Wound rotor induction motor

[SilverArc]

Hi
I am struggling to find some information about a thumb rule that might determine a particular application might require a Wound rotor induction motor or a squirrel cage induction motor and "HOW DOES IT EFFECT THAT A VFD CAN BE USED WITH THAT PARTICULAR MOTOR"

We have a old used hoist motor that is a wound rotor induction motor 1000 HP, rated at 4.16 KV, which was earlier controlled using the resistor banks.

Now as in modern times, we want to use a VFD to control the same application they manufacture claims that if you just short the rotor of the old wound rotor, it may not have enough torque.

Can you advise, what is the relationship between VFD and rotor type.

Thanks

 

[ters]

I had somewhat similar question in January - use of VFDs with old WR motor. Many excellent comments were posted check

http://www.eng-tips.com/viewthread.cfm?qid=175258&page=11

at Electric motors & motor controls engineering forum

 

[SilverArc]

Thanks. I have to still go through this post but another issue you might be able to advise me.

I had a discussion about this issue with one of the manufacturers and he gave me this :

1. He mentioned that Current source VFD are available for voltages greater than 4160 V and Voltage source VFD are available only till 3300 V.

and For a mine hoisting application Single drum,and to have a closed loop control, we need a volatge source VFd tha can provide the required characteristics for this application that will be full torque at zero speed.
So we need to get out motor wound for a voltage less than 3300 V.
If any one of you have dealt with this situation, Could you kindly put a word.

thanks

 

[jraef]

1) Your vendor friend is sadly behind the times. You can get PWM drives up to 6900V now without transformers. With transformers, even higher voltages are possible.

2) Yes, to do hoisting you will need a full Closed Loop Vector Control VFD, which means you will need an encoder feedback from the motor shaft.

3)WRIMs can be connected to VFDs with the rotors shorted. The VFD will be capable of compensating for the rotor current issue. The problem with shorting the rotors plays to using soft starters. When not varying the frequency (as is the case with a soft starter), the shorted rotor current gets very high yet produces very little torque in proportion, meaning the rotor usually smokes before you get your load accelerated. This is NOT an issue for using VFDs, however... see below.

4) The chances of your old WRIM surviving very long being connected to PWM VFD are slim. The motor insulation will not be able to take it without some serious filtering. The necessary filtering and increased risk of damaging the motor anyway will likely outweigh the cost of replacing the motor.

For your piece of mind and the general longevity of the project, buy a new motor and tell the motor vendors that it will be used on a VFD application. You can also have them provide you with the encoder built-in, as well as a separate cooling source, another issue when running induction motors at slow speeds with VFDs.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
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[SilverArc]

Thanks Jraef,
when you mentioned PWM drives, you mean Voltage source VFD correct ?

I spoke to Siemens yestarday and they also mentioned that there Volatge source VFD is only available till 3300 V ( We need a voltage source VFD for a mine hoisting motor application, a current source VFD will not do the job).

Could you kindly advise me, who sells voltage source VFD at 4160 V and they can be used for a mine hoisting application.

Regards,

 

[jraef]

Yes, PWM implies voltage source. That is pretty much the only type of Voltage Source inverter on the market any more so I just use that term.

You are speaking to the wrong person at Siemens. The Simovert MV goes up to 6600V and is available with Closed Loop Vector Control as you will need.

http://www.sea.siemens.com/drives/product/ldsimmv1.html

Siemens also bought Robicon last year and Siemens/Robicon has 4160V PWM drives, even up to 13,800V. You must not be in the US because any Siemens office here would (should) know all about that. The only problem with the S/R drives is that they don't offer Closed Loop Vector, only Open Loop which would not be appropriate for a hoist drive.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376