What Causes Frequent Burn-Out of VFDs?

Frequent overloads?

The most common issues for VFDs are voltage spikes and harmonics , generally resulting in localized high voltage spikes.

There are many causes and the first data needed is the mode , area , and part that failed , if this is a recurring problem it can illuminate a great deal.

If you can give this info it will narrow the field of investigation considerably.

Also look at how often you are removing and re-applying the supply voltage to the VFD. Every time voltage is removed, the internal DC bus is discharged and has to be recharged every time voltage is resupplied. This can account for a significant amount of VFD wear. If you are frequently required to cycle the supply voltage to your load (I see this often when safety contactors are used), see if you can break the line on the load side of the VFD rather than the line side. Some drive brands will fault if asked to operate without an apparent load, so you may need a tattletale from your contacts to your drive controller.

Lots of potential answers to this question.

One problem I've seen is when the drive uses regenerative braking. This heat dissipated by the internal dump resistor can stress the electronics. Regeneration can also cause excessive voltage on the internal capacitors that feed the drive electronics.

So, if the other suggestions don't work, try reducing decceration rates or use an external load dump resistor. Jeff

Everyone's given good inputs here. One thing I can share (without repeating what others have said) comes from a seminar I attended years ago.

The facilitator mentioned that VFDs don't like capacitors. Those power factor correction types. If you're going to use capacitors, put them in a central location (usually the substation) instead of locating them in the same place or panel as the VFD.

Why would that be? All he said is that they (capacitors and VFD) don't like each other.

I was a little incredulous but this guy had been working in his profession for more than 20 years. In any case, the factory I worked in had the capacitors in a central location so there wasn't any concern on my part.

One other reason for burn-outs? A lighted match or lighter. In other words: sabotage.

V.F.D. is a secret organization within the children's book series A Series of Unfortunate Events by Lemony Snicket. It seems to be a MacGuffin plot device, similar to the sugar bowl, which keeps the series moving with the protagonists trying to uncover V.F.D.'s intentions or purposes. V.F.D. is also commonly used as an acronym to various related terms within the series, which helps to increase the character's confusion of what the initials actually stand for.

V.F.D. is a secret organization

Darn! Was that what this was about? Now, I'd have to revise my answer.

The reason for the burnout of VFD is the members yapping their mouths off to non-members, exposing the existence of the organization leading to its eventual disbanding or opening of its doors to ordinary people.

Two other possibilities that I have seen that may contribute to premature failure of VFD's is insufficient cooling (cooling airflow blocked by dirt or VFD located inside hot control cabinet) or VFD mounted to something that vibrates (don't laugh).

Hi DaceB;

I have not experienced a V.F.D Burn-Out. But, when I joined the firm I'm currently working with, I did an inspection of all our V.F.Ds and found that 3 of them were dissipating heat at 65 deg. cel. (measured from the outside cabinet walls by thermal gun), additionally the cabinet was small, not allowing good spacing between cabinet inside walls and V.F.D., their cooling exhaust fans had malfunction. Now 65 deg. cel. is no good temperature, compared to an ambient temperature of 40 deg. cel.

With that, we replaced the small cabinets which gave good breathing space, and installed cooling exhaust fans. At the end their operational temperature dropped to 45 deg. cel. and is currently maintained at that temperature.

Too much heat could loose soldered joints of V.F.D electronics, and probably burn out the electronics as well, which could lead to a something worse.

One of the things that I had been informed of when installing some new VFD's is that the power supply cables and the motor feed cable cannot be run in the same conduit.

Something about electro magnetic line resonance causing feedback on the motor lines causing the drives to get confused and run at higher loads.

Not sure about this one but you might want to give it a look see.

Any thoughts guys?

Are you referring to the three phase motor or the electronic VVVF drive itself? If it is the motor you refer to, I assume that it has an independently powered cooling fan. What is the kW rating and voltage of the drive?

Greg Lynch

Also take a look on moisture/humidity where your VFD's are installed. The run distance between your VFD and your load, Install as close as possible or as recommended by VFD manufacturers, some VFD tends to increase Vout at the load in longer run.

lastly, check insulation resistance of your load.

Here in the US, V.F.D. stands for Volunteer Fire Department. Burnout has an entirely different meaning in that instance!

In the context of electrical components I think VFD would almost allways refer to a Variable Frequency Drive.

Guest--

Burnouts can be quite impressive. When our municipal water and wastewater utility saw a large number of them in one pump station (over 8 drives in 2 months), we rented a power analyser and put it on the incoming line. Although we frequently saw spikes as high as 1.5 kV on the 480v waveform, as well as many other anomalies, the problem was ultimately found to be a manufacturing design defect. The input rectifier section was sized too closely to the drive's rating, so it "blew up" (literally). The manufacturer was closely involved, and supplied us with many warranty replacements until they finally recalled the entire model and gave us two of the next larger sized drives at no additional cost (we had to do a lot of juggling to get them into the space occupied by the smaller predecessors).

Work closely with your supplier and manufacturer; be honest; be firm when necessary. Review your specifications and environment to see if something was missed (we were specifying for no derating of anticipated lifespan for continuous operation on a given motor horsepower in an ambient of 40deg C, with the motor running at 115% of nameplate rating). Thus our drives were usually 50 to 100% oversized. Pricing was good because we solicited bids on an annual basis with a guaranteed number to be purchased during the year and with a guaranteed aggregate horsepower of the purchases (such as 12 during the year and totaling at least 1500 Hp). Our costs were way below the wholesalers' usual purchase costs.

Capacitors, mentioned by Vulcan in #5 cause the input voltage to be as much as 10-20% higher, so the rectifier front end exceeds its rated voltage and the DC bus can also exceed its ratings (causing the drive to fault if not burn out). Line and load reactors are a common fix for many problems, but these problems usually cause trouble for the motor (impedance mismatch to the motor windings causes the high-frequency drive waveform to reflect and impose as much as 100% overvoltage to the first few turns of the motor winding), or for the supply circuit.

If your VFD is supplying multiple motors (which are being separately switched on/off) or has other load-side controls such as contactors, this can cause the output transistors to burn out. Others posting have mentioned inadequate cooling, humidity, vibration, shock, etc. Add to these things like poor set-up (acceleration or deceleration ramps too steep, for example), poor control wiring, and internal problems with the motor itself (cracked rotor bars, etc.). Another thing to consider is the uniformity of the incoming power. If one phase has a voltage significantly higher (or lower) than the other two, then the currents on the three phases will be even more imbalanced, so one or two of the incoming rectifier sections could be overloaded and blow up.

Some VFD's have fast-acting rectifier fuses inside, to give protection from large fault currents and their accompanying energy releases. If your drives are protected by circuit breakers only, you may want to look at suitably fused disconnects in addition, or instead of CB's. Many times, the utility company is supplying its incoming voltage at the high side of the normal range (particularly if you are close to the substation), so check the incoming voltage to make sure it is comfortably within the drive's nameplate rating.

Since you havn't told us which components are burning out, more specific suggestions can't be made. Perhaps, you have posted the question simply to learn... (but the tone of your post suggests that you have a particular problem instead).

Regards--JMM

Exactly what is a VFD? And will it affect me if it burns out frequently?

In Electrical Engineering, a VFD is Variable-Frequency-Drive.

If you happen to be the production manager or the maintenance manager of a production facility, yes, you will be affected if it burns out frequently.

If you're the owner of the production facility, you make sure that everyone is affected by the frequent burn-outs so that everyone is motivated to find a cure (as our OP-original poster is doing).

As someone else posted, VFD could also mean Volunteer Fire Department and, yes, a burned out fireman could be cause for concern.

I would like to ask what a Variable Frequency Drive (VFD) does or what purpose it serves BUT I'm afraid to ask because I believe you will tell me to Google the subject or read more on the subject someplace else.

However, can you see why I might be interested to learn more from this amazing group of engineers rather than doing my own research???

Well, I guess asking someone for information counts as doing your own research . I might have to change my thinking then.

A VFD is a device that can change the frequency of the AC voltage going into a motor (in some cases, motors - plural). By doing that you can change the speed of rotation of the motor.

Is there any use for changing the speed? Yes, otherwise there would be no need for them! Say you have a wind tunnel and you want to set the wind speed to any value you want, from a gentle breeze, to a howling gale. You'd use a VFD for that.

There's lots more to VFDs and it will take me all day to type them all in. Besides, I don't know how much text I can type into this box . Seems pretty deep though.

Now, leaving VFDs and going to the subject of doing your own research. Okay, I'll have to revise my thinking that asking for information is not a form of research. It is actually, and I've done it myself several times. What I want to be clear about is, you shouldn't depend only on the people here on CR4 for all the information. That goes for everyone who asks here, not just you.

For one thing, the information you need might require extensive typing and I don't have all the time in the world. Also, some people ask vague questions or may be asking something that everyone understands as one thing but actually means another thing (read my signature below). Lastly, finding information on your own is a great training tool.