Speed control of Slip ring induction motor
The speed control of the Slip ring induction motor by chopper is shown in the figure A. The power circuit diagram of speed control of slip ring induction motor control is shown in the figure.
Working of Speed control of Slip
ring induction motor
The
ON and OFF time of chopper is
adjusted to get desirable speed of the motor. The three
phase rectifier converts AC into DC. The copper
losses are very high due to high content of harmonics at
the output of the rectifier. The
function of the inductor is to reduce ripple at the output of the
rectifier. When chopper CH
is ON, the resistance R2 is
short circuited. Similarly when the chopper CH is OFF, the xternal resistance is
equal to R1 + R2. The average external resistance can
vary by switching chopper.
Speed control by external resistance
The
effective value of external resistance is given by
Effective external
resistance =
R1 ( TON ) + ( R1 + R2 )(
TON + TOFF ) / ( TON + TOFF )
The speed
of the slipring induction motor depends upon rotor resistance. The
high speed operation of motor is obtained by low rotor resistance and vice
versa. The speed of the motor can be changed by ON – OFF control of
chopper. The transistor is
used as switching device for low power, GTO for
medium power and SCR for
high power requirement in the chopper circuit.
Circuit diagram of speed control of Slip ring induction motor by DC Chopper
Advantages of slip ring induction motor speed control by DC chopper
- Smooth control
- No wear tear
- Less maintenance due to control by semiconductor devices
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