VOLTAGE PROTECTION OF GENERATOR 1

[slavag]

Hi.
I would like ask you about voltage protection for generators ( high voltages generator from 30MW up to 600MW, turbo,disiel and gas turbime ).
As I see several companies used also overvoltages and also
overexcitation protection. For example GE recommend use only
overexcitation protection, it's covered also overvoltage
(I'm agree with this). But eroupean companies used both of them (O.K. today is not problem with numerical relay, but it's additional settings, contacts, testings ,etc).
What is your opinion.
When recommended used undervoltage protection for generator.
Someone used overload protection for trip of generator CB or send only alarms.
Last year we provide commissioning of protection for GE, Siemens, ABB and Alstom generators (new and retrofit).
Each generator mnf request somthing other.
Different also in requrements for trip matrix.
For example underfrequency send trip to LOR or only to CB,etc.
We have some standards or prefer continue build according to customer requrements?
Best Regards.
Slava

 

[ScottyUK]

For a big high value asset like a utility generator, over-excitation protection should be designed to protect the field winding on the rotor. It is a different function to stator over-voltage, although there is obviously a relationship between rotor field current and terminal voltage, especially in an islanded application. It is often tied in to the AVR but should be distinct from the over-excitation limiter which is part of the AVR's control function rather than a protection function. Over-voltage is usually implemented in addition to a V/Hz function designed to protect against over-fluxing. On a generator which is close coupled to the GSU transformer without an interposing breaker it is common for the transformer to run into over-fluxing problems before the generator.


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Sometimes I only open my mouth to swap feet...

 

[slavag]

Dear SkottyUK.
Thank you for your help.
Best Regards.
Slava.
P.S.
Thanks to davidbeach for FAQ:
What are good references for a Power Engineer?

 

[slavag]

Hi.
I installed both of them ( OE and OV).
In test time, before syncronazing ( field breaker was closed) OE protection ( high stage) was operated and send trip to LOR.
We checked with customer reason of trip checked DR and found some mechanical problem in AVR.
But intresting, that some old digital transformer 87T protection was operated also, we checked this protection before synch, it's worked correct.
We start again and agin new relays sended OE trip and old one sended 87T trip and more from that, new relays send also reverse power start.
Level of "fault" current was 5000(ct)x0.4(fault register)x0.76 (Ir/In refrence value)A= 1520A on 11kV!!!! w/o any load.
Volatge was 10.5kV and freq about 48.2Hz.
Trafo is 70MVA Y/D1 33/11kV.
Are possible????
Thank you .
Best Regards.
Slava

 

[ScottyUK]

It is certainly possible if the AVR is misbehaving: I've seen something similar when one of our AVRs lost an internal feedback signal and boosted the 15.5kV nominal generator output to about 22kV prior to the GSU transformer differential tripping the unit. I can't remember the exact values involved but there was a significant fundamental frequency component flowing in the transformer primary (LV) winding in addition to high levels of harmonics which caused the diff. scheme to operate. If your digital relay has an event recorder then configure it and use it. It will tell you a lot about what is going on. An storage oscilloscope set to trigger from the 87 relay contact and capture a dozen cycles prior to the trip would be very useful if there is no event recorder.

Is the OE protection part of the AVR or part of the relay? Does it directly measure field current?


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Sometimes I only open my mouth to swap feet...

 

[slavag]

Hi Skotty.
You are right, AVR lost internal feedback from function 60.
old diff relay have only fault registers ( if you know it's SPAD330).
New 87 trafo-generator unit protection dosen't work.
(I puted higer setting from SPAD330).
Generator now in operation and I back to home after commissioning.
I start think about 5-th harmonic block/deblock into SPAD330, in all case I will recommend to customer upgrade this relay to new one with DR.
OE it's part of relay, not AVR.
standard Volt per Hz functionality.
Protection relays operated twice: first time OE, second OV,
instead 11kV AVR boosted voltages up to 14.5kV.
Next mounth I will back to this plant and check again
setting of SPAD330 ( it's not our part, but it's part of whole system).
Thank you.
Regards.
Slava

 

[rbulsara]

Talking to some generator relay manufacurers may be very useful to pick brains of some their engineers.

Folks at Beckwith Relay (

http://www.beckwith.com)

came across as very helpful and knowledgeble when I atteneded their relay class a few years ago. Their classes were very helful too.

 

[davidbeach]

If your digital relay has an event recorder then configure it and use it. It will tell you a lot about what is going on.

What he said. The biggest, most important feature of numeric relays is their ability to tell you what happened and why. All the protection features are secondary.

 

[slavag]

Hi.
Relays sended us all needed information.We have fault report,event record and DR file.
We know what happended and "why".
My Q, what is a reason for this level of current, overflux?. I'm looking for some theoretical explanation.
For current we need close circuit, in this case CB was disconnected, no short circuit. Reactive current? Usaully
it's lower level of current.
I'm try understand what is a difference? Level of fault was 1.19V/Hz
I'm try understand why after field breaker was opened, relays sended to system reverse power start? Trafo was source? Accumulated energy?