VFD Voltages 4

[pop]

I am looking to find the best voltage for MOTOR-VFD solution at a 800-1000 kW. What is the Voltage trend worldwide for this power? 415 V, 690V or 11 kV.
Tanks
Peter

 

[jraef]

11kV (Medium Voltage) drives are very very expensive and the manufacturers who make them are fewer than at low voltages. The same is generally true of 11kV motors, and most Medium Voltage motors are made to order.

At 415V you will have more choices available for both the drive and motor, but that is a lot of current at that voltage, so cooling becomes and issue for both.

690V seems to be the trend now in that size range. Still considered "low voltage" (as opposed to Medium Voltage) but the current is significantly lower than at 415V. Most of the major players in the VFD and Motor industry have products readily available in that range.

JRaef.com
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[ozmosis]

As a VFD manufacturer for the global market, we see the majority of drives in the "400V" range. The range is important to be aware of as this covers 380V (a lot of Asian countries are operating at this level, and often quite a bit below). In Europe it will be 400V typically with countries like the UK on or around 415V, then you get to the USA and Canada. The nominal is 460-480V and quite often into the 500V range and then Canada and some parts of NA at 575V-600V. The good thing about (circa) 380-480V supplies is that the motors you use can be 'standard' type (off the shelf) whereby the insulation is important but not as critical as it is with 575-690V supplies. VFD's on supplies in this range will typically require an output filter to the motor to ensure the dv/dt effect at these higher voltages does not destroy the motor insulation.
690V is a growing trend, especially in the pharma/chem industry. We have just released a Sic (silicon Carbide) based VFD for this market that incorporates sinewave filter. The investment is high to develop but the result is good and well matched for this developing market.
As jraef points out, MV @ 11kv is very expensive for drives below 1MW. Not impossible but you have to take into consideration the expertise and support issues if going this way.
So, not sure if there is a 'best voltage' as you have to be able to cope with all thrown at you. If physical size is important then the 690V design is worth looking at but you need to consider all the effects/precautions of running a motor with a VFD at this voltage.

 

[oftenlost]

Another concern with motors operating above 6000VAC is the increased cost and downtime involved if the motor fails. These repairs are often priced at 50% more than the lower voltages, fewer coil shops make good coils and the cycle time for obtaining coils and for VPI processing are often increased which increases down time.

 

[jraef]

sed2d,
Your compatriots at Siemens/Robicon have told me that although they market smaller, they really don't manufacture a MV VFD under 200A (about 2800kW at 11kV) because of the cost and minimum size of the components. So even if someone buys one with a nameplate that says 800kW, you really are paying for a 2800kW drive.



JRaef.com
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[ozmosis]

I didn't know that Jeff. I guess that will keep you warm on those cold winter evenings, CHP!

 

[VxA]

Where are you at?

In the US and Canada, the company I work for has installed several VFDs on large ID fans in the range of 600hp-1500hp (450kW-1100kW) on 4160V. I'm guessing you're not in the US, as you stated the power requirements in kW rather than hp. We have also installed boiler feed water pumps in power plants at 6.9kV (they were 7000hp -- 5200kW).

 

[DickDV]

Part of the evaluation of motor-drive voltages certainly includes the length of the motor leads. The longer the leads, the less attractive lower voltages become due to the installed cost of heavy copper conductors and larger conduit.

On the other hand, MV at these KW's is way too expensive. Probably best to use the highest available LV which, generally is 600V in North America and 690V many places elsewhere around the world.

 

[pop]

Thanks all for your valuable input. Look like that 690 V is the best solution at this stage for motor power up to 1000 kW.
POP

 

[itsmoked]

Well... you will want to nail down a motor first as you may find a 480V just around the corner and not find a 690V or the other way around. If a 480V motor costs 20% less and the 480V VFD costs 15% less this may cancel out the larger wire costs.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Keith,
By his mentioning 415, 690 and 11kV he gave us a clue as to the fact that he is not in North America. 480V motors and a power source to run them are difficult to find outside of our little corner of the world. Good point otherwise though.

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

 

[itsmoked]

Ah yes good point, though my comment still stands just 415 verse 690. He should do the "economics math" not decide on the "desired math".

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ozmosis]

A large number of motors (maybe just IEC) are dual voltage 400/690V. I wouldn't see this voltage as difficult to come by, you've just got to make sure it is suitable for VSD use or the VSD has the necessary output filtering.

 

[waross]

Hi sed2developer;

A large number of motors (maybe just IEC) are dual voltage 400/690V.
The IEC motors typically use 3 windings and offer dual voltages by either a star or delta connection. The voltage ratio is 1.73:1
NEMA motors use 6 windings and offer dual voltages by either a series or a parallel connection. There is a buried connection and the motors cannot be changed from the normal star to delta in the field. There are also some legacy delta motors with 3 buried connections.
The voltage ratio is 2:1
The connection diagrams for a twelve lead generator give a good overview. The diagrams with the windings in series are applicable to most IEC motors.
The diagrams with a star point are applicable to most NEMA motors.
As always, there are exceptions. Even this statement has exceptions.
respectfully