What HP justifies 13.2kV Rating? 1

[PWR]

A customer is currently in the process of starting up a new 4000V rated 8000Hp compressor. He is considering something in the 8000-10000 Hp range for another new facility. Should he go to a higher voltage for that size? If so which? Are there many motor shops (this is in the US) that can handle motors over 4000V? Are higher voltage rated motors as reliable as 4000V?

 

[mpparent]

I believe it will depend more on what the existing distribution is. If 4kV is available I would use it. I'm no motor expert, but I would think that 4kV motors are more readily available. Maybe someone else can address that.

Mike

PS Also, I don't believe there is any difference in reliability between one voltage or another.

 

[ScottyUK]

In the UK motor loads of that size would be firmly in the 11kV class, although I think the US tends to run larger loads for a given voltage class than we do over here. 3MW is a typical breakpoint from 3.3kV to 11kV, although it obviously depends on the available supplies and other loads served; it would be unusual to set up a dedicated 11kV substation exclusively for one drive.


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[Mendit]

13.8Kv Motors are very reliable. This category sorts out the wheat from the chaff of motor builders, you will only find good reputable manufacturers offering them. One of the main advantages is power transmission to the motor. Many times the lines coming into the plant are 13.8 you would not need to transform this down. Your transmission wires are also smaller. This also sorts out the good motor shops from the not so good. Many motors in the 13.8 are VPI, personally I am not sold on VPI in this area, resin penetration is much tougher and tighter controlls are needed with insulation taping and coil cell structure. We prefer to use a B Staged coil slot section which has corona prevention taping and a VPI coil extension system. We currently buy rewind coils from the UK and ship them to the Canada for the rewinding, currently rewinding 11,000hp and just shipped 8800hp last week.

 

[johnnyw]

Check out NEMA MG-1 part 20 (or IEC 34-1 paragraph 4.7 for non US) for preferred motor voltage ratings. I believe above 10,000 HP either 6.6 kV or 13.2 kV is preferred by NEMA, but there are always exceptions and consideration of the distribution system and other loads may dictate the best choice as mpparent stated.

 

[motorspert]

At the 8000HP+ range I would say the majority of motors are 13.8kV. Reducing current 1300A (at 4kV) down to 400A (at 13.8kV) makes cabling etc much easier.
Of course the greatest influence is the distribution system and what capacity already exists.
As to windings and voltages, look at the manufacturers experience lists and you will find the main suppliers will have years of experience at this voltage and this output. With regard to the winding types, the VPI system is used by all the major manufacturers and has well documented benefits and leads to a more reliable insulation system - I agree with Mendit that it requires process control, but this shouldnt be a problem if reputable a manufacturers is selected. There are plenty around: GE, ABB, WEG, Alstom would easily do this type of machine and larger.
In terms of reliability, we see many failed motors each year and the majoriry of failures are more due to abuse or poor maintenance than design or manufacturing error. I suggest that you always select a totally enclosed machine, TEWAC or TEEAC and fit appropriate condition monitoring and a regular maintenance regime.