Dear Friends,

We have two Single facer units in our Corrugator machine called C/F and B/F which creates flutes of paper for producing Corruwall products. Each unit has a 95Kw DC motor with 4 Quadrant DC drive for variable speed operation. 3 phase supply for main circuit of drive is fed through a contactor. There is a set of two fuses/phase installed in drive thus three fuses for thyristor modules 1, 2 and 3 (where “+” DC output bus bar is connected) and next three fuses for thyristor modules 4, 5 and 6 (where “-” DC output bus bar is connected).
I have been facing a problem for last 30 days in C/F unit that the fuses of thyristor modules 1, 2 and 3 are blown out frequently. Normally machine runs smoothly without any problem but after 20-40 hours operation, fuses blown. It happened only 20% times that fuses of thyristor 4,5 and 6 blown but in most of the time, fuses of thyristor 1,2 and 3 blown. We have done following jobs till that time for the remedy;

1) Mechanical person checked but found no any jamming.
2) Interchanged the both drives (C/F and B/F) with each other.
3) Complete overhauled the C/F motor.
4) Made test of cables with magger.
5) Tighten the all connections.

After all the activities, problem still persists. We don’t face such problem at B/F unit.
Can any body help me out?

Hello AB2005

Happy new year.

This could be due to too high an acceleration or deceleration rate set resulting in high currents during speed changing. This can "age" the fuse if the current profile is getting close to the prearcing I2t of the fuse.
The problems can be due to a change in the supply voltage if things are running close to the wind at normal voltage and then the supply voltage is increased, it can push things to the limits.

Best regards,
Mark.

Hello mark,

Happy new year.

I have checked the variables of Acc and Dec and found them set at 50% limit while they can set at 100%. What do you recommend, set them at 100%?
What about supply voltage, it remains bewteen 350-390V.

Hello AB2005

The maximum rate of acceleration is related to the inertia of the load.
Although the drive can be set for "100%" and is now set at 50%, if the inertia is high then the energy required to achieve that rate of acceleration is higher and therefore the current is higher.
The actual rate of acceleration of the driven load is a function of the torque and the load inertia.

Measure the current during acceleration and deceleration and see how it compares with the drive ratings.

If the drive has a current limit, try reducing the current limit a little. This should override the acceleration and deceleration settings if they are too fast.

Best regards,
Mark.