electricpete
Electrical
We had an 800hp motor associated with a radial-flow centrifugal pump trip on instantaneous current. The instantaneous trip is set well above locked rotor amps (verified as-found setting afterwards).
It was suggested that the cause of the trip may have been the abnormal fluid system lineup which allowed additional flow through the pump during start may have been the cause.
My viewpoint is that if motor has tripped on instantaneous (and setting verified well bove LRA), then we should be able to rule out all mechanical causes. Do you agree? My reasoning would be as follows:
Anything that places extra mechanical load on the shaft (up to an including a seized-shaft due to bearing failure) should increase the time duration that locked rotor current id drawn, but not the magnitude of the current. So these types of mechanical problems should cause a time-overcurrent trip, not an instantaneous trip.
Do you agree that mechancial causes can automatically be ruled out if motor trips on instantaneous (vs time overcurrent).
It was suggested that the cause of the trip may have been the abnormal fluid system lineup which allowed additional flow through the pump during start may have been the cause.
My viewpoint is that if motor has tripped on instantaneous (and setting verified well bove LRA), then we should be able to rule out all mechanical causes. Do you agree? My reasoning would be as follows:
Anything that places extra mechanical load on the shaft (up to an including a seized-shaft due to bearing failure) should increase the time duration that locked rotor current id drawn, but not the magnitude of the current. So these types of mechanical problems should cause a time-overcurrent trip, not an instantaneous trip.
Do you agree that mechancial causes can automatically be ruled out if motor trips on instantaneous (vs time overcurrent).