21548809 Gas Insulated Substation

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GIS – Gas Insulated Substation

Why GIS

Types of Substation Switchgears [AIS/HIS/GIS]

Space Reduction Analysis with AIS/HIS/GIS

400 kV / 220 kV GIS

400 kV side GIS

Single Line Diagram & Components of GIS

220 kV side GIS

2

Visual Comparison Between AIS & GIS Components

Techno - Economic Comparison Between AIS & GIS

Advancement in GIS

Life Cycle Cost Analysis – [AIS/HIS/GIS]

World Scenario -GIS



Gas Insulated Substations (GIS) is a compact, multicomponent assembly enclosed ina ground metallic housing in which the primary insulating medium is compressedSulphur hexafluoride (SF6) gas.

SF6 acts as an insulation between live arts & the earthed metal closure.

The introduction of SF6 gas has revolutionized not only the technology ofcircuit breakers but also the layout of substations.

The dielectric strength of SF6 gas at atmospheric pressure is approximatelythree times that of air.

It s ncom ust e, non tox c, co or ess an c em ca y nert.

It has arc-quenching properties 3 to 4 times better than air at equal pressure.

Space requirement is only 10 to 25 percent of what is required is aconventional substation.



GIS has small ground space requirements.

Gas insulated Substations have easy maintenance( nearly zeroMaintenance

Less field erection time & less erection cost.

For underground powerhouse of Hydro electric power project wherespace constraint is a major issue.

.

Non-Flammability & Non-Explosive , Oil-free & Less Pollution

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Surge Arrestor Bus Post Insulator

Capacitor Voltage Transformer Disconnector Live Tank-Circuit Breaker Dead Tank- CB



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Surge ArrestorBus Post Insulator

Capacitor Voltage

Transformer



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The weight and size of the GIS equipment do not change appreciably with the voltageclass as the bulk of the current – carrying components and enclosures have identical

dimensions for similar thermal and short time current.

The additional insulation required for the next voltage class is achieved by increasedgas density.

Owing to these flexibilities, a few manufacturers offer the same equipment for two

voltage classes like 170/145 kV .

Even when the GIS equipment is designed for an individual voltage class, thedimensions and weights of the equipment differ marginally.

Rated voltageRated voltageRated voltageRated voltage 145 kV145 kV145 kV145 kV 170 kV170 kV170 kV170 kV 245 kV245 kV245 kV245 kV

Bay width, mBay width, mBay width, mBay width, m 1.5 2.02.02.02.0 2.02.02.02.0

Table shows the dimensions, weight and floor loading for three voltage classes of GIS.

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Bay Depth, mBay Depth, mBay Depth, mBay Depth, m 3.33.33.33.3 3.353.353.353.35 3.43.43.43.4

Bay height, mBay height, mBay height, mBay height, m 3.2 3.43.43.43.4 3.43.43.43.4

Floor area, sq.mFloor area, sq.mFloor area, sq.mFloor area, sq.m 4.95 6.76.76.76.7 6.86.86.86.8

Volume,Volume,Volume,Volume, m3m3m3m3 15.84 22.78 23.12

Weight,Weight,Weight,Weight, kgkgkgkg 3800 5000 5700

Floor loading,Floor loading,Floor loading,Floor loading,kg/kg/kg/kg/sq.msq.msq.msq.m

765 750 840



Clearances

132 Kv132 Kv132 Kv132 Kv 220 Kv220 Kv220 Kv220 Kv 400 Kv400 Kv400 Kv400 Kv 765 Kv765 Kv765 Kv765 Kv

Clearance

for 132 Kv

Diff in Clearance

with Next

Voltage class

Clearance

for 220 Kv

Diff in Clearance

with Next

Voltage Class

Clearance

for 400 Kv

Diff in Clearance

with Next

Voltage class

Mini.Clearance

B/W Ph – Ph

1.22 m 0.84 m0.84 m0.84 m0.84 m 2.06 m 1.94 m1.94 m1.94 m1.94 m 4.0 m 3.6 m3.6 m3.6 m3.6 m 7.6 m

Mini.Clearance

B/W Ph - Ear


Sectional

Clearance

3.50 m 0.78 m0.78 m0.78 m0.78 m 4.28 m 2.22 m2.22 m2.22 m2.22 m 6.5 m 3.83.83.83.8 10.3m

Ground

Clearance

4.6 m 0.9 m0.9 m0.9 m0.9 m 5.5 m 2.5 m2.5 m2.5 m2.5 m 8.0 m

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Earth Clearance: this is the clearance between live parts and earthed structures, walls, screens and ground.

Phase Clearance: this is the clearance between live parts of different phases.

Section Clearance: this is the clearance between live parts and the terminals of a work section. The limits of this worksection, or maintenance zone, may be the ground or a platform from which the man works.



145 Kv (132 Kv)145 Kv (132 Kv)145 Kv (132 Kv)145 Kv (132 Kv) 245 Kv (220 Kv)245 Kv (220 Kv)245 Kv (220 Kv)245 Kv (220 Kv) 420 Kv420 Kv420 Kv420 Kv 800 Kv800 Kv800 Kv800 Kv

(765 Kv)(765 Kv)(765 Kv)(765 Kv)

Clearance Diff in Clearance Clearance Diff in Clearance Clearance Diff in Clearance

Minimum Clearance for Different Voltage Level [GIS]

or 132 Kv

wit Next Voltage class

or 220 Kv

wit Next Voltage class

or 420 Kv

wit Next Vo tageclass

Centre-to-

centre distance

of phases


Right-of waywidth 1.3 m 0.2 m0.2 m0.2 m0.2 m 1.5 m 0.60.60.60.6 mmmm 2.1 m 0.5 m0.5 m0.5 m0.5 m 2.6 m

External

diameter

240 310 470 620

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Gas pressure at

20 C

420 420 420 420



Specifications for 400 KV GIS (ELK-3)

1 Rated Voltage 420 Kv420 Kv420 Kv420 Kv

2 Rated Power Frequency withstand voltage 650 Kv650 Kv650 Kv650 Kv

3 Rated Lightning impulse withstand voltage 1425 Kv1425 Kv1425 Kv1425 Kv

4 Rated Switching Impluse withstand voltage 1052 Kv1052 Kv1052 Kv1052 Kv

5 Rated Frequency 50 Hz50 Hz50 Hz50 Hz

6 Busbar current 6300 A6300 A6300 A6300 A

7 Feeder Current 4000 A4000 A4000 A4000 A

8 Rated Short time Withstand Current 63 KA63 KA63 KA63 KA

1 Rated Volta e U toU toU toU to 300300300300 KvKvKvKv

Specifications for 220 KV GIS (ELK-14)

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2 Rated Power Frequency withstand voltage 460 Kv460 Kv460 Kv460 Kv

3 Rated Lightning impulse withstand voltage 1050 Kv1050 Kv1050 Kv1050 Kv

4 Rated Switching Impluse withstand voltage 850 Kv850 Kv850 Kv850 Kv

5 Rated Frequency 50 Hz50 Hz50 Hz50 Hz

6 Rated Continuous Current 4000 A4000 A4000 A4000 A

7 Rated Short time Withstand Current 50505050 k kk kAAAA



400 kV/ 220 kV Substation with 5 bays at 400 kV and 7 bays at 220 kV

2 nos. 315 MVA, 400/220/33 kV three phase Auto Transformers

Gas Insulated Switchgear type ELK -3 at 400 kV and ELK-10 at 220 KV fromABB Switzerland

Substation commissioned in 2007.

***** .

Power supplied to Delhi Transco at 220 KV.



To ICT 1 To ICT 2

18From # # # From * * * *Bus Coupler Bay



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1. Barrier insulator2. Busbar Gas Compartment3. Feeder Gas Compartment

4. CB Gas compartment5. Voltage transformer

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Bus bars

Circuit Breakers

Disconnecting switches

Earthing switches

Current transformers

Voltage transformers

Cable and boxes

Gas supply and gas

monitoring equipment

1.Circuit Breaker2.Operating mechanism

(CB)3.Current Transformer

5.Maintenance earthing switc6.Fast acting earthing switch

7.Voltage transformer8.SF6 Bushing 22



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A circuit breaker is an automatically-operated electrical switch designed to protectan electrical from damage caused by overload or short circuit.

Its basic function is to detect a fault condition and, by interrupting continuity, to

.

Unlike a fuse, which operates once and then has to be replaced, a circuit breaker canbe reset (either manually or automatically) to resume normal operation

Current interruption in a high-voltage circuit-breaker is obtained by separating two contactsin a medium, such as SF6, having excellent dielectric and arc quenching properties.

After contact separation, current is carried through an arc and the arc is interrupted &

cooled by a gas blast of sufficient intensity.



Each CB comprises three single-phase metalenclosed breaker poles.

Each Pole consists of operating mechanism, theinterrupter column with 2 interrupting chambers inseries & the enclosure with the basic su ortstructure.

To guarantee simultaneous interruption, thechambers are mechanically connected in series.

One grading capacitor guarantees an equalizedvoltage distribution.

Assembly of Metal enclosedBreaking poles 25



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Making use of arc energy to produce the pressure necessary to quench the arc and obtaincurrent interruption. Low current interruption, up to about 30% of rated short-circuit current, isobtained by a puffer blast.

A valve between the expansion and compression volumes.

When interru tin low currents the valve o ens under the effect of the over ressure eneratedin the compression volume. The blow-out of the arc is made as in a puffer circuit breaker by

compression of the gas obtained by the piston action.

In the case of high currents interruption, the arc energy produces a high overpressure in theexpansion volume, which leads to the closure of the valve and thus isolating the expansion volumefrom the compression volume.

The overpressure necessary for breaking is obtained by the optimal use of the thermal effect.27



Each Pole of the CB is equipped with the Hydraulic spring operating mechanism.

It combines the advantages of both Hydraulic operating mechanism & Spring energystorage type.

A Hydraulic pump moves oil from low pressure reservoir to high pressure reservoirside of the energy piston.

Opening & Closing of CB is initiated by trip coil actuation. 28



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Current transformer (CT) is used for measurement of electric currents. Currenttransformers are also known as instrument transformers.

Current transformers are commonly used in metering and protective relays inthe electrical power industry.

When current in a circuit is too high to directly apply to measuring instruments,a current transformer produces a reduced current accurately proportional tothe current in the circuit, which can be conveniently connected to measuringand recording instruments.



Voltage transformers (VTs), also referred to as “Potential transformers" (PTs), areused in high-voltage circuits.

They are designed to present a negligible load to the supply being measured, to

a ow protect ve re ay equ pment to e operate at ower vo tages, an to ave aprecise winding ratio for accurate metering



The single pole inductive voltagetransformer is connected to switchgear with the connecting flanges witha barrier insulator.

The primary winding is insulatedwith SF6 gas & connected to highvoltage terminal.

The primary winding is wounded on

the top of the core & secondarywindings.

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e secon ary w n ng s connec eto the terminals in the external

terminal box through a gas tightmultiple bushing.



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Disconnector and Earthing switches are safety devices used to open or to closea circuit when there is no current through them.

They are used to isolate a part of a circuit, a machine, a part of an overhead line or an underground line so that maintenance can be safely conducted.

The opening of the line isolator or busbar section isolator is necessary for safety, butnot sufficient. Grounding must be conducted at both the upstream and downstreamsections of the device under maintenance. This is accomplished by earthing switches.

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Disconnect switches are designed tocontinuously carry load currents and

momentarily carry short circuit currents for a specified duration.

The are desi ned for no-load switchin

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opening , or closing circuits where negligible

currents are made or interrupted (includingcapacitive current and resistive or inductivecurrent , or when there is no significantvoltage across the open terminals of theswitch.



Fast earth switch and maintenance earth switch are the two types of earth switches usedfor gas insulated sub-station systems.

Fast earth switch is used to protect the circuit-connected instrument voltage transformer

charge stored online during isolation / switching off the line.

Use of fast earth switch provides a parallel (low resistance) path to drain the residual staticcharge quickly, thereby protecting the instrument voltage transformer from the damages thatmay otherwise be caused. The basic construction of these earth switches is identical.

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Wave Trap

Capacitance

VoltageTransformer

LighteningArrestor

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Capacitor Voltage Transformers convert transmission class voltages to standardized low andeasily measurable values, used for metering, protection and control of the high voltage system.

Additionally, Capacitor Voltage Transformers serve as a coupling capacitor for coupling highfrequency power line carrier signals to the transmission line.



Lightning Arresters or Surge Arresters are alwaysconnected in Shunt to the equipment to be protected,they provide a low impedance path for the surgecurrent to the ground

Line trap also is known as Wave trap. It traps Hi-frequency communication signalssent on the line from the remote substation and diverting them to the telecom/

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e e pro ec on pane n e su s a on con ro room roug coup ng capac or and LMU).

This is relevant in Power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecomcompany network.



SF6 – Air Bushings are used for connecting to open terminal equipment &Overhead transmission lines.

SF outdoor bushings allow the enclosed switchgear to be connected to overheadlines.

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CABLE TERMINATION (Fig - a): High-Voltage cables of various types are

connected to SF6 switchgear via cable connection assembly & also it enables theGIS & Cables to be tested separated

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Transformer connection (Fig - b) consists of Oil/SF6 bushing, the enclosure, the maincircuit end terminal & removable connection.

For Hi-Voltage test on GIS, transformer is isolated from switchgear by dismantlingthe removable connection

Fig - bFig - a



The insulating and interrupting capability of the SF6 gas depends on the density of the

SF6 gas .

The pressure of the SF6 gas varies with temperature, so a mechanical or electronictemperature compensated pressure switch is used to monitor the equivalent of gasdensity.

Gas Density Monitor is directly mounted on the enclosure. The gas pressure acts onmetal bellows, with a reference volume for compensation of the temperature.

In case of gas leakage a micro-switch is actuated. Thresholds for refilling (first stage) or lock-out alarm(second stage) can be mechanically set. The response character is shown in

the Molier diagramme.

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Isolating Gas Pressure isgenerally 350-450 Kpa at 20 deg

.

Quenching gas pressure isabout 600-700 Kpa

Outdoor Equipment exposed toarctic conditions contains amixture of SF6 & N2.

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An autotransformer is an electrical transformer with only one winding.

The winding has at least three electrical connection points called taps. The voltagesource and the load are each connected to two taps.

One tap at the end of the winding is a common connection to both circuits (source andload). Each tap corresponds to a different source or load voltage.

432 nos. 315 MVA, 400/220/33 kV three phase Auto Transformers



An autotransformer for power applications is typically lighterlighterlighterlighter and lesslesslessless

costlycostlycostlycostly than a two-winding transformer, up to a voltage ratio of about 3:1voltage ratio of about 3:1voltage ratio of about 3:1voltage ratio of about 3:1 -beyond that range a two-winding transformer is usually more economical.

In an autotransformer a portion of the same windingsame windingsame windingsame winding acts as part of both

the primary and secondary winding.

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To Line-4 To Line-3 To Line-2 To Line-1Bus CouplerBay

From ICT 1 From ICT 2



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47



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(For Further Space reduction)

Gas Insulated Transformer (GIT) Instead of Oil Immersed Transformer (OIT).

SMART GIS - Integration of Electronic CT’s & PT’s

Combined Earthing Switch & Disconnector

54



55



Natural Cooled type

56Forced-Gas-Circulated , Forced-Air-

Forced-Gas-Circulated , Natural-Air-Cooled



57



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GIT OIT

Medium SF6 Insulating oilTurn Insulation PET film Cellulose paper

Conservator Not Required Necessary

Pressure Relief Device Not required Necessary

Others Fundamentally Same



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Nonflammability – Gas insulated transformers , using incombustible SF6 gas asinsulation and cooling medium, enable to remove a fire fighting equipment from

.

Non Tank – explosion - Pressure tank enables to withstand the pressure rise in case ofinternal fault.

Compactness – Since conservator or pressure relief equipment is not necessary, height

of transformer room can be reduced approximately 2 – 2.5 meters.

Easy installation – oil or liquid purifying process is not necessary in case of gas-insulated

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transformer.

Easy inspection and maintenance work -Only SF6 gas pressure shall be basicallymonitored during periodically inspection.



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The Combined sensors are the Rogowski coil for current measurement and thecapacitive divider for voltage measurement

A combined current and volta e sensor has been develo ed to re lace the

conventional current and voltage transformers in GIS.

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1. Serial Optic Link 2. Voltage sensor 3. Rogowski Coil



Why Combined Voltage & current Sensor ?

Advanced CT’s without a magnetic core (Rowgowski coil) & Capacitive sensor havebeen developed to save space and reduce the cost of GIS.

The output signal is at a low level, so it is immediately converted by an enclosuremounted device to a digital signal

Small size - Helps to optimize the use of space in the switchgear

Lighter weight means less material usage and lower life cycle costs (LCC)

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arge ynam c range - perm s m n m za on o num er o sensor ypes nee e animprovement of some protection functions.

Protection and measurement functions combined.

Lower losses mean lower LCC (Life Cycle Cost)



–

Current Transformer

The current sensor is based on a Rogowski coil (acoreless inductive current transformer).

Voltage Measurement – Voltage Sensor instead ofVoltage Transformer

65

The voltage sensor is based on a capacitive electrical

field sensor (Capacitive ring sensor).

The capacitive ring, which acts as a voltage sensor,also has a linear characteristic and is very simple interms of the insulation.



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1. Busbar with Combined DS & ES2. Circuit-breaker3. Current sensor (Rogowski coil)

4. Electro-optical voltage transform6. Make-proof earthing switch7. Control cubicle

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1. Busbar with Combined DS & ES

2. Circuit Breaker3. Current Transformer4. Voltage transformer5. Combined DS & ES with cable sealing

end

6. Hi-Speed ES7. Control Cubicle



The DSES incorporates the two functions of a disconnector and a maintenanceearthing switch as a result saving the space in GIS.

This is achieved by a sliding contact characterized by three defined positions:- disconnector open / earthing switch closed

- disconnector closed / earthing switch open-disconnector open / earthing switch open

The use of one moving contact for the disconnector and the earthing switch inhibitssimultaneous closed position of both switches.

68Busbar with CombinedDisconnector & Earthing Switch



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Depending on the direction of movement

Combined disconnector and earthing switch is mounted at the front, andacts via bevel gears and an insulating shaft on the three parallel contact pins.

the contacts act as disconnector or earthingswitch (maintenance earthing switch).

By means of a crank handle, manualoperation of the combined disconnector andearthing switch is also possible.

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(O & M)

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Life cycle cost

AIS GIS



Planning and engineering 100% 80%

Real estate 100% 40%

Secondary equipment 100% 100%

Earthwork, civil work, structures 100% 60%

Electrical assembly and erection 100% 70%

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Outage 100% 50%

Life cycle costs after 10 years 100% Max. 70%



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Optimizing of acquisition costs Cost of Acquisition



Acquisition costs are mainly influenced by the layout, the redundancy concept and therequirement area for the installation.

The optimization of the layout and the redundancy can be supported by LCC analysis which takeinto account the different reliability figures of the different technologies.

Cost of Acquisition

The goal is to achieve optimal availability of the substation with minimized costs.

Optimizing of costs of ownership

The costs of ownership are dominated by the maintenance strategy and the reliability of theswitchgear. By means of LCC analysis, the different maintenance strategies can be simulated.

Pure corrective maintenance can be compared with time-based or reliability – centeredmaintenance.

Cost of Ownership

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Optimizing of renewal costs

LCC calculations assist in determining the optimal date for replacing an existing substation.

Aged equipment requires intensified maintenance, more specialized experts and spare parts.

The effect of investment costs of new equipment with reduced maintenance costs can be balancedwith the increased expenditure for intensified maintenance of the old equipment

Cost of Ownership



Cost of GIS is high.

e e o s a ec e y cer a n ac ors suc as: con uc ve par c es,partial discharges and contamination (decomposition products, water, etc

Gas Insulated Substations (GIS) can be used for longer times without anyperiodical inspections.

However, conducting contamination (i.e. aluminum, copper and silver particles) could seriously reduce the dielectric strength of gas-insulated

.

SF6 has been identified as a greenhouse gas, safety regulations are beingintroduced in order to prevent its release into atmosphere.

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The first GIS’s were put in operation in 1967 in Switzerland and Germany.

The GIS in German is still in o eration whereas the GIS in Switzerland were

recently decommissioned after 35 years of operation without major fault or gasleak.

An assessment made on SF6 gas leakage over the lifetime of the first GIS andconcluded that overall leakage rate was about 0.4% per year.

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Pls write your comments & feedback to

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21548809 Gas Insulated Substation

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