| UHV DC transmission project has the characteristics of long transmission distance and large capacity,which is of great significance to China’s "West-East Power Transmission" and global energy Internet.The converter station is a very important part of the UHV project,and the determination of the safety net distance of the valve hall is a key technical problem for the safe operation of the converter station.Therefore,the study of long air gap discharge characteristics of the typical large size fittings has become a top priority.On the other hand,in order to ensure the large-scale output of clean energy such as wind power,solar energy and hydropower in the west,UHV DC transmission lines will inevitably pass through high altitude areas which up to 5000m.Long gap discharge characteristics in low altitudes and in high altitude areas are quite different,so choosing the appropriate altitude correction method is of great significance to ensure the safe operation of UHV transmission lines in high altitude areas.In this paper,according to the test method recommended in the standard GB/T 16927.1-2011,the switching impulse discharge test of the large size fittings was carried out,from which observations was made and the physical process of the discharge was given.And the discharge voltage data of the typical air gap at the altitude of 0m,2200m and 4300m was obtained.According to which the typical air gap discharge characteristics and the impact of the wall on the impulse discharge voltage of the fitting are analyzed.At the same time,the typical gap discharge characteristic curve obtained by the test.The formula of the relationship between the electrode size and the gap distance,the formula of the critical radius of the grading ball and the formula of critical diameter of the grading ring is obtained.In this paper,the advantages and disadvantages of the three commonly used altitude correction methods are compared by the measured data.The comparison results show that the fitting degree of DL/T620-1997 and IEC60071-2 is relatively good,and the correction result has certain reference significance,but its applicable altitude and the length of air gap are limited.Therefore,a progressive altitude correction method based on the above-mentioned test data is proposed.The test data proves that the correction method--interpolation method has a relatively small error and a wider applicable range of altitudes.According to the progressive altitude correction method,the relationship between the switching impulse discharge voltage and the gap distance of the typical gap at the altitude between 0m and 4300m is calculated by using the test data at altitude 0m and 4300m.Two calculation methods of safety net distance is proposed based on this interpolation method and a safety net distance calculation program of the valve hall of the converter station is designed.Finally,the effectiveness of the safety net distance calculation program is verified by a practical example. |
