I have a customer with a small welding shop. No access to 3 Phase power, so he has a rotary phase converter which he uses to power a few pieces of equipment. The phase converter has a 20HP idler and multiple run caps.
One of these is a small twisting machine he purchased a couple years ago to twist square bar for ornate gates/railings etc. The twister utilizes a small 3P motor with a FLA of 3.7A @ 220VAC.
Apparently a couple of weeks ago he attempted to use it, and one or more of the windings shorted out.
The company he purchased the unit from came and pulled the motor, rewound it (or had it rewound), and reinstalled. Their tech said it failed due to a power issue at the shop, causing the motor to draw too much current.
I was forwarded an email from the tech which stated that when the motor was bench tested (unloaded) at their shop it drew ~2.5A @ 212V, yet when connected on location it drew 4A @ 244V.
I stopped by on Friday on my way to another site, expecting to find a failure with the phase converter that was causing the motor to single phase. However, that doesn't seem to be the case.
I did some quick tests as I was short on time, and found some strange variations with the voltage and current between phases. I expected the higher voltage reading between A and C, due to the phase converter being so lightly loaded. I didn't expect the values between B and C, nor the current being so high and varied.
No load was the motor pulled from the transmission. Base load is the motor connected to the transmission. Light load is twisting some 1/2" square bar. Light load 2 is twisting the same size bar, but this time with an additional 9A load on the phase converter due to another piece of equipment running at the same time.
One of these is a small twisting machine he purchased a couple years ago to twist square bar for ornate gates/railings etc. The twister utilizes a small 3P motor with a FLA of 3.7A @ 220VAC.
Apparently a couple of weeks ago he attempted to use it, and one or more of the windings shorted out.
The company he purchased the unit from came and pulled the motor, rewound it (or had it rewound), and reinstalled. Their tech said it failed due to a power issue at the shop, causing the motor to draw too much current.
I was forwarded an email from the tech which stated that when the motor was bench tested (unloaded) at their shop it drew ~2.5A @ 212V, yet when connected on location it drew 4A @ 244V.
I stopped by on Friday on my way to another site, expecting to find a failure with the phase converter that was causing the motor to single phase. However, that doesn't seem to be the case.
I did some quick tests as I was short on time, and found some strange variations with the voltage and current between phases. I expected the higher voltage reading between A and C, due to the phase converter being so lightly loaded. I didn't expect the values between B and C, nor the current being so high and varied.
No load was the motor pulled from the transmission. Base load is the motor connected to the transmission. Light load is twisting some 1/2" square bar. Light load 2 is twisting the same size bar, but this time with an additional 9A load on the phase converter due to another piece of equipment running at the same time.