Haibin Shen

Calculation method for voltage distribution of the controlled metal oxide arrester

Equivalent capacitance of thyristor used in thyristor valve of the controlled metal oxide arrester (CMOA, shortly), C<inf>T</inf>, changes with thyristor terminal voltage, ϕ<inf>T</inf>. When voltage distribution of CMOA is calculated, such characteristic should be considered. Combining field-circuit combination method and variable rule of CT with ϕ<inf>T</inf>, a calculation program was put forward. Firstly, electric field numerical calculation models of MOA1, MOA2 and MOR were made and an equivalent capacitance network was calculated. Then function of C<inf>T</inf> and ϕ<inf>T</inf> was solved by test and curve fitting. Secondly, equivalent circuit of CMOA was founded. The function of C<inf>T</inf> and ϕ<inf>T</inf> was substituted to the circuit. Function between electrode voltage, ϕ<inf>Fi</inf>, and CMOA voltage, ϕ<inf>s</inf> could be calculated by iterations. Finally, the function between ϕ<inf>Fi</inf> and ϕ<inf>s</inf> was substituted to electric field numerical calculation model and variable rule of voltage distribution by ϕ<inf>s</inf> was solved. The calculation program was verified by tests. Results indicated that it was effective to calculate voltage distribution of CMOA.

Overvoltage control strategy and techniques of the UHV controllable metal oxide surge arrester

According to mitigation effect of the controllable metal oxide surge arrester (CMOA) on switching overvoltage and absorbing energy of the CMOA components, the main parameters, suach as system threshold voltage at thyristor triggering moment Uso, and controllable ratio α, were specified. The control strategy of the CMOA for switching overvoltage was then drawn up. Due to the special characteristic of operating conditions of COMA thyristor valve, a new control and measuring technique was put forward. The influencing factors on the accuracy of the technique were analyzed. It indicates that breakdown voltage deviation of breakdown diode and voltage sharing rate deviation of thyristor valve are two main factors affecting control accuracy of CMOA. However, errors could be controlled within the allowable range. In order to testify the control and measuring technique, an 110kV CMOA was manufactured, which was used to testify its operation characteristic. And its response properties on impulse current and voltage were tested and discussed. It is shown that thyristor valve could operate at the set threshold value. After the valve was closed, its residual voltage reduced to 0 straightly, and residual voltage of CMOA had a reduction of 25%. Turn-on relay time of thyristor valve was 3.0μs, less than the set value. Hence the control strategy and techniques of CMOA was realized correctly.