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Accident Shutdown of Hydro Generator
Accident shutdown of two hydro generator working without load (less that 200 kW) while energizing a power transformer of 12.5 MVA, 110kV/30kV. Can someone explain this phenomenon?

Hi to the community of Control.

I working on a hydro-power project of 15 MW (3x5MW generator) in Cameroon. The project is having a booster station (6.3kV to 110 kV) with two power transformer, a transmission line of 110 kV, and a step down station (110 kV to 30 kV) having also two transformers and load panel for power distribution.

We are correctly doing the load test of the power plant in isolated grid.

1- we started two generator

2- we energized the booster station with the two power transformer working in parallels.

3- We closed the transmission line circuit breaker to energy the line.

4- One of the step station transformer was energized. And we were testing the protection setting and tripping of the order transformer. When the checking was ok we tried to change the transformer powering the step down station.

But suddenly transformer made a big noise a the generator at the power house shutdown immediately by opening the generator breakers. The SCADA Emergency shut down; event logger told us that the two units stopped because of high frequency 140 % of the rated frequency (50 Hz).

Can someone explain this phenomenon?