Design of a generating substation with the description of designing a transformer. Here we show some basic components of a substation. and we also show the parameters and calculation to design a transformer of a specific ratings.
CCS335 _ Neural Networks and Deep Learning Laboratory_Lab Complete Record
Design of substation
1.
2. INTRODUCTION
A substation is a part of an electrical generation, transmission,
and distribution system.
Substations are important components of the electrical
infrastructure required to keep reliable electricity available for
customers.
The main functions are to receive energy transmitted at high
voltage from the generating station , reduce the voltage to a
value appropriate for local distribution and provide facilities
for switching.
3. Classifications of Sub-station
On basis of Nature of duties
Step-up or Primary Substation
Primary Grid Substation
Step-down Substation
On basis of importance
Grid Substation
Town Substation
On basis of design
Indoor type Substation
Outdoor type Substation
o Pole mounted Substation
o Foundation mounded Substation
On basis of Service Rendered
Transformer Substation
Switching Substation
Converting Substation
On basis of Operating Voltage
High Voltage Substation
Extra High Voltage Substation
Ultra- High Voltage Substation
4. STEPS OF DESIGNING A SUBSTATION
Step-1 : Selection of a substation switching system
Step-2 : Preparation of a key plan which should show the location of all components
of a substation and their interconnections
Step-3 : Selection and ordering of equipment
Step-4 : Engineering support for licensing and permitting
Step-5 : Civil and structural design
Step-6 : Electrical layout design
Step-7 : Control design
Step-8 : Construction support
8. TRANSFORMER
A transformer is an electrical device that transfers electrical energy
from one coil called primary coil to other coil secondary coil
through electromagnetic induction .
Transformers are classified into two types based on the conversion
of voltage level. These are step-up and step-down transformer.
Different transformer used in generating substation
Generator Transformer
Station Transformer
Unit Auxiliary Transformer
Instrument Transformer
18. POTENTIAL TRANSFORMER
Used to step-down high voltage to lower voltage level in order to make
measurement easy and optimized.
Primary winding having higher number of turns connected to high voltage
side.
Voltmeter has very high resistance thus, PT behaves as an transformer
operating on no load.
Since load is low so, VA rating of PT is low in range of 50 to 200 VA.
One end of secondary is connected to the ground for safety reasons
19. CURRENT TRANSFORMER
Used to step-down high current to lower current level in order to make measurement
easy.
Primary winding having lower number of turns connected to high current side.
Secondary winding having higher number of turns connected to measuring
instrument.
Secondary should not be open-circuit ,to protect high voltage across terminals.
The current error is due to the watt loss component of the excitation current .
The phase angle error is proportional to the reactive component Ir.
The ratio error can be corrected by an amendment to the turns ratio,
20. RELAY
Relay is the device that open or closes the contacts to cause the operation of the
other electric control
Gives the commands to the circuit breaker on fault detection.
There are two configurations NO(normally open) and NC(normally closed).
TSM(time setting multiplier) is used to vary response time of relay.
PSM(plug setting multiplier) is used to set the pick up current level of the
relay.
Rotating disc is placed on bearings called jewel bearing to decrease friction
21. CIRCUIT BREAKER
Used to open the circuit carrying current, based on relay
signal.
Circuit breaker rating is selected based on most severe fault
(LLG).
In order to quench arc proper arc quenching medium and
designs are used.
Types:
• SF-6 – Sulphur Hexa Flouride Breakers (36 kV to 765 kV) very
good arc quenching as well as insulating properties which make
it ideally suitable for use in a circuit breaker.
• Vacuum circuit breakers(up to 33 kV)- Consists of small
cylinder enclosing the moving contacts under a high vacuum.
• Air Blast Circuit Breaker 11 to 1100 KV
22. SELECTION CRITERION OF RELAYS &
CIRCUIT BREAKER
Specifications of Relay
Coil Resistance
Coil voltage
Carry current
Maximum switch Current
Maximum switch Voltage
Release Time
Thermal Emf
Life Expectancy
Specifications of Circuit Breaker:
Making Capacity
Breaking Capacity
Rated Voltage
Rated Current
Rated Frequency
Operating Duty
Short circuit Current
23. INSULATORS
Insulators are used to protect current carrying wires from human contact and natural
corrosion.
Insulator has to withstand the potential stresses between conductor and earth.
The shortest distance between conductor and earth, surrounding the insulator body is known as
flashover distance.
Types:
• Pin Insulator ( up to 33 kV )
• Post Insulator
• Suspension Insulator-
• Strain Insulator
• Stay Insulator
• Shackle Insulator
Pin type Post type Suspension type
Shackle type Strain type Stay type
24. ISOLATORS
Isolators are used to remove a part of the line for maintenance purpose.
Isolators work on no load i.e. current flowing through them during operation in zero.
Isolators are generally used on both side of the circuit breaker.
Types of isolators-
• Single Break Isolator- Only one terminal connects and disconnects
• Double Break Isolator- Has locking mechanism
• Pantograph Isolator- Works on forces of stress or tension, and usually no locking
mechanism is present .
Isolator can be used to connect a auxiliary line when main line is under maintenance.
25. LIGHTNING ARRESTER
Lightning arrester are used for protection from lightning and
switching surge.
Lightening leads to very high voltage which can cause insulator
breakdown.
Any transient wave with a voltage peak exceeding the spark over
voltage must cause it to break down.
The breakdown current is passed to ground by the arrester.
Lightning arrester are placed close to the equipment that is to be
protect.
26. COMMON BUS CONFIGURATION
SINGLE BUS
Consist of one main bus which is energized all the time and to which all circuits are connected.
SECTIONALIZED BUS
This arrangement is basically two or more single bus schemes, each tied together with bus
sectionalizing breakers.
MAIN AND TRANSFER BUS
consists of two independent buses, one of which, the main bus, is normally energized. Under normal
operating conditions, all incoming and outgoing circuits are fed from the main bus through their
associated circuit breakers and switches.
27. COMMON BUS CONFIGURATION
RING BUS
A ring bus configuration is an extension of the sectionalized bus arrangement and is accomplished by
interconnecting the two open ends of the buses through another sectionalizing breaker.
BREAKER-AND-A-HALF
In this arrangement, three circuit breakers are used for two independent circuits; hence, each circuit
shares the common center circuit breaker, so there are one- and-a-half circuit breakers per circuit.
DOUBLE BREAKER–DOUBLE BUS
In the double breaker–double bus configuration, any circuit breaker can be removed from
service without interruption of any circuits. Faults on either of the main buses cause no circuit
interruptions. Circuit breaker failure results in the loss of only one circuit.
28. LOAD FLOW STUDY- THE NECESSITY
AND IMPORTANCE
A power system being an electric network model involving complex powers rather than impedances, the direct analysis of the
circuit is not possible. So, we use power flow study to plan and design the future expansion of power systems and optimize the
operation of existing systems.
Load Flow study provides information such as magnitude and phase angle of voltage at each bus and the real and reactive power
flowing in each line
Once we know the four quantities (P,Q,V,𝛿) for a particular bus in a power system network, we can proceed to calculate line flows
and losses occurring in between the lines connecting the buses.
Hence, the data obtained from load flow study can be used for economic scheduling of generators, finding steady state value,
plotting voltage profile of the system and for future expansion of the power system importantly.
Moreover algorithms can be developed for such computations making calculations much less troublesome, accurate and fast.
Accordingly, Gauss Seidel and Newton Raphson have come out on top as the most preferred formulations.
29. Conclusion
Substation is the heart of the electric power system, so the design should be
such that it provides continuous, quality and desired power at the distribution
end with least voltage drop. Moreover, substation design demands the most
careful attention to detail in power system due to the fact that they are operate
in the open at very high voltages (not usually lesser than kV) and involve
electromagnetic fields of considerable strength which may have detrimental and
hazardous effects on the surroundings if not taken care of properly.
1>Apart from being a gas, it is noninflammable, non-poisonous and odourless. When arcing takes place through the gas, some by-products are produced due to breakdown of the gas. These by-products are a hazard to the health of the maintenance personnel therefore should be properly taken care of.
2>The only disadvantage of using SF6 to some extent is suffocation. In case of leakage in the breaker tank, this gas, being heavier than air settles in the surroundings and may lead to suffocation of the operating personnel. However, it is non-poisonous.
1>at the first current zero, dielectric strength across the contacts builds up at a very much higher rate than that obtained with conventional circuit breakers
2>High vacuum gap recovers most of its dielectric strength within 10 micro seconds. The arc products are immediately forced to quickly extinguished. It is almost maintenance free switchgear.
3>small size of the breaker allows significant savings in space and material compared to earlier designs employing air magnetic technology
When the insulator is wet, its outer surface becomes almost conducting. Hence the flashover distance of insulator is decreased. The design of an electrical insulator should be such that the decrease of flashover distance is minimum when the insulator is wet. That is why the uppermost petticoat of a pin insulator has umbrella type designed so that it can protect, the rest lower part of the insulator from the rain. The upper surface of the topmost petticoat is inclined as less as possible to maintain maximum flashover voltage during raining.
The rain sheds are made in such a way that they should not disturb the voltage distribution. They are so designed that their subsurface at a right angle to the electromagnetic lines of force.
Suspension Insulator-Each suspension disc is designed for normal voltage rating 11KV
Strain Insulator-Suspension string is used to for high tensile load of conductor
1>Isolators separate a certain circuit from the electricity mains and discharge any residual current, left in the circuit, to the ground
2>Since CB contacts are not physically visible to maintenance workers(mostly installed remotely), thus isolators are used for further safety.
1>Separate earth should be provided for each LAs. LA ground leads should not be connected to the station earth bus.
2>Arresters are installed both on the High Voltage and Low Voltage side of the transformers
