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.

 

[R-fur]

As well as KVA you also need to look at KVAr. Can the generator supply the required KVAr for the motor? As James said your set up should be ok but check the ratings.