ELECTRIC POWER

SUBSTATIONS, COMPONENTS

AND FUNCTIONS BY

ENGR. ISIBOR SIMEON, MNSE, MNIEEE, MAIP

MD/CEO SIB ENGINEERING LTD

CIVIL SERVICE CLUB, MABUSHI-ABUJA

PRESENTED AT

THE INTERNATIONAL CONFERENCE AND EXHIBITION ON POWER AND TELECOMMUNICATIONS (ICEPT 2015), OSHOGBO.

OUTLINE

� Introduction

� Basic Power System

� Substations

� Classifications of Substatations

� Components of Substations

� Conclusion

ABSTRACT

This paper is an overview of major components used in power system.

All components of power system are virtually seen in substations.

This discussion focuses on substation, classifications and on some

major components that can be found and are in regular use in

substations.

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INTRODUCTION

Electric power is produced at the power generating stations, which are

generally located far away from the load centers.

High voltage transmission lines are used to transmit the electric power from

the generating stations to the load centers.

Substations are basically transformation or switching stations. They receive

power transmitted at high voltage from the generating stations and reduce the

voltage to a value suitable for distribution. .

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Electric Power Systems are comprised of components that transform other forms of energy into electrical energy and transmit this energy to a consumer.

Electric power system equipment are electrical components used in the generation, transmission, protection, distribution, control and utilization of electric power in the industries, factories, offices and homes. [1, 2]

BASIC POWERR SYSTEM

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Substations are assembly of electrical

components to form a link between

generating stations, transmission systems

and distribution systems.[3]

SUBSTATIONSSUBSTATIONSSUBSTATIONSSUBSTATIONS Single line schematic arrangement of power substation

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CLASSIFFICATION OF SUBSTATION

Substations may be classified in according to service requirements and

constructional features.

According to service requirements it is classified into:

Transformer Substations: They are used to transform power from one

voltage level to another voltage level. They are further classified into Step-up

substations, Primary grid substations, Secondary substations and Distribution

substations.

Switching substations: These substations are meant for switching operations

of power lines without transforming the voltage.

Converting substation: are meant for either converting AC to DC or vice

versa. Some are used to change the frequency from higher to lower or vice

versa for industry utilizations.

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CLASSIFFICATION OF SUBSTATION

According to constructional features, substations are classified into:

Indoor substations: All equipment of the substation are installed within the

station buildings.

Outdoor substations: All equipment such as transformers, circuit breakers,

isolators, etc., are installed outdoors.

Underground substations: In thickly populated areas where the space is the

major constraint, and cost of land is higher, under such situation the substations

are laid underground

Pole mounted substations: This is an outdoor substation with equipment

installed overhead on a H pole or 4 pole structure.

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COMPONENTS OF SUBSTATION

Power Transformers:

Power transformers are used in generation and transmission

network for stepping-up the voltage at generating station and

stepping-down the voltage for distribution.

Figure 3.Power Transformer [5]

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Instrument Transformer

Instrument transformers are used to step-

down the current or voltage to measurable

values. They provide standardized, useable

levels of current or voltage in a variety of

power monitoring and measurement

applications.

These are further classified into two types.

a. Current Transformers

b. Voltage Transformers

Both current and voltage instrument transformers are designed to have predictable characteristics on overloads. [3]

a. Current transformer

b. Potential Transformer

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Circuit breakers Circuit breakers are used for opening or closing a circuit under normal as well

as abnormal (faulty) conditions. The circuit breakers are used to break the

circuit if any fault occurs in any of the instrument. Different types of CBs

which are generally used are oil circuit breaker, air-blast circuit breaker,

vacuum circuit breaker and SF6 circuit breaker.

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Isolators or Isolating switches:

Isolators are employed in substations to isolate a part of the system for general

maintenance. Isolator switches are operated only under no load condition.

They are provided on each side of every circuit breaker.

Lightning arresters (LA):

Lightning arresters are the protective devices used for protection of equipment

from lightning strokes. They are located at the starting of the substation and

also provided near the transformer terminals.

Earth switch:

It is a switch normally kept open and connected between earth and conductor

for the purpose of safely discharging the residual charges on the conductor or

circuit to earth. They are provided for the safety of personnel carrying out

work on a piece of equipment.

Wave trap:

This equipment is installed in the substation for trapping the high frequency

communication signals sent on the line from remote substation and diverting

them to the telecom panel in the substation control room. [3].

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Coupling capacitor:

A coupling capacitor is used in substations where communication is done by AC

power line. It offers very low impedance to high frequency carrier signal and allows

them to enter the line matching unit and blocks the low frequency signal.

Auto-Reclosure Facility

This facility is normally incorporated into High Voltage circuit breakers that are used

for controlling the operation of overhead transmission lines and distance protection

scheme. This type of circuit breaker restores continuity of supply after a transient

fault interruption. Otherwise, it will open permanently if the fault persists. [2]

Insulator

The purpose of the insulator is to insulate the electrically charged part of any equipment from another charged part or uncharged metal part. In case of the high voltage overhead transmission and distribution insulators are used to insulate the live conductor from the transmission towers. The insulators used in transmission and distribution system are also required to carry large tensional or compressive load.

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Capacitor Voltage Transformer (CVT):

A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay.

DC Power Supply

DC power is used to feed essential services such as circuit breaker trip coils and associated relays, supervisory control and data acquisition (SCADA) and communications equipment.

Bus bar:

This is a very low impedance and high current carrying capacity conductor having multiple numbers of incoming and outgoing lines electrically connected and operating at the same voltage.

Bus scheme:

The Bus scheme is the arrangement of overhead bus bar and associated switching equipment in a substation.

The operational flexibility and reliability of the substation greatly depends upon the bus scheme.

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Criteria for Selection of Bus Bar Scheme The Main Criteria to be considered during Selection of one Particular Bus Bar Arrangement among Others are (i) Simplicity of system. (ii) Easy maintenance of different equipment. (iii) Minimizing the outage during maintenance. (iv) Future provision of extension with growth of demand.

Bus Bar Arrangements Some very commonly used bus bar arrangements are: � Single Bus System � Single Section Bus System � Double Bus System � Double Breaker System � One and Half Breaker Bus System � Transfer Bus System � Double Bus System with Bypass Isolator � Ring Bus System

Their single line representation are as shown in the next slide.

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Fig Fig Fig Fig 6.8 Ring Bus System6.8 Ring Bus System6.8 Ring Bus System6.8 Ring Bus System 6.7 Double Bus System with Bypass 6.7 Double Bus System with Bypass 6.7 Double Bus System with Bypass 6.7 Double Bus System with Bypass

Isolator Isolator Isolator Isolator

Fig 6.6 Transfer Bus Fig 6.6 Transfer Bus Fig 6.6 Transfer Bus Fig 6.6 Transfer Bus SystemSystemSystemSystem Fig 6Fig 6Fig 6Fig 6----5 One and Half Breaker Bus 5 One and Half Breaker Bus 5 One and Half Breaker Bus 5 One and Half Breaker Bus

System System System System

Fig 6.4 Double Breaker Fig 6.4 Double Breaker Fig 6.4 Double Breaker Fig 6.4 Double Breaker SystemSystemSystemSystem Fig 6.3 Double Bus System Fig 6.3 Double Bus System Fig 6.3 Double Bus System Fig 6.3 Double Bus System Fig 6.2 Single Section Bus System Fig 6.2 Single Section Bus System Fig 6.2 Single Section Bus System Fig 6.2 Single Section Bus System Fig 6.1Fig 6.1Fig 6.1Fig 6.1 Single Bus SystemSingle Bus SystemSingle Bus SystemSingle Bus System

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S/N System Function

1. Substation Earthing system

- Earth mat

- Earthing spikes

- Earthing risers

To provide an earth mat for connecting neutral points, equipment body, support structures to earth. For

safety of personnel and for enabling earth fault protection. To provide the path for discharging the earth

currents from neutrals, faults, Surge Arresters, overheads shielding wires etc. with safe step-potential and

touch potential.

2. Overhead earth wire shielding or

Lightning masts.

To protect the outdoor substation equipment from lightning strokes.

3. Illumination system (lighting)

- for switchyard

- buildings

- roads etc.

To provide proper illumination to substation yard.

4. Protection system

- protection relay panels

- control cables

- circuit breakers

- CTs, VTs etc.

To provide alarm or automatic tripping of faulty part from healthy part and also to minimize damage to

faulty equipment and associated system.

5. Control cable For Protective circuits, control circuits, metering circuits, communication circuits

6. Power cable To provide supply path to various auxiliary equipment and machines.

7. PLCC system power line carrier

communication system

For communication, telemetry, tele-control, power line carrier protection etc.

8. Telephone, telex, microwave, OPF For internal and external communication

9. Auxiliary standby power system For supplying starting power, standby power for auxiliaries.

10. Fire Fighting system

- Sensors, detection system

- water spray system

- fire port, panels, alarm System.

- water tank and spray system

To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to

affected region to pinpoint location of fire by indication in control room.

ASSOCIATED SYSTEM IN SUBSTATION Functions of Associated System in Substation is as shown in table below Table: Functions of Associated System in Substation [3]

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CONCLUSION This paper provided an insight into the basics of substations and

major components of power systems. The functions of some

components and different type of substations were discussed. It is

not exhaustive. The associative systems in a substation were

highlighted in the table. Discussions on them may be subsequent

or at other fora. However, these basics are enough as guide to an

interested investor and for engineering personnel in the sector.

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THANK YOU

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REFERENCES 1. Electrical Engineering Tutorials: Electric Power Systems and its ... http://www.powerelectricalblog.com/2007/03/electric-power-systems-

2. Ewesor, P. O. (2010): Practical Electrical System Installation Work And Practice, 2nd Ed., Petvirgins Partners Publishing, Benin city, Nigeria, pp125-140 (ISBN: 978-978-904-915-8)

3. Single Line Diagram of Substations-VTU e-Learning Centre:

http://elearning.vtu.ac.in/18/enotes/10EE65/unit1-a-DB.pdf

4. Emmanouil A. (2013) High Voltage, Power Substation. [Online] Available from: http://electrical-engineering-portal.com/high-voltage-substations-overview-part-2

[Accessed: 25th August, 2015]

5. Ravalika V. (2015) Maintenance and Operation of An Electrical substation of 220/132. [Online] Available from:http://www.academia.edu/6620996/ [Accessed: 25th August 2015]

6. Electrical Bus System and Electrical Substation Layout: [Online] Available fromhttp://www.electrical4u.com/electrical-bus-system-and-electrical-substation-layout/

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