Answer / srb

It is because as the resistance is added in rotor ckt,no doubt impedance increases due to which current decreases but the effect of improved pf predominanats the inc. impedance & hence torque inc. After some tym when motor has achieved considerable speed effect of inc impedance predominanats over improved pf & hence torque decreases.

Answer / nilkanth tailor

THEIR R BASICALLY TWO TYPES OF INDUCTION MOTOR
1) SLIP RING I.M.
2) SQUIRREL CAGE I.M.

GENERALLY, IN HIGH STRATING TORQUES MOTOR(DC SERIES
MOTOR) HAS HIGH STARTING CURRENT, AND ITS VERY DIFFICULT TO
CONTROL THAT CURRENT...BUT IN SLIP RING I.M THIER IS HIGH
TORQUES PRODUCE WITH LOWER STARTING CURRENT THAT IS MAIN
ADVATAGE...

THE MAIN DIFF BET. SLIP AND SQUIRREL CAGE I.M. IS THAT

1)The rotor of the slip ring motor has more windings than a
squirrel-cage rotor so that induction voltage is higher and
the current for the same field strength lower.
2)During start-up the a typical rotor has 3 poles connected
to the slip ring. Each pole is wired in series with a
variable power resistor.
3)During start-up the resistors reduce the field strength
in the stator. As a result the inrush current is reduced.

Answer / k.prakashchandra

The pf is improved

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