Does a drive isolation transformer do the same thing as a line reactor?

A question we get sometimes is: Is a line reactor the same or better than a drive isolation transformer from a harmonic mitigation standpoint? 

A question for whether a line reactor and a HMT or a drive isolation transformer are the same really comes down to what's the benefit of those devices. And for a line reactor that has 5% impedance and a transformer of the same KVA size or impedance percentage 5%, those two are going to have the same reduction in terms of the choke effect or the constriction effect of the harmonic current. So they're going to limit that harmonic current. 

The other benefit of the transformer is electrical isolation from high frequencies, but you can also use multiple transformers to do phase shifting. So, let me show you what I'm talking about. The main benefit of a line reactor, feeding a load. For example, a VFD that produces harmonic currents. If that's a 5% line reactor and I have a transformer that's 5% and it's feeding the same VFD, the benefit is of course that the current is going to look the same, which means that the harmonic benefit or the reduction in harmonics is the same. 

So without that, let's say that we didn't have the 5% line reactor, or we didn't have the isolation transformer. This is what our current might look like. So either case,  if I didn't have the line reactor or isolation transformer, this is the benefit. And again, this is really all about the impedance factor. It's constricting the current. 

The other thing that I mentioned was if you did have two, let's say an isolation transformer here and an isolation transformer here. We mentioned this in a couple of our videos, but we can do phase shifting. So, for example, if we have Delta, Delta and Delta, Y we can get 12 pulse cancellation and cancel our fifth and seventh at the common point up here. We end up with harmonic reduction by using that transformer. 

Ultimately, what it comes down to is if somebody asks you – should I put in a line reactor or an isolation transformer? Here's what they look like. This is a line reactor. This is an isolation transformer. The obvious answer is by cost, a line reactor makes the most sense. If I'm going to do harmonic reduction from a phase shifting standpoint, then transformers can make a lot of sense.