Lora-based Smart Sensor for PD Detection in Underground Electrical Substations

The paper deals with the development of an IoT smart sensor for the monitoring of Partial Discharges (PD) in underground substations. The sensor consists of (i) an ultrasonic receiver for the detection of discharges, (ii) a programmable conditioning circuit that adapts the output of the ultrasonic receiver to the noise floor of the environment, and (iii) a digital section of processing and transmission of eventual warning message if the presence of discharges is detected. Given the challenge of transmitting messages from underground substations, LoRaWAN has been adopted as transmission technology. In the paper, several tests for the sensor assessment have been reported. In particular, the analog section has been assessed through tests in high voltage laboratory; it was so possible to tailor the conditioning circuit to the ultrasonic signal and to establish the alarm thresholds, comparing the sensor signal with a reference instrument for PD detection based on the electrical method. The performance of the transmission module has been evaluated through on field tests, placing the transmission module in a manhole. Finally the entire smart sensor has been assessed through tests in a real electrical substation. All tests have shown that the developed sensor is capable of detecting discharges with a reliability comparable to reference systems currently used by electrical energy distributors, and that LoRaWAN transmission has remarkable reliability also in underground environments characterized by thick concrete walls and high electromagnetic interference.