gas insulated substation full report

[seminar class]

presented By :
Arupananda Pattanaik

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GAS INSULATED SUBSTATION
Introduction
 It is a one type of switchgear.
 The term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects.
 There are 3 types of switchgear.i.e
1. AIS
2. HYBRIT GIS
 GIS
 Gas Insulated Substations (GIS) is a compact,multicomponent assembly enclosed in a ground metallic housing in which the primary insulating medium is compressedSulphur hexafluoride (SF6)gas.
 SF6acts as an insulation between live parts & the earthed metal closure.
 Gas insulated switchgear is used in industrial areas to fulfil high-energy demands by space saving design with a minimum of cost
 SF6 switchgear installed in Canada in a 550 kV substation with 100 kA
 Comparison between AIS &GIS
AIS
 Air-insulated substation:- An electric power substation that has the busbars and equipment terminations generally open to air.
 It utilizes insulation properties of ambient air for insulation to ground.
 Very fast electromagnetic transients (VFT) in air insulated substations (AIS)
 Air Insulated Substation (AIS) makes it possible to install High Voltage substations that take-up less space
 These are more cost-efficient than conventionally designed outdoor infrastructures.
 Image of AIS
 Hybrid Gas Insulated Switchgear
 Small equipment cost.
 It takes less area.
 High reliability similar to GIS substation.
 Easy extension.
 It is a combination of AIS and GIS.
 GIS
 Gas Insulated Substations (GIS) is a compact,multicomponent assembly enclosed in a ground metallic housing in which the primary insulating medium is compressedSulphur hexafluoride (SF6)gas.
 SF6acts as an insulation between live parts & the earthed metal closure.
 Gas insulated substations are particularly suitable for underground construction beneath public buildings.
 Gas insulated substation mainly used for a power transmission system or a sub-station system, of which outgoing bus bar is shortened to reduce consumption of the outgoing bus bar
 Sulfur Hexafluoride
 A colorless, odorless, non-toxic, liquified gas. Shipped as a liquid under its own vapor pressure.
 Sulfur Hexafluoride gas, which is itself inert.
 It disassociates in the presence of an RF field to form reactive fluorine ions.
 SF6acts as an insulation between live parts & the earthed metal closure.
 The dielectric strength of SF6 gas at atmospheric pressure is approximately three times that of air.
 pace requirement is only 10 to 25 percent of what is required is a conventional substation.
 SF6 can be prepared from the elements through exposure of S8 to F2. This is also the method used by the discoverers Henri Moissan and Paul Lebeau in 1901
 It does not react with molten sodium, but reacts exothermically with lithium.
 Of the 8,000 tons of SF6 produced per year, most (6,000 tons) is used as a gaseous dielectric medium in the electrical industry,
 it has a much higher dielectric strength than air or dry nitrogen.
 This property makes it possible to significantly reduce the size of electrical gear.
 Properties
 Molecular formula SF6
 Molar mass 146.06 g/mol,
 Density 6.164 g/L (gas, 1 bar)
1.329 g/ml (liquid, 25 °C)
2.510 g/cm3 (solid, −50.8 °C)
 Melting point- 50.7 °C (triple point)
 Boiling point− 64 °C (209 K) (subl.)
decomp. at ca. 500 °C (773 K)
 Solubility in waterslightly soluble
 Solubility in ethanolsoluble
 Specification of GIS
 The weight and size of the GIS equipment do not change appreciably with the voltage class.
 The additional insulation required for the next voltage class is achieved by increased gas 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, the dimensions and weights of the equipment differ marginally.
 Component of GIS
 Bus bars.
 Circuit Breakers.
 Disconnecting switches.
 Earthing switches.
 Current transformer.
 Voltage transformers.
 Cable and boxes.
 Gas supply and gas monitoring equipment.
 Circuit Breakers
 A circuit breaker is an automatically-operated electrical switch designed to protect from damage caused by overload or short circuit.
 Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.
 Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
 Current interruption in a high-voltage circuit-breaker is obtained by separating two contacts in 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.
 Current transformer
 Current transformer (CT) is used for measurement of electric currents.
 Current transformers are also known as instrument transformers.
 Current transformers are commonly used in metering and protective relays in the electrical power industry.
 Voltage transformers
 Voltage transformers (VTs), also referred to as “Potential transformers" (PTs), are used in high-voltage circuits.
 They are designed to present a negligible load to the supply being measured, to allow protective relay equipment to be operated at lower voltages, and to have a precise winding ratio for accurate metering
Disconnecting switches
 Disconnector switches are safety devices used to open or to close a circuit when there is no current through them.
 These 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, but not sufficient.
 Life cycle cost AIS GIS
 Planning and engineering 100% 80%
 Real estate 100% 40%
 Primary equipment 100% 120%
 Secondary equipment 100% 100%
 Earthwork, civil work 100% 60%
 Electrical assembly 100% 70%
 Maintenance 100% 50%
 Outage 100% 50%
 Life cycle costs after 10 years 100% 70%