Bitzer NES20Y-40P Compressor Part winding start starting issues

[Trumby]

Hello I have been asked to assist in fault finding on the above refrigeration compressor the unit is wired as a part winding 20 HP 3 phase 415 volt 32 amp run current with an approximate starting current of 98 amps.
This is supplied from a 31KVA Stanford Genset.
The 50 amp “Schneider NSX100B with a TM 50 D overcurrent trip mech” there is also a “Mikro IDT overcurrent relay NX204A in the protection circuit”, Genset circuit breaker tips at a measure inrush of approximately 65 amps,
I believe the Genset has been wrongly sized any assistance will be appreciated
Cheers Trumby

 

[James]

I would expect a 30KVA generator to be able to start a 15kw motor, however there are a few issues with refrigeration motors to take into account.

mostly they are direct online start and this can lead to over 5 x rated current being used to start.
a compressor that size probably has a heater in the base of the motor / compressor unit to keep the oil and refrigerant warm enough to process.
a fairly normal quote from a user guide would be to leave the unit powered up for at least 6 hours before attempting to start it.

I used an online calculator for sizing a generator for a 20hp motor and it came out with 75KVA
I think this is unnecessarily cautious in its over spec to allow for start-up but your 31KVA might be a little small at only 2 x rated motor load.

a quick email to the fridge manufacturer might be worthwhile, just ask them the recommended generator size for the fridge and see what they say.