Calculating DC field amps

[vm3118]

Just curious on how you calculate dc field amps on a motor that hasnt been installed yet? Its a 200 HP 460 volt dc motor FLA is 357 We are testing and recording info on spare motors. Thanks for your help

 

[Cold Fusion]

The one time I had to have that type of information, and did not have the mfg data - I called the manufacturer.

cf

 

[ohmhead]

Well a 200 hp dc 460 volt motor example armature 350 amps field amps 10

a 200 hp dc 460 volt motor example armature 280 amps field amps 30


Speed- torque- rpm- design of motor- temp- voltage of armature to field current data is a bigg factor i argee with CF ask manufacturer for info .



But take a look here its kinda interesting http://classes.engineering.wustl.edu/jee4350/docs/Synchronous Machine.pdf

 

[Besoeker]

Just curious on how you calculate dc field amps on a motor that hasnt been installed yet? Its a 200 HP 460 volt dc motor FLA is 357 We are testing and recording info on spare motors. Thanks for your help

You can't usually calculate it. As the others have indicated, you should get the information from the manufacturer. If the motor exists you could maybe measure the resistance of the field winding and work out what it would be if you know the excitation voltage. Bear in mind that what you'd get is the cold field resistance. It may be as much as 20% higher at operating temperature.

My guess, stress guess, based on experience is that your field current will be 15A or less. I have played around with DC shunt and compound wound machines for a few decades. I don't recall any where the shunt field was more than 2-3% of the armature current.
But we all get surprises from time to time. And some of them aren't nice.

Ask the manufacturer.