The Design and Test of a Digital Relay for Transformer Protection

The inrush current-detection algorithm for the protection of transformers presented in [3] was coupled with a differential overcurrent algorithm and implemented on a popular eight-bit microcomputer system. Multiplication and division was avoided, enabling the use of relatively low-cost processing hardware. A hardware model centered around a transformer generated current data for the data acquisition system. This system translated the time-continuous analog data into the time-discrete digital input data for the algorithms resident in the microcomputer. The algorithms, operating in real time, provided outputs correctly, indicating the presence of either inrush, fault, or low differential current conditions.