Current Interruption Transients Calculation, 2nd Edition

Appendix GSpecial Case: Generator Circuit Breakers TRVs

G.1 Introduction

Generator circuit breakers are those applied between a generator and the generator step‐up transformer as shown in Figure G.1. The current interruption cases to be considered are:

1. System‐source faults (fault at point A in Figure G.1) where the fault current is supplied by the system and the transient recovery voltage (TRV) is determined by characteristics of the step‐up transformer and added surge capacitors as applicable.
2. Generator‐source faults (fault at point B in Figure G.1) where the fault current is supplied by the generator and the TRV is determined by the characteristics of the generator and added surge capacitance as applicable.
3. Out‐of‐phase current switching where the fault current depends on the phase angle between the generator and the transformer side voltages and the combined impedances of the generator and the transformer. The TRV is determined by the difference between the generator and transformer side oscillations.
4. Step‐up transformer high‐side faults where the current is supplied by the generator and limited by the generator and transformer impedances in series. The TRV is determined by the difference between the generator and transformer side oscillations.
5. Generator circuit breaker load currents can be as high as 50 kA. Load current switching is not a frequent switching duty, usually only in the event of load rejection, but the circuit breaker must have this capability demonstrated ...