Design of an Automatic Transfer Switch for Grid-Solar Systems to Determine Transfer Accuracy and 7-Day Stability

Abstract

The increasing dependence on electrical energy in residential buildings requires a reliable Automatic Transfer Switch (ATS) to maintain uninterrupted power supply during grid disturbances. This study presents the design and development of an ATS for a Grid–Solar Power System (PLN–PLTS) using an Outseal PLC as the primary controller and an ESP8266 (Wemos D1 Mini) as the Internet of Things (IoT) communication module. The proposed system integrates Modbus RTU communication for data exchange between the PLC and ESP8266 and utilizes MQTT with a Node-RED dashboard for real-time monitoring and data logging. Experimental evaluations were conducted using resistive (10 W incandescent lamp), capacitive (10 W LED lamp), and inductive (40 W electric fan) loads under various PLC time-base settings of 200 ms, 100 ms, 50 ms, 40 ms, and 30 ms. The results indicate that reducing the PLC time base significantly improves the switching performance, with the optimum configuration achieved at a 30 ms time base, producing an actual transfer time of 30 ms and a standard deviation of 0 ms in both PLN-to-PLTS and PLTS-to-PLN transitions. Furthermore, a continuous 24-hour operation over seven consecutive days demonstrated stable system performance, maintaining supply voltages between 218.4 V and 226.9 V and operating temperatures below 39 °C while providing uninterrupted monitoring and reliable power transfer. These findings confirm that the proposed ATS is fast, accurate, stable, and suitable for continuous residential power management applications.