The Design of Digital Overcurrent Relay With IEC 60255 Time Curve Characteristic Based on an ATmega16 Microcontroller

The use of digital technology ensures the accuracy of protective relay operation, especially in the protection algorithm and operating time. Digital technology is employed through a lightweight and compact microcontroller, an ATMega16, which is expected to have long operating life and simple maintenance. The ATmega16 has shown satisfactory results in performing computations for the protection algorithm, especially in over-current protection. To do current sensing, the current flow is read through the Hall effect sensor. The function of time-current curve characteristics works according to the IEC 60255 standard and to an inverse function that can be set based on user requirements. The fastest relay operating speed is limited with consideration to reduce the error of decision-making in transient condition, and the response time of signal conditioner circuit. The peak-value reading method is found to provide the most rapid response, with the update every 10 milliseconds. Tests with the dynamic and static load indicate that the protective relay designed is immune to the transient phenomena such as DC offset and the motor starting currents.