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Synchronous motor field discharge resister

Synchronous motor field discharge resister

Synchronous motor field discharge resister

(OP)
I am looking for any rules of thumb about sizing synchronous motor field discharge resister.  One just has motor name plate data.  I want to keep the discharge voltage around 500 volts, as I will be using a solid state field applacation panel.

Motor Data: 500 HP, 514 rpm, 4000 volt, 69 amp,   .8 PF, 60 Hz      field: 250 volts  32 amps

The motor will be started across the line, no load condition.  The load is a two-piston compressor.

RE: Synchronous motor field discharge resister

The way I have approached this problem is to consider the winding as a battery with 2 separate resistances, one is the field resistance the other is thwe discharge resistor.
I would rather have the greatest voltage drop on the external resistor than on the winding resistance resistor. Since the field resistance is about 7.8 ohms, I would go slightly higher e.g. 8 to 10 ohms.
There are several other ways to approach this problem as well.

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