The idea came to me in preparation for my ‘Introduction to Electric Motors Course’ that I offer free-of-charge to my customers apprentices. The course starts off with an introduction to electromagnetism, then as the day progresses I’ve got coils wound and describe how three phase works and a rotating magnetic field is generated. The only problem with that is that I’m talking about it, not showing it. Then an idea popped into mind…Why not use magnetic paper and see if I can see the magnetic field rotating?

When we receive a DC motor for service we will profile the commutator to assess the condition. The last picture shows one in an ‘as received’ condition. The differences in the segment heights is what the surface of the carbon brush sees. If not smooth, then it will wear the brush away quicker than it should. Then, you’ve got more maintenance to do than you’d want to. Or, more chance of an in-service failure happening. Imagine the difference between a cobbled street and the surface of a racetrack. That’s the best analogy I can come up with.

One of our customers had been struggling with bearing currents on a particular motor for some time. I am not going to mention any names, but this customer is in the top tier when it comes to reliability and understanding bearing currents. They had performed some very good analysis and had still been unable to solve the problem. In an act of desperation, they had replaced the inverter for new and miraculously the bearing currents disappeared. They had not changed any parameters, and the replacement inverter was the exact same manufacturer and model. So what was going on?

I do see and hear ‘The rotor has been balanced’. This is an incomplete statement. Rotor balancing is covered by an international standard ISO 21940. There are differing balance grades. The better the grade, the better something has been balanced. A standard electric motor from most OEMs will be balanced to grade G6.3, batter than that is G2.5, better than that is G1.0. We balance all rotating elements at Fletcher Moorland to G1.0, we do that because it’s the right thing to do. Reliability improves because of it, the wear on the bearings is less from the outset.

By storing bearings on their sides, the loading is shared equally between the balls lessening, or totally removing the chance of false brinelling. It’s pretty simple when you know isn’t it? There’s more that you can do too. Firstly though, when you look around your stores, explain to your stores manager why you’re putting the bearings flat. I do see many storerooms where bearings are stored on their sides. But if you don’t know, you don’t know.

You switch a machine off for a shutdown because you think it’s the right thing to do to save energy. Then you come to switch it on again. Guess what? that capacitor can’t do what it’s supposed to do. Your machine doesn’t power up. Then, which is quite common, you keep trying to power up your machine. There might be a bit of a bang, and some smoke appears. You certainly have a problem then.