Instrument current transducer for protective relaying systems

The article suggests improvements for measurement circuits used in electromechanical and microprocessor relays designed for protection of motor drives against open phase condition. The improvement of protections can be done with the use of instrument negative sequence current transducer designed by the authors. The transducer receives information about the state of the protected equipment from Rogowski coils. A research has been done on transients in instrument current transducers connected to an electric drive with asynchronous motor in the following conditions: the drive is powered from a three-phase positive sequence voltage source and one of the phase conductors is open while the motor is working. The obtained results and recommendations can be used with protection systems of electrical equipment at power facilities and in other environments.