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ammadsafdar
Member

Join Date: May 2011
Posts: 7

Back Power Relay Issue

05/23/2011 5:51 AM

Hi. I am having a problem of back power in one of the plants. Issue is that all the parameters are stable. Active power never goes to negative. It remain at 1.5 MW but back power relays behaves in a strange way. P < - ( Active) operates out of the blue. It is running normally at +0.206 and suudenly turns + sign to - ant turbine trips. Sometime it gradually goes to negative and trips. But I and U always remain positive. I have checked cabling, continuity, relpacing the relay and the socket. Every thing is done. Now somebody has told me the VA rating of CT can be an issue. It 400/5 CT with 10 VA and 25 meter long cable. Can somebody help me out?
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peterd
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Join Date: Dec 2005
Location: Willenhall, UK
Posts: 159
#1

Re: Back Power Relay Issue

05/24/2011 8:30 AM

Are the CTs connected directly to the reverse power relay or do they have shunt resistors inbetween? I have serviced equipment where intermittent fault on the resistors have caused random tripping.

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ammadsafdar
Member

Join Date: May 2011
Posts: 7
#3
In reply to #1

Re: Back Power Relay Issue

05/24/2011 12:38 PM

Thanks peter and Olehwi.. CT is connected to Simeas Q then to simeas T and then to Back power relay.. Mean all in series.

One more strange thing is that CT ratio is 400/5. Current in actual is 96 amp. And on the SEB back power relay I can see actual current as 96 ampere but it is reading the conversion factor of 400/ 5 as 96 /0.22

THis is also strange i guess it should be linear. If back power relay is showing me 96 amperes, that are correct, then 96 should be equal 1.2
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olehwi
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Join Date: Jun 2010
Location: Canada
Posts: 139
Good Answers: 6
#2

Re: Back Power Relay Issue

05/24/2011 10:16 AM

The reverse power relay would not trip if the system was stable and the power would not reverse. Every system has transients - and your system is most likely suffering from some transients. The transients are typically caused by a load being switched ON of OFF and the governor on your unit not responding properly. The reverse power may be there just for a fraction of a cycle - but enough to trip the relay . . .

You need to adjust the speed of response of the relay, . . . most of these have an integrator that delays their output proportionally to the amount of reverse power.
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JSCadman
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Join Date: Feb 2010
Posts: 16
Good Answers: 2
#5
In reply to #2

Re: Back Power Relay Issue

05/24/2011 7:42 PM

Olehwi - Gave you a GA for that. Maybe out to 2 - 2.5 system time constants. I would also make sure that my CT could drive those 3 loads in series. If CT is not putting out enough current due to excessive resistance, it can act "oddly" during those transients.
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muditmah
Commentator

Join Date: May 2011
Posts: 84
Good Answers: 1
#4

Re: Back Power Relay Issue

05/24/2011 2:36 PM

have you checked relay and CT connections ? Are they correct and as per logic. May be CT polarity needs to be checked too. Also if its is microprocessor relay check switch group functions values .

Reverse power also depends upon the phase angle or the vector of voltage and current. Moresoever, Reverse power comes under Tripping method A and E which specify that may be turbine fuel inlet valves are getting closed abnormally due to which generator CB is tripping on reverse power.

there might be many causes for the problem. Check out in detail.
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Christopher Brown
Participant

Join Date: Aug 2011
Posts: 1
#6

Re: Back Power Relay Issue

08/30/2011 6:01 AM

RE : QUOTE from ammadsafar may 2011

Hi. I am having a problem of back power in one of the plants. Issue is that all the parameters are stable. Active power never goes to negative. It remain at 1.5 MW but back power relays behaves in a strange way. P < - ( Active) operates out of the blue. It is running normally at +0.206 and suudenly turns + sign to - ant turbine trips. Sometime it gradually goes to negative and trips. But I and U always remain positive. I have checked cabling, continuity, relpacing the relay and the socket. Every thing is done. Now somebody has told me the VA rating of CT can be an issue. It 400/5 CT with 10 VA and 25 meter long cable. Can somebody help me out?

Hello Ammadsafdar

We are having this exact problem now on one site today August 2011 and I am thinking the problem lies in the relay firmware. How did you solve this or is it an open item I have checked everything else ( I think)

chris
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Users who posted comments:

ammadsafdar (1); Christopher Brown (1); JSCadman (1); muditmah (1); olehwi (1); peterd (1)

Previous in Forum: Fault Diagnostics of Induction Motors   Next in Forum: Require Help with Voltage Dip Problem in Distribution Line

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