VFD's - How important is a line reactor / transient suppression?

[Allan Speers]

A question for our resident electrical gurus:


I've been running a 3 HP VFD on my TS for ten years now, with no problems. However I was just reading the docs on a new Fuji unit I'm considering for my planer, and it says that for "CSA" compliance, one must install transient suppression on the supply side. I've never had this, and am wondering how important it is, since such devices aren't cheap. (The unit I have was expensive, so might have built-in protection.)

Are VFD's very prone to spike damage? (With most electronics, it's no spikes but brown-outs that kill them.)

Would it be enough to put a couple of big corcom filters on the service entrance?

Also, This particular drive has an optional "line reactor." available, for $160. Am I correct that this is some type of spike protector?

[Dan Hintz]

I would imagine industrial settings is where this is geared towards, where "clean" power is not as readily available as in the home.

[Peter Kuhlman]

The CSA compliance thing seems weird.
VS drives have been known to send noise back up the power line that potentially can cause issues for other equipment. A line reactor can reduce this. This was a serious problem when drives first hit the market but is far less of an issue now with better designs. Your fluorescent lighting will cause similar issues. Multiple drives help cancel this out.
I installed many drives in industrial usage. The line reactors were well worth installing to protect the drive from line side damage. They also benefit the motor if installed on the load side of the drive. They will also work when feeding a drive single phase power as long as they are properly sized.
I suspect but don't know for sure that the CSA statement refers to back fed noise - harmonics - to protect neighbors. Really don't see this as an issue. A line reactor in my experience is well worth the cost to protect a drive. Normally with commercial stuff the cost was about 10% of the drive. No idea for small home use type equipment.

[Allan Speers]

I suspect but don't know for sure that the CSA statement refers to back fed noise - harmonics - to protect neighbors. Really don't see this as an issue. A line reactor in my experience is well worth the cost to protect a drive. Normally with commercial stuff the cost was about 10% of the drive. No idea for small home use type equipment.


Does anyone know of an reasonably inexpensive option for this? I may at some point have 3 VFD's running, so I'm thinking of adding protection to the entire shop sub box. It has a 100a breaker, but would never pull more than 40a at one time.

[Brian Lamb]

I personally think you don't need any of this. I have had two VFD's in Felder equipment since 2001, on my manual mill since about 2003, and on my recently acquired CNC mill (about 3 years ago), but that one was made in 1992. All of them work just fine, have been in numerous locations with everything from home to industrial power and never had any issues.

[Rich Riddle]

I am guessing you are located in Canada with our friend Rod if your express concerns about CSA compliance. Down here in the States it doesn't much matter.

[Silas Smith]

One thing to consider is that in the last 10 years the price of a 3 hp VFD has come down considerably. I recently picked one up for a little more than $200 and its a decent model. Go above 3hp though and it starts to really jump up in price. For your situation, I would look at the replacement cost and ask if the cost of "insurance" is worth it.

[Malcolm McLeod]

http://www.ab.com/support/abdrives/documentation/techpapers/Line%20Reactors%20and%20AC%20Drives1.pdf

Allen-Bradley site gives good explanation of when/where/why to use reactors.

[Trevor Howard]

I'm an industrial Electrician, and we probably have about 2-250 varies VFD throughout 3 plants, 1 in Mexico.
None of these have reactors/filters on the incoming supply. A majority of these have been running the 20 years I've worked here.
Just my 2 cents and experience

[Art Mann]

Looks like a solution still looking for a problem to me.

[Ken Fitzgerald]

I think the requirements are really dependent on the electrical environment in which the VFD is being used. Remember, the manufacturer will probably list what is necessary for the most extreme case so that if a problem is generated, the user can't say they weren't informed.

As others have stated and history has shown here at SMC, VFDs potentially can create electrical noise which could feed back via the wiring and cause interference for other devices. Here at SMC, IIRC, there have been people who noticed that when using their PM 3520B lathe, 2 HP, 3phase motor with a VFD, they had RF interference (static) on their radios / stereos.

I can tell you that for certain MRIs that I dealt with professionally, we brought in an outside engineering company to perform interference tests while the hospital engineering staff cycled different devices (HVAC fans, air conditioning devices, pumps, emergency generators, etc.) while electrical interference and mechanical vibration was monitored. If the electrical interference was too high or the mechanical vibration too high, the hospital had to take, in some cases, extreme measures to remedy those electrical and mechanical problems.

In the one case with which I was involved, the hospital's contractor had to drill 16, 12" holes down to bedrock and pour reinforced concrete pillars on which to pour the concrete floor. The concrete floor was poured on those 16 pillars and didn't make direct contact with the walls to minimize mechanical vibrations being conducted via the walls. This was the remedy for the mechanical vibrations.

They would have had to filter as suggested here to prevent electrical interference with other devices (HVAC fans, pumps, generators, etc.).

[Malcolm McLeod]

In majority of installs I've seen there is no need for reactors. The VFD is more susceptible to being degraded by other devices, than it is to degrade them. I cannot imagine a need for them in a home shop, and probably not in most small commercial operations. (If you are having VFD failures, check what the neighbors are doing to a shared electrical transformer.) From the link above by A-B (who manufactures VFDs, reactors, and all the bells and whistles to go with them):

Summary:
A reactor is not a magic wand or a silver bullet but can prevent certain problems when applied properly.
For the most part, a reactor at the input or output is not automatically required. Reactors can be helpful in
providing some line buffering or adding impedance especially for drives with no DC link choke. For small
drives they may be needed to prevent inrush or provide reduction in current harmonics when many small
drives are located at one installation. At the output they should only be used to correct low motor
inductance and not as a motor protection device.

Use a reactor:
To add Line Impedance.
To provide some light buffering against low magnitude line spikes.
To reducing Harmonics (When no link choke is present).
To compensating for a low inductance motor.
Only as part of a filter for reflected wave reduction.

[Rich Riddle]

Looks like a solution still looking for a problem to me.
Such an eloquent, concise, and apt way to say it.

[Allan Speers]

Thanks, guys. Great responses.

It was a question worth asking, but clearly not something to worry about.