This paper presents a novel algorithm for trip circuit monitoring using output contacts with integrated current and voltage measurements. The algorithm validates output contact closure and discriminates output contact failure from other problems in the direct current (dc) circuit, closing one of the last gaps of relay self-testing capabilities.
The output contacts employ an anisotropic magneto resistance current sensor that provides high-accuracy dc current measurements over a wide range, while also providing the ability to reject common-mode magnetic fields, which can affect other dc current sensor technologies when measuring low-level currents. The contacts also include a voltage sensor, which provides an analog measurement and a binary status that mimics a traditional binary input wired across a trip contact. Both current and voltage measurements are captured at 10 kHz and are provided to the algorithm at 1 kHz.
The algorithm can be used to flag successful, failed, or indeterminate output contact operations. Event records from laboratory testing show how output contact operation can be accurately determined, even in applications with parallel trip paths or in situations with sequential tripping, potentially reducing or eliminating the need for periodic manual maintenance. The paper also covers applications in which the algorithm can be used for verification of dc circuits to assist with NERC PRC-005 compliance, the detection of circuit failures missed by traditional monitoring methods, and the characterization of circuit and coil performance for condition-based monitoring. Finally, the paper explores how enhanced contact monitoring can be used in breaker failure schemes.