DC superimposed lightning impulse voltage test method and significance

作者： GOZ Electric 时间：2024-08-18 09:24:15 阅读：39

    In China's ultra-high voltage projects, gas insulated metal enclosed switchgear (GIS) has the characteristics of small footprint, long maintenance cycle, small environmental impact, low maintenance workload, and high operational reliability. It has significant advantages such as low operating costs and has been widely used. After the GIS bus is opened, there is residual DC voltage on the bus, which will cause the accumulation of surface charge on the basin insulator. When the bus is closed, the residual DC voltage and the closing operation impulse voltage may cause flashover on the GIS bus. Network, this phenomenon has occurred many times during the debugging process of China's UHV AC engineering system. Carrying out the superimposed impulse voltage test when the GIS bus of this voltage level has residual DC voltage is a necessary method to study the improvement of the insulation level of the GIS bus.

 Domestic and foreign researchers have conducted some research on DC superimposed impulse voltage test methods and GIS bus flashover characteristics. Wang Yuan et al. built a coaxial cylindrical cavity test model, preloaded a 126kV basin insulator with an outer diameter of 260mm and a height of 500mm with a +100kV DC voltage, and then superimposed the impulse voltage. The results show that the superimposed voltage is more powerful than a single lightning impulse. The flashover voltage under the action of voltage drops significantly, and as the pre-applied DC voltage time becomes longer, the flashover voltage under the action of superimposed voltage becomes lower. A plexiglass cavity was built, and an epoxy resin insulator model with a diameter of 25mm and a height of 15mm was developed to simulate a basin insulator, and a DC superimposed lightning impulse voltage test was carried out. The results show that: when the DC voltage and lightning impulse voltage have the same polarity, ,The flashover voltage under superimposed voltage is almost ,the same as that under separate lightning impulse voltage, but when ,their polarities are opposite, the flashover voltage will ,decrease with the increase of DC voltage. Shigemitsu et al. installed an epoxy gasket with a diameter of 62mm and a height of 25mm between coaxial cylindrical electrodes to simulate a GIS cavity and study the flashover characteristics of basin insulators under the action of DC superimposed impulse voltage. Test results It shows that when the DC voltage and impulse voltage have opposite polarities, the flashover voltage under the superimposed voltage has an obvious downward trend compared with the flashover voltage under the lightning impulse voltage alone⒃. To sum up, there have been some studies at home and abroad on the flashover characteristics of insulators when DC superimposed impulse voltage, and the test methods are worth learning from. However, the voltage levels tested in these studies are low, or the cavity models are small, which is different from the actual There is a gap in the GIS bus. In order to study the insulation characteristics of GIS busbars when residual DC superimposes impulse voltage in actual ultra-high voltage engineering, it is necessary to establish a test platform of actual size to carry out experimental research. There are few previous literature studies.

     Build a DC superimposed impulse voltage test circuit, develop a 1100 kV series 550kV GIS bus test platform, conduct DC superimposed lightning or operating impulse voltage tests with different amplitudes and different polarities, and study the flashover characteristics of the GIS bus when the basin insulator is in a clean state.

1Test loop and method

 1.1 Test circuit

     The schematic diagram of the DC superimposed impulse voltage test circuit is shown in Figure , and the on-site wiring diagram is shown in Figure 2. The white line is the wiring diagram. The rated output voltage of the DC voltage generator is 1200kV, the rated current is 20mA, and the nominal voltage of the impulse voltage generator is 4800kV. Through theoretical calculation, a 30nF/10m DC blocking capacitor is selected to protect the impulse voltage generator from the impact of DC voltage. A 500kQ/10m protective resistor with optimized external insulation is selected to protect the DC voltage generator from the impact of impulse voltage. A 3600kV The resistor-capacitor voltage divider is used to measure the voltage waveform of the superposition test.

1.2 GIS bus test platform developed

     The developed 1100kV series-connected 550kV GIS busbar test section is shown in Figure 3. The test product consists of 6 parts: bushing, isolation switch, transition unit and busbar test section, including 1 1100kV bushing, 1 1100 kV isolation knife switch, 1 There are a transition unit between the bushing and the isolating switch, a 1100 kV busbar test section, a 1100 kV and 550kV busbar docking transition section, and a 550kV busbar test section. Each air chamber is separated by a basin insulator. The isolation switch provides an isolation fracture that meets the requirements, and the transition unit is used for the connection between the bushing, the isolation switch and the test busbar. A very fast transient over-voltage (VFTO) measuring device is installed in the transition section between 1100 kV and 550kV busbar. Six observation windows are designed in the transition section between 1100 kV and 550kV busbar and the 550kV busbar test section for observation. Discharge phenomenon in basin insulators.

1.3 Test methods

     Conduct individual impulse voltage or DC superimposed impulse voltage tests on the developed 1100 kV string 550 kV test platform. The lightning and operating impulse voltages used in the test are 550kV busbar lightning and operating impulse rated withstand voltages of 1675kV and 1300kV respectively, and 1100kV busbar lightning and operating impulse rated withstand voltages of 2400kV and 1800kV. There are four DC voltage options: 90, 225, 360, and 450 kV.

     Considering the influence of different polarities, different combinations of positive and negative polarity DC voltages and positive and negative polarity impulse voltages are tested. For example, the lightning impulse voltage test of 90kV superimposed on 1675kV includes 4 combination tests, +90kV superimposed on +1675kV, + 90kV superimposed -1675 kV, -90 kV superimposed +1675 kV and -90kV superimposed -1675kV. The other DC voltage and impulse voltage superposition test methods are the same. Do each combination of superposition tests 10 times. Use a camera to take pictures to determine the location of the air chamber where the flashover occurred.

     In the test, first increase the DC voltage to the required amplitude, pre-charge for 30 minutes, and then apply the impulse voltage. If a flashover occurs on the bus, record the DC voltage and impulse voltage at the time of flashover. After each discharge occurs, the test air chamber is processed, the flashover traces on the basin insulator are wiped, and the discharge points on the central guide rod and cylinder wall are polished to keep the entire air chamber clean for the next time. test.