steam turbine electrical generator problem 1

[un421ate1]

Got a steam turbine 700kva 480volt generator that runs in parallel with utility, when loaded to about 65% capacity generator breaker opens and phase undervoltage trip is indicated on
beckwith m-3420 generator protection device.

Only occurs when generator capacity exceeds 65%.

Any suggestions, guesses or similiar truly welcome.

 

[davidbeach]

What is the setting, and what is the actual voltage at time of trip? What is the generator output in kW and kVAr at time of trip?

 

[dpc]

You might check the excitation limits on your voltage regulator.

As David says, you should monitor the actual generator voltage as you increase load. First step is to determine if the relay is actually seeing a low voltage condition or not.

I can't remember for sure, but there may be additional event data stored in the M-3420 that can be downloaded.

 

[slavag]

Hi Un421ate1 .
Possible other:
Prime mover send this trip, not electrical protection.
Undrevoltage trip was result of mechanical trip.
Possible two option of 27 function block:
1. By CB aux. contact.
2. By <0.2Un blocking logic.
BTW, it was first synchronazing or not?
If not, 99% it wasn't protection problem. Maybe, maybe.. AVR problem.
Regards.
Slava

 

[slavag]

Oops. Forgot something.
Possible also other problem.
Check your VT wiring and set of 27 function.
Did you have 60 function at the setting and it is provide block to 27function? Check fusses in the VT wiring, I forgot that in US, for the VT connection dosen't used MCB's with aux. contacts for 27 ( and sevral others) blocking.
Regards.
Slava

 

[ScottyUK]

Does this machine run in power factor control? If so, what PF is it trying to maintain?


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

 

[waross]

For those who understand the concepts but are unfamiliar with the numbered functions that the protection designers use, here's a link to the standard device numbers.

http://en.wikipedia.org/wiki/ANSI_Device_Numbers

I generally have to look them up myself.
respectfully

 

[slavag]

Bill, it's very good reference, but not enough today.
I'm from IECland, but must use in many cases ANSI numbers
( BTW, for my opinion, it's very good system, ANSI numbering and I think, preferd). We have today so much
variations:
50,50BF, 50B, 50AE
67, 67N, 67P, 67Q
32, 32N, 32P, 32Q
87T, 87G, 87L, 87B, 87GT
64R, 64G, 64S,
59N, 59, 59G, 59THD
etc, etc..
function 60=voltage balance, voltage differential, fuse blown
Regards.
Slava.
PS
BTW, according to OP.
Again, dilemma, I don't use for generators, function
27 ( undervoltage, U<, UVlow/high). Several sources strongly recommend use it, several are recommend used only one relay per bus or system, several use it only for pump storage units.

 

[un421ate1]

Many many thanx for suggestions, machine runs in power factor control via a beckwith scp 250 PF controller, set at about 0.7 ( figure as long as I don't exceed generator current limits should be OK, yes?)
Is it possible condition of bearings could effect air gap to extent it trips gen breaker on increasing load?
Again many thanx for suggestions.

 

[ScottyUK]

Is the 0.7PF lagging (VAr exporting) or leading (VAr importing)? If the machine is trying to maintain a constant non-unity PF then the machine terminal voltage will change unless the bus the generator is connected to is very stiff. I am guessing that the 0.7 PF may be leading in which case this may account for the behaviour you are seeing. Try running the unit at unity power factor and see if the problem goes away.


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

 

[chief]

Check your load limit setting on your governor control.

Offshore Engineering&Design

 

[un421ate1]

hello again and thanks,
the PF controller is a Basler250
running in PF control, I was under the impression that if I increase the excitation the PF will decrease from unity to a value less than one and that this will place more of a reactive load on the generator (subtracting from the utility thereby reducing costs)and that this method is okay providing the current is kept below the generator limits..
or am I doing something that I shouldn't ?

 

[ScottyUK]

Increasing the excitation from a low level (but within the stability limit of the machine) will increase the power factor from an initially leading value toward unity. Further increase in excitation will reduce the power factor toward a lagging value. The question is: which side of unity PF are you on?


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

 

[ScottyUK]

What am I thinking? 0.7 leading PF?? I doubt you would get anywhere near 65% load, more like 30% or so before you hit the stability limit.

On the assumption that the PF is 0.7 lagging, that will put you well into the rotor heating limited area of the capability curve of any normal generator and you may only be able to get 65% of rated power out the set at such a bad power factor. You haven't posted the curve for your machine yet but if you do I'll explain the different areas of the curve. Like I said earlier, run the set at unity PF and I think your problems will go away.


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

 

[slavag]

Scotty.
I think 0.7 leading PF and 65% of nominal load it's lower than any stability and heating limit.
Lagging PF is possible, but why in this case undervoltage trip.
Maybe need check Chief's option: "LOAD LIMIT"
Regards.
Slava

 

[ScottyUK]

Hi Slava -

We need more information don't we!




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

 

[slavag]

Agree

 

[davidbeach]

We need more information don't we!

Gee, that sounds a lot like what I posted as the original response, and those questions have yet to be answered.

 

[chief]

Should also mention to check for sticking or maladjusted linkage between governor and throttle control valve.

Offshore Engineering&Design

 

[un421ate1]

Hi scottyUK
took your suggestion and adjusted PF to about 0.9
So far generator not tripped out at higher power levels.
thanks again for assist.