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Khamlichi A.,High Voltage Technological Center | Donoso G.,Red Electrica de Espana | Garnacho F.,Technical University of Madrid | Denche G.,Red Electrica de Espana | And 2 more authors.
IEEE Transactions on Industry Applications | Year: 2016

Very fast transient overvoltages (VFTOs) due to switching operations can appear between the gas-insulated substation (GIS) enclosures and the cable sheaths and between these grounding parts and the substation Earth structures. These VFTOs achieve hundreds of kilovolts, provoking hazardous disruptive discharges for human safety. This paper includes 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 (SVLs) between the GIS enclosure and the cable sheath is also needed to avoid uncontrolled discharges. The selection of these SVL according to insulation coordination rules is presented in this paper, ensuring electrical safety without affecting the current mode of exploitation of the 220-kV GIS or the cable. © 1972-2012 IEEE.

Garnacho F.,High Voltage Technological Center | Khamlichi A.,High Voltage Technological Center | Valladolid A.,High Voltage Technological Center | Simon P.,High Voltage Technological Center | Valcarcel M.,High Voltage Technological Center
IEEE Transactions on Power Delivery | Year: 2014

The k-factor function, called the test voltage function, in present standards IEEE Standard 4-2013 and IEC 60060-1, was determined years ago for voltages not higher than 100 kV and with relative overshoots around 15%. This paper presents the results of k-factor tests carried out for greater voltages up to +1.32 MV (equivalent to air-gap distances d = 2.5 m) and many test conditions. These test conditions are relative overvoltages, β′ up to 35%, different damping ratios: from δ = 0 (overshoot) to δ=35% (oscillating waveform), and different electrical configurations of a nonhomogenous electric field using air gap factors K = 1 (rod plane) up to K =1,45 (rod conductor). The results show that the present k-factor function stated in both standards does not represent insulation behavior for large air-gap distances when the gap factor K is around 1. Only when the gap factor K increases to 2, are the experimental k-factor values closer to the standard k-factor function. A general formula for the k-factor, depending on the oscillation frequency, gap distance, and the electric-field nonhomogeneity, k (f, d ,K) is derived from the performed tests, taking also into account the k-factor results of the recent bibliography. © 2014 IEEE.

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