Current Transformers (CT) are the devices in which the secondary current used for calculation is proportional to the primary current produced by the electrical network. For this purpose, the primary current is tapped from the transmission line and stepped down in the secondary for measurement purposes. In series with the current lead, the connection to the primary winding circuit is…
Electrical Substation
Electrical Substation is most common word for an Electrical Engineer or Engineering Student. You will find all practical problem and solution for making and maintain an electrical substation in real life.
Maintenance of GIS: Experience has shown that the internal parts of Gas Insulated Substation are so well protected inside the metal enclosure that they do not age and as a result of proper material selection and lubricants, there is negligible wear of the switch contacts. Only the circuit breaker arcing contacts and the Teflon nozzle of the interrupter experience wear…
Installation: The GIS is usually installed on a monolithic concrete pad or the floor of a building. It is most often rigidly attached by bolting and/or welding the GIS support frames to embedded steel plates or beams. Chemical drill anchors can also be used. Expansion drill anchors are not recommended because dynamic loads may loosen expansion anchors when the circuit…
Electrical and Physical Arrangement: For any electrical one-line diagram there are usually several possible physical arrangements. The shape of the site for the GIS and the nature of connecting lines and/or cables should be considered. Figure 1 compares a “natural” physical arrangement for a breaker and a half GIS with a “linear” arrangement. Most GIS designs were developed initially for…
Gas Monitor System: The insulating and interrupting capability of the SF6 gas depends on the density of the SF6 gas is at a minimum level established by design tests. The pressure of the SF6 gas varies with temperature, so a mechanical temperature-compensated pressure switch is used to monitor the equivalent of gas density. GIS is filled with SF to a…
Surge Arrester: Zinc oxide surge arrester elements suitable for immersion in SF6 are supported by an insulating cylinder inside a GIS enclosure section to make a surge arrester for overvoltage. Because the GIS conductors are inside in a grounded metal enclosure, the only way for lightning impulse voltages to enter is through the connections of the GIS to the rest…
Bus: To connect GIS modules that are not directly connected to each other, and SF6 bus consisting of an inner conductor and outer enclosure is used. Support insulators, sliding electrical contacts, and flanged enclosure joints are usually the same as for the GIS modules. Air Connection: SF6-to-air bushings are made by attaching a hollow insulating cylinder to a flange on…
Circuit Breaker: GIS uses essentially the same dead tank SF6 puffer circuit breakers used in AIS. Instead of SF6 -to-air as connections into the substation as a whole, the nozzles on the circuit breaker enclosure are directly connected to the adjacent GIS module. Current Transformers: CTs are inductive ring types installed either inside the GIS enclosure or outside the GIS…
GIS is assembled of standard equipment modules (circuit breaker, current transformers, voltage transformers, disconnect and ground switches, interconnecting bus, surge arresters, and connections to the rest of the electric power system) to match the electrical one-line diagram of the substation. A cross-section view of a 242-kV GIS shows above the construction and typical dimensions. Construction of GIS Substation: The modules…
A gas-insulated substation (GIS) uses a superior dielectric gas, SF6, at moderate pressure for phase-to-phase and phase-to-ground insulation. The high voltage conductors, circuit breaker interrupters, switches, current transformers, and voltage transformers are in SF6 gas inside grounded metal enclosures. A photo of Gas Insulated Substations 420kV. The atmospheric air insulation used in a conventional, air-insulated substation (AIS) requires meters of…