基于桥臂电流反演分析的混合换相换流阀避雷器能量监测方法

Existing controllable commutation converters and hybrid commutation converters mainly dissipate energy through arresters when turning off large currents. However, repeatedly interrupting large currents may cause the arresters to overheat and be damaged. Therefore, it is crucial to monitor and protect the energy of converter valve arresters. Both traditional LCC and CLCC employ a monitoring scheme that counts arrester operations. However, in actual operating conditions, the arrester's single energy accumulation varies across different faults. The scheme that uses the maximum number of operations cannot fully utilize the arrester's remaining energy, reducing the number of possible turn-offs. Therefore, this paper proposes a method to invert the bridge arm current from off-valve current measurements, enabling precise monitoring of arrester energy accumulation across different turn-off currents. First, based on the corresponding relationship between the AC side current and the bridge arm current of the HCC converter valve during steady-state operation and grid-side faults, a method for bridge arm current calculation is proposed by identifying the conducting bridge arm through the valve control CP signal, and the effective conditions are analyzed. Subsequently, the distribution law of the bridge arm transient current is investigated under various current turn-off conditions. The turn-off current is divided into three states according to whether the arrester operates and whether the dynamic buffer circuit RC is fully charged. Finally, based on the current distribution law, arrester energy calculation methods for different turn-off currents are derived, enabling effective monitoring of arrester energy. Based on the relevant parameters of the Lingbao Project, the PSCAD simulation results for the HCC converter valve indicate that when the turn-off current is less than 213 A, the arrester does not operate, and no energy is accumulated. When the turn-off current is between 213 A and 1 428 A, the arrester operates, but the voltage across the buffer-circuit capacitor C does not reach the arrester operating voltage. When the turn-off current is 1 428 A, the voltage across the buffer circuit capacitor reaches the arrester operating voltage, and the energy consumption is maximized. The RTDS test results show that for a 100 ms single-phase ground fault, the average turn-off current is 0.96 kA, the error monitored by the proposed method is 2.2%, and the energy absorbed by the arrester after 6 consecutive turn-offs accounts for only 4.02% of the total energy. For a 100 ms three-phase metallic ground fault, the average turn-off current is 3.75 kA; the monitoring error of the proposed method is 2.27%, and the energy absorbed by the arrester after 6 consecutive active turn-offs accounts for 51.1% of the total energy. According to the simulation and RTDS tests, the following conclusions are drawn. (1) There is a corresponding relationship between the AC side current and the bridge arm current of the HCC converter valve during steady-state operation and grid-side faults, and the valve control CP can be used for bridge arm current calculation. (2) During the active turn-off of the HCC converter valve, the current transfer characteristics of the bridge arm differ when turning off different currents. Arrester energy accumulation can be divided into three stages based on whether the arrester operates and whether the buffer-circuit capacitor reaches its maximum voltage. (3) Due to differences in the number of faulty phases and the degree of voltage drop, the active turn-off current of HCC varies slightly. Still, the monitoring error of the proposed method does not exceed 5% under various faults. With this method, the remaining energy of the arrester after dealing with a 100 ms single-phase ground fault is increased from 0 to a maximum of 95.98%, which significantly improves the energy utilization level of the arrester.