What could be causing heavy sparking on load for this DC motor?

[hiren desai]

Hey there...

We are working on one DC motor after it was overhauled.
DC Boom Motor 100 KW for Portrek Crane

We have performed Servicing, Re varnishing,Commutator skimming undercutting Setting of Brush.and test the motor on no load.Motor was running perfect without sparking.

When motor was fixed on crane just couple without load it was giving heavy sparking.

We have opened three times motor to find the fault but Motor is perfectly OK.
Even Drop test/armature windings/field interpole megger as well as ohms are also perfect.
Even we changed carbon brush original Morgan.

We have check all the possibilities for Sparking:

Following Check/test we have carried out.

1. Defective Carbon Holders. - in good condition.
2. Carbon brushes – Replaced.
3. Uneven condition of Commutator - Surface is even.
4. Armature windings - Windings are in good condition
5. Field/Interpole windings - Good condition
6. We also looked for shorts or opens in the armature circuit and for grounds shorts or opens in the field winding circuits. – No Shorts/open found.
7. Drop Test - OK


Can anybody help me out on this matter what could be the reason ?
One motor thing they swept one similar motor in place of this motor and it was running perfectly fine.that was also overhauled by us.

I have doubt on Compensated windings which comes below commutator ?
But not sure this DC Motor contain the same without opening armature wires.
is that anyway to check compensated winding without opening armature windings.

We do not carry any load testing facilities.only No load.

Can anybody help me out on this matter what could be the reason ?

 

[Asymptotic]

1. Does this motor have a series field? If so, "bump test" it against the shunt field to determine their polarity in relation to one another. Drop testing ought to have uncovered this, but mistakes happen, and something on the order of 1 in 30 to 1 in 40 motors I've sent out to repair shops have had their armature or field leads mis-marked upon return.

2. Does the motor have interpoles? Their polarity may be backwards.

3. Are all the field pole shims originals, and have they been returned to their original locations?
Seemingly insignificant changes such as using stainless steel shims instead of brass or other materials (changing flux linkage), and altering shim pack height (thus changing the air gap) can yield similar symptoms.

4. Armature and series field wire size may also play a role. Don't believe it would cause heavy sparking, but I recall a particular 300 HP "U" frame motor which sparked lightly under load and failed about every 6 months. After multiple attempts to correct the problem the local rewind shop couldn't explain why, but when we sent it to the manufacturer's shop they found the lead wires were one size under specification (250 MCM instead of 300 MCM, if memory serves). The smaller wire could handle the current, but wasn't how the original motor was originally built, and changing the leads resolved both sparking and premature failure issues.