V5 Cell Failure in TMdrive-MVG

Some drives require pre-charge of the DC link prior to the inverter being placed in operation.

I would consult the Installation and Operations Manual to find out if this is required then determine if it is happening or not. The added DC Link charging current can be enough to result in a drive overload during starting.

More than likely you have a shorted drive component.

I would start by de-energizing the drive and performing simple continuity tests on all IGBT, diode, resistor, inductor, and capacitor components.

If you do not identify any shorted components I would then verify all power supply values to be within specifications. (Voltage & frequency)

If all power supplies are within acceptable limits I would disconnect the load and try energizing the drive.

If the drive fuses do not fail I would use an oscilloscope to probe the drive control circuits to verify proper operation and identify the source of failure.

In order to perform this test effectively you must have the factory OEM troubleshooting guide and schematics.

If you do not have a copy a call to Toshiba and/or a visit to their website will yield a copy.

If you do not have the proper test equipment or do not fully understand the test procedures it is in your best interest to contact Toshiba and arrange for on-site technical support service.

As far as substituting 415V for the 6600V supply: I would say no offhand however only Toshiba technical support can answer the question competently.

Good luck and stay safe.

WARNING!!!

You cannot test ANYTHING inside of a running / operating MV drive!!!!!!!

That particular drive is a "Multi-Level Inverter", aka "Cascaded H-Bridge" (CHB) inverter topology. This is a technology pioneered by Robicon, who lost their patent protection in 2011, at which time every other MV drive mfr jumped on the band wagon because it is inexpensive to make and provides some significant benefits over other types of Voltage Source Inverter topologies.

On of the advantages is that the output inverter stage is comprised of a series (cascaded) string of LOW voltage cells to create the MV output. So CAN you test a cell at low voltage? Absolutely! That's one reason they made it this way. But you do so on a BENCH, not inside of the drive.

If the SAME cell keeps blowing a transistor, it's likely one of a few possible reasons:

1. To make this work, there is a multi-output phase shifting transformer ahead of the drive, creating (in the case of 6.9kV) 36 individual low voltage outputs that feed the individual cells. (see drawing below). If the winding on that cell circuit is bad, you will damage each cell you put into that circuit in that spot.
2. If the firing circuit for that cell is bad, it will keep misfiring the transistors in that cell after you replace the transistors, damaging them again.
3. If the capacitors in that cell are bad, the DC bus in that cell will have too much ripple and damage the transistors.
4. If the precharge circuit for that cell is bad, it will damage the capacitors, then lead to #3 above.

This image would represent a 2300V drive, your would be 3x this

For those reasons, the mfr SHOULD have warned you to NEVER replace JUST the transistors within a cell, you replace the ENTIRE cell, then send the bad one to them for testing. This is true of ALL CHB topology drives on the market. Their salesmen sometimes TALK about how you can remove a cell and work on it on the bench, but if you speak to the SERVICE department, they will tell you that without VERY SOPHISTICATED troubleshooting skills and expensive diagnostic tools, you SHOULD NOT do so. Leave it to those who KNOW what to look for.

You should have a complete spare power cell and swap it out. If that's what you have and that's what you did, then it leaves only the transformer as the likely culprit, in which case prepare for a WHOPPING bill to replace it!

Here is the actual sketch from TMEIC for this 6.6kV drive.

They don't show the pre-charge circuit on this, but I cannot imagine they would be so foolish as to not have one. I think it's just a level of detail not suited for a website that is sales-oriented.