Mike,
Can you help me understand the difference between ballanced and unballanced 3 phase and what difference it could make if any. I understand the very basic concept of three phase power from my electronics course but am at a complete loss beyond that. So a quick primer would probably be a good idea so I can fathom all of the foibles that go along with multi phase power. Thanks for the great looking diagram too.
Bob
Thank You Bob, it's my pleasure to help out.
A balanced 3 phase circuit is a simple enough concept, all three power legs have equal voltages.
When you run a three phase motor on single phase input, the third leg is being induced(generated) rather than supplied.
this causes the third legs' voltage to be less than the voltage in the supplied legs, causing the unbalance... you can hear this in the buzz of a unloaded RPC. To balance the outputs between phases, we add RUN CAPACITORS between phases to add voltage to the circuit that is low, adding balance to the circuit, therefore operating the intended motor more efficiently , and saving money through a greater motor power factor.
In a perfect world we could 100% balance a 3 phase motor/converter, but since our incoming power is not constant, our loads are not usually constant, and internal motor conditions change literally every second of operation. Adding capacitors are kinda like adding shock absorbing batteries to a circuit, they take low input , store it for a length of time until the capacitor fills to it's rated charge, then discharges into the circuit, raising the voltage temporarily until it empties, the capacitor fills and discharges, 60 times a second here in the US, 50 times a second in Europe and some other countries.
Here's something interesting most do not know... A capacitor can only store DC voltage, even when used in an AC circuit.
so when we add capacitors, we are actually boosting an AC circuit with DC power to achieve an end.
I hope i have made the use of capacitors a little more clear, but if you have further questions i'm all to happy too share my knowledge.
Drop me a message, i'll be happy to help out the best way i know how.
mike
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