single speed and variable speed motor

[Abdel Rahman Mohamed]

Is there is any physical difference between single speed and variable speed motor?

 

[petersonra]

yes

 

[Besoeker3]

Is there is any physical difference between single speed and variable speed motor?

Do you mean variable speed as in controlled by a variable speed drive?

 

[GoldDigger]

Or variable speed as in a universal motor whose speed is controlled simply by varying the applied voltage?

 

[Besoeker3]

Or variable speed as in a universal motor whose speed is controlled simply by varying the applied voltage?

Yes, not enough information. I've had problems with motors not being suitably wound to cope with the high dv/dt of PWM variable frequency drives. In one case, four 760 kW machines had to be rewound. In that case, the "yes"answer Petersonra gave would have been correct. However, motor manufacturers are aware of this issue and I think motors are now made to be suitable for VFD operation.

 

[paulengr]

Dv/dt only affects the first couple turns. Normally when wound with magnet wire the turn to turn voltage is a few volts, in a NEMA standard motor you end up with a 1000-1200 V surge rating. By sleeping the first3-4 turns or using higher voltage wire it raises it to around 1800 V although nema chapter 31 inverter duty is only 1400 V. The improvement is modest. The second issue is cooling since the normal integral fan only allows down to 30-45 Jz with a constant torque load or about 15 Hz variable torque: Going further requires better cooling which is when we get to a true inverter duty motor. Not part of the standard but vpi makes a big difference too. Last phase separation papers are a must: And don’t cut them too short. Shock cord usually gets mentioned but that’s more of a high torque thing, something you have to do to help ATL motors.

We can tell instantly in the shop. If the entire stator is cooked it’s overheated. If there is only a small burn on each pole in the first couple turns it’s reflected wave.

Surge ratings for 600 V THHN are 2200 V and testing by NEMA shows actual #14 thhn tests to over 2800 V. VFD cable helps but the improvement is only about a 25 foot increase...a drop in the bucket. Very few applications hit the narrow window where it makes sense.

I work for a motor shop. One of these days I’ll video this:


Sent from my iPhone using Tapatalk

 

[paulengr]

Forgot to mention all this can be done to a standard motor to upgrade it after it burns up. Just ask. Most of your better brands and shops do this by default.

 

[Besoeker3]

Dv/dt only affects the first couple turns. Normally when wound with magnet wire

What is magnet wire?

 

[retirede]

What is magnet wire?

We always referred to any enamel insulated wire as “magnet wire.”

 

[Besoeker3]

We always referred to any enamel insulated wire as “magnet wire.”

Thank you. Education here always appreciated.:thumbsup:

 

[Abdel Rahman Mohamed]

Thanks and appreciate your feedback