Phynyx Industrial Products Pvt. Ltd.

5 TIPS FOR SLIP RINGS IN AC MOTORS

22.03.23 11:24 AM Comment(s) By Murtaza Farosh

After root cause analysis, experiments & observations we came across 5 key factors which are important for inspection/maintenance of slip ring motors.

Inspecting carbon brush wear and tear

1. Carbon Brush Inspection

It’s really important that you should be updated regarding the running condition of your carbon brushes and slip ring all the time. If it’s a 24/7 plant it’s a good idea to do inspection of brushes in the night switching off all the lights. You can observe sparks in the slip ring if any. The inspection interval should be as less as it can be. As it is easy to do inspection of the brushes, most of the time people take it casual. But the assessment of condition of brush and slip ring needs a skillful technician. Also properly closing the slip ring after inspection is job of responsible and sensible technicians as the consequence of ignorance are significant. Take the size of carbon brushes and make a profile for each brush. It will help you to find out the wear rate of each brush.

Inspecting Carbon Brush Holder Tension

2. Inspect Carbon Brush Holder Tension

It’s critical to keep a close eye on carbon brush holders. The tension of brush holders vary with time and operating conditions. A brush holder with less spring tension will not press the brush properly on the slip ring. A loose seating of the brush on slip ring will result in chattering in the slip ring. It will cause heat and spark in the slip ring. A high brush pressure on the other hand will cause a high wear rate of the brush. The simple way to check the tension is “pulling the holder tip by hand and then release it slowly all the way to the brush seat” each time you inspect your machine during schedule maintenance. Check that holder is not sticking anywhere in between its movement path and its tension is about same all the way. If you want precision, to your support many tools available in the market today of different types and costs to measure the brush pressure on the slip ring.
Inspecting carbon brush wear and tear

3. Slip Ring Surface

A good quality carbon brush and its proper seating on the slip ring will leave a shinny surface on the slip ring. The patina release by carbon brush during operation ensures the smoothness of the surface of slip ring. A bad relationship on the other hand will leave marks on the slip ring in the path of carbon brush movement.


Also the distance between carbon brush holder and the slip ring should be same for all holders. With time the slip ring may run out a bit because of carbon brushes movement. So the clearance of brush holder and slip ring may increase with time, but it should be within the tolerance mentioned in manufacturer.
Inspecting Carbon Brush Holder Tension

4. Carbon Dust Filters

The carbon dust filters is an important tool to keep your slip ring chamber clean. If the filters are choked or torn out the carbon dust will start accumulating in the chamber. It can stick between carbon brushes and holders and can cause hurdle in the smooth movement of the carbon brush in the holder. The result will be a loose seating of carbon brush on the slip ring and a spark. Dust filters are also disturbs the flow of cooling air in your slip ring. While choosing a dust filter always care about Filter Class, Nominal Air Flow, Pressure Drop, Maximum allowable Pressure, Maximum Allowable Temperature and dust holding capacity.
Inspecting carbon brush wear and tear

5. Slip Ring Cooling

As slip ring has a moving contact with carbon brushes it will always have relatively high temperature at it because of electrical connection and the friction between slip ring and carbon brush. Keep an eye on the cooling fans and cooling air path in the slip ring. Always keep slip ring away from atmospheric air as it contains moisture. Normally air flow monitoring sensors are put in the slip rings to ensure the smooth flow of cooling air. You can also put a temperature measuring sensor in order to keep an eye of slip ring temperature if there is a problem with slip ring or cooling system.

Murtaza Farosh

Director of Business Development Phynyx Industrial Products Pvt. Ltd.
https://www.instagram.com/phynyxind

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