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VFD blow up
8

VFD blow up

VFD blow up

(OP)
Hi all,

I am experiencing a problem with a VFD that seems to be getting damaged when the motor starts. The overcurrent protection of the VFD is set to around 70A, while the motor has a full load current of approximately 80A, 600V, 3-phase at FLA. I am wondering whether the issue may be caused by an inrush current or other reason.

RE: VFD blow up

You have 100% control over inrush current with a VFD. Your failure is occuring for other reasons.

What do you mean by damaged?

How many times has damage occurred?

RE: VFD blow up

(OP)
During the starting process of the motor, the VFD has broken down.

RE: VFD blow up

First start? You're on the left hand side of the bathtub curve. I would suspect a defect in the drive. Have you reached out to the manufacturer about warranty? Their response might help identify the root cause. In my case it was replaced no questions asked which indicates that they have experienced many commissioning failures.

RE: VFD blow up

How is the VFD set up to start?
Ramp rate?

What is the load doing at the start?
Do you have data on current vs time?

How old is it?
What did the vendor say?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: VFD blow up

(OP)
Thank TugboatEng and LittleInch,

TugboatEng,

I will contact the vendor.

LittleInch,

Wil more investigation about that. See below for your concerns.

How is the VFD set up to start? => Can you please elaborate on this question?
Ramp rate? => VFD units are factory set with acceleration and deceleration ramp rates set to 30 seconds.

What is the load doing at the start? => 40HP, Exhaust fan
Do you have data on current vs time? => Will ask the vendor to provide it

How old is it? => A few months old
What did the vendor say? => Waiting for vendor's response.

RE: VFD blow up

600V rated VFDs are a tricky thing. The transistors for them represent less than 10% of the test acceptance rate of the production lines. That means when testing the transistors to fill an order for 100 units tested for use at 600V, 900 will have failed and must be scrapped, making the 600V tested transistors very expensive. Some “bargain” drive manufacturers chose instead to use transistors that passed at 480V, which are less expensive, and take their own chances (with their customers) on the survival rate in the field. You may be suffering from this decision making process.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: VFD blow up

(OP)
Thank jraef for your comment.

You mentioned that only a 10% success rate can be guaranteed for 600V, which indicates a high potential failure rate for the drive side.

RE: VFD blow up

If you are trying to start a motor that is already turning (flying start), then you need to set the drive up to accommodate that. Otherwise you will see very large currents as the drive tries to start the motor thinking it is stationary.

Brad Waybright

The more you know, the more you know you don't know.

RE: VFD blow up

The motor is sized at about 80 kW for a 30kW load?

And why set the overcurrent at 70A for an 80A FLC motor?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: VFD blow up

(OP)
Thank thebard3 and LittleInch,

To thebard3,
I agree with your comment.

To LittleInch,

After reviewing the shop drawing, I noticed that the specification lists two full-load currents. Please refer to the attached file for clarification. I am a little confused about which one I should consider it.

RE: VFD blow up

43 Amps is the maximum VFD current.
The motor full load current is 36.8 Amps
40 HP, 575 Volts, 94% efficiency and 86.5% Power Factor correlates with 36.8 Amps Full Load Current.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: VFD blow up

James,

I am astonished that you do not seem to know how to read a simple table.

The header row of the bigger number clearly says "Power factor (%)"

The lower one clearly says "Current (A)"

So there is only one FLA, not two.

You still haven't answered most of the questions asked. Like what exactly is the "damage"?

Also what is the load? Can you find the fan curve.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: VFD blow up

(OP)
Thank Waross & LittleInch,

I spoke with the contractor, who informed me that the VFD had broken into pieces with a loud bang on the floor. He remembered that the fan operated correctly for a few months. He also mentioned that he does not have any information regarding your concern. I plan to visit the site next week to gather more information and site photos.

The load is the exhaust fan which was given clips earlier. I am not quite sure if the operation was done properly as per fan curve. Attached is the fan curve.

RE: VFD blow up

A fan will put extended stress on any starting system to overcome inertia. I'm sure you have taken this into account. Lots of mention of the fan motor and the VSD but nothing about the cable between them and in particular the length of that cable. Have you got a choke involved?

RE: VFD blow up

(OP)
Thank SilverfoxUK for your comment,

As far as I know, VSD is located near FAN and I will verify the distance of the cable. However, the fan has been operated on for a few months without a problem, this issue came out recently. I am skeptical that issues with the reason, harmonic, or fan insulation could be the cause of this problem.

RE: VFD blow up

Is it possible for draft to rotate the fan backwards?

RE: VFD blow up

"Broken into pieces with a loud bang" - What ???

Sounds like complete destruction and huge internal shorting, not "damage when starting".

And if it was working OK before then this is a simple failure of a unit which should be in its warranty period so sweep up the bits and return them to the vendor and demand another one or your money back...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: VFD blow up

2
Loud bangs and VFDs are never an application or programming issue. Never. This is either a component failure issue or an EXTREME voltage event. The only thing that can suffer a “Rapid Unplanned Disassembly Event” (RUDE) like that inside of a VFD are the capacitors. Capacitors can fail for a number of reasons, but rarely go RUDE unless it is something really big. I would be looking at the power quality at this site with an eye toward big events. If it has happened more than once, that’s even worse!

Quote (James64)

You mentioned that only a 10% success rate can be guaranteed for 600V, which indicates a high potential failure rate for the drive side.
No. The testing and failure rate takes place at the manufacturer of the transistors. The ones that get USED by (responsible) VFD manufacturers for 600V are already proven to be good. The issue I was raising is that there are some “less than responsible” VFD manufactures selling “600V” drives who choose to keep their costs down by using transistors that have only passed at 480V. They then take the financial risk of having to replace 600V drives that fail in the field under warranty (because they will generally fail fairly fast). The flaw with that philosophy is that even if the users get a replacement drive for free, they suffer down time losses and maintenance time to swap them out.

Another thing though, and please, I know it seems far fetched but I HAVE experienced this more than once and it does foment a RUDE event…. Did someone accidentally connect the line to the load terminals and vice versa?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: VFD blow up

I wouldn't say only the capacitors. I just had a VFD blow up starting with a diode failure that led to a sustained arc flash resulting in lots of catastrophic damage.

RE: VFD blow up

(OP)
Thank Waross,LittleInch,jraef and TugboatEng..

Quote (jraef (Electrical)3 Nov 23 17:37
Loud bangs and VFDs are never an application or programming issue. Never. This is either a component failure issue or an EXTREME voltage event. The only thing that can suffer a “Rapid Unplanned Disassembly Event” (RUDE) like that inside of a VFD are the capacitors. Capacitors can fail for a number of reasons, but rarely go RUDE unless it is something really big. I would be looking at the power quality at this site with an eye toward big events. If it has happened more than once, that’s even worse!)


Thank you for your tips.If we plan to purchase a VFD, it's important to verify the vendor beforehand. We have already complained about the broken VFD, but they are insisting that we purchase a new one.

Quote (TugboatEng (Marine/Ocean)3 Nov 23 17:55
I wouldn't say only the capacitors. I just had a VFD blow up starting with a diode failure that led to a sustained arc flash.l resulting in lots of catastrophic damage.)


Thank you for sharing the photos. I saw a VFD blow up for the first time, and it was a surprise.

RE: VFD blow up

To be a bit fair to the vendor, you haven't really investigated or proved what happened and where external events caused the issue.

Unless you can show no impacts then they will probably just blame installation errors or external events.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: VFD blow up

(OP)
Thank you for your tip, LittleInch.

I will share your input with the relevant person as much as possible.

RE: VFD blow up

(OP)
After checking the site, I noticed that the cable length would be around 50ft from the panel to VFD. The cable was inside a rigid conduit that was well-bonded to the ground. There has been an explosion on the AC incoming side of the VFD, causing the incoming circuit breaker to trip as well.. According to the motor specification, the full load amperage (FLA) is around 36.8A. The variable frequency drive (VFD) has 40HP with 63A and a circuit breaker rated at 100A was installed for this motor. "Was everything of the correct value?"

RE: VFD blow up

Those blue things are metal oxide varistors. They shunt transient over voltages. They have a limited amount of energy they can dissipate. A failure as you have seen indicates an extended over-voltage.

RE: VFD blow up

(OP)
Thank TugboatEng for your comment !! I am wondering if the overvoltage issue is a result of not having a line reactor between the AC incoming and VFD input. I am not sure how this overvoltage occurred.

RE: VFD blow up

I investigated some failures on heat pumps in a rural area. The MOVs had operated and the main control boards had failed in nearly a dozen heat pumps in the area. It turned out to be due a tree in the line - all failures were on the unfaulted phase. Comparing the ITIC/CBEMA curve ratings versus the utility effective grounding requirements (and I also looked up the MOV specs) there is a design gap where electronic equipment can be damaged by utility voltage rise on the unfaulted phases during a ground fault (fault induced overvoltage).
Not saying this is what caused your issue, but just an example of one possibility - utility overvoltage, perhaps due to a fault on the utility system.

RE: VFD blow up

(OP)
Thank you wcaseyharman for your comment.

RE: VFD blow up

If the caps have been left unenergized for long periods of time, they can pop on start up. Years ago Allen Bradley used to advise not applying full voltage to a drive that has sat more than a year. They used to recommend that you use one VFD to bring another VFD up to voltage, ramping the voltage slowly. Then let it run an hour. Then connect to the grid.

There are also control settings in the VFD that could help things. Look at your motor speed controls. The most common are open loop vector and V/f. If you are careful about your set up, and using reasonable acceleration and deceleration times, you can keep your inrush to below FLA. If you set the acceleration too fast, the VFD is going to do what it can to meet your requirements, and that might cause a considerable amount of inrush. This will increase the chances of failure.

RE: VFD blow up

(OP)
Thank you eeprom for your comment.

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