The 20 kV Substation power distribution system requires accurate temperature monitoring to prevent equipment failure caused by hotspots, especially in closed-type cubicles that do not allow direct inspection using thermographic tools. According to the SKDIR PLN 520 guidelines issued in 2022, temperature inspections are carried out periodically or conditionally on open equipment, but limited time and access can cause delays in detecting thermal disturbances. The device is designed using a BME280 temperature sensor and an SCT013 current sensor. Measurement data is sent to the LCD and an Android application in real- time, triggering a buzzer alarm and providing a warning to the Android application if the temperature exceeds a certain threshold. Experimental results show that when measuring temperature with a sensor distance of 30 cm from the finger area, the average error relative to the FLIR thermovision camera is 2.49%, while at a distance of 35 cm it increases to 7.29%. This shows that the sensor distance significantly affects the accuracy of equipment temperature readings inside the 20 kV cubicle. For current measurements, the system shows an average error of 2.83% against the clamp meter, which is considered accurate enough for early detection needs. Alarm response testing proves that the system successfully activates a warning if the temperature is ≥38° C and the temperature difference with the environment is ≥4° C, and is supported by a current value of >400 A as an indicator of heat source validation. In conclusion, the designed system
has proven to be effective in detecting potential hotspots in real-time within closed cubicle areas that are inaccessible to conventional thermographic tools.
Keywords: Hotspot, ESP32, BME280 temperature sensor, temperature monitoring.