Excitation limit operating Alarm

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Thread Starter

Fathi Hadloul

We having a frame 5 gas turbine and just complete the 48,000 Hrs services and would like to perform a performance load test. the unit has rich up to 14.1 MW and normally the unit is rated for 23 MW. we have faced an alarm which is Excitation Limit Operating (70 EX-LIM), we have other unit and was tested with the same and do not faced with Excitation Limit Operating (70 EX-LIM). the unit was loaded up to 16 MW with out any problems.

We have check the Excitation panel and found no much found.

Therefore kindly advice us back with your technical support for this matter.

Waiting for your feed back by return.

Thanks
Fathi Hadloul
Power Plant Coordinator
 
Fathi Hadloul... what are comparable measurements for both machines?

Specifically: MVA; MW; MVAr; kV; A; PF (Lag/Lead); Field V; and Field A?

Regards,
Phil Corso
 
Fathi Hadloul,

An over-excitation limit alarm means either the field voltage or the field current is excessive for the operating condition.

What kind of excitation system do the units have? The same on both machines?

Were there any Diagnostic Alarms on the excitation system?

Was any work done on the excitation system while the 48,000 hour maintenance was being performed on the machine?

Were the two machines connected to the same bus?

Does each machine have its own step-up transformer or do they share a common step-up transformer?

Have you inspected the brushes, brush rigging and slip rings of the machine with the problem? If so, what was the condition?

Were the brushes replaced on the machine with the problem during or after the outage? If so, were they shaped to match the curvature of the slip rings--either manually or from the supplier?

Again, what were the MW, MVA, MVAr (magnitude and "direction"--leading or lagging), pf (magnitude and "direction"--leading or lagging), generator terminal voltage, generator phase currents, field voltage and field current for both machines at similar loads (say 14 MW) so we can compare similar operating conditions to similar operating conditions?

Please write back to give the details. Your prompt and complete reply is appreciated.
 
F

Fathi Hadloul

Dear sir,

we observed An over-excitation limit alarm means. would you write a brief of problem encountered in regarding excitation to be clear picture? and in the mean time we are preparing our reply for your kind request.

Thanks
Fathi
 
An over-excitation limit alarm means either the field voltage or the field current is excessive for the operating condition.

This means that for some reason either the field voltage or the field current was above a setpoint for the load of the machine. Perhaps the setpoint was too low. Perhaps the exciter was operating in the wrong mode (FVR/FCR (Manual) instead of AVR). Perhaps there was a problem with the brushes and a high voltage drop was causing a higher-than-normal amount of excitation to be required to maintain the generator terminal voltage for that condition.

We are awaiting your kind reply to the questions so we can provide more concise answers. Sometimes, even just gathering the information can help to pinpoint the cause of the problem for the people at the site. But the answers to all of the questions are necessary for a more concise reply.
 
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