Hello:
I read a post about a year ago concerning unbalanced phases on motors. The issue was rotating (not reversing) phases to correct voltage problems - A to B, B to C, C to A. There was never an answer as to why this would help.
Here is my particular situation: 120/208Y service with Buck/Boost transformers bringing the voltage up to 230V (in an open delta) to a piece of industrial equipment (approx 100A circuit). This 3-phase connection lands in an equipment control panel which contains control circuits, a small heater, plus a few motors. The largest motor (~ 5 HP) would not function properly. This motor was controlled by a 20A/3 breaker in the control panel and it was tripping the breaker (even with the delay set to max). I used a clamp meter (didn't have anything better at the time) and the inrush was in the 70A range and it would then start slowly coming down, but not fast enough to prevent the breaker from tripping.
I remembered a post on this forum and advice from a former coworker that suggested rotating phases to correct voltage imbalance and I tried that here. It worked perfectly. The inrush current was comparable, but it fell off rapidly and did not trip the breaker. I tried about a dozen starts with success each time. To be sure I wasn't imagining it, I changed the leads back to the original configuration and retested and again the breaker kept tripping.
Can anyone explain why this would work? I was only changing the feed from the 20A breaker to the motor, not the 100A feed into the control panel itself. There is a control transformer in this panel which produces 120V for some of the electronics. I just do not understand how rotating the phases to the motor would solve this problem unless there was something wrong with the motor itself (such as the windings not being consistent).
Thanks.
-derek
I read a post about a year ago concerning unbalanced phases on motors. The issue was rotating (not reversing) phases to correct voltage problems - A to B, B to C, C to A. There was never an answer as to why this would help.
Here is my particular situation: 120/208Y service with Buck/Boost transformers bringing the voltage up to 230V (in an open delta) to a piece of industrial equipment (approx 100A circuit). This 3-phase connection lands in an equipment control panel which contains control circuits, a small heater, plus a few motors. The largest motor (~ 5 HP) would not function properly. This motor was controlled by a 20A/3 breaker in the control panel and it was tripping the breaker (even with the delay set to max). I used a clamp meter (didn't have anything better at the time) and the inrush was in the 70A range and it would then start slowly coming down, but not fast enough to prevent the breaker from tripping.
I remembered a post on this forum and advice from a former coworker that suggested rotating phases to correct voltage imbalance and I tried that here. It worked perfectly. The inrush current was comparable, but it fell off rapidly and did not trip the breaker. I tried about a dozen starts with success each time. To be sure I wasn't imagining it, I changed the leads back to the original configuration and retested and again the breaker kept tripping.
Can anyone explain why this would work? I was only changing the feed from the 20A breaker to the motor, not the 100A feed into the control panel itself. There is a control transformer in this panel which produces 120V for some of the electronics. I just do not understand how rotating the phases to the motor would solve this problem unless there was something wrong with the motor itself (such as the windings not being consistent).
Thanks.
-derek