MV motors working voltage

[usamaegypt]

Dears,
I know that there are motors working on 6.3 KV , 11 KV , and I would like to know whether there are motors working on 22 KV or not. Also , regarding the motor prices , I would like to know whether the motor price increased with the opertating voltage or what?
Best regards.

 

[jraef]

You can get synchronous motors made for up to 70kV that I know of.

Yes, price does go up with voltage. Basically, users tend to want to use as low of a voltage as they can get away with in order to keep the switchgear and control equipment costs down. So the highwer the voltage, the fewer motors are made at any given HP, until you get to the point where it becomes impractical to make a motor at a lower voltage. For instance, a 600kW motor at 3300V is going to be less expensive than a 600kW at 6000V, but you may not even find a 3000kW motor at 3300V because it would not make any sense at that voltage. But a 3000kW 6000V motor will be less than a 3000kW 11kV motor because anything above 6000V is typically made to order as an engineered system. At highr voltages there are no "book" prices available to compare, but sufice to say that level of custom handling means the volume is low, so the price will be higher.

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[usamaegypt]

Dear jraef,
thanks for your reply but I am speaking about asynchronous motors
Best regards.

 

[TommyOO7]

What's the application for the motor? Size?

 

[aolalde]

I have seen induction motors operating at 13.8 kV and very few working at 15 kV. You need to contact main manufacturers as GE, Teco-Westinghouse, Siemens, Toshiba, etc for a custom made design for 22 kV operation.

 

[jraef]

Why on earth would you want to run an asynchronous motor big enough to require high voltage? The power factor will kill you!

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[jtkirb]

I suspect this person is trying to get away from the cost of a transformer and lower voltage gear. You will find out...quickly...that this is not the route to take.

5000V motors (in the US) is a good workable voltage for very large motors.

JTK

 

[usamaegypt]

Dears,
These motors are for crushers and cement mills main drives where you need 4.4 MW motors. The reason we want to work on 22 KV is that the power tariff for 22KV is less than 11 KV for example.
Regards.

 

[edison123]

At 4.4 MW, 11 KV will be standard. I doubt whether you can get 22 KV motor.

* Homer Wisdom - "Operator, Give me the number for 911" *

 

[TommyOO7]

usamaegypt,

everything is possible, it's just a matter of time and money. Why don't you just ask a few of the biggest motor players to give you quotations for both options. Then discuss with them maintenance and operational cost and compare with energy savings on 22kV.

How does this sound to you?

Tommy

 

[jraef]

The reason why a utility charges less for bulk power at higher voltages is that they know you will be utilizing it at lower voltages, so the T&D costs and losses will be born by you instead of them. So in that light it appears to make sense to attempt to use your largest loads at the highest voltage possible so that you minimize losses in the transformers etc. However, the custom nature and expense of having 22kV motors and spares made for you will most likely outweigh the cost of transmission losses from using a more common voltage and switchgear class. Remember, you will need transformers anyway for other loads, so you are really just needing to consider the cost of additional capacity for your big loads, not the cost as stand-alone equipment.

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[dpc]

Motors above 13.8 kV will be quite expensive. In the size range you are looking at, it will likely make more sense to provide step-down transformer(s) and use a more standard motor voltage. The right voltage will depend on the mix of motor sizes and quantities that you have.

I'm sure any reputable motor supplier can give you budget-level pricing for the various voltages.

 

[magneticted]

Hi Gents

Contact ABB. They have developed the "MOTORFORMER".

A new motor concept for Synchronous machines, for compressors, refiners, blowers, etc. The big difference is a completely new cable winding technology which makes it possible to operate at voltages upto 150kv. That means the power can be taken directly from the high voltage grid

Range offered 4-6 POLE, 5-45 Mw 20-150kV

Regards

 

[waross]

Re; Synchronous vs. Asynchronous. I worked on an installation years ago in a mine concentrator plant. Each mill was driven by a pair of 6000 HP wound rotor motors.
There wer six mills for a total of 36000 HP installed. The reason for Asynchronous motors was that Synchronous motors don't work or play well together.
There is only a few mechanical degrees seperating the full load and the idling, rotating position of the shafts. It is very challenging to get them to share a mechanical load.
I have heard that there are synchronous motors designed to share a mechanical load, but I am not familliar with them.
Years ago I read a paper discussing running two alternators from the same prime mover. They made a special coupling that had an angular adjustment. The adjustmenmt was made on a trial and error basis until the alternators shared the load properly. The budget was basically,"If you can find the parts you need in the system, go ahead, otherwise forget it."
Re Power factor. There was a large building up on the hill housing two Synchronous Condensers.