top up as per specified level.
2. Breathing holes in silica gel breather should also be checked monthly and properly cleaned if required, for proper breathing action.
3. If the transformer has oil filled bushing the oil level of transformer oil inside the bushing must be vidually checked in the oil gage attached
to those bushing. This action also to be done monthly basis.
Daily Basis Maintenance and Checking
There are three main things which to be checked on a power transformer in daily basis and they are :
1. Reading of MOG (Magnetic Oil Gage) of main tank and conservator tank.
2. Color of silica gel in breather.
3. Leakage of oil from any point of a transformer.In case of unsatisfactory oil level in the MOG, oil to be filled in transformer and also the
transformer tank to be checked for oil leakage. If oil leakage is found take required action to plug the leakage. If silica gel becomes pinkish, it
should be replaced.
Yearly Basis Transformer Maintenance Schedule
1. The auto, remote, manual function of cooling system that means, oil pumps, air fans, and other items engaged in cooling system of
transformer, along with their control circuit to be checked in the interval of one year. In the case of trouble, investigate control circuit and
physical condition of pumps and fans.
2. All the bushings of the transformer to be cleaned by soft cotton cloths yearly. During cleaning the bushing should be checked for cracking.
3. Oil condition of OLTC to be examined in every year. For that, oil sample to be taken from drain valve of divertor tank, and this collected
oil sample to be tested for dielectric strength (BDV) and moisture content (PPM). If BDV is low and PPM for moisture is found high compared
to recommended values, the oil inside the OLTC to be replaced or filtered.
4. Mechanical inspection of Buchholz relays to be carried out on yearly basis.
5. All marshalling boxes to be cleaned from inside at least once in a year. All illumination, space heaters, to be checked whether they are
functioning properly or not. If not, required maintenance action to be taken. All the terminal connections of control and relay wiring to be
checked an tighten at least once in a year.
6. All the relays, alarms and control switches along with their circuit, in R&C panel (Relay and Control Panel) and RTCC (Remote Tap
Changer Control Panel) to be cleaned by appropriate cleaning agent.
7. The pockets for OTI, WTI (Oil Temperature Indicator & Winding Temperature Indicator) on the transformer top cover to be checked and if
required oil to be replenished.
8. The proper function of Pressure Release Device and Buchholz relay must be checked annually. For that, trip contacts and alarm contacts of
the said devices are shorted by a small piece of wire, and observe whether the concerned relays in remote panel are properly working or not.
9. Insulation resistance and polarization index of transformer must be checked with battery operated megger of 5 KV range.
10. Resistive value of earth connection and rizer must be measured annually with clamp on earth resistance meter.
11. DGA or Dissolve Gas Analysis of transformer Oil should be performed, annually for 132 KV transformer, once in 2 years for the
transformer below 132 KV transformer and in 2 years interval for the transformer above 132 KV transformer.
7.1.5 Transformer Testing | Type Test and Routine Test of Transformer
For confirming the specifications and performances of an electrical power transformer it has to go through numbers of testing procedures. Some
tests are done at manufacturer premises before delivering the transformer. Mainly two types of transformer testing are done at manufacturer
premises- type test of transformer and routine test of transformer. In addition to that some transformer tests are also carried out at the
consumer site before commissioning and also periodically in regular and emergency basis through out its service life.
Type of Transformer Testing:-
Tests done at factory
1. Type tests
2. Routine tests
3. Special tests
Type tests of transformer includes
1. Transformer winding resistance measurement

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2. Transformer ratio test.
3. Transformer vector group test.
4. Measurement of impedance voltage/short circuit impedance (principal tap) and load loss (Short circuit test).
5. Measurement of no load loss and current (Open circuit test).
6. Measurement of insulation resistance.
7. Dielectric tests of transformer.
8. Temperature rise test of transformer.
9. Tests on on-load tap-changer.
10. Vacuum tests on tank and radiators.
Transformer Winding Resistance Measurement
Transformer winding resistance measurement is carried out to calculate the I2
R losses and to calculate winding temperature at the end of a
temperature rise test. It is carried out as a type test as well as routine test. It is also done at site to ensure healthiness of a transformer that is to
check loose connections, broken strands of conductor, high contact resistance in tap changers, high voltage leads and bushings etc. There are
different methods for measuring of transformer winding, likewise
(1) Current-voltage method of measurement of winding resistance.
(2) Bridge method of measurement of winding resistance.
(3) Kelvin bridge method of Measuring Winding Resistance.
(4)Measuring winding resistance by Automatic Winding Resistance Measurement Kit.
Transformer Ratio Test
The performance of a transformer largely depends upon perfection of specific turns or voltage ratio of transformer. So transformer ratio test is an
essential type test of transformer. This test also performed as routine test of transformer. So for ensuring proper performance of electrical power
transformer, voltage and turn ratio test of transformer one of the vital tests. The procedure of transformer ratio test is simple. We just apply three
phase 415 V supply to HV winding, with keeping LV winding open. The we measure the induced voltages at HV and LV terminals of transformer
to find out actual voltage ratio of transformer. We repeat the test for all tap position separately
Reactors:-
current limiting reactors can reduce short-circuit currents, which result from plant expansions and power source additions, to levels that can be
adequately handled by existing distribution equipment. They can also be used in high voltage electric power transmission grids for a similar
purpose. In the control of electric motors, current limiting reactors can be used to restrict starting current or as part of a speed control system.
Types of Electrical Reactor:-
The reactors are normally classified according to their modes of applications. Such as,
1. Shunt Reactor
2. Current Limiting and Neutral Earthing Reactor(series reactor)
3. Damping Reactor
4. Tuning Reactor
5. Earthing Transformer
6. Arc Suppression Reactor
7. Smoothing Reactor etc.
From constructional point of view the reactors re classified as:
1. Air Core Reactor
2. Gapped Iron Core Reactor
From operational point of view they can be classified as :
1. Variable Reactor
2. Fixed Reactor.
In addition to these the reactor can also be classified as
1. Indoor Type Reactor
2. Outdoor Type Reactor.

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Shunt Reactor
This reactor normally connected in parallel in the system. Normal purpose of shunt reactor is to compensate the
capacitive component of current in the system. That means, this reactor is mainly used for absorbing VAR (Reactive
Power) generated due to capacitive effect of the system. In substation, shunt reactors are connected normally
between line and ground. The VAR absorbed by the reactor can be fixed or variable depending on the system
requirement. The variation of VAR in the reactor can be achieved by using phase control thyristors or by dc
magnetizing of the iron core. This variation can also be achieved by off line or online tap changer associated with the
reactor.
Series Reactor
Current Limiting Reactor is a kind of Series Reactors. Series Reactors are connected in the system in series. They are
normally used to limit the fault current in the system or to facilitate proper load sharing in a parallel power network.
When a series reactor is connected with alternator, we refer it is Generator Line Reactor. This is to minimize the
stresses during three phase short circuit fault. Series reactor may also be connected in series in the feeder or electrical
bus to minimize the effect of short circuit fault at other parts of the system. As effect of short circuit current in that
portion of the system becomes limited, the short circuitcurrent withstand rating of the equipment and conductors of that
portion of the system can be smaller. This makes the system cost effective. When a reactor of suitable rating is
connected between neutral and earth connection of a system, to limit the line to earth current during earth fault in the
system, it is called Neutral Earthing Reactor. When acapacitor bank is switch on in uncharged condition there may be
a high inrush currentflowing through it. To limit this inrush currentreactor is connected in series with each phase of the
capacitor bank.
How it work:-
A current limiting reactor is used when the prospective short-circuit current in a distribution or transmission system is calculated to exceed
the interrupting rating of the associated switchgear. The inductive reactance is chosen to be low enough for an acceptable voltage drop during normal
operation, but high enough to restrict a short circuit to the rating of the switchgear. The amount of protection that a current limiting reactor offers depends
upon the percentage increase in impedance that it provides for the system.
The main motive of using current limiting reactors is to reduce short-circuit currents so that circuit breakers with lower short circuit breaking capacity can
be used.
Current Limiting Reactor
They can also be used to protect other system components from high current levels and to limit the inrush current when starting a large motor.
Construction:-
It is desirable that the reactor does not go into magnetic saturation during a short-circuit, so generally an air-core coil is used. At low and medium
voltages, air-insulated coils are practical; for high transmission voltages, the coils may be immersed in transformer oil. Installation of air-core coils
requires consideration of the magnetic field produced by the coils, which may induce current in large nearby metal objects. This may result in
objectionable temperature rise and waste of energy.
Active/ReactivePower Control and Capacitor Bank:-

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The demand of active power is expressing Kilo Watt (kw) or mega watt (mw). This power should be supplied from
electrical generating station. All the arrangements in electrical pomes system are done to meet up this basic
requirement. Although in alternating power system, reactive power always comes in to picture. This reactive power is
expressed in Kilo VAR or Mega VAR.
The demand of this reactive power is mainly originated from inductive load connected to the system. These inductive
loads are generally electromagnetic circuit of electric motors, electrical transformers, inductance of transmission and
distribution networks, induction furnaces, fluorescent lightings etc. This reactive power should be properly
compensated otherwise, the ratio of actual power consumed by the load, to the total power i.e. vector sum of active
and reactive power, of the system becomes quite less.
This ratio is alternatively known as electrical power factor, and fewer ratios indicates poor power factor of the system.
If the power factor of the system is poor, the ampere burden of the transmission, distribution network, transformers,
alternators and other equipments connected to the system, becomes high for required active power. And hence reactive
power compensation becomes so important. This is commonly done by capacitor bank. we know that active power is
expressed = VIcosθ
Where, cosθ is the power factor of the system. Hence, if this power factor has got
less valve, the corresponding current (I) increases for same active power P.
As the current of the system increases, the Ohmic loss of the system increases. Ohmic loss means, generated electrical
power is lost as unwanted heat originated in the system. The cross-section of the conducting parts of the system may
also have to be increased for carrying extra ampere burden, which is also not economical in the commercial point of
view. Another major disadvantage, is poor voltage regulation of the system, which mainly caused due to poor power
factor.
The equipments used to compensate reactive power. There are mainly two equipments used for
this purpose. (1) synchronous condensers
(2) Static capacitors or Capacitor Bank
1.static capacitor bank
Static capacitor can further be subdivided in to two categories,
(a) Shunt capacitors
(b) Series capacitor
These categories are mainly based on the methods of connecting capacitor bank with the
system. Among these two categories, shunt capacitors are more commonly used in the power
system of all voltage levels. There are some specific advantages of using shunt capacitors such
as,
1.It reduces line current of the system.
2.It improves voltage level of the load.
3.It also reduces system Losses.
4.It improves power factor of the source current.
5.It reduces load of the alternator.
6.It reduces capital investment per mega watt of the Load.
Where, SR – 7KVAR, 6.6KV (Series Reactor) RVT –Residual
Voltage Transformer F –Expulsion type unit fuses
Final power factor is 0.92

Earthing of Transformer:-
Need of Earthing
• The neutral earthing of transformer is used to create a neutral for the delta side (which does not have a neutral
point on its own). The reason you put a transformer in there instead of directly creating a neutral point and
grounding it, is that you get some impedance in between due to the transformer, which would limit various
imbalanced currents and fault currents to a particular value. Note that this is usually a three-phase
transformer.
• If they are used on the star side, they are usually single-phase, and connected between the neutral and ground.
You don't need a three phase device here as the neutral point already exists.
• Neutral earthing transformers are very common on large generators. They are used to limit bolted fault
currents for these machines. They essentially allow you to insert a very small resistance (1-2 ohms) with an
ampere rating of around 200A to restrict line-to-ground fault currents for the generators to around 1 - 2 A.
• The earthing protects the personnel from the shortcircuit current.
• The earthing provides the easiest path to the flow of shortcircuit current even after the failure of the
insulation.
• The earthing protects the apparatus and personnel from the high voltage surges and lightning
discharge.
Considerations are made for the selection of the grounding:
• Transient overvoltage developed.
• The Magnitude of ground-fault current as a percentage of 3-phase fault current.
• Dip in line voltage due to fault conditions.
Generally, solid grounding is used for a low-voltage system up to 600V. For voltages up to 11KV resistance
grounding is used.
Advantages of earthing :-
• There is certainly a high cost involved, so there must be some advantages.
• In fact there are two. They are: The whole electrical system is tied to the potential of the
general mass of earth and cannot 'float' at another potential. For example, we can be fairly
certain that the neutral of our supply is at, or near, zero volts (earth potential) and that the
phase conductors of our standard supply differ from earth by 240 volts
• By connecting earth to metalwork not intended to carry current (an extraneous conductive
part or a an exposed conductive part) by using a protective conductor, a path is provided for
fault current which can be detected and, if necessary, broken.
Disadvantages of earthing
• The two important disadvantages are: 1. - Cost: the provision of a complete system of
protective conductors, earth electrodes, etc. is very expensive.
• Possible safety hazard: It has been argued that complete isolation from earth will
prevent shock due to indirect contact because there is no path for the shock current to
return to the circuit if the supply earth connection is not made . This approach,
however, ignores the presence of earth leakage resistance (due to imperfect
insulation) and phase-to-earth capacitance (the insulation behaves as a dielectric).

Types of earthing:-
1. Pipe Earthing
Pipe earthing is the best form of earthing and is very cheap in cost. In this method of earthing, a galvanized and
perforated pipe of approved length and diameter is placed up right in a permanently wet soil. The size of the pipe
depends upon the current to be carried and the type of the soil. Usually the pipe used for this purpose is of diameter
38 mm and 2.5 meters in length for ordinary soil or of greater length in case of dry and rocky soil. The depth at which
the pipe must be buried depends upon the moisture of the ground. The pipe is placed at a depth of 3.75 meters
(minimum). The pipe is provided with a tapered casing at the lower end in order to facilitate the driving. The pipe at
the bottom is surrounded by broken pieces of coke to increase the effective area of the earth and to the earth and to
decrease the earth resistance respectively. Another pipe of 19 mm diameter and minimum length 1.25 meter is
connected at the top to G I pipe through reducing socket. In our country in summer the moisture in the soil decrease
which cause increase in earth resistance. So a cement concrete work, is done in order to keep the water
arrangement accessible, and in summer to have an effective earth, 3 or 4 buckets of water are put through the
funnel connected to 19 mm diameter pipe, which is further connected to G I pipe. The earth wire (either G I wire or
G I Strip of sufficient cross section to carry faulty current safely) is carried in a G I pipe of diameter 13 mm at a depth
of about 60 mm from the ground). Care should be taken that earth wire is well protected from mechanical injury,
when it is carried over from one machine to another.
2. Plate Earthing

In plate earthing an earthing plate either of copper of dimensions 60 cm x 60 cm x 3 mm or of galvanized iron
of dimensions 60 cm x 60 cm x 6 mm is buried into the ground with its face vertical at a depth of not less than
3 meters from ground level. The earth plate is embedded in alternate layers of coke and salt for a minimum
thickness of 15 cm. The earth wire (G I wire for G I plate earthing and copper wire for copper plate earthing) is
securely bolted to an earth plate with the help of a bolt, nut and washer made of material of that of earth plate
(made of copper in case of copper plate earthing and of galvanized iron in case of G I plate earthing). A small
masonry brick wall enclosure with a cast iron cover on top or an R C C pipe round the earth plate is provided
to facilitate its identification and for carrying out periodical inspection and tests. For smaller installations G I
pipe earthing is used and for larger stations and transmission lines, where the fault current, likely to be high,
plate earthing is used.
3. Rod Earthing
In this system of earthing 12.5 mm diameter solid rod of copper or 16 mm diameter solid rod of galvanized iron or steel; or
hollow section 25 mm G I pipes of length not less than 2.5 meters are driven vertically into the earth either manually or by
pneumatic hammer. In order to increase the embedded length of electrodes under the ground, which is sometimes necessary
to reduce the earth resistance to desired value, more than one rod sections are hammered on above the other. This system of
earthing is suitable for areas which are sandy in character. This system of earthing is very cheap as no excavation work is
involved.
4. System Earthing
1.One designated terminal of the secondary of each potential current and auxiliary transformer shall be
connected to the main earthing ring by means of two separate and distinct connections made with 50 mm x
6mm GI flat
.
5. Equipment Earthing
• All masts, structures, fencing uprights and all outdoor equipment pedestals including auxiliary
transformer tank shall be connected to the earthing ring by means of two separate and distinct
connections made with 50mm x 6mm GI flat.
• All fencing panels shall be connected to the supporting uprights by means of two separate and distinct
connections made with 6 SWG G.I. wire. All the metallic door panels shall be connected to the
supporting uprights by means of two separate and distinct connections made with 6 SWG G.I. wire.
2.10.3.2
• The metal casing of potential and current transformers shall be connected to the mast/ structures by
means of two separate and distinct connections made with 50mm x 6mm GI flat. 2.10.3.3 The ground
terminal of lightning arrester shall be connected directly to the earth electrodes by means of two
separate and distinct connections made with 50mm x 6mm GI flat.
• The earth electrode shall be so placed that the earthing leads from the lightning arrester may be
brought to the earth electrodes by as short and straight a path as possible.

6. EarthingThroughWaterMains
In this type of earthing the GI or copper wire are connected to the water mains with the help of the steel binding wire
which is fixed on copper lead as shown below.
The water pipe is made up of metal, and it is placed below the surface of the ground, i.e. directly connected to earth.
The fault current flow through the GI or copper wire is directly get earthed through the water pipe.
Applications of Earthing
o Transformer Earthing transformers are widely used in three phase power system networks.
Proper grounding in the power source is preferred in several applications, as this provides
additional safety for the equipments connected with the network and for the operator also.
o These transformers are effectively provide an easy low resistance path for the fault current,
during the period of earth fault. Additionally they are used to hold the neutral shift within an
proper limiting range. Grounding transformers are used to generate an artificial neutral point for
ungrounded three phase system, like three phase delta connected system.
o The zigzag connection of the transformer helps to derive a common neutral point which is
further grounded via series current limiting reactor. In this way, the three phase system is able to
provide both single phase (line to ground) and three phase (line to line) power easily. This
ensures the profitable operation of power system networks.
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