The method of calculating the setpoint of the overcurrent protection with the function of the detuning from inrush currents for a circuit breaker on the basis of the electronic trip unit

Abstract This paper presents for the first time an attempt to specify the method for calculating the value of the overcurrent protection setpoint with the function of detuning from inrush currents for the electronic trip unit ETU. The principle of protection is described in detail on the basis of comparing the rate of current rise in the protected circuit with the settings recorded in the ETU memory in the form of a binary code. The algorithm of action for the ETU based on the digital signal controller DSC is presented. Methods are proposed for improving the reliability of overcurrent protection and reducing the number of false outages. The procedure for calculating protection settings has been considered. Moreover, previously developed methods for calculating protection settings with a detuning from inrush currents are not suitable for the principle described in this work and vice versa the presented method for calculating protection settings with detuning from inrush currents is not suitable for methods based on other principles.