Another method of reducing the starting current of a motor is to step down the voltage to the motor winding through the auto transformer such as is called the “Auto Transformer Reduced Voltage Starter”. This method is applied to high motor with large starting current.
Pressing the start push button will energize contactor S and timer TR. Contactor Y is also energized through normally closed contact TR (8-5). Instantaneous contact TR (1-3) will close immediately to maintain the circuit continuously energized. Contact Y (11-12) will open to ensure that contactor R will not be energized. Contact S (1-2,3-4,5-6) and Y (1-2,3-4,5-6) will close to connect the auto transformer T1, T2, and T3 to motor M, see Figure below (C). The motor M now receives reduced voltage.
After few seconds the timer delay contacts TR (8-6) will close. This will be de-energized contactor Y. Contacts Y (1-2,3-4,5-6) will open. Contact Y (11-12) will close to energize contactor R. Contact R (1-2,3-4,5-6)will close to connect the motor M directly to the lines L1, L2,and L3. Contacts R (11-12)will open to de-energized contactor S. Contactor S (1-2,3-4,5-6) will open completely isolate the auto transformers T1, T2 and T3 from the lines L1, L2 and L3. The motor is now running at is final full voltage operation. See figure below (D).
Pressing the stop push button will de-energize contactor R and timer TR. Contact TR (1-3) will open to ensure that even if the stop push button is depressed, contactors S, Y, R and timer TR will not be energized. Contacts S (1-2,3-4,5-6), Y (1-2,3-4,5-6), and R (1-2,3-4,5-6) will open to bring the motor into stop condition. The circuit condition is brought back to the one as shown in figures (A) to (D).
Control Operation
Figures below (A) and (B) illustrate the power and control circuit respectively of an “Auto Transformer Reduce Control Voltage Starter”. The control circuit consist of TR timers, contactors S, Y, and R.
(A) Power circuit of the “Auto Transformer Reduce Voltage Starter”.
Pressing the start push button will energize contactor S and timer TR. Contactor Y is also energized through normally closed contact TR (8-5). Instantaneous contact TR (1-3) will close immediately to maintain the circuit continuously energized. Contact Y (11-12) will open to ensure that contactor R will not be energized. Contact S (1-2,3-4,5-6) and Y (1-2,3-4,5-6) will close to connect the auto transformer T1, T2, and T3 to motor M, see Figure below (C). The motor M now receives reduced voltage.
(B) Control circuit of the “Auto Transformer Reduce Voltage Starter”.
After few seconds the timer delay contacts TR (8-6) will close. This will be de-energized contactor Y. Contacts Y (1-2,3-4,5-6) will open. Contact Y (11-12) will close to energize contactor R. Contact R (1-2,3-4,5-6)will close to connect the motor M directly to the lines L1, L2,and L3. Contacts R (11-12)will open to de-energized contactor S. Contactor S (1-2,3-4,5-6) will open completely isolate the auto transformers T1, T2 and T3 from the lines L1, L2 and L3. The motor is now running at is final full voltage operation. See figure below (D).
(C) Power circuit connection or the Auto Transformer Reduce Voltage Starter”.
Pressing the stop push button will de-energize contactor R and timer TR. Contact TR (1-3) will open to ensure that even if the stop push button is depressed, contactors S, Y, R and timer TR will not be energized. Contacts S (1-2,3-4,5-6), Y (1-2,3-4,5-6), and R (1-2,3-4,5-6) will open to bring the motor into stop condition. The circuit condition is brought back to the one as shown in figures (A) to (D).
(D) Power circuit connection of the “Auto Transformer Reduce Voltage Starter at the final stage of operation.
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