Requirement
The Transient Recovery Voltage (TRV) is the voltage which appears across electrical equipment shortly after a current interruption. The waveform of the recovery voltage actually depends on the circuit configuration (inductive or capacitive nature). For example, a circuit breaker should be able to interrupt a given current for any recovery voltage provided that this value does not exceed its assigned TRV value (this TRV value is specified in the 61071 IEC standards).
The replacement of a HV circuit breaker, particularly in the case of replacement of SF6 circuit breakers by vacuum ones, requires the TRV calculations to be rechecked.
It is necessary to check that the generated overvoltages respect both the insulation levels of the present network equipment and the IEC assigned values of the breaking device. If the overvoltage levels are too high, then the installation overvoltage protection equipment should be considered (for example capacitors which reduce the rising edge steepness of overvoltages, RC circuits, surge arresters...).
Realization
For the case of the replacement of the HV circuit breaker in an industrial site, Capsim built a numerical model in EMTP-RV taking into account the electrical properties of the elements present in the electrical grid. Parasite inductances and capacities which have a non negligible impact on the overvoltage levels were also considered in the model. Based on the most restrictive configurations for the dynamic calculations of the TRVs, Capsim identified the constraints in overvoltage and validated the sizing of a surge protector.
Results
This study was used by CAPSIM’s customer to specify the proper damping system and to ensure the safety of its installation in respect of overvoltage levels.
Transient recovery voltage during the tripping of a vaccum circuit breaker
