VFD power cell failure

[rian0201]

Hi,

I'm new to VFDs and one friend of mine asked me about the problem they had with their VFD.

The motor is 3.5MW induction motor with 4.16kV rated voltage. The VFD is fed from a 13.2kV line with an isolation transformer to 4.16kV inside the compartment.

The problem is that when there is a shutdown, due to a fault in the 13.2kV line, the power cell will be busted. If this is a normal shutdown sequence, it is okay for only few hours i think around 2 to 3 hours, and the VFD wont start and sometimes displays power cell fault.

Can anyone suggest reasons for power cell faults in VFDs?

I'm new to VFDs and its recording its not that detailed compared compared to a relay. I thought thatbthis may be a power quality issue at the source.

Thanks..

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[Jraef]

Depends on the type of VFD. At that size and voltage there are several options for how the VFD is designed, so "power cell" is not enough of a differentiator. Was it a power cell in the converter (rectifier) section or in the inverter (output) section that goes to the motor? If the failure was in the inverter, it's not likely a power quality issue.

If you don't know the specifics, post the brand and model, we can tell from that.

 

[Besoeker]

Hi,

I'm new to VFDs and one friend of mine asked me about the problem they had with their VFD.

The motor is 3.5MW induction motor with 4.16kV rated voltage. The VFD is fed from a 13.2kV line with an isolation transformer to 4.16kV inside the compartment.

The problem is that when there is a shutdown, due to a fault in the 13.2kV line, the power cell will be busted. If this is a normal shutdown sequence, it is okay for only few hours i think around 2 to 3 hours, and the VFD wont start and sometimes displays power cell fault.

Can anyone suggest reasons for power cell faults in VFDs?

I'm new to VFDs and its recording its not that detailed compared compared to a relay. I thought thatbthis may be a power quality issue at the source.

Thanks..

Sent from my vivo 1606 using Tapatalk

Big drive.
Does the power cell trip or actually fail? i.e, does failed hardware have be replaced? Expensive if it does.
What is the VFD powering? Is it regenerative - that is does it put power back into the supply?
Is the technology IGBT or GTO? ABB made GTO units in that sort of power range.

A bit more flesh on the bones might be helpful.

 

[kwired]

Hi,

I'm new to VFDs and one friend of mine asked me about the problem they had with their VFD.

The motor is 3.5MW induction motor with 4.16kV rated voltage. The VFD is fed from a 13.2kV line with an isolation transformer to 4.16kV inside the compartment.

The problem is that when there is a shutdown, due to a fault in the 13.2kV line, the power cell will be busted. If this is a normal shutdown sequence, it is okay for only few hours i think around 2 to 3 hours, and the VFD wont start and sometimes displays power cell fault.

Can anyone suggest reasons for power cell faults in VFDs?

I'm new to VFDs and its recording its not that detailed compared compared to a relay. I thought thatbthis may be a power quality issue at the source.

Thanks..

Sent from my vivo 1606 using Tapatalk

I have no experience with use of a VFD on medium voltages, but many basics are likely still the same. A VFD takes incoming AC voltage and rectifies it to DC voltage. The DC bus is more less the center of the whole thing and overvoltage/undervoltage faults and other monitored power supply conditions are often based on conditions of the DC bus. My guess is your "power cell" fault is related to a failure in a rectifier component, from either too much voltage or too much current, both, or even poor heat sinking conditions, though most of the heatsinking needed is on the inverter side of the bus when it converts back to a controlled AC current.

You may be missing or have non functioning surge supression on the supply side of the drive, or may even need line reactors to limit amount of current during transient conditions.

Add; others have mentioned putting power back into the supply - that would be taking energy from the driven load as it decelerates and putting it back into the source, that opens a door for all kinds of issues if not set up correctly. If not putting that energy back into the source it it will either need to be given up by the drive's heat sinks, or dumped into another load - typically a resistor to dissipate that energy gained from deceleration of the load. This also a place for overheating to occur if not designed properly for the application.

 

[rian0201]

The model is a Hyundai N5000-4000M6. The manual is downloadable from the internet.

The power cell is located at the inverter (output) going to the motor.

I was thinking that this is a "power cell" board control issue. But, what cause it? Sometimes, it says "W4, Cell abnormality, IGBT3 fault", I know that this IGBT is inside the power cell.

It was corrected by replacing the power cell boards - precharging board, power board, SCR snubbing circuit board, and the control board.

Say, if the error was IGBT3, what can caused such error or fault? Is it heat related? Or some other worst issue?

I have tried to look at the VFD parameters, they are using SLV control mode - sensorless vector control mode which was set by Hyundai.

Thanks

I was also thinking it could be a grounding issue.. As for heating, we have already corrected the cooling fans inside the panel.

 

[Ingenieur]

At that size it likely has a water cooling loop
if the 13.2 is lost is the cooling lost?
or is it on back-up power?

during a normal shutdown the loop runs until things cool down

is the iso xfmr phase shifting?

 

[Besoeker]

The model is a Hyundai N5000-4000M6. The manual is downloadable from the internet.

The power cell is located at the inverter (output) going to the motor.

I was thinking that this is a "power cell" board control issue. But, what cause it? Sometimes, it says "W4, Cell abnormality, IGBT3 fault", I know that this IGBT is inside the power cell.

It was corrected by replacing the power cell boards - precharging board, power board, SCR snubbing circuit board, and the control board.

Say, if the error was IGBT3, what can caused such error or fault? Is it heat related? Or some other worst issue?

I have tried to look at the VFD parameters, they are using SLV control mode - sensorless vector control mode which was set by Hyundai.

Thanks

I was also thinking it could be a grounding issue.. As for heating, we have already corrected the cooling fans inside the panel.

Do the IGBTs actually fail and have to be replaced? From this excerpt in their description you would need more than more than one failure to trip the drive.

In case of cell failure during operation, the faulty cell will be bypassed and the neutral point will be shifted (balance is restored through angle adjustment). 92% of the rated voltage can be output after the failure of one cell.

 

[Ingenieur]

After rereading
fails immediately on input power loss
fails shortly (2-3 hours) after being restarted after a normal shutdown?

are there any bypass or isolation contactors?

 

[rian0201]

Hi to all,

The vfd is placed in an air conditioned room. It is fan cooled that is placed in the panels. I guess based on the schematic, if there is power fail, the cooling fans shut off.. Still have to verify it is separate supply or not. But that's one idea.

And the transformer is phase shifting 6 phase..

Yes, the IGBTs were sometimes replaced. When power cell fail occurs, we tried to exchanged boards, IGBTs to isolate the faulty part.. Sometimes the faul is IGBT, sometimes the boards that I have named on my previous posts..

Yes, also I recently found that the power cell can be bypassed based on the manual, but this feature or option was not enabled in our vfd. Maybe I have to enable this one. i just don't know if could have other effects.

Also, the unbalance power cell bypass does this mean that the neutral voltage shifted to met the required line voltage? I have seen other brand have voltage neutral shift.

Thanks again..

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[rian0201]

After rereading
fails immediately on input power loss
fails shortly (2-3 hours) after being restarted after a normal shutdown?

are there any bypass or isolation contactors?

Yes it fails especially if the input voltage has faults. But fails shortly after a normal shutdown. Maybe still its something to do with cooling.

There are no isolation contactors or bypass.. From 13.2kv supply, then a breaker, then the vfd panel with the iso transformer, then the motor..

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[Besoeker]

Yes it fails especially if the input voltage has faults. But fails shortly after a normal shutdown. Maybe still its something to do with cooling.

There are no isolation contactors or bypass.. From 13.2kv supply, then a breaker, then the vfd panel with the iso transformer, then the motor..

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Well, I suppose you can't rule out cooling problems but most variable speed drives have over temperature protection, often alarm and trip, and that would be flagged up as a fault code.

Failing shortly after a normal shut down is a real puzzler. You have to wonder what failure mode is possible after it is shut down. Transient over voltages if the input voltage has faults maybe?

 

[Ingenieur]

The drive is listed as 96%+ eff
that is still over 100 kw of rejected heat

upon the normal shutdown do the fans continue to run for a period of time?
if not, do so
if time based increase it, if temp base perhaps lower the cut-off temp

if they shut down upon power loss get backup power for them

my guess is heat soak
fine when operating with the fans
not good upon shutdown

 

[Besoeker]

The drive is listed as 96%+ eff
that is still over 100 kw of rejected heat

upon the normal shutdown do the fans continue to run for a period of time?
if not, do so

It's not a bad idea. Almost all the drives we designed and manufactured had the cooling permanent running as long as power was available. Yes, it would have been more economical to stop them when the drive was stopped but generally the energy consumption for cooling was minuscule compared to the drive rating and most of the drives were on continuous process industries anyway.

A few did have run on timers specified by customers but I was never really convinced about their merits. If the drive is stopped the thermal energy generated by the power electronics stops.

 

[zbang]

my guess is heat soak
fine when operating with the fans
not good upon shutdown

It would be interesting to watch the power cell with an IR viewer for maybe 5-10 minutes immediately after run/shutdown/make-safe. I'd expect that the heat sinks to get hotter for a while before cooling off, and that might take them over-temp.

 

[Besoeker]

It would be interesting to watch the power cell with an IR viewer for maybe 5-10 minutes immediately after run/shutdown/make-safe. I'd expect that the heat sinks to get hotter for a while before cooling off, and that might take them over-temp.

But why? Why would they get hotter if you are no longer puting thermal energy into them?

 

[zbang]

But why? Why would they get hotter if you are no longer puting thermal energy into them?

Thermal conduction from the heat producer. With airflow, the surface of the heat sink might be 30C but the device being cooled could be 60C (and have a nontrivial thermal mass). Stop adding and removing heat from the system and all the components will attempt to equalize- heat from the device inside will continue to flow into the cooler sink, but little will be removed from the sink, so it warms. A lot depends on the thermal masses of device and HS, and whether the HS can also cool by radiation or convection.

(This is why running the fans after shutdown is usually a good idea.)

 

[rian0201]

Hi again,

Thanks.. I will try to do an IR scan with the power cells.. We will try to scan it after shutdown.. We have installed temperature devices, but these devices were installed at the transformer side.

I agree that the heat cannot change abruptly, and although there is no more heat supply during shutdown, there is also no cooling during that time.

I hope that this the main problem, and hope that this will be the solution.

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[Besoeker]

Thermal conduction from the heat producer. With airflow, the surface of the heat sink might be 30C but the device being cooled could be 60C (and have a nontrivial thermal mass). Stop adding and removing heat from the system and all the components will attempt to equalize- heat from the device inside will continue to flow into the cooler sink,/QUOTE]
But if there is no heat being generated there is nothing to flow.

 

[zbang]

But if there is no heat being generated there is nothing to flow.

What matters is that there is temperature differential between the parts. If there is a difference, heat will flow from the warmer to the cooler areas.

 

[GoldDigger]

What matters is that there is temperature differential between the parts. If there is a difference, heat will flow from the warmer to the cooler areas.

But in this case it is the initially hotter area (the semiconductor chip itself) that is vulnerable to heat damage, so any increase in heat sink temperature after power is cut off is unlikely to damage anything.
With an internal combustion engine it is possible for heat resistant hot spots to overheat normally cooler adjacent parts.

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