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Removing risk of eventual discharges between GIS grounding parts and cable sheath connected to the substation earth through a separate grounding
Research Areas
  • Electric engineering
The transient enclosure voltages (TEV) phenomena in gas-insulated substations (GIS), also known as transient ground potential rise (TGPR), is due to HV short duration transients which appear during switching operations such as disconnector opening and closing inside GIS substation. Especially, closing operations produce severe overvoltages between the GIS enclosure and the cable sheath and between these grounding parts and the substation earth structures (e.g., walls, floor and ceiling), when both parts are connected to the station ground through different grounding leads. This TEV can lead to hazardous disruptive discharges for human safety. Although the simplest solution, under the point of view of insulation coordination, would be connecting both parts with each other, this solution would not be convenient due to the effects derived from the circulating currents between the grounding system of both cable and GIS that would not be considered in design, especially if cable and GIS belongs to different utilities. According to the IEEE Std 1300-2011 and the CIGRÉ Electra Brochure No. 151 ?Earthing of GIS: An Application Guide?, the HV cable termination should include a sheath sectionalizing insulator between the parts electrically connected to the GIS enclosure and the cable sheath. This allows testing separate grounding and facilitates limiting circulating currents in the cable sheath. Furthermore, an adequate electrical insulation shall be provided between cable connection parts that are separately grounded. Bypass surge voltage limiters (SVL) may be required if a sheath sectionalizing insulator exists. The most commonly used bypass SVL for this application is non-linear resistor. However, the transients have very short rise times, the SVL need to be mounted very close to the gap to be protected and connected by short low-impedance leads are also requires. Moreover, the IEEE Std 1300-2011 and the CIGRÉ Electra Brochure No. 151 affirm that the number and characteristics of the non-linear resistors shall be determined and supplied by the cable termination manufacturer taking into consideration the requirements of the user and the switchgear manufacturer, but no criteria is given. The theoretical analysis of the wave propagation during closing operations in gas-insulated switchgear is introduced in this paper which enables it to evaluate the design parameters that influence the voltage distribution. This analysis is complement with online measurements in four different 220 kV GIS belonging to the Spanish TSO, REE, during real closing operations which allow determining the magnitude of TEV and comparing those with the theoretical results. The equations for insulation coordination are presented in order to select properly the bypass SVL residual voltage from the measurement data and considering the desired insulation level. This paper also include a sensitivity analysis of the different parameters in order to establish criteria to be adopted in the grounding system design of the GIS structures and the cable connection to mitigate transient overvoltages. The use of bypass surge voltage limiters (SVL) between the GIS enclosure and the cable sheath are also needed to avoid uncontrolled discharges. The selection of these SVL according to insulation coordination rules is presented to ensure electrical safety without affecting the current mode of exploitation of the 220 kV GIS, or the cable. Finally a recommended guide to install properly those bypass surge voltage limiters is presented in this paper.
CIGRE 2016
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CIGRE 2016 Session Proceedings
  • Autor: Abderrahim Khamlichi El Khamlichi (UPM)
  • Autor: Gonzalo Donoso (REE)
  • Autor: Fernando Garnacho Vecino (UPM)
  • Autor: Gregorio Denche Castejon (UPM)
  • Autor: Alvaro Valero (FFII)
Research Group, Departaments and Institutes related
  • Creador: Departamento: Ingeniería Eléctrica, Electrónica Automática y Física Aplicada
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