Sometimes the procedure is the culprit.
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Fundamental brought in our partner company, Acacia, to test a 2000 kW diesel generator with Acacia's proprietary software tool, PowerLens, which is developed by power engineers for the specific purpose of analyzing, commissioning, and troubleshooting power systems, captured a peak transient of 964 V.
This represented 246% of rated voltage suddenly appearing in the system. After further investigation, the source of the problem was the opening of the main generator breaker to the load bank before all the cooling fans were shut off. The generator breaker interrupted the inductive current to the fans and this sudden change caused the inductive reactance of the motors to try and maintain the inductive current flow.
Thus, a switching procedure created a damaging voltage that could fail motors and/or other equipment in the system. A simple operational procedure change was the solution: first remove all fans from service before opening the main generator breaker.
Figure 1: Transient recovery voltage from generator breaker switching.