urgent - rotor replacement spec 1

[electricpete]

Within the next hours I am interested to hear any comments of good stuff to include in rotor replacement spec.

I'm starting with basic: shall be capable of accelerating the driven load under conditions of 80-110% terminal voltage without injurious heating to the rotor or motor.

 

[Marke]

Hello ElectricPete

The rotor design will essentially determine the LRC and LRT of the motor, the full load slip and the maximum load inertia that the motor can start.
Unfortunately, a low slip rotor, which improves running efficiency, will generally result in a high Locked Rotor Current and a Low Locked Rotor Torque. Some specialised designs with thin deep rotor bars can achieve good starting characteristics as well as running charateristics, but can be limited in maximum load inertia.
Keep up the good work,
Best regards

Mark Empson

http://www.lmphotonics.com

 

[electricpete]

We are basically told by the manufacturer that we are stuck with what we get in terms of torque-speed characterics and current characteristics being different from existing motor. They will do the analysis to assure it accelerates the load safely. We will have to adjust our relay settings according to the new start time and currents.

 

[electricpete]

Well, due to time constraints, spec is written and manufacturer turned loose to build it. We will get a load test to verify thermal performance and option for torque speed test to verify their design torque speed curve... not sure exactly what that torque speed test involves. They will provide us with the design/test torque-speed and current characteristics so we can modify our relaying.

Anything major that was missed? I remember once vanstoja commented on this forum about somehow monitoring actual rotor end ring temperature during a start and establishing a spec limit somewhere in the neighborhood of 250C (?). (That thread appears to have disappeared unfortunately.) The manufacturer indicated this monitoring was not feasible.

 

[edison123]

epete,

when you say rotor replacement, I presume that you intend to use the existing stator. In such a scenario, wouldn't only supplier from whom you can get this rotor be the original manufacturer ? (since a new rotor from another manufacturer would be expensive given his tooling and design costs).

So, if the supllier for your replacement rotor is the OEM, who knows all the design data, I don't understand why you should give them any specs ? or for that matter, why they should refuse to give an identical rotor as the existing one so that you don't have to reset all your relays ?

 

[jbartos]

Suggesetions: Include the following in the spec:
1. Manufacturer shall provide computer simulation results of the motor being "capable of accelerating the driven load under conditions of 80-110% terminal voltage without injurious heating to the rotor or motor."
2. The motor load characteristics and duty should be induded in the spec or to be made available to the motor manufacturer.
3. Obviously, there might be a suitable clause included in the spec regarding "Motor Warranty".

 

[electricpete]

The supplier is the OEM. The motor was purchased from them 25 years ago. Their manufacturing methods have evolved very much such that they no longer can make anything close to the original rotor. We have also imposed on them strict turnaround time requirement which may have limited their range of options.