Design and Development of Rack-inMechanism of Air Circuit Breaker

Demand of electrical energy without interruption has increased nowadays. To meet the requirement, the reliability of each individual component should also be high. Air circuit breaker (ACB) is an automatically operated electrical switch, which is mainly used for low voltage power distribution. For easy maintenance and inspection, draw-out types ACB is used. Rack-in mechanism is used to connect and disconnect the breaker within a cradle by applying torque manually using rack-in handle. Typical rack-in mechanisms often require a high force to rack-in and rack-out of the circuit breaker, and the amount of force re-quired increases as the number of electrical contacts to be engaged increases. As the num-ber of contacts is increased, the force applied to actuate a typical rack-in mechanism may exceed ergonomic limitations. Lesser torque is desirable in manual rack-in operation to reduce human fatigue. Three rack-in mechanisms have been thought and direct translation type rack-in mechanism has been found optimum as per grid analysis comparing other rack-in mechanism. A prototype of selected rack-in mechanism was fabricated as per the CAD model to validate the results.