7 replies to this topic

[bob]

I had a tripping on my 1350 amps 400 V vsd some couple of days ago. The drive tripped on overcurrent and ANGU fault.
I disconnected the motor to the drive and put power back to the drive. The current read on the display unit of the drive without motor is around 400 A. If the drive is reading current, it seems most probable that either the IGBTS or capacitors are faulty. I am only reading 2 amps on the input side. The drive is configured V/F and the reference frequency set is 10 Hz.
How can the drive read so much current ?

Bob

[marke]

Hello Bob.
I would suspect that there is a problem either with one of the hall effect CTs, or the interface board for them. If there was a high current on the output due to a faulty IGBT, there would be a high current on the input.

Best regards,

[jraef]

I agree. A common design theory on sensors in protection circuits is to make them fail high, meaning that when working properly, they pull a reference rail voltage or current lower to represent the desired reading. That way if the device fails, the reference rail value goes to maximum or very high and gives a false trip, but shuts down the system. The alternative would be that the device fails and also fails to shut down the drive, risking a loss of the connected load.

Heh, forgot to log in.
Jraef

[bob]

Thanks jraef and Marke for your valuable posts. The drive was showing more than 400 amps on the panel display unit with almost zero current on he input side. However, we checked with an oscilloscope and noticed that the third phase was not fully fired ( half wave ).
I agree that the hall effect ct could be wrong but could a misfiring also cause current on the output side to be relatively high without any load being connected ?

Bob

[marke]

Hello Bob.
If one leg of one phase is not operating, you will get assymetry in the flux in the iron, this could result in a high DC current into the motor.
With the motor disconnected, no current should flow. If one leg of one phase is not being turned ON, it will not affect the
open circuit current.

If you operate the inverter at 10 Hz with a motor on the output, you will have a low current on the input relative to the output current. The inverter acts a bit like a transformer with the output voltage being 20% of line voltage at 10Hz (assuming a line frequency of 50Hz). The current on the input will be less than 20% of the current on the output at 10Hz.

Best regards,

[bob]

Hi MARKE,

We finally found the cause, it was an optical fibre which was partially broken . We fixed it and the drive is back to operation. Bu still without any motor connected, the display unit is showing high amps on the output. I presume the software is doing this.

Bob

[marke]

Hi Bob

Thanks for letting us know. I t is good to get a result!!

Bet regards,

[Subhashish]

hi Bob

Its good that your problem is solved .Can you let me know the make of Drive .
The phenomenon you described ( drive sensing current even if current doesn't flow i.e motor disconnected) is quite interesting .

Regards