Substation Equipments

EHV SUBSTATIONS

EHV SUBSTATION AND SUBSTATION EQUIPMENTS Karikalan.M, 21FEBRUARY 2012. Siemens Ltd.

Energy Transmission Power Transmission Solutions, Secondary Engineering

Siemens Ltd

Objective

Deals with the overall aspects of sub-station Covering all the equipments installed in a sub-station.

SUBSTATION Sub-stations are basically points in the power network where power can be pooled from generating sources, voltage levels transformed and power delivered to the load points

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Voltage levels in AC Substations Ultra High Voltages – 765KV,1200KV Extra High Voltages EHV - 132kV, 220kV, 400kV High Voltage HV -66KV

Medium Voltages – 6.6KV,11KV,33KV Low Voltages - 415V and below.

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COMPONENTS & TYPES OF SUB-STATION

A sub-station has the following components either partly or wholly: 1) bus-bars 2) incoming and outgoing feeders 3) surge arrestors 4) voltage transformers 5) current transformers 6) circuit breakers 7) disconnectors 8) earthing switches 9) wave traps 10) reactors 4

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COMPONENTS & TYPES OF SUB-STATION

11) battery banks 12) emergency diesel generator set 13) power line carrier communication 14) protection relays 15) control systems

16) illumination system 17) air-conditioning & ventilation system

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COMPONENTS & TYPES OF SUB-STATION Sr. No.

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Equipment

Function

1.

Bus-bar

Incoming and outgoing circuits connected to bus-bar. Automatic switching during normal or abnormal conditions.

2.

Circuit breakers

3.

Isolators (Disconnections)

Disconnection under no – loan condition for safety, isolation and maintenance.

4.

Earthing Switch

5.

Current Transformer

To discharge the voltage on dead lines to earth To step – down currents for measurement, control and protection.

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6.

Voltage Transformer To step – down voltage for measurement, control and protection.

7.

Lighting Arrester (Surge Arrester)

To discharge lightning over voltage and switching over voltage to earth.

8.

Shunt reactor

To provide reactive power compensation during low loads.

9.

Series Reactors

To reduce the short – circuit current or starting currents.

10.

Neutral-Grounding Reactors.

To limit the earth fault current.

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11 12.

13.

19.

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Line – trap

To prevent high frequency signals from entering other zones. Power Transformer To step-up or step – down the voltage and transfer power from one AC voltage to another AC voltage at the same frequency. Substation To provide an earth mat for connecting neutral Earthing points, equipment body, support structures to (Grounding) earth. For safety of personnel and for enabling System earth fault protection.. -Earth mat -Earthing spikes -Earthing risers Protection System To provide alarm or automatic tripping of faulty -Protection relay part from healthy part and also to minimize -Panels damage to faulty equipment and associated -Control cables system. -Circuit-breakers -CTs., VTs. etc. E T PS-HVDC-COE- Karikalan.M

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Circuit Breakers

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Why do we have Circuit Breakers?

To switch Transmission Lines, Transformers, Shunt Reactors, Capacitor Banks etc. To close/reclose an open circuit

And of course the most important to clear a fault to protect equipment, Power Grid and human life!

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Basic Schematic Fault analysing equipment

Protection relays

Station control

Instrument Transformers

Power System Circuit breaker

Communication Equipment

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CB CONTACT ASSEMBLY

A Look at Contact Assembly… Incoming Flange

Outgoing Flange

Main Contact, Moving

Moving contact Holder

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Arcing Contact, Moving

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Main Contact, Fixed

Arcing contact, Fixed

Fixed contact Holder

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Moving Contact

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Fixed Contact

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Current transformers

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CURRENT TRANSFORMERS

CT’s are used to provide isolation from the power system and reduction in magnitude to a level usable by relays and meters. TYPES OF CTS 1.LIVE TANK CT 2.DEAD TANK CT

Hair Pin Design Eye Bolt Design

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LIVE TANK CT

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DEAD TANK CT

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Eye Bolt Design

Primary steel pipe

Paper insulation

Seconday cores

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Hair-Pin design

1. Dome 2. Nitrogen filling valve 3. Primary terminal 4. Collar 5. Porcelain insulator 6. Primary conductor with insulation 7. Adaptor cylinder 8. Secondary cores

9. Base 10. Oil drain plug

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Current Transformers Protection accuracy classes

Accuracy classes (Protection) Maximum current error in % of IP Accuracy limit primary current = fL.IN Burden :SN

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Class

Ratio error

Phase

Composite

e

at In

displacemen

error at

t at In

fL.IN

 60 min.



5 P

 1 %

10 P

 3 %

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5 %

 10 %

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Factors for Protection

1. Accuracy Limiting Factor What is Accuracy Limiting factor ? It is the factor of over current above the rated current which determines the capability of CT to maintain the error at such a condition. 2. Composite error It is the error of the CT when this over current is applied.

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Example

Accuracy Limiting Factor/composite error For e.g if the class designation is 5P20 20 is the Accuracy limiting factor which signifies that when 20 times the rated primary current is applied the composite error of 5P( +/- 5%) is maintained.

Typical Class designations are 5P10, 5P20, 10P10, 10P20 etc.,

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CVT

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Capacitor Voltage Transformer

P1 C1

Intermediate Voltage : 10 to 20 kV/3

S1

C2

P2 25

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CVT Capacitor stack

Inductive VT 26

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CVT Secondary Voltage

CVT Secondary Voltage v = k * V * C1/ (C1+C2) V – Primary Voltage k – Secondary Transformation ratio Note: Puncturing of C1 – Secondary Voltage will increase Puncturing of C2 – Secondary Voltage will decrease

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VT

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Voltage Transformer :

Primary

U1

U1 n1  K U2 n2

n1 K: Transformation ratio

n2

U2

Secondary 29

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Transformer

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Transformer • A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors (the transformer's coils) without change in frequency. • A major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires. • By transforming electrical power to a high-voltage (and therefore low-current) form for transmission and back again afterward, transformers enable economical transmission of power over long distances.

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Power Transformer

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Convertor Transformer

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Isolators and Disconectors

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ISOLATORS/DIS CONNECTORS

Isolators (also referred as disconnectors) are off-load type switches. TYPES OF ISOLATORS

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ISOLATORS/DIS CONNECTORS

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Wave Trap

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Surge arrester

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Surge Arrestor • An electrical appliance used to protect electronic equipment against lightning overvoltage transients. • It is usually connected to wires (power phase line, signal line, zero line) and ground between being protective devices in parallel.

• During the lightning over-voltage the arrestor immediately limits the over-voltage amplitude which leads to protection of the equipment and systems, enabling the system to work properly.

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Surge Arrestor

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Bus Bar

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Sub Station Clearances Highest system voltage Minimum clearance (KV) phase & earth (mm)

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between Minimum clearance between phases (mm)

Sectional clearance (mm)

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320

320

2800

72.5

630

630

3000

123

900 (1100*)

900 (1100*)

3500 (4000*)

145

1100 (1300*)

1100 (1300*)

4000

245

1900 (2100*)

1900 (2100*)

4500 (5000*)

420

3400

4200

6500

800

6400

10000

10000

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AC C&P Design

SUB-STATION BUSBAR ARRANGEMENT Bus-bars are the part of the sub-station where all the power is concentrated.

The power from the sources is collected on the bus-bars by connecting the incoming lines. The power is distributed from the bus-bars by connecting the outgoing lines to them.

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Auxillary Power Engineering SINGLE BUSBAR SCHEME In this arrangement of bus-bars, all incoming and outgoing feeders are connected to the same bus. This type of bus-bar system is used mostly in small AC stations (low & medium voltage stations) This arrangement has the following advantages:  Low initial cost since each feeder has only one bus-bar  Relaying scheme is simple  Due to single breaker for one circuit, operation is very simple  Low Maintenance cost.

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Software Design

This arrangement has the following disadvantages:  All generators and incoming lines connected to the same bus lead to a high fault level on the bus  In case of any maintenance work on any part of the bus-bar, the whole station has to be shut down  In case of any fault on the bus-bar, there is complete outage of the whole station

 In case of maintenance work on any feeder circuit breaker, the feeder has to be disconnected till the work is completed

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SECTIONALISED SINGLE BUSBAR SCHEME

 This scheme is an improvement over the single bus-bar scheme .  The bus-bar has been split up into two parts with the feeders distributed over the two sections. This arrangement has the following advantages: 

Fault level of the bus due to incoming feeders can be reduced by operating the system with the bus-sectionaliser open

 During fault on bus-bar, the whole station does not suffer complete outage  Maintenance work can be carried out on one half of the bus-bars by taking it out of service instead of the whole station 47

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SECTIONALISED SINGLE BUSBAR SCHEME



This scheme is very common in low and medium voltage substations, particularly for indoor switchboards.



Grid sub-stations do not adopt this arrangement since it does not offer a completely reliable bus-bar system.

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SINGLE MAIN AND TRANSFER BUSBAR SCHEME



The single bus-bar scheme can be provided some flexibility by adding an additional bus-bar called the transfer bus-bar.

 With this transfer bus, one feeder from the main bus can be connected to the transfer bus, thus freeing the circuit breaker of the feeder for maintenance.  This scheme is mostly used in 132 KV or lower voltage sub-stations at the distribution level.

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SINGLE MAIN AND TRANSFER BUSBAR SCHEME Advantages and Disadvantages  This scheme combines the low cost and simplicity of single bus-bar scheme with a limited degree of flexibility.  Whenever any feeder circuit breaker has to be taken for maintenance, the feeder is connected to the transfer bus through the transfer bus isolator and the transfer breaker.  This arrangement does not offer any increased degree of reliability, it only provides the flexibility of maintenance of a circuit breaker without taking outage of line or bus-bar

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DOUBLE MAIN BUSBAR SCHEME



In this system, there are two main bus-bars and each feeder has disconnectors that can connect the feeder to any bus-bar.

 Thus some generators and feeders can be connected to any one bus-bar and the remaining generators and feeders to other bus-bar.

 we can have two systems running in the same station and any generator or feeder can be switched to any one system

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SINGLE MAIN AND TRANSFER BUSBAR SCHEME

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DOUBLE MAIN BUSBAR SCHEME

 The double bus-bar systems are mostly used in generating stations and grid sub-stations at higher voltages (usually 220KV and 132KV in India) where reliability and availability are critical issues.

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Limitation of Double Bus Scheme

Limitation of Double Bus Scheme: With this arrangement, any change-over from one bus to another has to be done under off-load conditions since the disconnectors are not made for switching loads and the two bus-bars are not connected together and hence there is no synchronism between the two bus-bars

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DOUBLE MAIN BUSBAR WITH BUS COUPLER

Now, any feeder can be changed over from one bus-bar to another without switching off, the only condition for doing so is that the bus-coupler should be closed with its disconnectors and the feeder disconnector connecting the incoming bus has to be closed first and then the other disconnector can be opened.

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DOUBLE MAIN WITH TRANSFER BUSBAR SCHEME

we have seen an arrangement that enables maintenance of circuit breaker without taking the feeder out of service. This was possible by addition of the transfer bus-bar and the transfer breaker.

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DOUBLE MAIN WITH TRANSFER BUSBAR SCHEME

Advantages: In both the double bus with coupler and double main with transfer schemes, during instances of bus faults, the faulty bus can be identified and all feeders taken on the healthy bus-bar while maintenance on the faulty bus can be carried out . Dis-advantages: In case of bus-fault, all breakers connected to the faulty bus-bar trip and thus the corresponding feeders are out of service. Till the faulty bus-bar is isolated and the feeders connected back to the healthy bus-bar and the breakers switched on again.

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ONE-AND-HALF BREAKER SCHEME



HERE TWO FEEDERS ARE CONTROLED BY THREE BREAKERS.



SO THESE TWO FEEDERS CONTROLLED BY THREE CIRCUIT BREAKERS IT IS CALLED ONE & HALF BREAKER SYSTEM.



The bus-coupler and transfer bus are eliminated.

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ONE-AND-HALF BREAKER SCHEME “I” Type

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ONE-AND-HALF BREAKER SCHEME “D” Type

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Typical One-and-Half System

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THANK YOU

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