Modelling Guide for Timber Structures - FPInnovations
DISTRIBUTION SYSTEM OPERATION AND CONTROL
1. ELECTRICAL POWER STREAM
Study on Distribution system operation and
control
by
Yohannes Feleke
Yohannes Getahun
ADVISOR PROFESSOR N.P.SINGH
2016
2. Objectives
General objectives:
• The general objective of this project is to study and understand operation
and control of distribution systems under normal operating conditions.
Specific objectives:
The specific objectives are: -
• To understand the basic structure of a distribution system and study
operation of different components of the distribution system.
• To analyze the operation of those components under normal and faulty
condition.
3. ELECTRICAL POWER SYSTEM OVERVIEW
Generating Sources: Generating sources consist mostly of synchronous
generators driven by steam, gas, or hydro turbines. Energy is delivered to the
transmission system through a step-up transformer.
Transmission System: The transmission system consists of separate
successive networks servicing the same geographical area. These networks operate
at different voltages and are tied together at substations. The transmission network
also serves to integrate neighboring power systems with the underlying system
through interconnections.
Distribution System: The distribution system is similar in structure to the
transmission system, however, each network covers a much Smaller geographical
area. The distribution system also provides service to individual customers, rather
than providing service to other systems
5. Substations
Substations are key parts of electrical generation, transmission, and distribution systems.
Substations transform voltage from high to low or from low to high as necessary. Substations
also dispatch electric power from generating stations to consumption centers. Electric power
may flow through several substations between the generating plant and the consumer, and
the voltage may be changed in several steps. Substations can be generally divided into three
major types:
Transmission substations :transmission lines operate at voltages above 138 kV.
Sub-transmission substations :Typically operate at 34.5 kV through 138 kV voltage levels
Distribution substations : Typically operate at 2.4–34.5 kV voltage levels
8. Operation of Distribution Systems
Distribution systems serve as the link from the distribution substation to the
customer. This system provides the safe and reliable transfer of electric
energy to various customers throughout the service territory.
(1)Supply Line (132kv)
11. LIGHTNING ARRESTOR
• A lightning arrester is a device used on electrical power systems to protect
the insulation on the system from the damaging effect of lightning.
• The typical lightning arrester also known as surge arrester has a high
voltage terminal and a ground terminal.
• Current from the surge is diverted around the protected insulation in most
cases to earth.
12. • CVT(Capacitor Voltage Transformer)
o To step down extra high voltage signals and provide a low voltage .
o For measurement or to operate a protective relay.
13. • EARTHING SWITCH
•Earth Switch is used to discharge the
voltage on the circuit to the earth for
safety.
•Earth switch is mounted on the frame
of the isolators.
•It is located for each incomer
distribution line and each side of the
busbar section.
14. LINE TRAP (WAVE TRAP)
Connected in series with the power (transmission) line.
It blocks the high frequency carrier waves (24 KHz to 500 KHz) and let
power waves (50 Hz - 60 Hz) to pass through.
It is basically an inductor of rating in Milli henry (approx 1 milli Henry
for 220 KV 1250 Amp.).
It has three main components:-
1. Main coil.
2. Tuning Device.
3. Lightning Arrestor.
15. ISOLATOR
• Disconnector or Isolator switch is used to make sure that an electrical circuit can be completely
de-energised for service or maintenance.
•These isolator are manually, remotely, or automatically operated.
Isolators
16. • CURRENT TRANSFORMER
Current transformers are used for Stepping down current for
measurement, protection and control.
Ratio: The CT is typically described by its current ratio from primary to
secondary. A 1000:5 CT would provide an output current of 5 amperes when
1000 amperes are passing through its primary winding. Standard secondary
current ratings are 5 amperes or 1 ampere, compatible with standard
measuring instruments.
• Bella substation have 600:1 for five feeders and 150:1
for one feeder.
17. Switching Apparatus
Switching apparatus is needed to connect or disconnect elements of the
power system to or from other elements of the system. Switching apparatus
includes switches, fuses, circuit breakers, and service protectors.
(a)Switches: Distribution switches are used to disconnect various parts of the
system from the feeder. These switches are manually, remotely, or
automatically operated. Typically, switches are designed to break load
current but not fault current and are used in underground circuits or tie
switches.
Switches are used for isolation, load interruption, and transferring service
between different sources of supply.
18. B) CIRCUIT BREAKERS
A Circuit breaker is an automatically operated electrical switch designed to
protect an electrical circuit from damage caused by overload or short circuit. Its
basic function is to detect a fault condition and, by interrupting continuity, to
immediately discontinue electrical flow.
All circuit breakers have common features in their operation, although details vary
substantially depending on the voltage class, current rating and type of the circuit
breaker.
Once a fault is detected, contacts within the circuit breaker must open to interrupt
the circuit.
Different techniques are used to extinguish the arc
: Lengthening / deflection of the arc
: Intensive cooling (in jet chambers)
: Division into partial arcs
: Connecting capacitors in parallel with contacts in DC circuits
20. c) Fuses:
These are standard devices used to protect portions of the circuit when a
breaker is too expensive or too large. Fuses can be used to protect single-
phase laterals off the feeder or to protect three-phase underground circuits.
The substation us fuse for250KVA auxiliary transformer instead of CB.
21. BUSBAR
SINGLE BUS WITH BUS SECTIONALISER(BELLA)
Busbars receive power from incoming circuits and deliver power to outgoing
circuits.
Advantages:
1. One complete section can be taken out for Maintenance
without disturbing the continuity of other section.
2. If a fault occurs on one section of the Bus, that faulty section
alone will be isolated.
Disadvantages:
It will be a little more costly with the addition of one isolator and some cases with
Circuit breaker, C.Ts and C&R panel.
22. POWER TRANSFORMERS
“step down” supply line voltage to distribution level voltage.
Distribution substations usually employ three-phase transformers.
For reliability and maintenance purposes, two transformers are typically
employed at the substation.
Bella SUBSTATION have two power transformers they are operated in
parallel.(132/15kv)
23. Transformer H.V. and L.V. Side Control Panel
(TR.FEEDER-1 parallel with TR.FEEDER-2).
R
S
T
TWO POWER TRANSOFRMER (20/25MVA)
One 250KVA auxiliary transformer are
there for inside(substation)activities.
24. Outgoing Feeders
Six number of outgoing feeders are connected to the substation bus to carry
power from the substation to points of service. Feeders can be run overhead
along streets, or beneath streets, and carry power to distribution transformers
at or near consumer premises.
Feeder1…………… bella-abuare-kashazchis
Feeder2…………… Bella-kebena-megenagna
Feeder3……………. Bella-menilik hospital-betemengst
Fedder4……………... Bella -Ferencay
Feeder5……………… bella-6Killo-piasa
Feeder6……………… us embassy
25. 6 outgoing feeders 5 of them have
600:1current ratio and one 150:1 CT
Feeder panel(bella-6Killo-paisa)
26. Under faulty condition
• A number of outgoing feeders are connected to the substation bus to carry
power from the substation to points of service. Feeders can be run overhead
along streets, or beneath streets, and carry power to distribution
transformers at or near consumer premises. The feeders’ breaker and
isolator are part of the substation low-voltage switchgear and are typically
the metal-clad type. When a fault occurs on the feeder, the protection will
detect it and open the breaker. After detection, either automatically or
manually, there may be one or more attempts to reenergize the feeder. If the
fault is transient, the feeder will be reenergized and the breaker will remain
closed. If the fault is permanent, the breaker will remain open and operating
personnel will locate and isolate the faulted section of the feeder.
27. CONTROL
Bella substation
Whenever there is a tripping of feeder, the shift engineer available at
respective sub- station refers the relay action, reset the relay and takes the
test charge. If the feeder is again tripped then he informs the same to
emergency team of that area for isolation and rectification of the faults.
Then this emergency team inspects all the sections of the feeder and
locates the fault. Then the team makes an arrangement for repairs of the
faults.
28. SCADA
SCADA stands for Supervisory Control And Data Acquisition.
It is a purely software package that is positioned on top of hardware to
which it is interfaced. ( via Programmable Logic Controllers(PLCs)) .
29. RESULTS
Bella SUBSTATION STRENGTHS
• Substation are maintained in very good hygiene.
• All required protections are in service for Most of the Power Transformer.
• All OLTC are electrically operable through AVR in most of the substations.
• All Power Transformers are provided with NGT (Neutral grounding transformer).
• Mostly Numerical relays are provided for protections.
• Earthing of Equipment’s in good condition.
• Shift Engineers is competent enough to handle all substation operations.
• Operational reports are regularly maintained in Hard Copy.
• Station battery is in good condition.
30. Network Reliability – Operations
• The Power transformers are fed by Single Radial Feeder and the Power
Transformers are running parallel.
• The six 15kV Feeders originating from different breaker.
• CT Ratio is not standardized.
• SCADA is not functional at substation.
• Meters & relays are automated/communicated.
• Reports analysis is missing.
• 15kV Single Line diagram is missing/ not updated.
• Load shedding observed at 15kV feeder Level due to loading constraints.
31. Network Reliability – control Maintenance
• There is Power transformer Schedule maintenance.
• Relay Maintenance process needs improvement.
• Wave trap Maintenance process needs improvement
• PLC is not working
Network Quality
• Feeders and Power Transformer reading shows Low Power factor < .90
34. Moving Average Method:
We used this method for the reason that it is trend and smoothing techniques for the accurate and
short term forecasting.
-4
-2
0
2
4
6
8
10
12
12:00 2:00 4:00 6:00 8:00 10:00 12:00 2:00 4:00 6:00 8:00 10:00
LOAD(MW)
TIME(HR)
monday actual and forecasted load
Forcaste load (MW) Actual load (MW) ERROR
36. Whenever there is a tripping of feeder, the shift engineer available at
respective sub- station refers the relay action, reset the relay and takes the
test charge. If the feeder is again tripped then he informs the same to
emergency team of that area for isolation and rectification of the faults. Then
this emergency team inspects all the sections of the feeder and locates the
fault. Then the team makes an arrangement for repairs of the faults. Till that
time all the consumers feeding from this faulty feeder remains affected if
feeder is radial. Typically restoration time of the fault is 2 to 3 hours. It may
increase in the monsoon season. Due to unavailability of proper monitoring
of the voltages and power factor at sub-stations, consumers are not getting
the quality power supply. It has been concluded that most of the distribution
system problems have caused by less attention given, poor management of
both personal and materials. So that carrying out capacity building activities
with participation of all the concerned people both technical and
management bodies.
37. • Power capacitors should be installed at 15 kV.
• Single Line Diagrams for all feeders with their DTs should be available with its
maintenance in-charge.
• There should be a scheme for partial restoration in case of feeder’s breakdown or
shut down.
• Local SCADA should be made available in substation.
• 15 kV - monitoring &control needs to be established from DCC(Distribution
Control center ).
• Load, Energy etc. Reports should be automated. SCADA & IT system for
Reliability Calculation should be installed.
• Sectionalizers are manually operated. These can be made a part of Distribution
SCADA by placement of motorized Ring Main Units along with the
communication system. This will facilitate speedy isolation & restoration of the
feeder during trippings.
38. • Fiber optics are to be provided for quick response.
• CT ratios and accuracy class of secondary need to be standardized
• Numerical relays need to be integrated to SCADA system to have all fault
data at control room along with recorded fault currents
• Network Diagram should be updated periodically.
• There is indication alarm problem in partial feeders should be maintained.