Calculating the Transient Recovery Voltages in Selecting Circuit Breakers for Electrical Installations with Rated Voltages of 110 kV and Higher
In clearing short-circuit faults, a transient recovery voltage (TRV) arises between the circuit breaker contacts, which may initiate repeated ignition of electric arc. For modern circuit breakers, including SF6 and vacuum ones, the maximum permissible TRV peak and rate of rise values are given in the GOST(State Standard) R 52565-2006. Earlier editions of the relevant standards contained the requirements only for air blast and oil circuit breakers. The use of modern electrical installations with circuit breakers selected without paying proper attention to TRV may lead to accidents with severe consequences. The article presents a theoretical and calculated comparison of the regulatory documents applicable to circuit breakers for rated voltages of 110 kV and higher and contains recommendations on calculating the TRV parameters that can be used as reference ones in checking the breaking capacity of high-voltage circuit breakers. Methods for calculating the parameters of TRVs with exponential, single-frequency and sawtooth waveforms are considered and compared with one another. Examples of calculating transients involving different TRV waveforms are given. The necessity of calculating TRV with a sawtooth waveform for SF6 and vacuum circuit breakers is pointed out. For updating the design conditions under which the maximum TRV rate of rise and peak values may occur, it is recommended to continue the study. In particular, it is advisable to determine the critical remoteness of a short circuit fault on the line side determined by the combined effect of power line parameters and short-circuit current values on the TRV.