over-frequency protection

[maypot]

Hi,

My 15 MW steam turbine driven set tripped on over-frequency( 51 Hz 5 cycles for a 50 Hz operation m/c )and some couple of hours after my electronic vibration transducer failed. The power supply of the transducer failed.The transducer operates on 240 V 50 Hz supply and is fed via a UPS. It is also worth mentioning that for about four minutes before tripping, the TG set was operating in island mode with a frequency between 50 and 50.9 Hz.
Is the failure a mere coincidence or could it be linked with the high frequency operation.
I believe that the over frequncy setting should be at 50,5 Hz for 10 cycles duration maximum.
Any comment ?

Bob

 

[alehman]

I would not think the frequency excursion could have damaged the power supply. Is it possible the voltage was too high? Did the UPS indicate any alarms (e.g. bypass not available)?

 

[maypot]

No alarm was recorded by the UPS but I honestly think that the culprit is current rather than voltage.
We know that a relatively high frequency result in lower impedance for capacitive circuit consequently in higher current flow.

 

[alehman]

The current in the capacitance would increase in proportion to the frequency (assuming the voltage is constant). At 50.9 Hz, the capacitive current would be 1.8% higher than at 50Hz.

 

[electricpete]

how about a voltage spike or transient during the trip?

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[maypot]

We did not record any spike during the trip. Furthermore, we experienced a ommunication problem between our PLC and the SCADA system some couple of hours after the breakdown. Fortunately, this was remedied after rebooting the system.