three phase motor - question about kW/HP-measurement

Assuming that the HP doesn't change because of the difference in frequency, I would say that the motor in question has a specified efficiency of 92% at full load. Not bad, IMHO. HP delivered should equal power consumed times efficiency.

ARM

In both cases, the power rating is the shaft power of the motor, and to get HP form KW, divide by 0.746, or to get KW from HP multiply by 0.746. The conversion is voltage and frequency independent. Note that the KW rating of the motor is not the same as the power drawn by the motor, that includes the losses and is the shaft power divided by the efficiency.

I think there is, but it is infinitesimal.

No. The difference is that on 60 Hz power, the motor delivers full rated torque at 20% higher speed! Since Hp is torque x speed, it therefore produces 20% more Hp (or watts) on US power.

Jon

Or 20% less torque, at the same HP.

You can't get something for nothing. More slip = more torque, but at a lower than rated speed. Since the motor is rated for a certain slip speed at 50 Hz, slip increases at 60 Hz, to provide the same performance, at a higher current.

OTOH, Increasing current in the windings can drive stator cores into saturation, increase I-squared-R losses (exponentially, mind you), among other things... and I =love= to wake up to that BBQ smell of rosin, phenolic, and enamel all burning at the same time :-)))

I had a buddy, back in the seventies, who called me up with a problem with a generator he had purchased (Army surplus). He said it was frying things, like his air compressor motor... stereo and TV and other electronics seemed to work fine with it, and it put out the required 120 volts. I plugged the shop fluorescents into it, and they flickered, then smoked (damned mag ballasts of the

70's). Then I accidentally touched the input RCA jack center conductor on the still-playing stereo, and heard that telltale 400-cycle hum...

oops! Frequency does matter. :-O

-- -john

~~~~~~~~ "The first step in intelligent tinkering is to save all the parts." - Aldo Leopold ~~~~~~~~

Extensive glossary of motor terminolgy:

-- -john

~~~~~~~~ "The first step in intelligent tinkering is to save all the parts." - Aldo Leopold ~~~~~~~~