DC Motor Lap Winding - Progressive vs Retrogressive Winding 1

[edison123]

I have a very basic question. In a simple lap winding of DC motors, if the armature winding is changed from progressive (i.e. one segment forward) to retrogressive (i.e. one segment backward), will it change the direction of rotation of the motor for the same armature and field polarities ? If the direction of rotation changes, then will the interpole-main field relationship change and result in vicious sparking on load ?

 

[DougMSOE]

Changing from progressive to regressive or visa versa will not change the direction of rotation. Only when you change the magnetic relationship between the shunt and armature fields will you change direction.
The question that I have for you is why change from one to the other?

 

[rhatcher]

I have to disagree. With all other things being the same, if you replace a progressive wound armature with a retrogressive wound armature, the rotation will change since the armature polarity is reversed. See this link for more info under the section "Troubleshooting Tips for Armature Rewinds":

http://www.easa.com/news/c0403.pdf

This would also change the relationship between armature polarity and interpole polarity so sparking would result under load.

The best way to see this is to take a sheet of lined paper and turn it sideways. Imagine that the space between the lines are commutator segments (bars). Mark a bar on your left as the positive brush location and about 10 bars to the right mark another one as the negative. Number the bars from left to right so that positive brush is #1 and negative brush is #10. Assume that the coils are wound such that if you go from the start lead to the finish lead you make a clockwise pattern. For a progressive winding, the coil start lead would be at bar 1 and the finish lead at bar 2. The next coil would start at bar 2 and finish at bar 3. Assuming current flow from positive to negative (from 1-10 in this case), the current in these coils would flow clockwise (from start lead to finish lead). For a retrogressive winding, the first coil start lead would be at bar 2 and the finish lead at bar 1, with the leads actually crossing behind the riser. The next coil start lead would be at 3 and the finish lead at 2. With a current flow from bar 1-10, the current flow in these coils would be counter-clockwise, or from the finish lead to the start lead. This results in a different armature polarity.

As for why Edison123 would want to change from one to the other, my guess is he is troubleshooting a problem and that if this change was made that it was not on purpose. Fortunately, reversing the leads at the brush box will correct this. Note that reversing the armature leads in the junction box would correct the rotation, but it would not correct the difference in polarities between the armature and the interpoles.

I hope this helps you Edison123.

 

[edison123]

Thx rhatcher for your confirmation of my suspicion. As you hit it on the nail, I was troubleshooting a vicious arcing problem in a 2000 HP DC motor, where the armature was rewound. I had already solved the problem by switching the leads at the brush holder end. I just needed the confirmation that the problem was caused by this winding change.

Thx once again and you get a star.

 

[rhatcher]

Thanks Edison123. I learned this this same way you did...the hard way. As it says in the link, this is not detected by the 'standard' tests performed on a rewound armature. However, it can be detected in an assembled motor by methods other than trial and error. The test used to confirm proper interpole polarity with respect to the armature will also detect armatures changed from progressive to retrogressive (or visa versa) and armature leads that are reversed at the brush holders.

 

[edison123]

btw, if you are by any chance a dc motor designer, I would like to cross check with you the following armature design:

Armature voltage - 800 V Speed - 1000 RPM Armature Current - 1975 Amps Poles - 6 Armature dia - 847 mm Armature length - 364 mm Armature Slots - 129 Commutator segments - 258 Interpole turns/pole - 3 (all interpoles connected in series with compensating winding). No. of compensating winding bars - 10 per pole (i.e. 5 turns per pole). Would the armature winding for this data will be simplex lap or duplex lap?
I calculated for simplex lap - no. of armature conductors in series as 86 and resultant flux density as 0.577 Tesla & ratio of (Interpole AT + Compensating winding AT)/ Armature AT as 1.116. Do you think this is a valid design ?

If it is a duplex lap winding, how will the above calculated parameters (conductors in series, flux density, ratio of (Interpole AT + Compensating winding AT) / Armature AT) change ?

Sorry, if I am troubling you.

 

[jbartos]

Suggestion: Visit

http://www.speedlab.co.uk/software.pdf

for PC-DMC software

 

[rhatcher]

Sorry Edison123, I do not have any experience with DC motor design. Any answer I gave you would be based on theory, not direct experience.

And, by the way, you are not troubling anyone by asking questions..that is the purpose of this forum.

Merry Christmas

 

[UKpete]

Just for the record, it is only the lap winding that is affected. A wave wound armature has identical characteristics regardless of being progressive or retrogressive. A lap wound machine can be distinguished from a wave wound by looking at the direction of the end-windings at the end of a slot (assuming they aren't completely obscured by the banding) - if they both point the same way i.e. clockwise or anticlockwise, it's lap; if one points clockwise and the other anticlock, it's wave.

 

[jbartos]

Suggestion: Visit

http://motorpro.komotek.com/download/ch5_MotorPro PMDC_eng.pdf

for:
Lap winding
Wave winding
Progressive winding type
Retrogressive winding type