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Bluekayak

Generator protection vs. coordination

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Scenario: 480V genset equipped with internal protective relay (27/59, 32, 50/51, 81O/U). Generator breaker set to coordinate with downstream feeder breakers and not to operate on a fault along the generator decrement curve. A time current curve based on manufacturer’s operating characteristics graphically illustrates that the cable damage curve for the generator feeder circuit conductors is adequately protected against short circuits and overloads. I’m not a generator protection expert; however it is my understanding that LV generators almost always have internal short circuit/overload protection and the function of the generator breaker is to protect the generator circuit conductors. Any thoughts?

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In case manufacturer does not tell you truth about protection, it is better install your own, and another reason to do that if you do not know exactly how this protection works - maybe it protects each phase separately, and do you know what will occure in the 3-phase grid, feeding with 2 or 1 phase?

If there are asynchronous motors, they will stop and maybe burn out.

So when you have so misterious generator, it is better put additional 3-phase breaker after it.

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