Generator Under/Over frequency protection
Generator Under/Over frequency protection
(OP)
I would like your advice regarding generator under/overfrequency protection 81.
What are the recommended settings?
At which frequency should the generator be disconnected from the grid when the frequency is getting too high or too low.
I guess they depend on the size of the generator, of the country where the generator is installed, on the type of prime mover.
I can not find clear recommendations.
It seems that the setting are based on "experience".
Is there a website where we can have access to frequency protection setting recommendation for each country?
Thanks for your help,
What are the recommended settings?
At which frequency should the generator be disconnected from the grid when the frequency is getting too high or too low.
I guess they depend on the size of the generator, of the country where the generator is installed, on the type of prime mover.
I can not find clear recommendations.
It seems that the setting are based on "experience".
Is there a website where we can have access to frequency protection setting recommendation for each country?
Thanks for your help,






RE: Generator Under/Over frequency protection
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Section CC6 starting on page 134 and Section CCA3 starting on page 181 might be of interest. It's not a particularly easy document to read but contains a lot of information.
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RE: Generator Under/Over frequency protection
I'm not sure, if we have recommendation for each country.
Actually, setting of 81<> depend on type of generator and prime mover.
Second is depend on it's utilities or industrial applcation.
Several tips:
1. Overfrequency 81>. setting depend on mechanical overspeed protection ( main protection) That mean 81> is back-up protection.
Typical setting +5% for 1-2sec.
2. Underfrequency 81<.
Several levels:
1. Alarm: more or less 49-49.5Hz , time dependon applycation from 1 up to 5 sec.
2. In industrial applycation, decoupling level
more or less 48.5Hz for about 0.3-0.5sec.
After decoupling of course load shedding (it's other story).
3. Trip level it's from 47Hz for 1-2sec up to 47.5 for 10sec.
This data from my experience.
Regards.
Slava.
BTW for "first setting" I'm also use some "rule" +/- 5% for 2sec. that mean 52.5Hz/47.5Hz. also valible for many applycation.
RE: Generator Under/Over frequency protection
Overfrequency relays are used to prevent damage to a generator caused by overspeeding due to loss of load. Normally the governor prevents overspeeding and the overfrequency relay is a back up. Typical settings in the Uk would be 50.5-52Hz with a 0.5-1sec delay.
Regards
Marmite
RE: Generator Under/Over frequency protection
Frequency protection:
f< 47.5 Hz, 10s
f> 55 Hz, 0 s
Overfluxing protection:
U/f> = 1.1, T=10 s
U/f>> = 1.4, T=1 s
Machine is 37.5 MVA, steam turbine
Setting calculations are not mine, I cannot explain why these are chosen.
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RE: Generator Under/Over frequency protection