# Line reactors for Servo drives / motors or VFDs only?



## JRaef (Mar 23, 2009)

Any time you have a power converter that uses a diode bridge rectifier, and you are connected to a power source that has a kVA size 10x or more than the unit kVA, you have a situation where small line disturbances can have big effects on the power converter components and cause incremental damage. I consider them "cheap insurance".

That said, many servos are small(ish) and often connected to single phase power sources, so those are not going to have a 10x size differential. It's not that a reactor wouldn't help, it does, but it's not as imperative.


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## Jhellwig (Jun 18, 2014)

Most decent drives have the correction built in them most of the time.


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## oliquir (Jan 13, 2011)

servo drives are vfds also, just more sophisticated


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## JRaef (Mar 23, 2009)

oliquir said:


> servo drives are vfds also, just more sophisticated


Well, that depends, and even when true, I'd put it this way. Most 3 phase output servo drives are capable of running in open loop V/Hz motor to run an AC induction motor like a VFD would. However it is NOT true that most VFDs are capable of running 3 phase servo motors, the motor modeling capability it takes to do that is very sophisticated and since servos are generally small, small VFDs usually don't come with that kind of processing power. SOME do, but those that can are often more expensive than a servo driver and the less expensive versions typically cannot operate the servo motor with the same accuracy as a servo drive, so why spend the extra money for a servo motor if you are not going to get the added benefits?


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