Two 260KW DC shunt wound motors issue

[KARLOS]

Post Panamax Quay Crane, hoist:
Two 260KW DC shunt wound, separately excited motors, armatures in series & fields in series, output shafts directly coupled via a gearbox to two hoist drums

I was wondering if any of you gentlemen had come across motors used in the configuration above and could explain both the interaction between the two if their armatures had an imbalance (not a matched pair) and a possible solution short of replacement
Tks

 

[lukin1977]

I am having trouble understanding: "separately excited motors, armatures in series & fields in series"

 

[KARLOS]

Apologies if I didn't explain it clearly, the 2 motors have their armature contacted in series to the drive and the 2 motors fields are connected in series to the single field controller

 

[melspuds]

KARLOS,
Yes, that is a fairly common using DC motors for heavy lift cranes in steel mills, foundries, and steel fabrication shops, ect . Cranes lifting over 250 tons or more. I have seen hoists motors tied in series with shunt motors, series motors and compound wound motors, and all driving a separate gearbox and hoist drums. Even if the motors are not a matched set, I do not see a problem because of the separate hoist drums. Each motor is taking about one half of the load, also they both have separate upper travel limit switches (Youngstown).
Hope this helps,
Dave


ps: I believe that NASA Vehicle Assembly Building 2-350 ton cranes have the four motors (2/crane) tied in series to move the rockets very slowly.

 

[lukin1977]

maybe this can help you

http://www.lmpforum.com/forum/topic/1895-2-dc-motor-in-series-connection/

 

[roydm]

If the armatures are not a matched pair perhaps you can get them to share the load more evenly by adding a bypass resistor in one motor field, I assume weakening the field will also weaken the torque from the associated armature.
I seem to recall seeing DC motor schematics where the series field in one motor was wired to the armature of the other and VV. If one motor draws more current it strengthens the field of the other.