The importance of Semi-conductor fuses

[kpatterson]

Gentleman,
I had a drive failure. The drive is an older Parker SSD. Now the question is simple yet complicated. Apparently one of the SCR's failed, it was showing 0 ohms to ground which in turn took out a semi-conductor fuse on the input side of the drive.

As it so happens, we had one in stock and it is changed easily with a couple of phillips head screws.

Now comes the question about fusing. I ordered some semi-conductor fuse replacements because we had none in stock. In the meantime, can I install a time delay fuse that is slightly smaller in amperage? I have an old obsolete fuse that physically fits. The semi-conductor fuses are 125 amps, and this time delay fuse is 100 amps.

I am pretty certain the bad SCR is what caused the fuse to blow in the first place. Machine is down but needs to be up. So smaller amp time delay for the rest of the day?? Or wait it out and use the proper semi-conductor fuses when they arrive?

Hope you like the pic, I had some time to kill...
thanks!

[Cheller]

Semi-conductor fuses are basically high speed fuses designed protect delicate electrical components from over-current. Using high speed semi-conductor fuses is essential since they will provide an instant reaction to a short circuit or over-current situation. They will definitely reduce the amount of component damage from short circuit current.

If you choose to skirt this fact, you will run the risk of more extensive damage during a short circuit. Manufacturers use semi-conductor fuses in these drives for a reason. Basically you would be gambling.

(I personally would wait it out.)

[maintech]

I have to chime in here.... I personally know of a maintenance man who had blown semiconductor fuses in a large DC drive. (not saying who it was) Repaired the failure in the motor/drive system but didn't have any in semi-conductor fuses in stock.

So he went to a known working drive that was the same as the problem drive in the plant and removed the semiconductor fuses, replaced them with standard slo-blow fuses.

Basically he borrowed these extremely valuable fuses and installed the semi-conductor fuses into the drive that initially blew fuses. This held them over until proper fuses could arrive at the scene.

Rolled the dice using probability, in other words, took and educated gamble and won. (this time)