Paper Machine Drives Problem

[AbrarAhmad]

Dear All,
We have 8 AC Drives on 3 Rolls in our Press Section of Paper Machine which are arranged in Master/Follower fashion. These are divided in 2 groups comprising of 4 per group.
Yesterday we faced a surprising situation that 1 of the drive in first group was showing its RPM 10 meters/min less than all of the other 3 drives in that group. This was a follower drive whose master drive was showing the same RPM like all of the other 3 in that group. We changed the load sharing but the situation became out of control. Put it back to the original Set Point. We changed the draw set point but all in vain.At last we changed the encoder of that particular drive.It worked but all of this situation was surprising.Kindly help to avoid any future problem.

 

[Skogsgurra]

The encoders are the largest single prolem source on paper machine drives. So common, in fact, that whenever there is a problem in a section, the encoder is usually changed. Often, the problem is something entirely different, but changing encoders is what most people do anyhow.

Most drives have a built-in check function that warns when an encoder fails or has marginal phase or amplitude. If that function is disabled, you will not be warned. So, my advice is to enable encoder check, but do not make it stop the drive - just send an alarm to the control room.

Questions: What drive system do you have?Wat kind of speed measurement? Does speed control and measurement work off the same encoder - or are there separate encoders for the two tasks?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[AbrarAhmad]

Thanx skogsgurra. We are using ABB Sectional Drives and Individual drives. Our drives are ACS 800. Firmware version is 7.1. These sectional drives have the fibre optic link with the central server room. While we are using 3 controllers AC800M for their communication with DCS.Encoders are already built in the motors. We just connected them with 7 core cable. We are using their meaurement in the software for the calculation of Estimated speed and Actual Speed error. Actually ACS800 drives firmware calculates a model of the motor. It is DTC technology that is used with ABB Drives.Our DCS is of ABB make IT 800xA.

Best Regards,

 

[Skogsgurra]

You should not have any problems then. Unless you are looking at the estimated speed instead of encoder speed. Is the encoder supervision (sorry, I do not have the manual available) activated?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[edison123]

Gunnar

Could you expand on that encoders are the villains ? What sort of problems do encoders create and why ? Poor manufacturing, bad technology ?

 

[automatic2]

biggest problem I've seen with encoders is heat related, and/or mechancial failure due to misalignment.

 

[AbrarAhmad]

Dear skogsgurra,
How Encoder supervision can active? Also this problem should be related with master/drive link. In my opinion if master is ok then follower should follow the speed reference and there should not be any replacement of Encoder.
Best Regards,

 

[martinrelayer]

Hi!
I've seen encoders fail because of overtemperature and after they cool down they start to work normally
regs.