Squirrel Cage VS. Wound Rotor Motors

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new_ee

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Does anyone have any examples of each type?

Most of the time when I ask the mechanical guys whether it is a squirrel cage or wound rotor motor (for sizing short circuit and ground fault protection) they have no clue. I've even asked them to call equipment reps and that still didn't get us any further.

I know I need to educated myself more on motors, but as a EE sometimes it just isn't a high priority. I guess I figure the mechanical guys should be able to tell me.

An example recently was a larger 120V single phase exhaust fan. For most smaller ones (fractional horsepower) you typically use a 15 or 20amp breaker. Well this exhaust fan had an FLC of over 16amps so I knew I couldn't use a 15 or 20 amp breaker. So does it have a squirrel cage or wound rotor motor driving the fan?
 
Re: Squirrel Cage VS. Wound Rotor Motors

OK I just looked at table 430.52 (2002) and answered my own question (single phase motors are sized at 250% for a circuit breaker). And I found a new one. Lets just pretend my situation above involved a three phase exhuast fan. Wound rotor or Squirrel cage?
 
Re: Squirrel Cage VS. Wound Rotor Motors

One more note. Does 430.55(2002) come into play here? Combined overcurrent protection. Would I just size the circuit breaker as overload and short circuit/groun fault?
 
Re: Squirrel Cage VS. Wound Rotor Motors

A squirrel cage motor is very common and probably what you have. The rotor is made up of many laminations of metal with copper bars inlaid parallel to the shaft. Where a wound rotor motor would have 3 poles worth of windings on it's rotor, connected to 3 slip rings mounted on the end of the shaft, brushes ride on the slip rings the brushes connect to wires and are brought out of the motor. So you would have six leads, three for the rotor and three for the stator. Commonly the rotor would be connected to a drum switch and the resistance varied to control the motor. Or in my situation on draw bridges the stator is controlled by a thysistor drive and the rotor connected to a fixed resistance. My guess is with the new drives out today VFD's and so on you won't be seeing too many wound rotor motors.

[ January 27, 2006, 09:52 PM: Message edited by: Ken9876 ]
 
Re: Squirrel Cage VS. Wound Rotor Motors

If you want to learn lots about motors I'd look at Electric motor repair very informative By Robert Rosenberg and August Hand
 
Re: Squirrel Cage VS. Wound Rotor Motors

unusual to see any small wound rotor motors unless it is in a hand tool.
 
Re: Squirrel Cage VS. Wound Rotor Motors

unusual to see any small wound rotor motors unless it is in a hand tool.
Click to expand...
That wouldn't be a wound rotor motor, hand tool motors have a commutator a wound rotor motor has slip rings which are continuous. The motor in a hand tool would be universal motor
 
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