(help) input side of 3 vfds exploded

Status
Not open for further replies.
S

spahky9000

Member
We run our vfds remotely from a plc control center each time the operator pressed auto on the plc a vfds fused input L1 L2 L3 terminal blew right off the card and the mov exploded too this happened three times on three seperate vfds running three differn't motors.
We run off a generator but it checked out o.k. I have ordered three more vfds but i am nervous to put them up because we haven't determined what caused all of this mess. is it possible that 480v power went through the vfd but was not allowed to pass to the T1 T2 T3 terminals which overloaded the vfd due to a malfuntion on the controlside of the vfd to plc?

Thanks
 
spahky9000 said:
We run our vfds remotely from a plc control center each time the operator pressed auto on the plc a vfds fused input L1 L2 L3 terminal blew right off the card and the mov exploded too this happened three times on three seperate vfds running three differn't motors.
We run off a generator but it checked out o.k. I have ordered three more vfds but i am nervous to put them up because we haven't determined what caused all of this mess. is it possible that 480v power went through the vfd but was not allowed to pass to the T1 T2 T3 terminals which overloaded the vfd due to a malfuntion on the controlside of the vfd to plc?
Click to expand...

You do not push power into the VFD, so you can not cause it to fail simply by not taking power out of the T terminals.

The input to the vast majority of VFD's (for the past 10 yrs or so is a diode bridge rectifier with a capacitor on the rectifier output (this is a very simple explanation). The most common failure point is the capacitor, either due to age or to overvoltage. A voltage surge (i.e. lightning strike) could cause the capacitor to weaken with the eventual failure happening many months later. voltage surges can also affect MOVs.

Did the VFD's fail during startup or after they had been running?
 
080614-1658 EST

spahky9000:

A VFD will rectify the incoming AC and charge a bank of filter capacitors. The DC from the capacitors is processed to generate the variable frequency three phase AC that runs the motor.

MOVs are transient voltage limiters across the incoming lines, and possibly to common as well. That the MOVs blew means excessive voltage of a sufficient duration to overheat them.

My guess is a series resonance between the capacitors and the internal impedance of the generator caused a large capacitor voltage, and a large MOV voltage. Or the VFD and thus the MOVs are not designed for the applied input voltage.

.
 
Did you get VFD's with bypasses?
Check voltage, line load conductors.
All connections from service to VFD's
Possibly install temporary FAST operating fuses to minimize damage.
What size drives.
Do you have monitoring equipment to install on the input?
 
Exactly what are the plc's controling ?
The way it read to me is that the set-up is nothing more than a release of power.
It seems the sequencing of the plc' is Off ? Or not correct! )MO(

Why isn't the control of the application, both monitored before and afterward ? ... PLC's have there own limits, fire control and nirvana ?
 
The vfds were running normally for about 4 hours then the control room operator shutdown the drives( remotely from the plc ) when he noticed that one of his drives faulted into a err 7 ( serial link cable error ) after he cleared the fault and started the drive that faulted he went back to the plc touch screen and pressed system auto the first drive that started as they start in series blew the mov and the terminal strip off the card he then called me and told me it sounded like a shot gun went off we tried to start again in auto the next drive then exploded which also tripped the breaker . Just now i realized something the second and third drives should not have been able to come on as the plc should have recognized that there was a vfd fault and not gone on down the ladder but it didn't anyway after the second drive exploded the boss came in and he wanted to see what was going on so once again ( fools paradise huh ) the operator pressed system auto and then the third drive exploded. If it was a voltage surge then it was happening over the course of like 15 min so thats why im concerened about putting new vfds. thanks for any help.
 
What sort of 480V power do you have? Ungrounded delta, resistance grounded wye, corner grounded delta, solidly grounded wye, etc? Do you have drive isolation transformers? How are they grounded?

The MOVs are generally designed with the assumption of a solidly grounded wye supply. Any other system could blow the MOVs.

-Jon
 
spahky9000 said:
The vfds were running normally for about 4 hours then the control room operator shutdown the drives( remotely from the plc ) when he noticed that one of his drives faulted into a err 7 ( serial link cable error ) after he cleared the fault .......
Click to expand...

What was done to "clear the fault"?
 
It sounds like the MOV's were "stressed" at some time(s) in the past. Then with all of the loads off the generator output may have been above 480V because of the no-load voltage regulation. The MOV's couldn't handle this higher voltage and failed violently (a very common failure mode) taking the drive terminal with them.

Are these really just MOV's or are they actual UL Listed surge protectors (which include circuitry to protect against violent failure).

You need to determine how your system is grounded and what the no-load voltage is.

As you can see, right now I am focusing on the MOV's as the problem not the VFD's.
 
jim dungar said:
It sounds like the MOV's were "stressed" at some time(s) in the past. Then with all of the loads off the generator output may have been above 480V because of the no-load voltage regulation. The MOV's couldn't handle this higher voltage and failed violently (a very common failure mode) taking the drive terminal with them.

Are these really just MOV's or are they actual UL Listed surge protectors (which include circuitry to protect against violent failure).

You need to determine how your system is grounded and what the no-load voltage is.

As you can see, right now I am focusing on the MOV's as the problem not the VFD's.
Click to expand...

jim, what does mov abbreviate?
 
steveng said:
jim, what does mov abbreviate?
Click to expand...
Metal oxide varistor... They are designrd to conduct above a certain threshold voltage and they are designed to handle transient voltages.i.e. short duration spikes. They do often fail violently but it is usually because the spike was not of a short duration. I'ld be very suspicious of your 480 going in. The PLC is nothing more than an on/off switch.
 
spahky9000 said:
The vfds were running normally for about 4 hours then the control room operator shutdown the drives( remotely from the plc ) when he noticed that one of his drives faulted into a err 7 ( serial link cable error ) after he cleared the fault and started the drive that faulted he went back to the plc touch screen and pressed system auto the first drive that started as they start in series blew the mov and the terminal strip off the card he then called me and told me it sounded like a shot gun went off we tried to start again in auto the next drive then exploded which also tripped the breaker .
Click to expand...

What Lou said!

Sounds like a DC fault ran wild, than got blown off the wall by the AC!

Are the circuits monitored ? -???

On my job, a bearing was lost on a motor, then the same VFD that happened to control it lost it's own control fan,(basicially a computer fan)

Why I touched it, cause tech had said earlier that it ran up a temperture inside to over 150?C, the VFD told him so, and faulted w/ code error the VFD had registered every fault. The machine was also reset to, I was there as the fans started singing from the AH ... Seems we both forgot about the CPU aspect. This was on Friday with the restart.
OK, I didn't, he did... Saturday is when I found it warm to the touch.
It was shout down for the rest of the weekend.
 
Last edited:
Is the PLC simply giving these VFD's a start signal or are they also operating line contactors supplying the drive? From your post I'm not sure if the line voltage is on the drive at all times or is being switched? We have had experience with certain drives (PF4&40) that this has happened and found out later they had recalls which of course we were never notified. Same situation though power was applied to the drives and they would blow 3, 4 at a time MOV's. Another thing to look at when the drive is powered check your bus voltage at 480 should be around 600. If bus voltage is fluctuating you may have the need to install reactors on the line side. Just my 2 cents hope it helps!:grin:
 
Few inputs Spahky,....

a) Drive size HP

b) Drive rated voltage?

c) Can you elaborate on Auto ..does it cascade the running of three motors?

d) Do you have Overvoltage protection on Generator and the VSD panel? (If not please incorporate it using Overvoltage relay).

e) What blew OFF? the capacitors ..or MOV? or rectifiers.

f) Is it possible that the load ( equipment driven by the motor is jammed)

g) Is the drive powered using a contactor or is it always ON and logic input is used to RUN it.

h) If the drive is always powered ON then MOV fault can be ruled out as they will fail even before the RUN command is given

The fault seems to have occurred when RUN command has been given,that points out to internal power components.

Cheers.
 
jim dungar said:
It sounds like the MOV's were "stressed" at some time(s) in the past. Then with all of the loads off the generator output may have been above 480V because of the no-load voltage regulation. The MOV's couldn't handle this higher voltage and failed violently (a very common failure mode) taking the drive terminal with them.

Are these really just MOV's or are they actual UL Listed surge protectors (which include circuitry to protect against violent failure).

You need to determine how your system is grounded and what the no-load voltage is.

As you can see, right now I am focusing on the MOV's as the problem not the VFD's.
Click to expand...
That MOVs failed in two different drives, one after the other, seems to suggest a supply overvoltage problem.
Maybe the AVR on the generator has failed?
I'd measure the output voltage of the generator before running anything else from it.
 
Status
Not open for further replies.
Top