kent grimsley
Member
- Location
- west springfield ma. u.s.
If I have a 208v 3phase 3 watt circuit with 28.8 amps on each leg with 6 watts on each leg and a lose phase L1 to L3, is there a formula that I can calculate what the amoerage would be on L2?
When you say a lose (loose? lost?) phase from L1 to L3, are you saying that it is an open delta? If so, that will have no direct effect on the line currents in each of the secondary phase lines.If I have a 208v 3phase 3 watt circuit with 28.8 amps on each leg with 6 watts on each leg and a lose phase L1 to L3, is there a formula that I can calculate what the amoerage would be on L2?
thanks for the Welcoming, this is a extra credit school problem. Forgetting about the watts because I don't think it applies, I have a 208 v 3 phase circuit with 28.8 amps per leg under normal conditions.The question is what would be the amperage on L2 if i lost the L1 to L3 leg. I can not find a formula to help me calculate this
Could be.kwired:
The problem (as relayed) is not the loss of a phase line (like L3) but rather that one of the source windings (L1-L3) is open.
This converts the closed delta to an open delta. The effect of that on the currents in the other two windings is what is asked for.
To determine that we do not need to know the nature of the load, just that it is balanced, including phase angles, on all three legs.
At least that is the way I see it.
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What GD and K are eluding to is that a 208V 3? 3W (W meaning "wire" in this case) is typically and conventionally supplied from a 208/120V 3? 4W wye system supply source. I do not believe this has any bearing on your problem.If I have a 208v 3phase 3 watt circuit with 28.8 amps on each leg with 6 watts on each leg and a lose phase L1 to L3, is there a formula that I can calculate what the amoerage would be on L2?
No, you are not. IOW, you are thinking correctly.I asked for more info on this and was told that it is a 208v 3 phase 3wire feeding a hanging unit heater. I believe that if I lost the L1 and [to] L3 element I would still be feeding 2 elements with L2 and my amperage would not change. Am I wrong to think this way?
If it had a 3? blower motor, that would complicate the problem to the degree you could not provide a definitive answer, or have to cover multiple scenarios in your answer. Did you lose just the L1-L3 heating element or the element and the corresponding winding in the motor? For the former, L2 would remain the same. For the latter, L2 would change, but by how much would depend on how the motor reacts to losing a winding, so no concise answer without assumptions.Thanks, as far as the fan goes. based on the information given that it was a balanced load with 28.8 amps per phase wouldn't that mean that it was a 3 phase blower motor? If it was single phase motor wouldn't one phase be a little higher?
Keep it simple - maybe a radiant heater with no blower - that would be realistic and simple.Thanks Smart$, for the lack of any additional info given I will keep it simple and just say the amperage stays the same