Generator MVAR sudden drop

C

Thread Starter

Chaitanya

Hi All

Problem - Frame 6B machine MVAR suddenly dropped from 6.5 MVAR to -16.6 MVAR.Details :

Total 5 GAS turbines were in service at 00:28 and one of the machine MVAR dropped from 6.5 MVAR to -16.6 MVAR, Power factor remained same at 0.936 and Gen Volt Dropped below 9.8KV and it was observed other machines MVAR increased to compensate the VAR.

No maintenance activity done on this machine from past 4 to 5 months related to Gen or Turbine.

The alarms we recieved during this event and prior to this event in MARK V are :

00:27:06.843 TRUE FORCED LOGIC SIGNAL DETECTED
00:27:09.000 FALSE FORCED LOGIC SIGNAL DETECTED
00:27:37.000 TRUE Voter mismatch,<S> _L0067_SP
00:27:37.031 TRUE DIAGNOSTIC ALARM <C> <Q>
00:27:37.000 FALSE Voter mismatch,<S> _L0067_SP
00:28:36.000 TRUE Voter mismatch <R> SVL
00:28:36.000 TRUE Voter mismatch <R> SFL2
00:28:41.000 FALSE Voter mismatch <R> SVL
00:28:41.000 FALSE Voter mismatch <R> SFL2
00:28:54.000 TRUE Voter mismatch <T> SVL
00:28:54.000 TRUE Voter mismatch <T> SFL2
00:29:00.000 FALSE Voter mismatch <T> SVL
00:29:00.000 FALSE Voter mismatch <T> SFL2

Same alarms kept toggling upto 15min.

Is there any relation to LOGIC FORCING DETECTED ALARAM to this ? because we recieved this alaram just before the MVAR drop.

In actual there was no LOGIC FORCING done but how this alarm got generated ?

If there is any relation to both or anyone faced similar problem give your views

ty
 
Hi Chaitanya,

In your case, there is a surplus loss in reactive power. so definitely, there must be problem in field excitation. From your posted events, i can say there is a link between forced signal and reactive power loss. First of all, i want to know what is description of that forced signal. Once it got activated, it went off within a second. But something holding that signal for another 15 mins (i am not sure about this duration)..it may be be timer also....so plz check for the presence of any timer block in your logic corresponding to that forced signal. after this event, other machines have raised their reactive power limits because of the active reactive power controller..thats normal..please post more details to help you more...!!!
 
Hi Mr. Chandru

We didn’t force any signal at that time but we received that alarm & that is what I am asking is there any chance to happen like this?
We even tried to simulate to force particular Logic and unforced it, it cannot be done in 3 sec time.

When the actual MVAR dropped the operator didn’t notice the drop, later (after 1 Hr.) when he checked the system he found that this particular GT in -16 MVAR and he normalized the VAR by increasing it and machine responded normally.

We checked the AVR system there is no Alarm and it is normal (both Main & Stand-by).

But in Generator relay under excitation event was recorded. (But we didn’t receive any alarm regarding that, only when they checked relay events it was found)

If anything more data required let me know..

Will be waiting for your feedback

ty
 
HI,

I am adding some more data regarding this problem

00:27:06.843 TRUE FORCED LOGIC SIGNAL DETECTED
00:27:09.000 FALSE FORCED LOGIC SIGNAL DETECTED
The above alarm occurred @ one time only.

We found in <C> core some DCC errors, we are cleared up.<pre>
date Time Bus#1 KV
11/21/2012 0:24:00 127.34
11/21/2012 0:25:00 127.34
11/21/2012 0:26:00 127.34
11/21/2012 0:27:00 127.47
11/21/2012 0:28:00 126.33
11/21/2012 0:29:00 126.33
11/21/2012 0:30:00 126.33
11/21/2012 0:31:00 126.21
11/21/2012 0:32:00 126.21
11/21/2012 0:33:00 126.61
11/21/2012 0:34:00 126.93
11/21/2012 0:35:00 127.07
date Time BUS#1 Hz
11/21/2012 0:24:00 50.15
11/21/2012 0:25:00 50.15
11/21/2012 0:26:00 50.15
11/21/2012 0:27:00 50.15
11/21/2012 0:28:00 50.15
11/21/2012 0:29:00 50.15
11/21/2012 0:30:00 50.15
11/21/2012 0:31:00 50.15
11/21/2012 0:32:00 50.15
11/21/2012 0:33:00 50.15
11/21/2012 0:34:00 50.15
11/21/2012 0:35:00 50.15
date Time GT#1 DVAR
11/21/2012 0:24:00 7.56
11/21/2012 0:25:00 7.56
11/21/2012 0:26:00 7.56
11/21/2012 0:27:00 12.23
11/21/2012 0:28:00 11.20
11/21/2012 0:29:00 11.20
11/21/2012 0:30:00 11.20
11/21/2012 0:31:00 11.20
11/21/2012 0:32:00 11.20
11/21/2012 0:33:00 9.92
11/21/2012 0:34:00 8.73
11/21/2012 0:35:00 8.73
date Time GT#2 DVAR
11/21/2012 0:24:00 6.50
11/21/2012 0:25:00 6.50
11/21/2012 0:26:00 6.50
11/21/2012 0:27:00 -16.67
11/21/2012 0:28:00 -15.39
11/21/2012 0:29:00 -15.39
11/21/2012 0:30:00 -15.39
11/21/2012 0:31:00 -15.39
11/21/2012 0:32:00 -15.39
11/21/2012 0:33:00 -15.39
11/21/2012 0:34:00 -15.39
11/21/2012 0:35:00 -15.39
date Time GT#3 DVAR
11/21/2012 0:24:00 7.16
11/21/2012 0:25:00 7.16
11/21/2012 0:26:00 7.16
11/21/2012 0:27:00 11.50
11/21/2012 0:28:00 11.50
11/21/2012 0:29:00 11.50
11/21/2012 0:30:00 11.50
11/21/2012 0:31:00 11.50
11/21/2012 0:32:00 11.50
11/21/2012 0:33:00 10.44
11/21/2012 0:34:00 9.34
11/21/2012 0:35:00 8.19
date Time GT#6 DVAR
11/21/2012 0:24:00 8.52
11/21/2012 0:25:00 8.52
11/21/2012 0:26:00 8.52
11/21/2012 0:27:00 11.58
11/21/2012 0:28:00 11.58
11/21/2012 0:29:00 11.58
11/21/2012 0:30:00 11.58
11/21/2012 0:31:00 11.58
11/21/2012 0:32:00 11.58
11/21/2012 0:33:00 11.58
11/21/2012 0:34:00 10.48
11/21/2012 0:35:00 9.48
date Time GT#1 KV
11/21/2012 0:24:00 10.59
11/21/2012 0:25:00 10.59
11/21/2012 0:26:00 10.59
11/21/2012 0:27:00 10.59
11/21/2012 0:28:00 10.59
11/21/2012 0:29:00 10.59
11/21/2012 0:30:00 10.59
11/21/2012 0:31:00 10.59
11/21/2012 0:32:00 10.59
11/21/2012 0:33:00 10.59
11/21/2012 0:34:00 10.59
11/21/2012 0:35:00 10.59
date Time GT#2 KV
11/21/2012 0:24:00 9.97
11/21/2012 0:25:00 9.97
11/21/2012 0:26:00 9.97
11/21/2012 0:27:00 0.00
11/21/2012 0:28:00 9.95
11/21/2012 0:29:00 9.95
11/21/2012 0:30:00 9.95
11/21/2012 0:31:00 9.95
11/21/2012 0:32:00 9.95
11/21/2012 0:33:00 9.95
11/21/2012 0:34:00 9.95
11/21/2012 0:35:00 9.95
date Time GT#2 132KV side current Amp
11/21/2012 0:24:00 90.09
11/21/2012 0:25:00 90.66
11/21/2012 0:26:00 89.82
11/21/2012 0:27:00 116.58
11/21/2012 0:28:00 121.11
11/21/2012 0:29:00 140.28
11/21/2012 0:30:00 151.80
11/21/2012 0:31:00 144.57
11/21/2012 0:32:00 146.04
11/21/2012 0:33:00 147.45
11/21/2012 0:34:00 142.62
11/21/2012 0:35:00 137.73</pre>
Thanks
 
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