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.
1
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. .
2
BASIC POWERR SYSTEM
Electric
Power
Systems
comprised of components
transform other forms of energy
electrical energy and transmit
energy to a consumer.
are
that
into
this
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]
3
SUBSTATIONS
Single line schematic arrangement of
power substation
Substations are assembly of electrical
components to form a link between
generating stations, transmission systems
and distribution systems.[3]
4
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.
5
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.
6
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]
7
Instrument Transformer
a. Current transformer
Instrument transformers are used to stepdown 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.
b. Potential Transformer
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]
8
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.
9
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].
10
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.
11
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.
12
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.
13
Fig 6.1 Single Bus System
Fig 66-5 One and Half Breaker Bus
System
Fig 6.2 Single Section Bus System
Fig 6.6 Transfer Bus System
Fig 6.3 Double Bus System
6.7 Double Bus System with Bypass
Isolator
Fig 6.4 Double Breaker System
Fig 6.8 Ring Bus System
14
ASSOCIATED SYSTEM IN SUBSTATION
Functions of Associated System in Substation is as shown in table below
Table: Functions of Associated System in Substation [3]
S/N
1.
2.
System
Function
Substation Earthing system
To provide an earth mat for connecting neutral points, equipment body, support structures to earth. For
- Earth mat
safety of personnel and for enabling earth fault protection. To provide the path for discharging the earth
- Earthing spikes
currents from neutrals, faults, Surge Arresters, overheads shielding wires etc. with safe step-potential and
- Earthing risers
touch potential.
Overhead earth wire shielding or To protect the outdoor substation equipment from lightning strokes.
Lightning masts.
3.
Illumination system (lighting)
To provide proper illumination to substation yard.
- for switchyard
- buildings
- roads etc.
4.
Protection system
To provide alarm or automatic tripping of faulty part from healthy part and also to minimize damage to
- protection relay panels
faulty equipment and associated system.
- control cables
- circuit breakers
- CTs, VTs etc.
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 For communication, telemetry, tele-control, power line carrier protection etc.
communication system
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
To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to
- Sensors, detection system
affected region to pinpoint location of fire by indication in control room.
- water spray system
- fire port, panels, alarm System.
- water tank and spray system
15
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.
16
THANK YOU
17
REFERENCES
1. Electrical Engineering Tutorials: Electric Power Systems and its ...
http://www.powerelectricalblog.com/2007/03/electric-power-systems2. Ewesor, P. O. (2010): Practical Electrical System Installation Work And Practice,
2nd Ed., Petvirgins Partners Publishing, Benin city, Nigeria, pp125-140 (ISBN: 978978-904-915-8)
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-substation18
layout/