# How many rotor bars does a motor have?

Contents

## How many rotor bars does a 2 pole motor have?

Fig. 1 shows the rotor speed and developed electromagnetic torque during acceleration of a fully loaded 4kW two-pole induction motor with S = 24 stator slots and R = 20 rotor bars.

## What is a motor rotor bar?

Rotor design

The rotor windings are made up of rotor bars passed through the rotor, from one end to the other, around the surface of the rotor. The bars protrude beyond the rotor and are connected together by a shorting ring at each end. The bars are usually made of aluminium or copper, but sometimes made of brass.

## How do I check my rotor bars?

The rotor induces currents back in the stator windings. These currents appear as side bands around the supply line frequency (60 HZ) peak, and are a function of the motors number of poles and slip frequency. By comparing the sideband amplitudes, you can estimate the number of broken rotor bars.

## What do rotor bars do?

Current flow through the rotor bars develops the rotor field. The field of the stator and the generated field in the rotor interact to produce torque. As the torque is produced, the rotor begins to speed up. The difference in speed is reduced as the rotor speed approaches synchronous speed.

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## What are rotor bars used for?

The shape and depth of the rotor bars can be used to vary the speed-torque characteristics of the induction motor. At standstill, the revolving magnetic field passes the rotor bars at a high rate, inducing line-frequency current into the rotor bars.

## How is rotor current calculated?

i.e., Rotor current frequency = Fractional slip x Supply frequency (i) When the rotor is at standstill or stationary (i.e., s = 1), the frequency of rotor current is the same as that of supply frequency (f’ = sf = 1× f = f).

## Which type of rotor is best for a turbo alternator?

Smooth cylindrical type rotor is generally used for high speed alternators or turbo alternators.