A New Vibration Testing Platform for Electronic Current Transformers

Abstract

With the growing global interest in developing future smart grids, nonconventional instrument transformers have been given much attention. In contrary with the classic magnetic core current transformer, electronic current transformer (ECT) does not exhibit saturation, is of small volume, and can generate a digital signal complying with the recent digital communication protocols such as the IEC61850. However, the measurement accuracy of the ECT is influenced by the mechanical vibration caused by the adjacent circuit breaker (CB) operation and the bus bar electromagnetic forces generated due to short-circuit currents. According to the GB/T 20840.8 and the IEC 60044-8 standards, the root mean square of the ECT output current should not exceed 3% of the rated secondary current after 5-ms duration following a CB operation or a large current of a short duration. Current ECT vibration compliance test does not correlate the ECT output current with the CB or the large current signal to correctly identify their ending moment. As such, the current testing technique may reveal inaccurate outcomes. This paper proposes a new vibration testing platform for ECT in which the status of the vibration source is synchronously correlated with the ECT output signal. A status monitoring circuit is proposed and implemented to achieve synchronous acquisition and comparison of the CB status and the ECT output current. In addition, a primary current sensor is designed to accurately realize the end time of any short-time large current. A software platform is developed to correctly identify the CB breaking moment and the end of the large current. The robustness and superiority of the proposed testing platform are validated through extensive simulation and practical analyses.