Practical design of generator surge protection

Generator withstand voltages, overvoltages from the power system, and arrester capabilities are critically reviewed. The specified withstand is compared with tested breakdowns for some 248 coils in five large machines using DC, power frequency, and impulses. System stresses normally prescribed for lightning are supplemented to included HV line faults, circuit breaker closing, reignitions and restrikes, fault clearing, arcing faults on the isolated phase bus, harmonic line resonance, ferroresonance, transformer HV to LV faults, the effects of stuck breaker poles, and other contingencies. It is found that internal winding stresses may be amplified due to resonance and slot reflection effects. The vulnerability of arresters to temporary overvoltages is considered. Practical guidelines for the design of generator surge protection are provided