Differential Current Monitoring for the Detection of Inter-Turns Short Circuits in Power Transformers

M. MEIRA; E. MOMBELLO; G. R. BOSSIO; C. VERUCCHI; R. ÁLVAREZ

Resistencia

Congreso; IEEE ARGENCON 2020; 2020

UTN Facultad Regional Resistencia

Inter-turns short circuits are a cause of failure that can result in high impact damage to the integrity of power transformers. Their early detection is essential to reduce repair and service interruption costs. One of the primary protections of power transformers are the conventional differential relays, which can detect inter-turns short circuits. However, if the fault involves a few turns, the differential relays are not able to detect it until the inter-turns short circuit progresses due to dielectric and thermal effects to a more severe fault. Therefore, it is of special interest to develop strategies that detect early-stage faults. These strategies can be supplementary and incorporated into the digital differential relays to improve their sensitivity. This paper proposes an algorithm for detecting inter-turns short circuits based on monitoring differential currents. From the analysis of the excitation currents of a power transformer, a single fault indicator applicable to differential currents is determined. Through laboratory experimental tests on a 10 kVA three-phase transformer specially designed to simulate faults, it was shown that for this case study the algorithm is sensitive to faults involving 1.5 to 3.3 % of the winding depending on the phase involved with a current in the fault loop of 1 pu. Moreover, the fault indicator is almost independent of the transformer´s load condition, working from no-load condition to overload.