Types of Substations, Main Components, And Its Major Functions-r0

8/13/2019 Types of Substations, Main Components, And Its Major Functions-r0

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TYPES OF SUBSTATIONS,

MAIN COMPONENTS,AND ITS MAJOR FUNCTIONS

BY

DR.MOHAMED A.ALI


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SUBSTATIONS:

Electrical Substations are a part of the power system acts as links between the Generating

Units and the Load Centers. They are simply nodal points of the power system helps

power to reach the consumers form power plants in a more reliable fashion. Electrical

Substation consists of a collection of Switching and protection equipments such as

Busbars, Circuit Breakers, Isolators, Earth Switch, Current Transformers, Potential

Transformers, Lightning Arresters or Surge Arresters, Series Capacitors, Shunt

Capacitors, Series Reactors, Shunt Reactors, Power Transformers, Line traps or Wave

traps and control cables and Power line carrier Communication Systems. There are

different types of substations present in the power system. Main function of Substations

are to receive the electrical power transmitted at high voltage from the Generating

stations to step down the voltage appropriate to an appropriate value for local distribution

Some substations are simply the switching stations where different connections between

various transmission lines are made. Some substations acts as converting substations

stations and converts AC power to DC power and transmits the power in HVDC manner

and once again convert back to AC power at the other end. Substations are convenient

place for installing Synchronous Condensers at the end of the transmission lines for the

purpose of improving power factor. Reactive Power Control in the power system is

carried at the Substations Where Synchronous Condensers are used to compensate the

Reactive Power.


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SECTION I:

DIFFERENT TYPES OF SUBSTATIONSI. Step-up or Step-down Substations:These Substations are available in the Generating Side (Generating Plants) and in

Distribution Side (Load Centers) of the Power System. This Substations are used for

Stepping up the voltage form (11kV, 13kV, 21kV) generating voltage to (220kV and

420kV and above) transmission voltage.

Step down Substations are used for stepping down the voltage that is transmitted

(220KV,420kV) to Step-down voltage to (132kV,66kV) for distributing the voltage. This

Primary Distribution Voltage is further Stepped down to the Secondary Distribution

Voltage (11kV) and this is further stepped down to (440kV,220kV or 110kV) at the

consumer terminals.

II. Switching Substations:These Substations are Used to Switch the power among different circuits for reliable

transfer of power to the Consumers. Different Switching Configurations are followed

such as

1) Double Busbar Scheme

2) One and Breaker Scheme

3) Single Busbar Scheme

4) Main and Transfer Busbar Scheme

5) Ring main Scheme

III. Conversion Substations:This Substations are Used at the HVDC transmission systems to Convert the AC power

to the DC power and transmitted in the High Voltage DC format and once again convert

back to DC to AC on the Other end of the HVDC transmission System.


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SECTION II:

DIFFERENT SUBSTATION TYPES BASED ON DESIGNI. Outdoor Substations:In this type of Substations all the switchyard equipment such as busbars, circuit breakers,

isolators, earth switches, Current Transformers, Voltage Transformers etc are present

under the sky. Outdoor substations are applicable to all ratings and types of substations

are best suited for the high voltage ratings (220kV above).

II. Indoor Substations:

In type of Substations all the switchyard equipment are present inside a building. Thistype of substations are limited for Voltage rating of (66kV) because as the ratings

increases further phase clearances also increases results in large size of the building.


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SECTION III:

BASED ON THE DESIGN CONFIGURATIONI. Air Insulated SubstationIn Air Insulated Substation all the live parts of the equipment are surrounded by the air.

Busbars, isolators, Switches, bushing terminals etc all the live terminals are exposed to

the atmosphere.

II. Gas Insulated SubstationThis type of substations is typically employed where the space requirement is the major

factor in cities and large towns. This type of substations has the advantage of more

reliability and compactness. In this Substation Sulfur Hexafluoride (SF6) gas is used as

dielectric and insulating medium for all the live parts of the equipment. In Gas Insulated

Substation all the equipment is enclosed in the closed modules filled with Sulfur

Hexafluoride gas (SF6) gas. Sulfur Hexafluoride gas has the advantage of having high

dielectric strength and high electronegative behavior. These two properties make the

substation 1/10 th of the conventional substation.

III. Hybrid SubstationHybrid Substation is a mixture of both Gas Insulated Substation and Air Insulated

Substation. In this Substation some components are enclosed in the SF6 gas modules and

some are same as conventional substation type.


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SECTION IV:

MAIN COMPONENTS OF SUBSTATIONS

Electric Substations are the part of the power system and used for transferring power

from generating points to load centers. Some of the important components of substation

will be listed below.

I. Busbars:Various incoming and outgoing circuits are connected to busbars. Busbars receive power

from incoming circuits and deliver power to outgoing circuits.

Bus Bars

See all 19 ph

II. Surge arrestors or Lightning arrester:Surge Arresters or Lightning Arresters discharge the over voltage surges to earth and

protect the equipment insulation from switching surges and lightning surges. Surge

arresters are generally connected between phase conductor and ground. In a Substationsurge arrester is located at the starting of the substation as seen from incoming

transmission lines and is the first equipment of the substation. Surge arresters are also

provided near the transformer terminals phase to ground. Two type of surge arresters are

1. available Gapped Arresters,2. Gapless Zinc Oxide arresters.


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Lightning Arrester or Surge Arreseter

III. Isolators or Disconnecting Switches:Isolators are provided for isolation from live parts for the purpose of maintenance.

Isolators are located at either side of the circuit breaker. Isolators are operated under no

load. Isolator does not have any rating for current breaking or current making. Isolators

are interlocked with circuit breakers

Types of Isolators are

1. Central rotating, horizontal swing2. Centre-Break3. Vertical swing4. Pantograph type

Isolators


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IV. Earth Switch:Earth Switch is used to discharge the voltage on the circuit to the earth for safety. Earthswitch is mounted on the frame of the isolators. Earth Switch is located for each incomer

transmission line and each side of the busbar section.

V. Current Transformer:Current transformers are used for Stepping down current for measurement, protection and

control. Current transformers are of two types

1. Protective CT2. Measuring CT

Current Transformer


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VI. Voltage Transformer:Voltage transformers are used to step down the voltage for measurement, protection andcontrol. Voltage transformers are of two types.

1. Electro magnetic type2. Capacitive VT located on the feeder side of the Circuit Breaker.

Voltage Transformer

VII. Circuit Breaker:Circuit Breaker is used for Switching during normal and abnormal operating conditions.

It is used to interrupt the short circuit currents. It is used to interrupt short circuit currents.

Circuit Breaker operations include.

1. Closing2. Opening3. Auto reclosing

Circuit Breaker is located near every switching point and also located at the both ends of

every protection zone.


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SF6 Circuit Breaker

VIII. Power Transformers:Power Transformers are used to step up or step down a.c. voltages and to transferelectrical power from one voltage level to another. Tap changers are used for voltage

control.

Power Transformer


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IX. Shunt Reactors:Shunt Reactors are used for long EHV transmission lines to control voltage during low load period. Shunt reactors is also used to compensate shunt capacitance of transmission

line during low load periods. Usually Shunt reactors are unswitched.

Shunt Reactors Bank

X. Shunt Capacitance:Shunt capacitors are used for compensating reactive power of lagging power factor.

Shunt Capacitors are used for improving the power factor. It is also used for voltage

control during heavy lagging power factor loads. Shunt Capacitors are located at the

receiving stations and distribution substations. Shunt Capacitors are switched in during

heavy loads and switched off during low loads.


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Shunt Capacitor Bank

XI. Series Capacitor:Series Capacitors are used for some long EHV a.c lines to improve power transferability.Capacitors are located at the sending end / receiving end of the lines. Series Capacitors

are provided with by pass circuit breaker and protective spark gaps.

Series Capacitors


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XII. Series ReactorsSeries reactors are used to limit short circuit current and to limit current surges

associated with fluctuating loads. Series reactors are located at the strategic locations

such that the fault levels are reduced.

Series Reactors

XIII. Lightning Protection:Lightning protection is used to protect substation equipment from direct lightning strokes.

Lightning Masts are located at the outdoor yard. Overhead Shielding wires are used to

cover entire outdoor yard.

Lightning Masts


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XIV. Isolated Phase Bus System:Isolated Phase Bus System provides connection between Generator and the mainTransformer. It carries very high currents.

Isolated Phase Bus Duct

XV. Neutral Grounding Equipment:Neutral Grounding Equipment are Resistors and reactors. They are used to limit the short

circuit current during ground fault. They are connected between neutral point and ground.

neutral Grounding resistor


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XVI. Line Trap:Line Trap consists of Inductive coil usually connected in the outdoor yard incoming line.Line traps are usually mounted above Capacitor Voltage Transformer (CVT) or on

separate structure.

Wave Trap or Line Trap

XVII. Insulators:Used for Insulation purpose. Different types of insulators are porcelain, Glass, Epoxy.

Porcelain Insulators


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XVIII.Power Cables:Power Cables are used to carry the power. They are single core and three core. Types ofpower cables are PVC insulated, XLPE insulated.

XLPE insulated Power Cable

XIX. Control Cables:Control Cables are for protection, control and measurement etc.. They are of low voltage

and PVC insulated. Control Cables are Multi core and Shielded.

XLPE insulated Control Cables


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XX. Station Earthing System:Station Earthing System includes Earth Mat and Earth electrodes placed below ground

level. These Earth Mat and Earth electrode is connected to the equipment structures,

neutral points for the purpose of Equipment earthing and neutral point earthing.

Function earthing system is to provide low resistance earthing for

1. Discharging currents from the surge arresters, overhead shielding, earthing switches2. For equipment body earthing3. For safe touch potential and step potential in substation.

Earthing Mat

XXI. Metering, Control and Relay panels:To house various measuring Instruments, control Instruments, Protective relays. They are

located in air-conditioned building. Control Cables are laid between Switchyardequipment and these panels.


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Metering and Control Panel

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Types of Substations, Main Components, And Its Major Functions-r0