VFD voltage dip consideration 2

[JOHNCOCOA]

I'm running a generator sizing program and I have two VFD's (15 hp and 20 hp). I can select each of these for up to 25% permitted voltage dip (to reduce the size of the generator), but now I'm having trouble finding VFD's with greater than 10% permitted voltage dip. Any suggestions?
Thanks and have a happy new year!!
-J

 

[DickDV]

Drives built for the international market will have a much broader input voltage range. For example, ABB's 460V class drives are good from 380 -10% to 500 + 10%. Other brands are out there that do the same.

 

[ozmosis]

What do you define as a voltage dip? there is a difference regarding the tolerance defined by a VFD, typically +/-10% of 380~480(or higher)Vac and the capability of a VFD to cope with a power dip (sag). If it is ms or secs or minutes or constant then it will have a large impact on the VFD design.
Most VFD's will have an undervoltage trip limit way below the level shown in the voltage tolerance, but it will be time dependant.
If you are looking for power ride through then this can be defined for a short period of time but if you are looking for a VFD to operate at a lower voltage than the nominal over a long period of time then this will not only push the current demand in the VFD but screw up the motor you are connected to. You can only provide a maximum output subject to the input.

 

[JOHNCOCOA]

oz, thanks for the reply. I'm talking about what the VFD can handle in the electrical system. Specifically, there's a chiller with two 50hp (non-VFD) compressors. during generator operation, when these compressors start the voltage will dip as the generator controls compensate. I wanted to see how other folks dealt with the issue.
With further investigation on the side, I was able to figure that the only time I had a problem was when the entire building came on as a block load... by staggering the AHU and chilled water components on initial start up via the BAS, I was able to keep VD below 10%.

Thanks Dick and oz!
-John

 

[ozmosis]

John
An interesting read is this:

http://www.pbworld.com/library/technical_papers/pdf/61_DieselEngine.pdf

I've referred to it a number of times looking at the different types of loads and how they should be started on gensets.