2 winding motor torque speed curve (separate winding)

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W@ttson

W@ttson

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I am used to regular NEMA rated motors and for them to exhibit the typical A, B, C, D, E torque speed curves:
https://www.electricalengineeringtoo...r-designs.html
As shown in the link above. The curves are created by the design of the machine's slots and teeth of the rotor and stator.

I recently needed to use a two speed two winding motor (separate winding). I asked the motor manufacturer for a NEMA D motor, and they said that 2 winding motors do not come in a NEMA class but are rated as "2CT" or 2 speed Constant Torque. What is the Torque speed curve of a 2 speed motor that is considered "Constant Torque"? I need to evaluate what I can expect the startup and breakdown torque to be.

Thank you
 
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Jraef

Jraef

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According to NEMA, design classifications like A, B, C and D do not apply to multi-speed motors, because technically they are all "specialized" motors. So you get what the motor mfr designs into it. I have always just assumed that a 2S2W motor will have Design B torque/speed characteristics on each speed.

Why are you wanting Design D torque/speed characteristics on a 2 speed motor? Were it me, I would just use a VFD to change the speed with Vector Control to get the high torque capability out of a motor selected for the desired torque.

By the way, your motor guy was describing the configuration of a 2 speed 1 winding motor, not 2S2W. With 2S1W motors there are 3 different ways of designing the motor for different applications; Constant HP, Constant Torque or Variable Torque. In a CHP motor, the nameplate will show the same HP at the two speeds, meaning the torque INCREASES at the lower speed. In a Constant Torque version, the HP changes at a 2:1 ratio (Low HP is 1/2 the High HP) because the torque is remaining constant. In a Variable Torque version, torque DECREASES with speed, so the HP change is more dramatic (Low HP is 1/4 the High HP).
 
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W@ttson

W@ttson

Senior Member
Location
USA
Jraef said:
According to NEMA, design classifications like A, B, C and D do not apply to multi-speed motors, because technically they are all "specialized" motors. So you get what the motor mfr designs into it. I have always just assumed that a 2S2W motor will have Design B torque/speed characteristics on each speed.

Why are you wanting Design D torque/speed characteristics on a 2 speed motor? Were it me, I would just use a VFD to change the speed with Vector Control to get the high torque capability out of a motor selected for the desired torque.

By the way, your motor guy was describing the configuration of a 2 speed 1 winding motor, not 2S2W. With 2S1W motors there are 3 different ways of designing the motor for different applications; Constant HP, Constant Torque or Variable Torque. In a CHP motor, the nameplate will show the same HP at the two speeds, meaning the torque INCREASES at the lower speed. In a Constant Torque version, the HP changes at a 2:1 ratio (Low HP is 1/2 the High HP) because the torque is remaining constant. In a Variable Torque version, torque DECREASES with speed, so the HP change is more dramatic (Low HP is 1/4 the High HP).
Click to expand...

Can't use drive because this is a backup system and it needs to be able to operate even under an electronic failure of a drive. The 2S2W motor does have the two HP as you describe.

Thank you, I will assume a NEMA B design curve for each.
 
W@ttson

W@ttson

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Location
USA
spraymax6 said:
Can't use drive because this is a backup system and it needs to be able to operate even under an electronic failure of a drive. The 2S2W motor does have the two HP as you describe.

Thank you, I will assume a NEMA B design curve for each.
Click to expand...

to expand, it does the two HP but also the two speeds. so it is a 1200RPM, 30HP and 600RPM, 15HP
 
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