Experimental Research on Lighting Impulse Characteristics of the 500 kV Transmission Line Parallel Gap at High Altitude Area

Abstract:
With the commissioning of Chuan-Zang, Zang-Zhong and A-Li power interconnection projects, the Xizang power grid has entered the 500 kV extra-high voltage era. As a diverting lightning protection measure, the parallel gap can be an effective supplement to the blocking protection measures such as lightning arresters. Combined with the power industry standard DL/T 1293-2013 and the State Grid Corporation of China enterprise standard Q/GDW 12065-2020, two gap types’ values of Z/Z0 are designed to be 85% and 90%. The grounding side electrode and high-voltage side electrode cover depth are 1:1. The lightning impulse 50% discharge voltage and volt-second characteristics test of the insulator string and parallel gaps were carried out at the high-altitude test base. The parallel gaps’ optimal structure and the corre-sponding structural size parameters were proposed based on the test results. Research shows that the 50% lightning im-pulse discharge voltage values of 42 insulators with 146mm units are +2035.94 kV and -2174.08 kV. Compared with the insulator string, the 50% lightning impulse discharge voltage values of 85% type parallel gap are +1728.59 kV and -1892.68 kV, which are 15.10% and 12.94% lower, respectively. And the 50% lightning impulse discharge voltage val-ues of the 90% type parallel gap are +1810.62 kV and -2005.90 kV, which are 11.07% and 7.74% lower than values of the insulator string, respectively. Due to the impulse voltage generator’s output limitation at the high-altitude test base, the volt-second characteristics of 500 kV insulator strings could not be measured directly. According to the lightning impulse volt-second characteristics test data of 15 and 25 insulators, the positive and negative lightning impulse volt-second characteristics of single insulators are calculated, respectively. The maximum error of the volt-second character-istics fitted by these two insulator strings is about 4.4% and 1.4%, both of which are less than 5%. Thereby the positive and negative lightning impulse volt-second characteristic curves of the 42-unit insulator string are obtained. The positive and negative lightning impulse volt-second characteristic curves of the 85% type parallel gap are at least 16.88% and 12.66% lower than that of the insulator, which meets the technical requirements of 10%. Moreover, there is no pro-tection failure during the test. This experimental research could be a great significance to the design and application of the 500 kV parallel gap in high altitude areas.