Generator Under/Over frequency protection

[obut4]

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,

 

[ScottyUK]

The UK transmission system operator published 'The Grid Code' which specifies behaviour required from generators, particularly under falling frequency conditions where CCGT's really struggle to maintain output. Aside from that. there will be an overfluxing relay which looks at the voltage as a function of frequency and will trip the unit to protect against over-fluxing. Often the GSU transformer will run in to over-fluxing problems before the generator itself.

http://www.nationalgrid.com/NR/rdon...C-F36862E1FF3E/21011/zFullGBGridCodeI3R23.pdf

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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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Hi.
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.

 

[Marmite]

In the UK (50Hz) typical settings for an embedded generator for underfrequency would be 47-49Hz for typically 0.5-1sec. The frequency setting should be as low as possible since most utilities have underfrequency load shedding schemes which iteratively disconnect blocks of load as the frequency falls below a sequence of preset values. In the Uk the lowest preset value is 47Hz. ie all the load that can be shed will have been shed if the frequency drops to 47Hz. Above this value it is still possible that sufficient load can be shed for the system frequency to recover to 50Hz. Underfrequency tripping of embedded generators above 47Hz reduces the probability of the national network recovering from the initial overload.
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

 

[lz5pl]

Just an example from our recent commissioning:
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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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[obut4]

Thanks for your help