Unidrive SP feedback problem

Hi,

I am wondering if you can help us with a problem that we are having on a 75kw unidrive SP with a closed loop system. It is connected to a 75kw hoist motor. The problem we are having is that the drive keeps tripping out on O.ht1 and OV errors and is very unstable. We have eventually pointed it down to the fact that we are getting interference on the encoder cable in the trailing cable festoon. We have tried replacing the cable but this has not solved anything. We tried connecting the earth by the drive side to the drive earth as well as the panel earth and the drive then immediately when I try run the drive it trips out on OI.AC. The encoder side of the cable is floating.

We cannot seem to be able to remove the interference?

Fitting a fiber optic encoder is one way of eliminating noise in wiring.

Alan

Is an existing installation that has been running for years?

Check your Screening and Motor Earthing - I have seen people use a separate Cable for the festoon for the encoder (Able to shield it correctly)

Hi,


Yes it has been running for years, and just recently had a mechanical fail which once it was fixed we noticed the problem although I did find out that the drive had been tripping before. It seems we might have got it running by running the encoder cable around the power cable and so far it seems to be working.

The encoder may be on the way out
A bad encoder has a "grind" feel when you turn it by hand
If you have the right tools changing the encoder may also assist

We changed the encoder and it did not help. also the motor seemed to have a knocking sound so we thought the bearings were on their way out so we changed this as well. only to find out it was the drive that was causing the motor to make this noise.

What length are the cables?
Are you using the "on board" feedback or going to an SM module?

If you know the details of the encoder, see what the voltage range is. The SP can provide I believe 5V, 8V, and 15V with the onboard input. IF you have a 5V encoder, it may benefit you to go to a 15V to make it a little more noise immune. Or, possibly you already have a higher voltage encoder and a lower supply voltage was selected by mistake.

I should also add that the faults you are getting are indicative of too much regen energy.
Are the trips happening mostly when you are lowering the hoist? Do you have an external regen resistor on this?