UFLS (Under frequency load shedding) in Islanded generation

[NickParker]

What is the typical time delay used in an under-frequency load shedding scheme for an Islanded generation, and what criteria are used to determine this time delay?

1. Should the under-frequency load shedding (UFLS) scheme be combined with a rate of change of frequency (df/dt) along with a time delay?
2. Or should it only use under-frequency relay settings with a time delay?

 

[davidbeach]

There are probably many different approaches but things that should be considered include generator response to block load additions and making sure that the load shedding is always fast enough that the generators can recover fast enough to avoid tripping on underfrequency (noting that the "underfrequency" trip might be a mechanical underspeed trip).

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[cranky108]

There is also a practical minimum limit on UFLS detection. Going below that limit will cause mis-operations of the UFLS system. I believe that limit is about 3 cycles.