7th Sem. Seminar Presentation 2013, EEE Dept.

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Under the guidance of Mr. Preeti Ranjan Sahu

Presented by

Gas Insulated Substations

INTRODUCTION :

Definition :

Usage :

Components :

(SF6) gas :

Safety :

GIS advantages and disadvantages :GIS Requirements :

CONCLUSION : 

GIS Assembly

INTRODUCTION :

INTRODUCTION Conventional substations requires, small installation size, protection against atmospheric pollution and moisture, noiseless operation, nonexplosive and flame resistant, reduced maintenance, minimal radio interference, but totally enclosed substations using SF6 gas as insulation that are also known as GIS is now in widespread use in the electrical power industry .

Gas Insulated Substations (G.I.S)

Gas Insulated Substations (G.I.S)

• Definition :

• A gas insulated substation (GIS) is a substation that uses a superior dielectric gas, sulfur hexafluoride (SF6), high-voltage.

• The basic principle of gas-insulated equipment :

• Is that the high-voltage current- carrying parts are within a metal enclosure and are held in a concentric configuration by cast epoxy spacer insulators.

• The space between the conductor and the enclosure is filled with sulfur hexafluoride gas under moderate pressure.

Gas Insulated Substations (G.I.S)

• Usage :

• Gas insulated substation mainly used for a power transmission system or a substation system, of which outgoing bus-bar is shortened to reduce consumption of the outgoing bus-bar.

• The equipment can be designed for any bus scheme.

Gas Insulated Substations (G.I.S)

• Components :• 1 → Circuit breaker.

• 2 → Disconnector (Isolator).

• 3 → Ground switches.

• 4 → Bus-bar.

• 5 → Transformer.

• 8 → Outgoing bus-bar for electr-ically connecting the gas insul-ated substation with bus-bar.

• 9 → Outgoing portion of the tra- nsformer being arranged in accor-dance with extendingdirection of outgoing bus-bar.

Gas Insulated Substations (G.I.S)

• (SF6) gas :• The dielectric medium is the sulfur hexafluoride (SF6) gas,

• SF6 has been used as an insulating medium inelectronic devices, power apparatus, and HVDC converter stations.

• Its excellent properties make it ideally suited both as an insulating and as an arc-quenching agent.

• SF6 gas is colorless, odorless, chemically inert, nontoxic, nonflammable, and non-corrosive.

• Its dielectric strength is greatly superior to that of air, and it is close to 100

• times as effective as air in quenching an electric arc.

Gas Insulated Substations (G.I.S)

• Safety :

• The live parts and supported on at resin insulators. Some of the insulators are designed as barriers between neighboring modules such that the gas does not pass through them.

• The GIS has gas-monitoring system. The gas density in eachcompartment is monitored.

• If pressure drops slightly, the gas is automatically tapped up with further gas leakage, the low-pressure alarm is sounded or automatic trippingor lock-out occurs.

GIS Assembly:ESSENTIAL PART OF GIS1.Bus bar2.Circuit breaker3.disconnector(line or bus)4.Earthing switch(line or bus)5.Current transformer(feeder/bus)6.Voktage transformer(feeder/bus)7.Feeder disconnector8.Feeder earthing switch

Gas Insulated Substations (G.I.S)

Gas Insulated Substations (G.I.S)

• GIS advantages and disadvantages :

• GIS Disadvantages :

• 1. Excessive damage in case of internal fault. Long outage periods as the repair of damaged part at site may be difficult.

• 2. Requirement of cleanliness is very stringent. Dust or moisture can cause internal flashovers.

• 3. Such substations are generally indoor, so they need a separate building. This is generally not required for conventional outdoor substations.

Gas Insulated Substations (G.I.S)

• GIS advantages and disadvantages :

• GIS Disadvantages :

• 4. Procurement of gas and supply of gas to site is problematic, adequate stock of gas must be maintained.

• 5. Project needs almost total imports including SF6 Gas. Spares conventional substation is totally indigenous up to 400 kV.

Gas Insulated Substations (G.I.S)

• GIS advantages and disadvantages :

• GIS Advantages :

• 1. Reduced required space: The space occupied by SF6 installation is only about 8% to 10 % of that a conventional outdoor substation. High cost is partly compensated by saving in cost of space. A typical (420/525) kV SF6 GIS requires only 920m2 site area against 30000 m2 for a conventional air insulated substation.

• 2. Reliable: The complete enclosure of all live parts guards against any impairment of the insulation system.

Gas Insulated Substations (G.I.S)

• GIS advantages and disadvantages :

• GIS Advantages :

• 3. Reduced maintenance and consequently, lower costs.

• 4. The safety is increased: As the enclosures are at earth potential there is no possibility of accidental contact by service personnel to live parts.

• 5. From 30 kV to 500 kV they might result cheaper than conventional units. High flexibility and application versatility provide unique, and economic overall concepts.

Gas Insulated Substations (G.I.S)

• Hence, to solve this problem, smaller installations are needed, which should also comply the following requirements:

• 1. They shall be insensible to climatic influences.

• 2. They can be raised outdoors, inside a building or underground.

• 3. They require reduced maintenance.

• 4. They are silent.

• 5. They should not generate radio-electric disturbances.

• 6. They shall not imply danger for the nearby populated.

Gas Insulated Substations (G.I.S)

• GIS Requirements :

• The following requirement are important to satisfy, the requirement of GIS can be summarized as :

• 1. Conductors which conduct the main circuit current and transfer power these are of copper or aluminum tubes.

• 2. Conductors need insulation above grounded enclosures, conductors also need phase to phase insulation, in SF6 requirements are met by cast resin insulators and SF6 gas insulation. GIS these insulation

• 3. Gas filled modules have nonmagnetic enclosures, enclosures are of aluminum alloy or stainless steel, aadjacent modules are joined bymeans of multi-bolts tightened on flanges.

Gas Insulated Substations (G.I.S)

• GIS Requirements :

• 4. Various circuit components in main circuit are: CB, Isolator, Earthingswitches for conductors, CTs, VTs, cable-ends, Bushing-ends and Bus-Bars, each of these main components has its own gas -filled metal enclosed module.

• 5. Gas filling, monitoring system.

• 6. Auxiliary low voltage DC and low voltage AC supply system, control, protection and Monitoring systems.

• 7. The bus-bars are conducting bars to which various incoming andoutgoing bays are connected. In SF6 GIS the bus-bars are laidlongitudinally in GIS hall. The bays are connected to bus-bars cross- wise, bus-bars are either with a three-phase enclosure or single phase enclosure.

CONCLUSION : CONCLUSION GIS are some important areas to be studied include more

conservative designs better particle control&improved gas handling&decomposition product management techniques Achieving&maintaining high levels of availability requires a more integrated approach to quality control by both users and manufactures

Gas Insulated Substations (G.I.S)

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