Damage caused to VSD from insulation tester voltage

[Munkey]

Hi,

Can any one advise me about the actual damage caused to a frequency drive if flashed with 500 vdc from an insulation tester?

I have an ABB ACS800 0100 drive (100kw) that has been flashed by someone. The drive uses IGBT modules fired from a control card, will it be the IGBT modules that have been damaged? These control a 400 volt 4 pole induction motorist speeds up to 3000 rpm (100hz).

I am confused to what actual damage this would cause. ....

 

[mheyes]

Does the drive power up ok without any fault codes on the display? if it powers up ok I would assume there is no lasting damage to the drive. We always fit an isolation contractor to the output side of the drive (see drawing).

 

[Darkwood]

Has it been zapped on the input side or output side and what are the respective voltages for both input and output in normal running conditions?

 

[Munkey]

Hi guys,
The test was performed on the output from the drive. It now powers up, but will only run in scalar mode rather than the normal direct torque control mode. If run in DTC it faults on overcurrent.

The drive is a 3P 400 v input driving a 3P 400 v nominal output.

Really simple setup, but since this insulation test it will not run in DTC even with no load on the motor.

Any and all ideas welcome!!

 

[Munkey]

Hi mheyes,

I would normally have a contactor on the incoming side of the drive, this then acts as with the emergency stop circuit. Would it not cause any problems switching the output? What is the contactor normally used for?
Estop control?

 

[mheyes]

On the acs550 there are some board fuses near the drive stage capacitors but unless you are good with a soldering iron would sent it to a drive specialist for repair

 

[mheyes]

Just to explain the control drawing : there are two 37kw NVR contractors that pass three phase to a busbar rail so if an e-stop is pressed all three phase is lost. Hope you are with me so far

There is an auxiliary contact on the pilz safety relay so when the NVR drops out so do the isolation contractors.

I no this is very ott but it stops sparks with meggers blowing up expensive drives.

The NVR contractors are ab guard master

Isolation are normal Siemens contractors rated to suit the motor

 

[Munkey]

So the main supply is under estop control aswell as the output?

This is just to totally isolate the drive under estop conditions?

 

[Darkwood]

You may have damaged the current monitors in some way as the torque control uses them to gauge the torque, this may also be why your getting overcurrent trip. Try running it in scaler and see if you can have the current up on display and see if its reading ok...Its possible there isnt anything amiss with drive and you genuinely have overcurrent which would stop DTC working possibly stopping motor from running or depending on set-up - at a set low speed.
You say you have run motor off load but has it got any gearing ?

 

[mheyes]

Yes in e-stop mode or maintenance mode all drives are isolated.

We adopted this standard about three years ago. A blue chip client requested it in there spec. I must admit at first I thorght it was overkill but it works well. Sometimes maintenance sparks megger motors and give no thorght to the drive. We also do the same on servos and some soft starters

 

[Wazzajnr]

Just a thought, has this motor got an encoder? I'm guessing it has if it's used in torque mode?
If so, it could be faulty feedback from the encoder giving the drive duff info and causing the O/C. Seems to me that if it'll run in scalar mode the drive should be OK

 

[Munkey]

The load is belt driven, and with the belts removed it runs only in scalar.

All parameters are the same, whether run in DTC or SCALAR. Motor data and limits unchanged.

ABB drives just use three PCB mounted CT's so if one/any had a fault it would show in both running modes.

This is very puzzling, and as the drive is abroad I don't have access. I need to try and sort it from afar.

Unlucky!

 

[Wazzajnr]

sounds very much like a feedback issue to me

 

[Darkwood]

Are you using DTC alone as internal calcs of drive or have you got speed monitors for accuracy at 0-speed with torqe hold, or are you set up with an encoder as Wazzajnr suggests which isnt true torque control but line speed control, what does the machine do.. i guess you are winding or unwinding a product onto or from a drum.

 

[Munkey]

There is no encoder fitted. There is no feedback to the drive. The DTC mode calculates, then compares this calculation to the reference value. I think this is how it goes!

 

[Munkey]

I'm lucky in that I think the process will allow the use of the drive in SCALAR. I'm just concerned that there may be an underlying issue that could cause further problems down the line.

 

[Wazzajnr]

I've just remembered having exactly the same issue with a siemens drive a couple of years back. Turned out the electrician had wired the motor in delta instead of star (or vice versa, can't remember which now)
The drive has motor models for running in sensorless vector which from memory is same as DTC mode. With the wiring incorrect it can run to a fashion but i was getting overload trips and DC bus O/V on that one.
Maybe if they've disconnected to do the tests they didn't connect it back up correctly??

 

[Darkwood]

What does the machine do, is it possible as a cheaper route to fit an encoder and use feedback loop to control motor speed thus eliminating need for torque option, but still need to establish what issue is to see if it is going to come back and cause problems.

 

[Munkey]

From what I've been told, the problems arose because they did not disconnect the drive prior to testing.

I would have expected the IGBT modules to take the brunt of whatever damage the test had done, and this would have materialised in a short circuit fault, not overcurrent.

 

[Munkey]

The machine is a centrifuge. A large barrel shaped hollow bowl that spins at speeds up to 1200 rpm with a screw conveyor inside that turns at a differential speed to the bowl. All run from variable speed drives. The drive that is faulty is the bowl drive. This normally stays at a single speed the screw conveyor drive normally does a lot of speed changes due to fluctuations in torque. It is a large density separator, solids from fluid basically. Bowl weighs around 8 tonnes!