To Develop a System for Powering on Electronic Release of Air Circuit Breaker (ACB) at 5% of Line Current

Abstract

Air Circuit Breaker (ACB) is a switching device used for making and carrying current under normal condition and breaking current under abnormal condition. Current Transformer (CT) is used in air circuit breaker for the protection and measurement purpose. The CT design consists of Iron core & Rogowski coil. Rogowski coil is used for the measurement of the current owing through the breaker and Iron core is used to generate the required power for the display of Electronic release. During normal operation, current owing through the breaker will be displayed on the Electronic release and under the abnormal conditions, the electronic release trips the ACB based on the signal it gets from the CT. Iron CT iron is used as core material. CT secondary winding is in layers of enameled copper. The turns are wound opposite to each other. The end of both the winding are insulated with each other. The upper limb should be wound with the upper limb turns and the lower limb turns should wound with the lower limb turns. Moreover, CT is connected to the protection and control unit through the wire harness. Rogowski coil is used for the metering purpose. It senses the current and gives signal to the microprocessor which have high input resistance and so it measures the voltage across the secondary output terminal of Rogowski coil. In Rogowski coil, the winding is wound on the air core. As the winding is wound on the air core the Rogowski coil is linear and it can't saturate. Rogowski has much smaller mutual coupling between primary conductors and secondary winding than CT. Therefore, the Rogowski output is very small and it can't drive the burden as iron core CT. In the existing design of CT, the display of release gets powered ON at the 20% of single phase current or at 10% of three phase current. A need is felt based of customer and market requirements to upgrade this design of CT in such a way that the CT is able to Power ON the display of Electronic release at 5% of three phase current. To cater this requirement of powering ON of electronic release at 5% of three phase current, existing design of CT and Electronic release needs to be studied and improvements needs to be proposed.