Design of a Force-Based System to Achieve Current Limiting in a Circuit Breaker

Abstract

In case of a short circuit fault current where the magnitude of the current increases to a high value it is needed to open the breaker as fast as possible simultaneously maintaining the features that are exhibited under normal operating conditions of the breaker. In this paper, a circuit breaker analyzer was used to measure the time taken by the existing Air Circuit Breaker to switch from ON to OFF condition once the signal is given. Mathematical models were developed to represent the positions of the linkages of the contact system and the forces that were generated in the contact system of the breaker. The present work aims to retrofit the existing breaker and therefore the initial challenge is to find out the space for using the secondary trip unit. The simulation for the concept is carried out in motion analysis software to analyze the system behavior. A Transfer function is developed to find out the forces coming on the various links in the short circuit condition and at different link configurations. A biasing torsion spring for flexible link Arrangement was designed and the Torque required on the Layshaft to reset the Mechanism is also estimated using the spring design tool. After finalizing the dimension and configuration of the secondary trip mechanism, the Transfer function was developed to find out the force required at the contact to delatch the mechanism. Crystal ball analysis was carried out on this transfer function to generates the mean and standard deviation values for the output variable and also the top sensitive dimensions for the design.