SUB STATIONS

Introduction Sub Stations are important link between

Generating stations and Distribution networks. They step down the EHV to HV as per the

requirement of the customers. Stability of the system, reliability of power

depends on the type of layout chosen and components used in the sub stations.

Hence great care has to be taken to select the layout and critical equipment for the SS.

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Transmission line Yard in Receiving StationOut door yard in Generating Station

Out door yard in Generating station

Basic Requirements

Total land area & Ease of extension Soil condition & Soil resistivity Right of way for incoming and outgoing lines Facility to move heavy Equipments Load Centre System Security Operational Flexibility Simplicity of protection arrangement Ability to limit short circuit levels Maintenance Cost

Types of layouts

Single Busbar System Single Busbar System sectionalising arrangement Double Busbar system Single Busbar with ring Bus Double Busbar with Transfer Bus One and Half Breaker arrangement Mesh type arrangement

Standard clearances

VOLTAGE PHASE TO PHASE PHASE TO EARTH

400 KV 4.000 Mtrs 3.50 Mtrs

230 KV 3.350 Mtrs 1.650 Mtrs

110 KV 1.675 Mtrs 1.000 Mtrs

66 KV 1.220 Mtrs 0.750 Mtrs

33 KV 0.915 Mtrs 0.610 Mtrs

Standard clearances

VOLTAGE CLEARANCE

GROUND CLEARANCE

SECTIONAL CLEARANCE

400 KV 8.000 Mtrs 10.000 Mtrs

230 KV 5.500 Mtrs 4.270 Mtrs

110 KV 4.600 Mtrs 3.350 Mtrs

66 KV 4.600 Mtrs 3.050 Mtrs

33 KV 3.650 Mtrs 2.750 Mtrs

22 KV 3.650 Mtrs 2.750 Mtrs

11 KV 3.650 Mtrs 2.600 Mtrs

Standard Bay Width

VOLTAGE BAY WIDTH

400 KV 27.000 Mtrs

230 KV 15.900 Mtrs

110 KV 9.500 Mtrs

66 KV 7.000 Mtrs

33 KV 4.600 Mtrs

22 KV 3.800 Mtrs11 KV 3.500 Mtrs

Single Busbar System

Single busbar with a sectionalizing arrangement can be erected to give more flexibility for operation and maintenance.

Single busbar with ring shaped bus can be Constructed for connecting many feeders from the substations.

Single Bus Scheme1

Single Busbar System

This system consists of a single bus to which various feeders are connected.

In case of a fault in bus / maintenance entire bus bar has to be shut down.

Provides least flexibility. Simple and most economical. This type of layout is adopted for Small and

Medium size Substations and Power stations.

Double Bus Scheme1

Double Busbar System Double Busbar system consists of two buses to which all the

feeders emanating from a substations, are connected by suitable switching arrangement.

Provides more flexibility, continuity of supply and periodical maintenance on the bus is also possible without Total shutdown.

In this arrangement the busbars are called Main and Reserve Busbars.

A Breaker can be introduced between the buses to have more operational flexibility.

A double busbar system with a Transfer bus are constructed to have more reliability and easy maintenance of Equipment.

Main & Transfer Bus Scheme1

Double Bus & Transfer Bus Scheme

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One and a Half Breaker System1

Double Busbar System

In this arrangement three circuit breakers are used to control two feeders

Any circuit breaker can be switched off without difficulty for maintenance works.

This system has high security against loss of supply. Suitable for switch yards of large Generating stations

handling large quantity of Power in individual circuits/feeders.

High cost but system security is very high.

Ring (Mesh) Bus Scheme1

Ring (Mesh) Bus Scheme

In this arrangement three circuit breakers are used to control two feeders

This type of layout is used to minimize the no of Breakers used in a Substation.

The breakers are connected in the mesh formed by the buses. The circuits are tapped from the node points of the Mesh.

Four breakers are utilized to control eight circuits. This arrangement is widely used in United Kingdom.

33/11 KV Substation (Regular) - SLD1

33/11 KV Substation (Regular) - Plan1

110/22 KV or 110/11 KV Substation - SLD1

110/22 KV or 110/11 KV Substation - Plan1

230/ 110 KV Substation – SLD (Single Bus)1

230/ 110 KV Substation – Plan (Single Bus)1

230/ 110 KV Substation – Plan (Double Bus)1

230/ 110 KV SS – SLD (Main & Transfer Bus Scheme)

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230/ 110 KV SS – Plan (Main & Transfer Bus Scheme)

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230/ 110 KV SS – SLD (Double Bus Scheme)1

230/ 110 KV SS – Elevation (Double Bus Scheme)

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400/230 KV SS – SLD (One and a Half Breaker System)

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400/230 KV SS – Plan (One and a Half Breaker System)

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Standard clearances in outdoor sub-stations1

Main Equipment in Substation Power/Auto Transformers, Circuit Breakers, Instrument Transformers, Surge Arresters, Control and Relay Panels, Station Batteries and Battery Chargers, DC and AC Panels, Control Cable, Isolators with and without Earthing Device, Capacitors, Reactors, Busbar materials, Insulators, Connecters etc.

Types of SS Transformer Substation: Transformer are installed to transform

power from one level to another as per needs. Switching Substations: This substation are erected for switching

operation of power lines with out transforming the voltage. Power factor correction Substation: This substation installed to

increase the power factor to minimize losses. Frequency Changer Substation: This substation installed where

speed controlled of motor required. Converting Substation: This substation convert A.C to D.C or vice

versa. Industrial Substation: This substation installed for supply power

only to industry.

Types of SS Paralleling sub station. The SS where power from

different source of generation are paralleled. Two system has to get connected (parallel), synchronizing facility needed .

Must have reliable Communication with Load dispatcher and generating stations.

Double bus with a transfer bus arrangement will be most ideal type of layout

Major receiving station : The power handled by the station is high.

One and a half breaker layout will be suitable. Reliable communication, duplicated protection system, Spare

capacity of Auto transformer , good security in system are needed.

Generating station layout Depends on the Nos of generator in the station. Should have a layout which should not affect generation even one unit is

shut down Double bus with transfer bus is most suitable. However a single bus

scheme with two feeders can be considered for a station with single generating unit

Should have reliable communication with Load dispatcher and receiving station.

Located adjacent to the power house. Indoor / outdoor AISS or GISS are generally considered suitable for major

generating stations. In under ground power generating stations transformer yard is located near

the generators and the EHV is taken thru EHV cables to the outdoor yard.

Main Equipment in Substation

Selection of right type of Layout, Equipments of adequate ratings and correct Protection system will make the Power system Safe, Secure and also give operational Flexibility.