Design and Implementation of Differential Relay for Power Transformer Protection

This paper illustrates the design and implementation of a differential protection relay for protecting transformers in power distribution systems. Transformers are a key component of the electric power system, and protecting them is essential. Faster and more specific protection is needed since the transformer itself may sustain damage during an electrical failure. Overcurrent relays cannot provide accurate and quick operation for transformers because they use time grading and directional detection. Differential protection mechanisms are used for the above reasons. The core concept of the differential protection system is Kirchhoff’s first law, which states that the sum of the currents going to a node is equal to the sum of the currents flowing away from it. The differential protection scheme detects the difference between the current entering a segment and that leaving it. When there is a difference between entering current and leaving current, the protection is active only. The problem is that an inrush current, also known as a magnetizing inrush current, is only transitory and lasts for a few milliseconds. It is worth mentioning that the inrush current is substantially larger, ranging from two to ten times that of the transformer’s ordinary rated current. In this paper, Kirchhoff’s voltage law (KVL) is also applied with a special programming algorithm to design differential relays to overcome the inrush effect. CT and PT are used as current and voltage sensors, and the Arduino Mega 2560 R3 is programmed to perform the IEC 60255-187-1:2021 standard differential protection relay (using minimum pickup of 87T = P.U. at 0.3, slope-1 = 30%, slope-2 = 60%, and break point between slope-1 and slope-2 = 2.0, delay time: 01 cycle). The differential relay provides voltage and current protection as well as inrush current protection of the power transformer. There is a provision for storing voltage and current data for future analysis.