motor rewinding from 480v to 575v 8

[MULU007]

Hi Everyone,
A vendor mistakenly sent us two motors, one rated at 460V and the other at 480V, while our Motor Control Center (MCC) operates at 575V. Each motor is equipped with a Variable Frequency Drive (VFD). Due to the long lead time for obtaining 575V motors, we are considering rewinding the stator windings to match the 575V requirement. Upon consulting rewinding shops, we received mixed responses. One shop confirmed the feasibility of the task, while the other warned that these special motors might warp due to the heat involved in stripping the wire for rewinding. Will the 575v produce more torque that can damage the pump/blower fan (after rewinding)? The first motor is a new air blower motor, and the second is a used Seepex Progressive Cavity pump used in a wastewater plant for pumping anti-foaming material. My question is: would rewinding these motors be an effective solution for our application?"

 

[BrianPetersen]

Whoa, hold it! Is this a motor driven through a VFD and your MCC is supplying power to the VFD which is in turn supplying the motor - or have I misunderstood what you are doing?

If the MCC is supplying the VFD then the important thing is whether the VFD can handle the 600V input; the output of the VFD to the motor can be (almost) whatever you want it to be within reason, and the motor need not be rated for 600V input because that isn't what it's going to be seeing. Which means ... we need some more information about the VFD.

Are you sourcing the motors in Canada? I see the CSA markings. That size of motor should be readily available through Canadian suppliers as such a thing is very common here.

 

[MULU007]

Hi Brian,
Thanks for the reply. This site is in Northern Ontario Canada. Yes, your understanding is correct. VFD is in the MCC itself and is rated for 575v.
As a part of the solution, the electrical contractor proposed to provide a 460-575v transformer, but they quoted a high price owing to the travel and hotel stay. So thinking of other cost effective options. The rewinding shop quoted comparatively less than the transformer install option. I have requested for the nameplate details for the vfd.
Also, if I clip the voltage level to 460v in the vfd, wouldn't the speed be limited to a lesser value? V/f ratio---frequency will be less than 60hz to clip the voltage to 460v.

 

[waross]

We used to service a plant that had a mix of 460 Volt motors and 575 Volt motors.
The incoming 600 Volt service fed a PDC and a 575 Volt MCC.
A pair of auto-transformer in open delta stepped down to 480 Volts for a 480 Volt MCC.
There was no easy way to change a motor feeder from the 480 Volt MCC to the 600 Volt MCC.
It was common for a machine at one voltage to be replaced with a machine using the other voltage.
The solution?
Two small lighting transformer connected in an open delta auto-transformer configuration.
Round off the 1.94 Amps to 2 Amps.
In auto-transformer step-down configuration, the 120 Volt winding must pass both the motor current and the current for the 480 Volt winding.
o the 120 Volt winding must pass 2 Amps plus (2A x 120V/480V) or 0.5 Amps.
With 2.5 Amps through the 120 Volt winding you will need two 120V x 2.5A = 3000 VA transformer.
This will be much cheaper than a rewind.
I have also encountered 600V > 480V auto-transformer connections where a plant with 600 Volts needs temporary power and the only rental generators available are 480 Volt generators.
Try it.
You'll like it.

The voltages to ground on the 480 Volt side will not be equal but the circuit is safe and is code compliant.
If someone is a stickler for symmetry, and cost is no object, you may buy one more transformer and use a three phase wye auto-transformer configuration.

The voltages with the three phase configuration will be 277 Volts and (347V - 277 V =) 70 Volts.
Good luck finding a 277V/70V transformer.
Common practice is to use standard 480V/120V transformers. The 120 Volt windings will still carry the same 2.5 Amps so the same 3000 VArating is needed, but due to the under utilization (lower voltage than rated) of the transformers, the cost is increased by a ratio of 3/2.
Go with the two transformer solution.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[edison123]

Motors can be rewound for any voltage within reasonable limits.

In your case, I suggest before going the 575/460-480 V step down transformer route (sans the price gouging 'travel and hotel stay'), try out the 460-480 V/ 60 Hz operation with your VFD to see if it works. First one costs money while the second one, none.



Muthu

http://www.edison.co.in

 

[BrianPetersen]

If it is a decent VFD, you can configure the V/Hz relationship to whatever you need it to be within reason. It is not locked to supplying a fixed relationship. No transformers, no rewiring - just a configuration setting in the VFD.

 

[LionelHutz]

As already posted, set the VFD V/Hz ratio so it outputs 460V @ 60Hz. Just be mindful of the motor current vs VFD rated output current which means you can't match the VFD to the motor using HP, you have to match by current. It might need one bigger VFD size if they are already HP matched.

 

[zlatkodo]

The windings of this motors can be redesigned for 575V.
Power and torque remain the same if the frequency is not changed.
New windings cannot damage the pump or fan in any way.
It is true that any motor can be damaged during excessive heating of the windings when removing the old winding, but in proper service, motors are heated in an oven only to the allowed temperature and never with a burner, open flame, or similar.
Additionally, the motors are small enough that old windings can probably be removed, and slots cleaned without heating (cold stripping).
ACW

 

[waross]

Using small auto-transformers to adjust voltages between 480 Volts and 600 Volts is a economical and time proven technique.
However,
With a VFD, I agree with Brian and Lionel.
Just configure the VFD for 460 Volts.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[petronila]

Just note if the motor is redesigned to 575 V, the original nameplate should be replaced: 1 hp, 575 V, 1.55 A. Also, if the core dimensions allows, the rewinding give you the opportunity to increase the power output. Even though this is a simple redesign, for avoiding early damage of the new winding all materials and rewinding procedures used during the repair MOST be Inverter Duty.

Best Regards,

Petronila

 

[MULU007]

Hi Everyone,
thank you all for your wonderful comments. I had proposed revised settings for the VFD but the operation team were not quite inclined for it. Finally, both motors have been sent for rewinding here in Hamilton ON. Waiting to see the outcome. Will update.

 

[waross]

Let us know the cost of the rewinds.
How about spares?
I feel your pain.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Luka Haiden]

Rewinding the motors to operate at 575V could be a viable solution, but it's essential to consider potential risks and challenges. While some rewinding shops may confirm feasibility, others may warn about potential issues such as warping due to heat during rewinding. Additionally, operating the motors at a higher voltage could potentially increase torque, which may affect the performance and lifespan of the pump or blower fan. It's crucial to thoroughly evaluate the specifications of the pump and blower fan to ensure they can withstand the increased torque and voltage.