ELECTRICAL POWER STREAMStudy on Distribution system operation and control by Yohannes Feleke Yohannes Getahun

ADVISOR PROFESSOR N.P.SINGH

2016

ObjectivesGeneral 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.

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

OVERVIEW

SubstationsSubstations 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 levelsDistribution substations : Typically operate at 2.4–34.5 kV voltage levels

substation

Operation of Distribution SystemsDistribution 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)

SINGLE LINE DIGRAM

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.

• 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.

• 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.

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.

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

• CURRENT TRANSFORMERCurrent 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.

Switching ApparatusSwitching 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.

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

INDOOR(11KV) AND OUTDOOR(132KV)

SF6 breaker rating

132KV SF6 CB

Indoor Breaker (1250KVA, vacuum type)

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.

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.

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)

Transformer H.V. and L.V. Side Control Panel (TR.FEEDER-1 parallel with TR.FEEDER-2).

RS

T

TWO POWER TRANSOFRMER (20/25MVA) One 250KVA auxiliary transformer are

there for inside(substation)activities.

Outgoing FeedersSix 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

6 outgoing feeders 5 of them have 600:1current ratio and one 150:1 CT

Feeder panel(bella-6Killo-paisa)

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.

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.

SCADASCADA 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)) .

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.

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.

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

Following Formulae has been used for loss calculation

Moving Average Method:We used this method for the reason that it is trend and smoothing techniques for the accurate and short term forecasting.

12:00 2:00 4:00 6:00 8:00 10:00 12:00 2:00 4:00 6:00 8:00 10:00

-4

-2

0

2

4

6

8

10

12

monday actual and forecasted load

Forcaste load (MW) Actual load (MW) ERROR

TIME(HR)

LOAD

(MW

)

CONCLUSION AND RECOMMENDATIONUpgrading the capacity of the 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. 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.

• 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.

• 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.

THANK YOU!