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I have a DC motor with independent excitation, power by a ward-leonard system. The nominal voltage applied to the motor is 250 V. I have to calculate what regulation(%) to apply to the generator so that the motor rotates at 500 rpm. I calculated that for the motor to have that speed it needs a voltage of 121.44 V applied at the terminals and that for the generator to supply that voltage it needs EMF of 138.6 V. In my notes, I have that to calculate the regulation I need to following formula, where U0 is the generator's EMF, Un the nominal voltage at the terminals and U the voltage at the terminals:

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According to this formula I get a regulation of 6.9%. But I don't really get this formula. Why do I divide the voltage difference by Un and not U0?

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1 Answer 1

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The formula seems to calculate speed regulation defined as the speed change due to load torque change. That will be proportional to the change in voltage drop across the armature resistance.

What you appear to be trying to calculate is the generator field excitation required to produce the armature voltage from the generator that the motor requires for the given speed.

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