Withstand Capability Testing and Limitation Measurements on Du/dt and Di/dt of Thyristor Valve of the Controllable Metal Oxide Surge Arrester

Du/dt is voltage rise rate in off-state of thyristor. Di/dt is current rise rate in on-state of thyristor. Du/dt and di/dt are key parameters that determine working security of thyristor valve of the controllable metal oxide surge arrester (CMOA, shortly). Combining with the Jindongnan via Nan yang to Jingmen UHV AC pilot project of China, the maximal values of du/dt and di/dt of thyristor were simulated. Required parameters were put forward. The maximal du/dt was 28.3kV/μs and the maximal di/dt was 87kA/μs. Du/dt and di/dt mustn´t exceed critical value du/dt_crit and di/dt_crit. Though du/dtcrit and di/dt_crit could be provided by factory, they should be tested by actual application condition because actual application condition may be different from the testing condition. So, by testing, the maximal withstand capacity of du/dt and di/dt was tested by actual application condition. Comparing test results with required parameters indicated that the maximal withstand capacity of du/dt of 2.0 to 3.0 inch thyristor was not less than 45kV/μs which was more than required 28.3kV/μs. Limiting measurement was not needed. The maximal withstand capacity of di/dt was between 865 A/μs and 910A/μs which was much less than the required 87kA/μs. Limiting measures were needed. Study indicated that di/dt could be limited within allowable range by current limited reactor. However reactor may affect limiting switching over voltage of CMOA. So, appropriate values of reactor should be selected. Study indicated that reactor value might be between 3 and 5 mH. In such range, the current limited reactor has wee influence on CMOA limiting effect on switching over voltage.