VFD Output Reactors

[X49]

I'm designing a facility that has several 150-250hp pump motors on VFD's. The distance from the VFD's to the motors is less than 50ft. The motors will be inverter duty rated. The cables can either be armored cable with 1000V insulation, VFD cable, or individual wires with 1000V insulation.

I've been told that we should include output reactors as "cheap insurance", but the drive manufacturer does not require them for this short distance.

The way I see it, the reactors will help with motor efficiency & motor temperature even if voltage transients & insulation stress aren't an issue. Opinions?

 

[dpc]

Just one more thing to fail and they have their own losses, which are not insignificant. I would not put them in if I didn't think they were needed to deal with voltage issues.

Not sure how much they really reduce motor losses.

David Castor

http://www.cvoes.com

 

[X49]

I should also note that these are 600V 6-Pulse drives.

dpc, you make some good points. They also cost money, take up space, heat the VFD enclosure, and lower the voltage available at the motor terminals. They don't really seem like "cheap insurance" in this case.

 

[MAGTiger]

If you price 1.5% reactors, I think you'll find them to be a small fraction of the cost of a motor, particularly at 250hp. The more important question you should answer is what is the importance of the process. If it is an application that you cannot afford to have shut down unexpectecdly, then get the reactors. If it isn't that important then you are probably ok. But you'd be better off with the armored cable than the VFD type, it has less capacitance. output filtering is commonly done in downhole pumping applications because of the high cost of pump replacement. As far as the reactor being one more thing to fail. Well, if it does fail then it's a wake up call that the motors are next and you need to have a porofessional evaluate the application. Kinda like taking a canary into a coal mine.

Neil

 

[jraef]

I use the cheap insurance statement a lot. I'm with MAGTiger here, it's not the cost of the reactor, it's the cost of down time and the cost to pull the motor to consider.

The beauty of a reactor is, it's just copper wire on an iron core, there isn't a lot to "fail" in that system. It not only protects the motor from something that happens in the VFD, it also helps to protect the VFD output transistors from motor winding and lead cable faults. Adding a reactor delays the rise time of a fault (inductive time constant) and can give the VFD that few extra milliseconds it needs to turn off the transistors before they pop.


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[sparengineering]

What kind of VFD's are you using. Do they have switchable modulating frequency? If yes use lowest frequency may be 4 khz. The manufacturer of the VFD's have to recommend proper solution, using of reactors or not is a part of IGBT switching frequency and the distance together with the type of cables you are using.

 

[itsmoked]

250hp
reactors

You should at least do the math on the wasted energy and any subsequent air conditioning loads.

Keith Cress
kcress -

http://www.flaminsystems.com