Photo from Stress Analysis of HVDC Circuit Breakers for Defining Test Requirements and its Implementation article (CIGRÉ Winnipeg 2017 Colloquium)
Given a breaker operation time, the magnitude of the driving voltage, the making angle, circuit inductance and the frequency of the generator become the design parameters for sufficient di/dt as well as for sufficient energy supply.
The dielectric stress after a current interruption can be supplied by a separate DC voltage source but practically this poses several challenges. This capacitor remains charged during the entire energy absorption period to a value equal to the TRV of the breaker. This can be deployed to provide dielectric stress after interruption .
An equivalent circuit diagram of the test circuit with a test object (the HVDC CB) shown in Figure.
3 short-circuit generators and 3 step up transformers are used. The master breakers(MB) have to switch off a primary generator-side current within a single loop. The making switch(MS) needs to be set precisely to switching in the fault current in order to create ‘DC like’ conditions during the fault suppression time of DC CBs . AC CB (AB1) and the triggered make gap, are added to the circuit for galvanic isolation of the supply circuit from later to be added DC source and over current protection.