How to avoid circulating currents in multi-speed, two-winding machines
"I have rewound a two-speed, two-winding motor. The high speed runs fine — the no-load current seems right. But when I test the low speed, the amps are far too high at rated voltage. It draws significantly above the rated current, at no-load! I know that the windingdata is correct. What could be wrong?" This is one of the most common problems we encounter at the EASA office. The solution is almost always the same. There are three questions we ask in return:
- What are the two speeds?
- What are the number of circuits in each winding?
- What jumpers are used to connect each winding? The responses to these three questions almost always lead to the same conclusion: The two windings are connected in such a way that the de-energized winding has circulating currents which induce voltage into the energized winding.