DC Drive and Thyristor Protection-Fuse Failure

You say this occurs when a supply failure occurs.

If your drive is a regenerative S6R drive and the system is regening when the supply failure occurs, then you almost certainly will have an inverting fault and blow fuses.

Why are you having so many supply failures?

Are you sure the motor isn't flashing, causing a short circuit that takes your supply down?

If it is a regen drive what is the AC line volts and how stable is it?

How high does the Armature volts get? If it is too high with respect to the AC line, inverting faults happen far more frequently.

Do you operate in the field weakend range? Is your field supply "keeping up" with the dynamic speed changes?

More details are required.

ps:It is my business fixing these sort of problems. Are you in some nice warm part of the world?

The semiconductor fuse in AC side R and B phase and DC side blown when the main supply failing. Now this incident repeated about 10 times and blown about 20 to 25 fuses.

One of the things that can happen during a mains failure is that one phase fails prior to the other two. If this is what is happening and you are have a phase that is prone to failure for any number of reasons you can end up with your motor/generator set running on two phases and hence blowing the fuses.

I would suggest installing a system that will break the supply on all three phases in the event of any of the phases going out of tolerance Another step would be to replace the fuses with circuit breakers that can be reset.

Keep in mind the fusing is there to protect the equipment and people using the equipment. So if you are bothered by the cost of the fuses then you would be even more bothered by the cost of the damaged equipment if the fuses didn't blow.

i think , failure of the fuse during power failure may be due voltage spike happening at the on and off of the heavy inductive loads in the power lines. this can be overcome by surge suppressors in the power lines.

regrds , soby

There are a few posibilities

I am almsot certain then your drive is a regen type. When the drive is in a regen mode, (braking) the voltage across the SCR's is at peak and when one or more SCR's are not fired due to phase loss you wil blow a fuse (lucky , otherwise your drive is toast).

Options: 125A 480V 5% line reactor to dumpen the impedance on the incoming line (will also reduce harmonic currnets on the AC side)

A phase loss sensing is too slow to react and cut off the AC line, by the time it reacts the fuse is aleady gone.

Most pld fashion DC drives use DC output contcator. If that is teh case install and AC line contcator and surge supression filter ahread of it. Use semi conductoir fuses that has a seies connection cut off limit switch to take out the AC contcator when a phase is lost.

One more thing. Check with the DC drive manufcturer if the fuses you are using are the correct type and ratings for this drive.

You may contcat me for all this at 9065 845 3666 (day phone) ask for Joe Altman.

For logical trouble-shooting (you hope we can do) it is necessary to see the diagram.

Can you scan the diagram and enclose to this CR4?

It is so many possible sources of described failures.

We are also facing the same problem. I am sure that this is happening during regenerative mode only. We have AC line contactor and choke. The motor current rating is 340A and dc drive rating of 404A of L&T make.

@wonderla, I am from Palakkad, Kerala, India. If you already got a solution please inform me. My number is +919400317626. Or please drop your number i'll contact.