Using a 460V VFD in a 380V environment

[Beggar]

I have a 50 hp motor that is wound for 380V. I also have a 460V VFD. What kinds of issues might I face if I try to use that drive and motor in a 380V environment.

Another potentially germaine piece of info: The environment is a 50 Hz environment but I'm told that the motor will be run at 30 Hz.

I don't know the "why's" to this because the decisions were made by engineers who've left the company before I joined.

Questions:

1) What kinds of issues might I face?

2) Am I correct that for a given load, running the motor at 30 Hz will draw roughly 66% of the full-load current?

3) Can anybody point me to some good references (preferably a book I can buy but a web site would be fine) that would allow me to "get smart" on freq drives?

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[mc5w]

A 460 volt drive on a 380 volt system will just simply operate with the DC bus at a lower voltage. Most of them can be programmed to rum in this environment.

The output AC voltage will always be lower thean the input voltage. If you run the motor on 30 Hertz output the drive will put out 60% output voltage but your torque should be about the same. If a motor is running too slowly either the cooling fan will not blow enough air or the induced voltage in the rotor will drop to zero. Most motors will withstand 15 Hertz operation with factory cooling fan and 6 or 10 Hertz with a sperately powered fan.

Mike Cole, mc5w@earthlink.net

 

[DickDV]

Well, not quite so fast here! If the drive manufacturer is building "world" drives, then often the input voltage range is something in the range of 380-10% up to 500+10%. On the other hand, drives built specifically for the North American market are often rated 460V +/- 10%. Only the former will operate on 380V without faulting.

Be sure to put the correct motor nameplate data into the drive software. That way, the output will be limited to 380V/50hz and the motor doesn't know the difference. The drive will behave properly too. Be sure to check that the drive has the ampacity to fully power the motor.

As for motor current, that depends entirely on how heavily the motor is loaded. That statement is true at 30hz as well as at 50hz. Pretty much any 50hp motor should be able to tolerate a 2/1 speed turndown. More often 3/1 is ok in this hp range.

 

[jraef]

Beggar,
DickDV brings up a good point, mainly that all things are not equal among VFD manufacturers, so there is no generality that can apply. What VFD do you have? Many people who participate in this forum have a world of experience with VFDs and most likely several of us have (or can get) enough information on your to be able to give a better answer.

"Venditori de oleum-vipera non vigere excordis populi"

 

[Beggar]

The drive we have is a Baldor ZD22H440-EL. My understanding from a Baldor rep is that if we were to buy a new drive for this application then it would be special unit modified to run at 380V.


--------------------
Bring back the HP-15

http://www.hp15c.org

--------------------

 

[jraef]

That's funny. I read their manual and it DOES say that you can operate it at a reduced input voltage, but you just have to derate the current capacity (which I would have assumed anyway). Here is a link to their manual, the derating statement is on page 3-12.

http://www.baldor.com/pdf/manuals/722-803.pdf

"Venditori de oleum-vipera non vigere excordis populi"

 

[mc5w]

I used the word MOST. Some drives will NOT have enough logic and analog voltage to run the controls in a 380 volt environment. However, MOST drives built today are designed to run in both environments so as to avoid shipping the wrong voltage drive. If the customer gets the wrong voltage drive from the warehouse, there could be a problem.

Most drives today are built for only 2 voltage ranges. One range is 200 to 240 volts input and the other is 380 to 480 volts input. This keeps things simple from a manufacturing and stocking standpoint.

If you are in doubt, call the manufacturer to find out what the drive can do.

A possible alternative is to use buck boost tranformers to create a wye primary wye secondary autotransformer that steps up to 440 to 480 volts so that the logic and analog buses will have enough voltage. Three 220 volt 44 volt tranformers would give you about 264Y459 volts at no load. That should be good enough to run the drive.

Mike Cole, mc5w@earthlink.net

 

[mc5w]

I forgot the ACME (

http://www.acmepowerdist.com

) makes wye-wye autotransformers that can be used to step up from 220Y380 volts to 277Y480 volts on both 50 and 60 Hertz. On 60 Hertz ONLY you can do a step up from 277Y480 volts to 347Y600 volts. Same autotransformers will also work stepping down.

These are on page 21 of their catalog.

Mike Cole, mc5w@earthlink.net