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over-frequency protection

over-frequency protection

over-frequency protection

(OP)
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

RE: over-frequency protection

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)?

RE: over-frequency protection

(OP)
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.

RE: over-frequency protection

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.

RE: over-frequency protection

how about a voltage spike or transient during the trip?

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RE: over-frequency protection

(OP)
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.

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