Test For Inductor Motor :No-Load and Blocked Rotor Test

[shermaine]

For No-Load Testing

Any one knows why the no-load current and power of the motor expressed as percentage of their full-load values is considerably higher than those of a transformer?



For Blocked Rotor Test

Can the starting current be reduced to an acceptable value in practice?


Pls advise.
Thanks.[/u]

 

[Styx]

2nd question:

use a bank of resistors that are shorted out at startup

 

[shermaine]

Any one knows why the no-load current and power of the motor expressed as percentage of their full-load values is considerably higher than those of a transformer?

 

[Russlk]

The friction and wind resistance losses of the motor is higher than the magnetic losses of the transformer. The motor also has magnetic losses, but small compared to the other losses.

 

[shermaine]

Induction Motors

(1) How do we analysis a motor performance under load conditions?
(2) Can i say that if for a no-load speed control by varying supply frequency, the volatge will be reduced or increase according to the frequency.....Normally, what's the percentage of changes? Let say i got a motor at speed 50hz and voltage at 220Vspeed=1415 rpm. Then when i reduced the frequency to 10hz....the voltage becomes 72.6v and speed is 299rpm....How do i know the pecentage of drop?
Pls advise.Thanks.

 

[Russlk]

1. Use a prony brake for power output and ammeter, voltmeter for power input. See: **broken link removed**

2. I don't know about variable speed drives, but would expect RPM to be 283, not 299 RPM. Any voltage reduction would depend on how the voltage is generated. If it is an alternator, I would expect the voltage at 10 Hz to be 44 volts, everything being equal, but the voltage can be varied by the field current, so set it for what you want.

 

[shermaine]

Hello,

If the experiment that we did it is of the values i given to u.
Does it make any sense? What could be due to the error?
Pls advise.
Thanks.

 

[Russlk]

Not knowing the details of the experiment, I cannot answer.