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V-t Curve

V-t Curve

V-t Curve

(OP)
To set up a system, I need to know for a 100 HP and 200 HP ,600V induction motors , how long it takes after the main supply power is disconnected , the residual voltage on motor leads to drop to 25% of its rated voltage.
assume load is 100 %.

Thanks

RE: V-t Curve

It depends. The inertia of the load is an important factor. The best way to find out would be to measure the voltage at the motor terminals and cut the supply. You'll need something that records multiple samples per cycle.  

RE: V-t Curve

I assume you are looking for a bounding number... if the number is a little too high that's ok.

V = N * K * Phi
Phi decays according to the open circuit time constant - can be determined from the motor parameters. Can also be estimated from motor nameplate data (post everything you've got and I'll do it if you want).

N decays according to system inertia etc.

For a conservatively high analysis, ignore N and focus on the decay of Phi.  

I agree 100% that measurement is almost always better than calculation.  But in absence of measurement, we can still make a pretty good guess.

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