Several medium voltage (MV) power electronic applications, ranging from motor drives to circuit breakers, require high-bandwidth lossless, accurate, and isolated current sensors capable of measuring both dc and ac currents. In this paper, a compact, contactless current sensor based on a commercial-off-the-shelf (COTS) closed-loop anisomagnetoresistor (AMR) chip is proposed as a solution for the above applications. A special U-shaped busbar serves as the primary conductor to improve stray field immunity. The sensor design utilizes a low-profile, stacked assembly wherein the signal conditioning stage digitizes the AMR chip’s analog output for transmission back to the controller via optical fiber for extremely high isolation voltage and common mode impedance. A resonant current bus is used to provide isolated power to the sensor circuits. The designed prototype is easily scaled to handle higher currents due the modular plug-and-play architecture. Experimental results of the designed sensor in a MV circuit breaker are provided to demonstrate a maximum accuracy error of < 0.25%, an overcurrent detection time of < 100 ns and successful scalability property without channel cross-talk.
