The objective of the attached project is to simulate and analyse the transient recovery voltage (TRV) on high voltage circuit breakers. The circuit breaker itself is modelled by means of a breaker capability curve which is defined according to IEC62271-100.

For circuit breakers up to 100 kV the breaker capability curve is defined by a 2-parameter curve  and represents an envelope which must not be exceeded by the TRV. Otherwise a re-ignition is likely to occur. The objective of the TRV study is to investigate if voltage across each breaker pole remains below its TRV envelope.

The TRV envelope is calculated during the EMT simulation by a DSL model. The input parameters of the DSL model are the peak withstand voltage of the breaker and the slope of the envelope curve.

The projects represents an 80 MVA wind farm with 6 collector strings and 2 grid connection transformers. A shunt reactor is used for reactive power compensation with a rated power of 10 MVar. Switching off the shunt reactor will result in transient recovery voltages which have to be within the limit of the high voltage circuit breaker.   

Two study cases are defined analyse the capability of the breaker:

1. Current interruption at zero crossing. The current in each phase is interrupted at zero crossing. The switching event for each phase is configured so that it opens each pole of the circuit breaker when the instantaneous value of the current is zero.
2. Current interruption with current chopping. The current in phase C is chopped at an instantaneous value of 5 A. The switching event is configured to switch at an instantaneous value of 5 A at execution time. The switches in the other phases are opened at zero crossing

In the first study case, the TRV across the breaker poles remains below the breaker capability curve. However, when current chopping is considered in the second study case, the TRV envelope curve is exceeded. Additional measured such as surge capacitors are necessary here.