How to Protect Commutator of DC Motors Against De-Shaping?

Here's an option from the mechanical contact found in brushed DC motors.

Regards

Correct.

Total solution is a Brushless Motor. These come in all sizes & power.

But to upgrade may be costly and have to look for measures to reduced the problem in the existing system.

It is necessary to understand the limitations of equipment design, ease of use, cost and more.

The features of a DC machines [not brushless] that brushes and commutators wear due to migration of material; this is the reason that DC brushes include copper & marked (+) & (-) to minimise the wear & tear.

Additional steps given by one of the poster need to be considered.

A/ stop cleaning the filters daily. Every time a filter is changed or cleaned more dust enters the brush box

B/ check the brush grade

C/ check the brush tension, it should give 4 to 6 lb per 1"sq

D/ some chemicals present in the environment can lead to commutator erosion. Bring clean air in from outside.

What is your environmental contaminant?

What size motor, what voltage, what % load, duty cycle, Rated Rpm, running rpm, etc are all considerations.

Do you have black commutation or is there heavy sparking.

If the filters are truly plugged every day requiring them to be cleaned you need to think about getting fresh air piped in.

1) The m/c is a corrugated box maker in a corrugator plant. The environment is almost dusty.

2) Motor is 49KW, 550V, 126A, 61% load (normal load max 78A), 2530Rpm, running Rpm is almost 1700.

3) No any sparking but have deep lines and have black commutation.

4) The environment is dusty due to nature of work.

I have not found dry paper dust particularly aggressive. (Coal or ore dust is very agressive in comparison). Depending on machine floor conditions a corrugator could have some dusty areas. The dust will cause rapid plugging of the filters, and if the filters are removed the dust will quickly plug the air flow channels in the motor. In these cases we recommend external fresh clean air supply piped to motor. Be sure to verify the air pressure at the motor is adequate.

The speed and load should be OK for this size motor, especially since you have black commutation. However you are running at light load.

A color picture of the commutator would be helpful to determine how the film develops on your commutator. Is it an even groove or do you have threading? Depending on brush quality, current density, moisture in the air, chemical contaminants, etc. you may have too soft or too agressive brushes.

Some "grooving" is inevitable. I have seen motors with relatively deep grooves run with black commutation (good) for many years. Sparking, brush chatter or bounce, short brush life, broken brush shunts, out of round commutator, and similar conditions would indicate much greater problems.

If there is good film development I would resist the urge to stone the commutator to remove normal brush wear grooves. Stoning removes the existing film and removes copper from the commutator. You then begin the break in period and establishing a film each time.

Due to the light loading it would pay to reduce the number of brushes per arm. To low a current for the surface area of the brush can result in rapid wear due to a bad patina building up. If there are 5 brushes per arm remove 1 from each in a continuous band around the commutator. Do not stager the brush pattern it will ruin the commutator.

Good patina should be a dark chocolate brown, not black. If it is black and can be wiped off the commutator you are getting oil or silicate contamination.

If it is a non regen DC drive (infrequent stops) it becomes a natural to replace with a VFD and a TEFC AC motor (problem machine gone!). The total cost may be less than a replacement DC machine. If the speed is fairly critical you may be able to get away with a sensorless vector drive such as the ABB ACS800 series, or Rockwell PowerFlex 700 series, or a Mitsubishi drive. We have had good luck with all those makes.

Whats the load (%) on the motor?

The load has an impact on the commutator, together with some of the factors mentioned by others (brush grade and duty cycle). For a certain duty cycle and load the brush grade used on the motor will be, lets say x. However if the load on the motor is different (lets say less kW's) with a different duty cycle the brush grade will change to y.

The brushes must operate at a certain temperature (this temperature is different for different brush grade's) to obtain minimum wear and optimal performance. As we all know temperature is directly related to current and current directly related to, load and duty cycle. Therefore the temperature the brushes operate at, is directly related to the load and duty cycle.

If the brushes operate at a too low or to high temperature you will have excessive brush wear and commutator problems as you described.

First good post reading down from the top. GA.

Thanks to all to participate in this thread.

The motor is LEROY SOMER brand type LSK 1324 VL, 49KW, 2530RPM, 185Nm. The DC drive is Control Technique Mentor 2. The pictures of Commutator are as following;

Sorry. I could capture these as there was a very little space near motor.

How many hours (years) do you have on that com?

I suspect it needs to be pulled and turned, mica cut, etc.

That is extreme wear pattern.

Com film does not look too bad. No threading.

Clean air supply would probably help.

Motor is 4 years old.

How many hours (years) do you have on that com? Almost 1.5years.

I am searching for a "non-electric" Thermometer type device which I install with motor body to see its temperature. Does anybody knows such a device?

That is too short a life.

If it has been turned once before you may not have much life left in it. Before replacing the motor I would definitely look at AC VFD options---eliminate the com all together.

What is the max/min depth of the slots and the width? To be honest I've seen far worse and not worried about them. The patina looks fine.

There are many magnetic base thermometers available I tool catalogues.

I hope that was during a brush change that you took those pictures. You appear to be missing a row of brushes in the upper picture.