Rotary Phase Converters
- Thread starter jnamp
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kwired
Electron manager
- Location
- NE Nebraska
Have you read through article 455?
kwired
Electron manager
- Location
- NE Nebraska
Well lets start with
Hopefully your converter is marked with input voltage and current for one place to start.
Now that aside consider that you only have two lines carrying the same load that normally would be divided among three lines if supplied with true three phase source. That means it will draw approximately 1.73 times the current for same power at single phase as compared to the same power at three phase.
I'm guessing you figured you needed conductors somewhere in the neighborhood of 90 - 100 amps for a 20 hp motor @ 240 volts.
Since you said you have a 30 hp converter it's marked input rating is likely at least 135 up to maybe 160 amps.
Efficiency and power factor ratings probably make the main difference of exactly what the rating is.
Hopefully your converter is marked with input voltage and current for one place to start.
Now that aside consider that you only have two lines carrying the same load that normally would be divided among three lines if supplied with true three phase source. That means it will draw approximately 1.73 times the current for same power at single phase as compared to the same power at three phase.
I'm guessing you figured you needed conductors somewhere in the neighborhood of 90 - 100 amps for a 20 hp motor @ 240 volts.
Since you said you have a 30 hp converter it's marked input rating is likely at least 135 up to maybe 160 amps.
Efficiency and power factor ratings probably make the main difference of exactly what the rating is.
broadgage
Senior Member
- Location
- London, England
If the equipment is old and lacks a proper data plate, then a rule of thumb is to allow one KVA per horsepower, for motor losses and imperfect power factor.
So 20 HP may be assumed to be about 20KVA.
If one also allows for a 240 volt nominal service being actually 230 volts at the motor, then that gives a running current of 87 amps.
If one allows for the actual voltage being 220, which is likely with a service on the low side and a long feeder or branch circuit, then the running current would be about 91 amps.
So 20 HP may be assumed to be about 20KVA.
If one also allows for a 240 volt nominal service being actually 230 volts at the motor, then that gives a running current of 87 amps.
If one allows for the actual voltage being 220, which is likely with a service on the low side and a long feeder or branch circuit, then the running current would be about 91 amps.
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