Factors and relationships affecting high-altitude charged impulse discharge voltage

作者： GOZ Electric 时间：2024-10-19 09:37:49 阅读：19

There is a certain relationship between the altitude correction factor and the altitude, electrode structure and gap distance. If the altitude and electrode structure are the same, the change in gap distance will also cause a corresponding change in the altitude correction factor, and it is within a reasonable range. In Table 1 above, no matter under any gap structure conditions, the altitude correction factor is different, and there will be more or less differences between them. When the operating area is at an altitude of 2000m, the test value and analysis value of the correction factor here are relatively close. As the altitude of the operating area gradually increases, the difference between the two values will further increase. At an altitude of 2000m, the maximum error between the two values of the altitude correction factor is 3.74%; at an altitude of 3000m, the maximum error between the two values is 5.3%; at an altitude of 4300m, the maximum error between the two values is 7.7%. This change fully demonstrates that in the existing standards, the application of the m parameter method is not applicable to areas with an altitude exceeding 3000m, so the parameter value must be re-determined. As shown in the figure, the gap between the test value and the analysis value of the correction factor at an altitude of 4300m is the largest, and at different altitudes, the correction factor decreases with the increase of the gap distance, and there is a negative correlation between the two. This also shows that the increase of the gap distance will further weaken the influence of atmospheric parameters on the discharge voltage. The reason is that in the long gap discharge process, streamer discharge and ignition discharge often occur at the same time. Various atmospheric parameters have a significant effect on streamer discharge, but not on ignition discharge. With the increase of the gap distance, the proportion of ignition discharge increases, which weakens the influence of various meteorological parameters on the entire gap discharge voltage, so there is a negative correlation between the two.

1. Improved m parameter correction method

It has been found that if the air density decreases to a certain level, the insulation strength of the air gap will also decrease accordingly. From the perspective of temperature and humidity, if these two values increase, the insulation strength of the air gap will also increase. It can be concluded that air pressure can comprehensively reflect air density, temperature and humidity, so the discharge voltage of external insulation can also be corrected by relative air pressure. Under normal circumstances, when the altitude increases, the atmospheric pressure index will decrease.

2. Minimum safe distance for live working at altitude

IEC61472-2013 recommends a relatively simple method to analyze the safe distance for live working. In this test, the maximum operating voltage for 750kV transmission lines is 800kV. Based on the discharge characteristics of the test area, the minimum value of the safe distance for live working can be determined when the altitude is 0. If the risk level of live working does not exceed 10 (-5th power), then the withstand voltage of gap 1 is 1445kV, gap 2 is 1447kV, gap 3 is 1459kV, and gap 4 is 1463kV. Through a series of operational practices, if the operator works in a low-altitude area, the tolerance level of the air gap can meet a series of safe working requirements. Therefore, when the operator operates in a high-altitude area, in order to effectively protect the personal safety of the operator and reduce the probability of unsafe accidents, effective measures must be taken to ensure that the absolute tolerance level of the gap in the high-altitude area reaches a certain standard, and ultimately ensure that its hazard rate is lower than the limit value. Combined with the above-mentioned related formulas, the algebraic values can be used to analyze the altitude correction factor Ka and the minimum safe distance at 2000m, 3000m and 4300m respectively.

3. Conclusion

The increase in altitude will increase the altitude correction factor under different gap structures, and the increase in gap distance will reduce the altitude correction factor. Based on the test results of 3000m and 4300m, the analysis method of the altitude correction factor is clarified, and the reference value of the minimum safe distance for live working is also analyzed.