GIS

GAS INSULALED SWITCHYARD GAS INSULALED SWITCHYARD (GIS)(GIS)

IntroductionIntroduction

TYPES OF SWITCHYARDTYPES OF SWITCHYARD

AIS (Air Insulated AIS (Air Insulated Switchyard)Switchyard)

GIS (Gas Insulated GIS (Gas Insulated Switchyard)Switchyard)

What is GIS ?

GIS is metal-enclosed switchgear in which the insulation is obtained by an insulating gas other than air at atmospheric pressure

Insulating Gas Sulphur Hexafluoride(SF6) gas has excellent dielectric properties and is used as the insulating medium between energized parts and the metal encapsulation.

Constraints in space availability in urban areas and hilly terrain as well as increasing volume of city distribution networks led to evolution of GIS technology.

GIS was first introduced in 1965.

Reliability, Compactness, Economic Advantages has resulted in widespread applications

GIS technology widely accepted and employed all over the world.

Background

SF6 GasSF6 Gas SF6 is an excellent dielectric medium. Under SF6 is an excellent dielectric medium. Under

comparable conditions, its dielectric strength is comparable conditions, its dielectric strength is more than twice that of air.more than twice that of air.

SF6 is an excellent arc-quenching medium, for SF6 is an excellent arc-quenching medium, for the three following reasons :the three following reasons :

- SF6 high dissociation energy efficiently cools - SF6 high dissociation energy efficiently cools down the arc,down the arc,

- the fluor ions resulting from dissociation are - the fluor ions resulting from dissociation are highly electronegative and seize quickly the free highly electronegative and seize quickly the free electrons. These electrons. These are ineffective as current carriers.

- the very fast recombination of dissociated SF6 - the very fast recombination of dissociated SF6 molecules allows very severe voltage recoveries.molecules allows very severe voltage recoveries.

Dielectric Properties of SF6 Dielectric Properties of SF6 GasGas

PROPERTIES OF SF6

Heavy chemically inert non toxic gas

Colourless and odourless and non flammable

No poisonous effect on human body, but decomposition products are harmful.

It is gaseous at normal room temperatures and pressures

Density 6.16 g/l at 20 º C and 760 torr. (about 5 times the density of air).

Critical temperature 45.6 º C and can be liquified by compression

Liquification temperature under normal conditions is 27ºC at a pressure of

12 kg/sq.cm

This gas is highly stable. No permanent deterioration of the gas. Stability of the gas is such that it shows no sign of Chemical Change at temperatures well above those at which switch oil begins to oxidize and decompose.

Dielectric properties of SF6 remains unchanged even at low temperatures.

Contd…

PROPERTIES OF SF6

• Decomposition occurs on exposure to electric arc but the dissociation products being the lower order fluoride gases SF2 and SF4 (these largely recombine on cooling) plus some metallic fluoride in the form of an insulating powder. This and any remaining gases can be readily absorbed by actuated alumina in suitably placed filters.

MERITS OF GISMERITS OF GIS COMPACTNESSCOMPACTNESS HIGHER RELIABILITY AND HIGHER RELIABILITY AND

AVAILABILITYAVAILABILITY NEGLEGIBLE MAINTENANCENEGLEGIBLE MAINTENANCE ENVIRONMENTAL FRIENDLYENVIRONMENTAL FRIENDLY LOWER ERECTION TIMELOWER ERECTION TIME SAFETY SAFETY LOW LIFE CYCLE COSTLOW LIFE CYCLE COST

COMPACTNESSCOMPACTNESS

Compact dimensions.Compact dimensions. Land requirement is Land requirement is

10-20% of AIS.10-20% of AIS. Saving in land Saving in land

depends upon voltage depends upon voltage level.level.

May be installed in May be installed in middle of load centre middle of load centre of urban or industrial of urban or industrial area.area.

Impact of insulating medium on size of the Impact of insulating medium on size of the switchyardswitchyard

Voltage Voltage LevelLevel

Bay widthBay width

AISAISBay widthBay width

GISGIS

132 kV132 kV 12 m12 m 1 m1 m

220 kV220 kV 18 m18 m 2 m2 m

400 kV400 kV 27 m27 m 3.6 m3.6 m

765 kV765 kV 51.5 m51.5 m 6.5 m6.5 m

Single line diagram of a 765 Single line diagram of a 765 kV Switchyard kV Switchyard

765 kV Swyd. With 1 and half breaker scheme765 kV Swyd. With 1 and half breaker schemeSize of AIS = 451m X 355m, 10 BaysSize of AIS = 451m X 355m, 10 Bays

765 kV Swyd. With 1 and half breaker 765 kV Swyd. With 1 and half breaker schemescheme

Size of GIS = 151m X 295m, 10 BaysSize of GIS = 151m X 295m, 10 Bays

Comparision (Typical)Comparision (Typical)

Area (AIS) = 451m X 355m = 160105 m2Area (AIS) = 451m X 355m = 160105 m2 Area (GIS) = 151m X 295m = 44545 m2Area (GIS) = 151m X 295m = 44545 m2 Reduction in space = 72 %Reduction in space = 72 % This can further downsized if we replace This can further downsized if we replace

the one and half breaker scheme in AIS the one and half breaker scheme in AIS with double bus scheme in GIS as with double bus scheme in GIS as reliability (as availability of GIS with reliability (as availability of GIS with double bus is even better than AIS with double bus is even better than AIS with one and half breaker scheme)one and half breaker scheme)

GIS and AIS size comparison in NTPC GIS and AIS size comparison in NTPC ProjectsProjects

 Tapovan Vishnugad HEPP

520MW Koldam HEPP 800MW

Length 114 m 250m

Width 18m 240m

Area5624m2 (2052m2

+3572m2) 60000m2

No of Bays 7 9

Area /Bay 803 6666.66

Scheme Double Bus Breaker and Half

Area reduction in Percentage( per bay) 88 %

Example of Replacement of a Substation

Existing AIS substation (72kV-1200kA, 2 X 15MVA)

After replacement (Gas Insulated Substation)

REPLACEMENT/UPGRADATIONREPLACEMENT/UPGRADATION

GIS can be used for replacement of AIS GIS can be used for replacement of AIS in the event of growing power demand in the event of growing power demand without the additional land without the additional land requirements.requirements.

Space for existing 8-10 bay 132 KV AIS Space for existing 8-10 bay 132 KV AIS could be easily utilized for upgrading could be easily utilized for upgrading to 14-18 bays 220 KV / 400KV GIS.to 14-18 bays 220 KV / 400KV GIS.

RELIABILITY & AVAILABILITY RELIABILITY & AVAILABILITY

Less failure/ Less failure/ maintenance as maintenance as exposure of live exposure of live components to components to weather is eliminated.weather is eliminated.

Almost nil Almost nil maintenance upto 10 maintenance upto 10 years.years.

Due to enclosed bus Due to enclosed bus bar, bus faults are bar, bus faults are minimal.minimal.

MaintenanceMaintenance

Due to the tightly-sealed enclosures, GIS need minimum maintenance and therefore regarded as maintenance-free under normal operating conditions.

Visual inspection is carried out bay by bay without any need for outages or the opening of gas compartments.

Major inspection is not required before atleast

10 years of operation.

Erection and CommissioningErection and Commissioning Quick installation and erection is

facilitated because of :

Delivery of the GIS bays in easy-to-handle factory assembled modular units.

Use of relatively few special tools for erection.

Small number of system components

Contd……Contd……Commissioning:

Pre commissioning activities are not significant as the equipments are pre tested at factory.

Take less time to check all switching devices and electrical circuits.

All flanges are double-checked for tightness especially those fitted on site.

High voltage test done on primary circuit.

All tests are performed in accordance with IEC standards.

SAFETYSAFETY The metal encapsulated GIS The metal encapsulated GIS

provides high degree of safety for provides high degree of safety for operator and other personnel due to operator and other personnel due to the fact that , it is impossible to the fact that , it is impossible to touch any live part of switchyard.touch any live part of switchyard.

GIS equipments are built up in GIS equipments are built up in compartments and isolated from compartments and isolated from each other. This prevents spreading each other. This prevents spreading of failure.of failure.

Environmental ImpactEnvironmental Impact

SF6 has a high material-based global warming potential (GWP) and is included in the “six gas basket of the Kyoto Protocol”.

Research shows that the total worldwide emissions of SF6 contribute only about 0.1 percent of the overall anthropogenic greenhouse effect. This includes both the SF6 emissions from the use in electricity transmission and distribution systems (about 70-80 % of the global SF6 production) and those from all other uses.

Environmental ImpactEnvironmental Impact

The direct contribution of SF6 to greenhouse gas emissions is relatively low and the advantages of a reliable electrical system outweigh these negatives.

Lower system losses and less materials required during manufacture reduce the life cycle carbon emissions, potentially offsetting the negative effects of SF6.

Various life cycle analysis which considers materials, manufacture, ohmic losses and SF6 emissions shows that overall GIS contributes 30% less to global warming than AIS.

TECHNO-ECONOMIC TECHNO-ECONOMIC FEASIBILITY OF GIS FEASIBILITY OF GIS

Initial equipment cost is higher.Initial equipment cost is higher.

Merits/ Considerations in respect to Merits/ Considerations in respect to higher initial equipment expenditure higher initial equipment expenditure makes GIS techno-economic feasible.makes GIS techno-economic feasible.

Contd…… Contd…… Life cycle of GIS is about 50 years, where as for

AIS life cycle is 25 years. Approximate cost per bay for 400 KV of GIS & AIS

is as follows: - GIS 7-8 crores - AIS 4-5 crores. Hence initial cost of GIS is approximately 1.5-1.7 times that of AIS. When all merits over the life cycle of GIS is

considered then GIS becomes techno-economic feasible than AIS.

LIFE CYCLE COST OF GISLIFE CYCLE COST OF GIS

Switchgear Solution AIS GISLife Cycle cost    

Planning and Engineering 100% 80%

Real estate 100% 40%

Primary equipment 100% 150%

Earthwork, civil work, structures 100% 60%

Electrical assembly and erection 100% 70%

Maintenance 100% 50%

Outage 100% 50%

Life cycle costs after 10 years 100% 71%

Components of GISComponents of GIS Circuit breakersCircuit breakers Isolators Isolators Current TransformersCurrent Transformers Voltage transformersVoltage transformers Surge arrestorsSurge arrestors GIS bushingsGIS bushings GIS bus barsGIS bus bars

300 KV GIS Substation

APLICATION OF GISAPLICATION OF GIS

Underground and over ground power Underground and over ground power houseshouses

Grid substationsGrid substations Distribution sub stations in metrosDistribution sub stations in metros Refineries/chemical plantsRefineries/chemical plants Near sea coast, Polluted areas, Near sea coast, Polluted areas,

Desert etc.Desert etc.

GIS Switchyard GIS Switchyard LayoutsLayouts

Layout Plan of Tapovan Layout Plan of Tapovan Switchyard GIS HallSwitchyard GIS Hall

Section of Tapovan Section of Tapovan Transformer & GIS HallTransformer & GIS Hall

Isometric View of Transformer hall and Isometric View of Transformer hall and GIS FloorGIS Floor

TAPOVAN POTHEAD YARDTAPOVAN POTHEAD YARD

Cross Section of Parbati Cross Section of Parbati HEPPHEPP

Cross Section of Lower Cross Section of Lower Subansari HEPPSubansari HEPP

Manufacturers of GISManufacturers of GIS

AREVA, FRANCEAREVA, FRANCE SIEMENS, GERMANYSIEMENS, GERMANY ABB, SWITZERLANDABB, SWITZERLAND HYOSUNG, KOREAHYOSUNG, KOREA HITACHI, JAPANHITACHI, JAPAN TOSHIBA, JAPANTOSHIBA, JAPAN

CONCLUSIONCONCLUSION

GIS is getting acceptance on account of technical GIS is getting acceptance on account of technical merits.merits.

Excellent adoptability due to Low space Excellent adoptability due to Low space requirement and high dielectric strength of SF6 requirement and high dielectric strength of SF6 gas.gas.

Safety to operators and equipment.Safety to operators and equipment. Short erection and commissioning time.Short erection and commissioning time. Reduced requirement of maintenance.Reduced requirement of maintenance. Initial cost of GIS is higher than AIS, but when all Initial cost of GIS is higher than AIS, but when all

merits and life cycle cost of GIS is considered then merits and life cycle cost of GIS is considered then GIS becomes techno-economic feasible than AIS.GIS becomes techno-economic feasible than AIS.

THANK YOUTHANK YOU