How many rotor bars in a motor

In order to avoid torque, noise and harmonics problems, there are specific rules for the selection of number of induction motor stator slots and rotor slot combination. You have no items in your shopping cart. Blog Tags. How to know the Number of rotor Bars in Induction Motor? Tags: Induction Motor. Leave your comment Registered user only.

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Jump to Topics on this Webpage. Why Do Rotor Bars Crack? Print This. Cracked Rotor Bars in Electric Motors Cracked rotor bars or cracked rotor bar shorting ring connections are a major source of problems for many electric motors, and detecting them can require the use of specialized rotor testing equipment.

There are three interacting phenomena that lead to cracked rotor bars : Repeated starting Thermal expansion Centrifugal forces Let's take a look at each of these in more detail. Repeating Starting When an electric motor starts, the rotating magnetic stator field is going to apply alternating forces very rapidly to each rotor bar and the forces diminish as the rotor accelerates.

Thermal Expansion The laminations are made of steel, while the rotor bar is made of copper. Centrifugal Forces As the rotors in a motor spin, they experience centrifugal forces that are strong enough that retainer rings must be shrunk onto copper shorting rings to keep them in place.

Growler Test for Rotor Bars The Growler test looks for discontinuities in the current flow through the rotor. Single-Phase Rotor Test Another test for detecting a cracked rotor bar is the single-phase rotor test, and for this test the motor remains assembled. High Current Rotor Test The high current rotor test involves applying high current through the shaft of the rotor after it has been removed from the stator.

Induction Motor Current Analysis aka, Current Spectrum Test The most accurate and reliable test for cracked rotor bars would be the induction motor current analysis, also known as the current spectrum test. Vibration Spectrum Test The vibration of an electric motor under load will modulate at a rate equal to the number of poles x slip frequency. Need More Info?

As a loose rotor bar passes a winding slot, the magnetic force causes it to momentarily lift and then drop. The number of winding slots will be between about 25 and The bad news is that you will not know the number of winding slots and it is very difficult to find out.

The good news is that the vibration is accompanied by a precise sideband - 2 x FLine.