2.5 mega watt dc motor

[Dilawar amjad]

We are using a the subject motor in seamless tube mill piercer application, the specs of the same are as under.
armature voltage: 930 volts dc
Base speed: 393 RPM
Motor rated current are 3600A at 300 RPM on 720 volts, 2830A at 393 RPM and 930 volts
Imax is twice on both above conditions.
Field Current: 120 Amperes

We have been in operation from the last couple of months, and the motor is being driven by Simatics DCM (Siemens) 7600 Amperes single quadrant drive with four thyristor stacks of 1900 amperes each.Recently we are having some fault having code F60038 (Overspeed threshold overshot) a couple of time in a day. The maximum speed for positive direction of rotation (p50380) of master drive is set on 150%, while that of negative direction of rotation(p5083) is set on 150% and this above setting for other three slaves are set on 200% for both postive and negative direction of rotation. The motor current is set on 70% of drive rated current i.e. 5320 amperes.
Kindly give your valuable advice for this remedy.
Best Regards

 

[IRstuff]

And what does Siemens say about this?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Dilawar amjad]

Thanks I forgot this possibility of getting advice from Siemens.

 

[LittleInch]

Dilawar,

You might want to delete your post and actually answer the question. Sarcasm doesn't work well online.

This does sound like a very specific question which isn't easy to answer remotely.

Also tell us what investigations you've done so far (checking sensors, wiring etc).

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[crshears]

Hi LittleInch, I'm confused...

I didn't detect any sarcasm at all, not by any of the posters...and I can't tell from your post if you're "speaking" to the OP, or to someone else, or to two different individuals in the same post.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[LittleInch]

It was addressed to the OP.

Now maybe I read it wrong, I don't know but it read like a sarcastic reply to me and in any event it didn't answer the question being asked by IR stuff.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IRstuff]

and we still don't know what Siemens said about their error code on their equipment.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[crshears]

Ah.

I saw IRStuff's question as rhetorical, meaning "How about you go to Siemens first and see what they have to say, and if you still have issues, we'll be here."

FWIW I'm curious about Siemens' response as well...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[IRstuff]

I also read as sarcastic, but the bottom line is that the OP has a very expensive piece of equipment that appears to be malfunctioning, and Siemens is the first place to ask these questions; the OP gave neither a, "Siemens says blah, blah," nor "Siemens says squat."

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Dilawar amjad]

Thanks to all of you in showing your deepest concern in resolve this very issue,We are in contact with Siemens china, who commissioned this drive they asked us to check the concentricity of the encoder, which is OK. Now they are in process of evaluating other possibilities and perhaps recommend to further fine tune the device. I will let you guys know the updates as soon as they are available.
Regards

 

[Dilawar amjad]

My intention had never been to be sarcastic, but my reply above might reflect this impression for which i really feel sorry.
Regards

 

[Artisi]

I also was of the opinion that what Little Inch was pointing out was a little abrupt etc, but giving the benefit of the doubt - maybe it was simply an error in language.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[jraef]

As a gross general rule, "Over speed" faults are (barring component failures) the result of the process "pulling" on the motor to where the rotor is driven faster than the commanded speed. Not knowing the nature of your machine I can't begin to speculate how that could happen, but it's something I would be looking for.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Dilawar amjad]

Thanks, You seem to be right, as the tripping we are having are periodic after rolling 16 or so billets and than after resetting the rolling resumes without fault for another 16 or so billets i.e. without tripping.
I will update as soon as some more data is available.
Regards

 

[Dilawar amjad]

Today we observed some other & new facts regarding the 2.5 MW motor. Attached find the three graphs showing trends of rolling. Two shows the tripping curves where as one is of smooth rolling.

Also we found out that Motor rated current is set at 2800 amperes & current limit is set at 200 % i-e at 5600 amperes. This is what we observed that current limits at 5600 amperes throughout the rolling sequence.

The bearings & encoder thing is again checked & seems OK. We believe that Speed loop P gain is the parameter causing the trip. From the trends, we conclude that the speed loop gain is set too high & the drive is trying to match the RPM very quickly causing an over shoot error. From the drive help, currently the gain is set to 75 % which is also default with range of 0 to 100 %. The drive parameter help says that it should be adjusted to 10 % initially & then raised based on application and dynamic response of the motor. What I believe that the gain shall be reduced to around 10 to 20 % to smooth the drive speed chase, and the trip over shoot error can be avoided.
Kindly advice based on recent data.
Thanking in anticipation.

 

[Dilawar amjad]

second tripping attached

 

[Dilawar amjad]

Smooth/successful rolling trend is attached