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

RAÚL ÁLVAREZ; GUILLERMO BOSSIO; CARLOS VERUCCHI; MATIAS MEIRA; ENRIQUE MOMBELLO

Resistencia, Chaco

Congreso; IEEE ARGENCON 2020. Biennal Congress of IEEE Argentina Section; 2020

IEEE Argentina

Inter-turnsshort circuits are a cause of failure that can result in high impact damage tothe integrity of power transformers. Their early detection is essential toreduce repair and service interruption costs. One of the primary protections ofpower transformers are the conventional differential relays, which can detectinter-turns short circuits. However, if the fault involves a few turns, thedifferential relays are not able to detect it until the inter-turns shortcircuit progresses due to dielectric and thermal effects to a more severefault. Therefore, it is of special interest to develop strategies that detectfaults in the early stages of their occurrence. These strategies can besupplementary and incorporated into the digital differential relays to improvetheir sensitivity. This paper proposes an algorithm for detecting inter-turnsshort circuits based on monitoring differential currents. From the analysis ofthe excitation currents of a power transformer, a single fault indicatorapplicable to differential currents is determined. Through laboratoryexperimental tests on a 10 kVA three-phase transformer specially designed tosimulate faults, it was shown that for this case study the algorithm issensitive to faults involving 1.5% to 3.3% of the winding depending on thephase involved with a current in the fault loop of 1 pu. Moreover, the faultindicator is independent of the transformer's load condition, working fromno-load condition to overload.