Verification of Characteristics of Selected Current Transformers and Protection Relays

Protection circuits, specifically current transformers and protection relays, are an important part of electrical networks, enabling safe operation and suppression of dangerous transients and fault conditions. While current transformer requirements and specifications have been standardized for many decades, the aging and wear process of field-installed units has not been a focus of documentation, especially in view of the climate and conditions of Central Europe. In the case of protection relays, works describing the fault recording function are not available, especially with real data. Therefore, this paper presents an experimental evaluation and description of both previously described problems. Measurements are performed per partes; a protection relay tester was used to link the two parts of the evaluation. Due to the intended goal of using the results for estimating the components of the distribution network components and implementing and developing a reliability-centered maintenance strategy, only fault-relevant values (protection cores error ratio, fault recording function) are used. The evaluation is carried out on two oil current transformers (CT) and four protection relays from three manufacturers. The highest current recordings, the evaluation of the error ratio and the values are presented, illustrated and discussed.