rotors

There is nothing like riding an elevator and getting stuck before you get to the right floor.

Have you ever been stranded with strangers, high up in a building, wondering if the elevator will fall?

Elevators and other large-load driving machines require confidence from their users, so they use motors like squirrel cage induction motors that contain rotors.

Read on to find out more about the rotors inside induction motors, how they can sometimes break, and help with repairing them.

What Are Rotors?

A rotor is the internal part of a motor that transfers power to or from the machine. How exactly does it create torque?

Excitation current creates a magnetic field around the rotor, which produces a magnetic field around the rotor bars. Because the magnetic fields are attracted to each other, the rotor begins to turn in the same direction as the field around it. The rotation induces an electric current.

What Do Rotors Look Like?

Squirrel cage rotors are the internal part of a motor that looks like a hunk of metal with a bar through it. In actuality, the hunk of metal contains bars to form a cage that looks like a squirrel cage, where the rotor gets its name. Then the bars are shorted together at each end.

Originally patented by Nikola Tesla as the rotating transformer, this motor is what we know today as the induction motor. Squirrel cage motors are the most common type of three-phase motors.

These types of rugged motors can be used to drive machines with large loads. Especially in machines that do not require varying speeds, like elevators, large fans, hoists, or printing presses, squirrel cage motors are popular because of their low maintenance requirements.

How Rotors Can Break

Rotors, especially those in squirrel cage motor, are very straightforward electrical elements, and therefore unlikely to cause problems. This is why these types of motors are the most popular. However, breaks do happen occasionally.

Rotors break when multiple stresses are applied at the same time. Stresses from the rotation, the heat, the vibration, when applied together, can cause a break where the end ring joins the bar, where the penetrates the core, or in the slot where the rotor bar is.

Broken rotor bars are the most common type of failure in a squirrel cage motor. The more starts your motor has under its belt, or the more wear and tear on it, the more likely the rotor bar is to break.

Rotor bars also break because of high heat, and the motor generates heat during operation. The heat makes the rods grow larger; when the rods expand, they put stress on the rotor bar that can cause cracks. Rotor bars can also break if another bar breaks.

Fixing Your Rotor Bars

No matter the reason your rotor failed, there is a successful process for rotor rebarring.

If you have specific types of rotors, such as hermetic, magnesium, high slip, or even double-caged rotors, we can help. Contact us today for help with your rotor repair.