Turn-to-turn fault detection in transformers using negative sequence currents

Abstract

A power transformer is one of the most important and expensive components in any power system. Power transformers can be exposed to a wide variety of abnormal conditions and faults.Internal turn-to-turn faults are the most difficult types of faults to detect within the power transformer. The IEEE Standards documents have revealed that there is no one standard way to protect all power transformers against minor internal faults such as turn-to-turn faults and at the same time to satisfy basic protection requirements: sensitivity, selectivity, and speed.This thesis presents a new, simple and efficient protection technique which is based on negative sequence currents. Using this protection technique, it is possible to detect minor internal turn-toturn faults in power transformers. Also, it can differentiate between internal and external faults.The discrimination is achieved by comparing the phase shift between two phasors of total negative sequence current. The new protection technique is being studied via an extensive simulation study using PSCAD®/EMTDC™ 1 software in a three-phase power system and is also being compared with a traditional differential algorithm.Relay performance under different numbers of shorted turns of the power transformer, different connections of the transformer, different values of the fault resistances, and different values of the system parameters was investigated. The results indicate that the new technique can provide a fast and sensitive approach for identifying minor internal turn-to-turn faults in power transformers.

Turn-to-turn fault monitoring methods in electrical power transformers-State of the art

“…The performance of conventional negative sequence current (NSC) method during transformer energization is analyzed in this section. It has been claimed in previous studies that the presented NSC method is robust against the inrush current and can detect the TTFs during energization. It uses the line current to estimate the NSC component in the primary and secondary of the transformer.…”

“…However, TTF in transformer causes the asymmetrical component in currents and voltages. The NS‐based methods calculate the NS in primary and secondary line currents and use them to detect the TTF in initial stages. For this purpose, the magnitude and phase angle of the NS are determined by using discrete Fourier transformation.…”

“…The NS method acts similar to the differential relay. This approach is introduced in previous studies . It is reported that the sensitivity of the NS method (3%) is better than the differential relay (10%).…”

“…The NS method for fault detection was proposed for transformers and transmission lines and then the other researches followed it as a novel fault diagnosis method . Similarly, restraint is required during inrush and over‐fluxing cases.…”

Flux‐based method to diagnose and identify the location of turn‐to‐turn faults in transformers

“…A brief review on the presented methods for TTF detection are listed in Table 1, and the advantages and disadvantages of these are specified. These methods can be categorised into three classes including: Current and/or voltage components based [5–9]. Frequency characteristic based [10–13].…”