DC Motor Nameplate Info

[johnnyw]

Hi all, I have an older 200 HP Reliance RPM DC motor (stab. shunt) with a dual voltage field (300/150 Volt). The armature is 500 volt & 320 amp. The speed is 1150/1750 RPM (constant torque to 1150 w/ blower and constant power from 1150 to 1750). I've measured the resistance of both field windings (F1-F2 and F11-F22) to be 41.3 ohms at room temp.

My question is regarding the nameplate info. on the field which says:

Field volts: 300/*150
Field max. amps: 3.77
Field amps: **
*Sep. Exc. **2.88/1.5-HFA-F1F2F11F22

Based on ohms law before the winding heats up and increases the winding resistance, I get the following:
Using the high voltage connections and applying 300 volts will yeild about 3.6 amps, and using the low voltage connections and applying 150 volts will yield about 7.3 amps.

So how do I interpret the nameplate data
"*Sep. Exc. **2.88/1.5-HFA-F1F2F11F22"?

Does this mean 2.88 amps using the high voltage connections and the windings are at their max. temperature?

Does this mean 1.5 amps using the high voltage connections while the motor is at 1750 RPM?

Why would the low voltage field connection (150 Vdc) exceed the field max. amps nameplate value?

And HFA?

I have a call in to the Rockwell/Reliance support group, but I figure one of you out there surely knows. Any help would be appreciated. Thanks.

 

[aolalde]

That is a kind of tricky information. In reality that field is not intended for dual voltage. The maximum voltage is 300 Volts and the minimum voltage is 150 Volts.
That is why the maximum current results when you apply 300 Volts. For speed increase weakening the field you can go down to 150 Volts for commutation stability purposes but your field current will drop to one half.

 

[raisinbran]

Johnnyw,
I think what you want to do is to connect the windings in series all of the time. That is what the F1F2F11F22 is telling you. If you apply 300 volts to the winding, you will get 3.65A (plus any tolerance for the 300V supply). At higher currents (greater than 3.77A), you might damage the windings.
HFA - hot field amperes - should be 2.88 amps at "max" operating temperature at approximately 300V. 150 volts is the approximate minimum recommended voltage and the expected "hot" current is 1.50 amperes. The speed of the motor is based on load and field current, not field voltage. To keep a constant current as the temperature is changing, the voltage will need to change until the temperature stabilizes, but those voltage numbers on the nameplate will get you in the ball park.
Raisinbran

 

[DickDV]

The field voltages given on the nameplate are for the convenience of those whose DC drive does not have a field regulator but simply a field voltage supply.

The HFA or Hot Field Amps is far preferred and is given for those who have drives with active field regulators.

The 2.88amps is for constant field excitation up to base speed of 1150 with reduced field current for field weakening or overspeed operation. At maximum speed of 1750rpm, the field current should be down to the 1.5amp marked on the nameplate.

While at hot field conditions the voltages should work out about to 300 and 150, they may not and especially will not if the field is anything other than operating temperature. The 3.66amp figure is max and would be seen only at cold start if you do not have a field regulator system.