crane control question [urgent] 3

[electricpete]

I have never worked on a crane motor.

I vaguely remember someone explaining the to me once the control circuit for our 5-speed crane motor. A wound rotor motor. It is the analog style, not the microstepper type. I think it is around 20 years old.

I have been asked to go in to work tomorrow morning on my day off to assist in troubleshooting our crane motor which has tripping problems. They tell me FLA of the motor is 37.5A. The motor draws less than 37.5A in all speeds except the 2nd speed. In the 2nd speed it draws 60A.

To me it seems clear I need to look at once going on in the control circuit outside the motor in the 2nd speed.

So now some questions:
1 - Is there any site that explains 5-speed crane control circuits? Is it just 5 different resistance values switched into the rotor circuit or something a little more complicated? I tried googling and haven't found it yet. I will probably be able to see the control drawings at 7:00 but I'd like to look berfore then if possible.

2 - What kinds of things should I look at.

If you have any advice you can offer right away...
I'm going to check back here at 6:30 AM tomorrow to see if any suggestions that I can use.

Thx in advance

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[busbar]

 
e-pete, is 60 amps at the second speed equal on all phases? I would examine the rotor-resistor tapswitch contacts for an (intermittent/open) problem, but that would seem more likely to result in some degree of imbalance. Running voltages, currents and offline resistances on stator terminals and sliprings through speed variations may be worth checking, as well as near-equal running AC millivolt-drop tests on controller and starter contacts.

Part of the challenge with crane motors and controls can be the moving-component aspect.

 

[BJC]

Check the resistor bank and all the contactors that close to bring in the different stages and the cables.
If it's a bridge crane they are usually in wire cages that protect the pigeons from the resistors but not the resistors from the piegons. It could also be water, dust, crane operator cooking pot pies or just things wearing out.

 

[edison123]

pete,

I agree with busbar and BJC. Looks like contactor or resistor problem.

Good luck.

 

[jraef]

I totally agree with them as well. Bird droppings are a common problem, even inside of buildings. The resistor cage makes for a nice warm roost that is easy for them to hold on to. And if a tap switch or a contactor were bad you may end up with too little resistance in that step, resulting in increased current for that speed.

Here is a link on the basics on multistep WR control, but be forewarned, it is a .doc file, so you should save it to a disk and scan before launching.

http://www.eeco-net.com/eec/uploads/EMRS Wound Rotor Motors.doc

"Venditori de oleum-vipera non vigere excordis populi"

 

[ScottI2R]

E-Pete,
IF it is bird poo, Spikes on the top kind of agitate those trying to roost......but then they just take it out (or let it out) all over the freshly washed cars! That is what we have done. Check contactors for failures. Just saw this last week.
Oh, and if it is the first one, fill up your windshield washer fluid!

Scott

In a hundred years, it isn't going to matter anyway.

 

[tmcgett]

It seems to me that a contactor controlling a resistor bank would not cause a current spike. And being that all steps but 2nd are working properly I would suspect that the resistor run for 2nd step is shorted.
( Crane tech in training )

 

[mc5w]

You might have some control wires swapped causing the speeds to be out of sequence.

You also need to investigate the timing relays that keeps the speeds from coming up too fast when somebody "floors" the controller. Your second speed could be cutting in too soon.