The challenge for busbar disconnectors of gas insulated switchgear (GIS) in a 420kV mixed technology (Hybrid) substation (MTS)

摘要

The demand for electrical energy in the southern part of Germany, with environmentallyfriendly power generation of increasing on-shore and especially off-shore wind farms in thenorthern part of Germany, puts high requirements on existing power transmission lines andsubstations in the 420kV range. The existing 420kV substations have to be modified for thehigher energy transmission, from the northern to the southern part of Germany. Transmissionlines will be operated on their current limits (transmission loads up to 3000 MVA) whichcause feeder currents up to 4000A in the substations. This brings attention to the capability ofthe busbar disconnectors and their behaviour during busbar-transfer operations.In the product related international standard IEC 62271-102 (2001) [1] the related bus-transfervoltage (transfer voltage) for 420kV Air Insulated Substations (AIS) is given with 300V,while 20V is standard for Gas Insulated Substations (GIS). For the rated bus-transfer current,one common value for air-insulated and gas-insulated disconnectors is given with 1600A.This value considers a current distribution during commutation from one busbar to the otherbusbar of 80%/20% and therefore, a feeder current up to 2000A. The 1600A was chosen asbeing typically the highest current which can be switched, although the rated currents of thedisconnectors may be substantially higher.These given values for the bus-transfer voltage are not sufficient for the case in which an AISsubstationis modified by using the existing AIS-busbars and installing GIS bays. TheseMixed-Technology Substations (MTS) are used due to the higher number of bays which canbe installed on an existing footprint. Additionally, a greater flexibility in the substationlayouts can be achieved. Investigated substation configurations, which authorize the operatorfor bus-transfer operations, are double- or multi-busbar arrangements or substations using atransfer busbar for maintenance. The distance, respectively the impedance, of the AIS busbarconfiguration over the closed coupling bay is very important for commutation. In addition, thefeeder current and the load situation on the busbar, define the transfer voltage on thedisconnector before, during, and after the bus-transfer operation. Although these voltages are very small compared to the system voltage of the substation, ithas to be considered, because the switching capability of the disconnector is very limited tothe design. Therefore, the transfer voltage can exceed the values related to the IEC standard.To find and define the maximum value of the transfer voltage for the specific investigatedsubstations, studies were done on typical configurations for TenneT TSO GmbH. Theevaluation has shown that the busbar transfer voltages for GIS-disconnectors used in hybridsubstations are very well in the range of the values given for AIS configurations. In additionto the above mentioned reasons and from the specific high energy transmission, the requiredbus-transfer current has to increase up to 3200A. This is twice the recommended rating in theapplicable standard.With these results, the technical performance of GIS busbar disconnectors have to beincreased for the investigated hybrid substations. The contact system and the drivemechanism have to be modified to achieve the necessary technical requirements. The standardGIS disconnector designed according to the IEC 62271-102 fulfils the requirements for MTSsolutions with limitation of transfer-currents and/or –voltages. The new developed high-speeddisconnector (HSDS) allows extending AIS substations with GIS technology, withoutrecommendations for operation in any MTS configuration.