26-06-2012, 03:30 PM
development and design of compressed Gas Insulated Substations
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INTRODUCTION
The development and design of compressed Gas Insulated Substations (GIS) and compressed Gas Insulated Transmission line (GITL) equipment have progressed drastically for the last three decades throughout the world because of the excellent insulation properties of Sulphur hexafluoride (SF6) gas [1]. The Gas Insulated Substations equipment such as compact substations and transmission lines is rapidly becoming an important part of high voltage transmission systems and they are used in key positions in the power transmission network, where there is insufficient space for an open air substation, or the land costs are prohibitive.
Disconnectors (Isolators)
Isolators are placed in series with the circuit breaker to provide additional protection and physical isolation. In GIS systems, motorized isolators are preferred. The fixed contacts are separated by an isolating gas gap. During the closing operation, this gap is bridged by the moving contact. A firm contact is established between the two contacts with the help of spring-loaded fingers or the multi-lam contacts. The isolation gap is designed for the voltage class of the isolator and the safe dielectric strength of the gas. Figure 1.10 shows a cross-section of an isolated-phase GIS isolator. Isolators in high voltage GIS operate at SF6 pressures of 0.38 MPa to 0.45 MPa. The operating speed of the isolator moving contact ranges from 0.1 to 0.3m/sec [2].
Circuit Breaker
The circuit breaker is the most critical part of a gas insulated sub-station system. The circuit breaker in a gas-insulated system is metal-clad and utilizes SF6 gas, both for insulation and fault interruption. The SF6 gas pressure in a circuit breaker is around 0.65 MPa. The circuit breaker is directly connected to either current transformers or the isolators in gas.
Current Transformer
The conventional sub-stations use either live-tank or dead-tank type current transformers with Oil/SF6 insulation. A porcelain insulator is used to insulate the low potential section of the current transformer from the high voltage zone.
Earth Switch
Fast earth switch and maintenance earth switch are the two types of earth switches used for gas insulated sub-station systems. The maintenance earth switch is a slow device used to ground the high voltage conductors during maintenance schedules, in order to ensure the safety of the maintenance staff. The fast earth switch, on the other hand, is used to protect the circuit-connected instrument voltage transformer from core saturation caused by direct current flowing through its primary as a consequence of remnant charge (stored online during isolation/switching off of the line).
[attachment=25611]
INTRODUCTION
The development and design of compressed Gas Insulated Substations (GIS) and compressed Gas Insulated Transmission line (GITL) equipment have progressed drastically for the last three decades throughout the world because of the excellent insulation properties of Sulphur hexafluoride (SF6) gas [1]. The Gas Insulated Substations equipment such as compact substations and transmission lines is rapidly becoming an important part of high voltage transmission systems and they are used in key positions in the power transmission network, where there is insufficient space for an open air substation, or the land costs are prohibitive.
Disconnectors (Isolators)
Isolators are placed in series with the circuit breaker to provide additional protection and physical isolation. In GIS systems, motorized isolators are preferred. The fixed contacts are separated by an isolating gas gap. During the closing operation, this gap is bridged by the moving contact. A firm contact is established between the two contacts with the help of spring-loaded fingers or the multi-lam contacts. The isolation gap is designed for the voltage class of the isolator and the safe dielectric strength of the gas. Figure 1.10 shows a cross-section of an isolated-phase GIS isolator. Isolators in high voltage GIS operate at SF6 pressures of 0.38 MPa to 0.45 MPa. The operating speed of the isolator moving contact ranges from 0.1 to 0.3m/sec [2].
Circuit Breaker
The circuit breaker is the most critical part of a gas insulated sub-station system. The circuit breaker in a gas-insulated system is metal-clad and utilizes SF6 gas, both for insulation and fault interruption. The SF6 gas pressure in a circuit breaker is around 0.65 MPa. The circuit breaker is directly connected to either current transformers or the isolators in gas.
Current Transformer
The conventional sub-stations use either live-tank or dead-tank type current transformers with Oil/SF6 insulation. A porcelain insulator is used to insulate the low potential section of the current transformer from the high voltage zone.
Earth Switch
Fast earth switch and maintenance earth switch are the two types of earth switches used for gas insulated sub-station systems. The maintenance earth switch is a slow device used to ground the high voltage conductors during maintenance schedules, in order to ensure the safety of the maintenance staff. The fast earth switch, on the other hand, is used to protect the circuit-connected instrument voltage transformer from core saturation caused by direct current flowing through its primary as a consequence of remnant charge (stored online during isolation/switching off of the line).