60Hz motor to run at 50Hz
60Hz motor to run at 50Hz
(OP)
I have been asked to look into a problem of a belt driven fan from the US running here in Australia on 50Hz, drawing far too much current. I am attempting to obtain more info from the site which is across country, but at this stage my question is fairly general, and I am assuming no other abnormal conditions.
The nameplate specifies operation at either frequency as followes:
60Hz 1780RPM 75HP 230/460V 184/92A
Service factor 1.25 230/115A
Eff 94.1/93
50Hz 1475RPM 75HP 208/415V 210/105A
Service factor 1.0 210/105A
Eff 93/91.7
There are 6 individual field coils which were connected by the local electrician as series delta. (ie 2 coils in series for each side of the delta). It has a star-delta starter but only overloads as the fan outlet damper is opened.
It is being supplied at 415V 3 phase 50Hz and is supposedly drawing max amps at only about 45% full load.
Would you expect a standard 60Hz wound motor to be capable of the same 75HP at 50Hz given there is a voltage reduction from 460 to 415VAC?
I would appreciate anyones comments.
The nameplate specifies operation at either frequency as followes:
60Hz 1780RPM 75HP 230/460V 184/92A
Service factor 1.25 230/115A
Eff 94.1/93
50Hz 1475RPM 75HP 208/415V 210/105A
Service factor 1.0 210/105A
Eff 93/91.7
There are 6 individual field coils which were connected by the local electrician as series delta. (ie 2 coils in series for each side of the delta). It has a star-delta starter but only overloads as the fan outlet damper is opened.
It is being supplied at 415V 3 phase 50Hz and is supposedly drawing max amps at only about 45% full load.
Would you expect a standard 60Hz wound motor to be capable of the same 75HP at 50Hz given there is a voltage reduction from 460 to 415VAC?
I would appreciate anyones comments.
Rod Nissen
nissen@powerup.com.au





RE: 60Hz motor to run at 50Hz
RE: 60Hz motor to run at 50Hz
RE: 60Hz motor to run at 50Hz
However, your motor has multiple windings that are connected to suit the voltage and frequency of the supply. As can be seen by the rating plate details, the current (therefore torque) increases when connected at lower voltage and frequency. Note that the service factor reduces from 1.25 to 1.0 at these lower values so the motor will trip sooner if overloaded.
RE: 60Hz motor to run at 50Hz
As regards horsepower, it is useful to look at actual electrical input for the two conditions (per the nameplate): 73.3 KVA @ 60hz and 75.5 KVA @ 50hz. Bottom line here is that you can get 75 HP in either case, but with less reserve at 50hz.
As far as power output versus current, I agree with xnuc that you should look at the load you are trying to drive. You might also check voltage and current per phase and insulation resistance to ground for each winding (isolated from the other windings) to be sure that imbalance is not a contributor.