VFD Blowing IGBTs
VFD Blowing IGBTs
(OP)
Hi all.
Anyone got any experience with a motor causing the IGBTs of a drive to go short-circuit? I have a 690V, 3000Amp drive and approx 1800Amp motor on a propulsion application. Drive to Motor is within 5metres of each other.
I can't tell if it's the IGBT or it's internal anti-parallel diode but in frequency mode and just 1% reference the current goes from normal to over 2500A on the display (and its audible) after 3 seconds from start with a 10 second ramp. I had limited the current to 50% so the drive should have tried to limit. Checking the drive and an IGBT module is short-circuit. Again and its getting expensive!
Without the motor connected and no problems with the drive running with noting connected - after replacing the bad IGBT ofcourse.
I've had problems in the past with dynamic braking units blowing up due to highly inductive resistors (thick wire wound ones) until I fitted fast acting anti-parallel diodes across them.
I wonder if a motor fault can keep killing my drive. It has been running for 2 years.
Anyone got any experience with a motor causing the IGBTs of a drive to go short-circuit? I have a 690V, 3000Amp drive and approx 1800Amp motor on a propulsion application. Drive to Motor is within 5metres of each other.
I can't tell if it's the IGBT or it's internal anti-parallel diode but in frequency mode and just 1% reference the current goes from normal to over 2500A on the display (and its audible) after 3 seconds from start with a 10 second ramp. I had limited the current to 50% so the drive should have tried to limit. Checking the drive and an IGBT module is short-circuit. Again and its getting expensive!
Without the motor connected and no problems with the drive running with noting connected - after replacing the bad IGBT ofcourse.
I've had problems in the past with dynamic braking units blowing up due to highly inductive resistors (thick wire wound ones) until I fitted fast acting anti-parallel diodes across them.
I wonder if a motor fault can keep killing my drive. It has been running for 2 years.





RE: VFD Blowing IGBTs
You need to measure what is happeneing instead. And then, it is not a voltmeter and a clamp you shall use, but a fast differential probe (or isolation amplifier) and a CT with voltage output plus a fast oscilloscop with enogh channels.
What you need to measure is Motor voltage and motor current. Remember that it takes some experience to measure the true voltage. There are edges with rise times in the 200 ns (0.2 us) order of magnitude and with peaks reaching up to 2.5 kV. So you need someone with the right equipment and the right experience to do the measurements. Sometimes, the drive manufacturer can help out, but not always. The motor manufacturer seldom understands what is needed to measure and how to do it. I have seen what they do and it is best described as wrong, wrong and wrong.
See attached recording for an example.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD Blowing IGBTs
Your problem might be in the current transducer or its auxiliary circuitry. At these low frequencies - 1 % of rated means half-period times in the seconds range - it can sometimes happen that the power supply cannot cope (not designed to deliver voltage for a second without ripple) and that will make Iact look very bad and produce the result you describe. And you will definitely hear the ripple in the motor current. Like you said you do.
What happens in other modes? Ever tried sensorless vector mode?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD Blowing IGBTs
Did this happen after three years without problems? Then it is well worth checking all components in the current measurement part of the inverter. Capacitors, and resistors are known to go bad sooner or later in some makes of large drives.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD Blowing IGBTs
In sensorless vector the motor mag current is 800A and as soon as the drive starts it imediatley trips with a current inbalance fault and I see the current go through the roof. So I put the drive in Frequency mode.
There is more history to this drive.
10 months ago this problem started and the manufacturer performed all the tests you suggested and didn't catch anything. A motor repair shop (in situ) measured, measured, measured and found nothing untoward. After changing everything easily changeable - and I understand every single card, control cable and IGBT module with the CTs - the faults persisted and then stopped after changing the output reactors. That was after 4 months.
Two months ago, there was one IGBT short-circuit fault. Changed and OK 'till now.
There is another identical drive of this type onboard. No issues.
So I suspect that the motor is doing something. I hear from 2 sources of similar experiences of a motor condition that causes a transient that the drives can't cope with. Different manufacturers drives.
Is this possible?
RE: VFD Blowing IGBTs
Or do the measurements yourself. It is not difficult. You just have to do everything right if you want answers and insights that you can work from.
I can give you directions if you mail me. Put 'EngTips' and 'DrivesRock' in the subject line.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD Blowing IGBTs
Still wondering where all the current should come from if running in frequency mode and having no load on the motor. Or do you run the motor always with load?
RE: VFD Blowing IGBTs
As the drive O/P current is generated by PWM a clip on ammeter won't measure properly.
I think that the current is flowing through a short-circuit IGBT from the DC+ to - and/or its partner in series for that leg of the phase.
RE: VFD Blowing IGBTs
RE: VFD Blowing IGBTs
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