Accurate modelling of very fast transient overvoltages in a 245kV GIS and research on protection measures

Abstract

Based on 245kV GIS substation, very fast transient over voltages caused by disconnecting switch operation of GIS is simulated and calculated in this paper with B2SPICE program. The different protection measures are compared and analyzed, such as adding ferrite rings, adding opening and closing resistor, metal oxide arrester and R-C absorber. A low voltage experiment was conducted to estimate transient overvoltage's during switching operation. These transient voltages are recorded by using surge sensor and digital storage oscilloscope with sample rate 1GS/s and 500MHz frequency range. Suppression techniques are employed practically to verify the validation of simulation results. The simulation results are closely matched with the experimental results in the case of ferrite rings application in reduction of maximum peak of VFTO generated during switching operation.

Study of very fast transient overvoltages and mitigation techniques of a gas insulated substation

“…These RC filters are paralleled next to the power transformer to protect it from the VFTOs. The typical values of R for different types of loads are in the range of 50 to 400 ohms and that of C in the range of 0.01 to 0.2 [16]. The RC filters can effectively suppress the VFTOs but they have no effects on the open ends of the GIS components.…”

“…The mitigation of these VFTOs is a very important issue of the GIS. There are some mitigation techniques developed which has been extensively used by the industries like shunt resistors [10], ferrite rings [11][12][13][14][15] and RC filters [16] etc. There is still need to be more exploration in this area of the development of more reliable and effective techniques to mitigate the VFTOs of the gas insulated substation.…”

Mitigation of Very Fast Transient Overvoltages at the More Sensitive Points in Gas-Insulated Substation

“…Using ferrite rings around a GIS conductor as in Figure 8, can absorb the transient energy when the disconnecting switch restrikes to inhibit the VFTO. The ferrite rings around a GIS conductor can be simplified to a set of nonlinear inductance and nonlinear resistance, in series with GIS conductor as shown in Figure9 The equivalent resistor of the ferrite ring is taken equal to the surge impedance of GIS bus bar, while the equivalent inductance is taken as 0.02mH [7,8]. Figs.10 and 11 show the VFTO generated at Vtr and Voc points, respectively.…”

“…R parallel with c, have been widely used to protect load. Also, RC filters have been widely used in vacuum circuit breakers to suppress the over voltages of the arcing [7]; its principle is to use R to make energy attenuate and capacitors C to reduce the circuit oscillation frequency. In this work RC filter is paralleled next to the main transformer to protect it.…”

“…In this work RC filter is paralleled next to the main transformer to protect it. For different kinds of load, the resistance R is ranged from 50 to 400 ohm and the capacitance C is taken from 0.01 to 0.2 uF [7]. The changing in VFTO values with changing the values of R and C is shown in Table 3.…”