Overvoltage protection in hydroelectric generators

[sigshane]

Hello all. I have a question about our hydrogenerators, particularly in overvoltage relay 59.

Our one-lines state that the unit undervoltage relay 27U1 will initiate electrical shutdown (5E) on undervoltage, but the overvoltage relay 59U1 will only raise an alarm (annunciation).

Why does the 59 not shut the unit down? I understand that every application is unique, but generally, do 59's initiate shutdown, and if no, why not?

Thanks in advance,

Shane Andrews
Power Plant Electrician trainee
U.S. Army Corps of Engineers

 

[robbietan]

IMHO, an overvoltage situation could be caused by over excitation of the generator or an abundance of power supply with few users on the grid. An undervoltage situation could mean that there is a large demand with few generators. In any case, an undervoltage situation is a cause of concern while an overvoltage situation is not

 

[sigshane]

Yes, after running through all of the scenarios and consequences of the two events, we deduced that since with an undervoltage condition comes high current, the unit itself is at a greater risk of damage, and should be shut down. With the overvoltage condition however, the exciter will virtually cease output, and stator current should be well below destructive levels also.

Thanks for your input!

Shane