Practical implementation of a new percentage-based turn-to-turn fault detection algorithm to transformer digital differential relay

摘要

Turn-to-turn fault (TTF) is one of the most prominent reasons for transformer failure. This fault typically initiates by involving only a few turns and can progress to a much more severe fault in a very short time. Therefore, it is critical for the transformer protective relays to detect the TTF in the early stages of its occurrence. The conventional differential relays, in general, cannot detect a minor TTF, and thus, a supplementary protective algorithm is usually required to improve the sensitivity of differential relays against TTFs. This paper proposes a percentage-based fault-related incremental currents method for the precise detection of a low-level TTF. The proposed method employs the positive and negative components of the incremental currents to discover a 1% TTF just after about two cycles of its inception. By introducing a novel operating and restraining signals, the characteristic curve of the proposed method is chosen similar to conventional percentage-based differential relays that are very familiar and understandable for the relay users. The performance of the proposed method is compared to the state of the art in the TTF literature such as the negative-sequence percentage differential method (NSPD) and extended Park vector approach (EPVA). Although all of these methods represent a similar promising performance, it is shown that it is much easier to determine the setting parameters of the proposed algorithm. The proposed method has been implemented into a real numerical differential relay as an add-on function. The excellent performance of the proposed relay is verified against the results of various experiments on a custom-built 2 kVA three-phase transformer.