Inception Phase Angle and Shape of Partial Discharge Signals Detected by Near-Field UHF Sensors

When using an antenna near a high voltage (HV) conductor for the partial discharge (PD) detection application, curiosity for understanding any share of capacitive coupling in this process will arise. In usual applications of the ultrahigh frequency (UHF) sensors, the antenna’s plates are not near an HV conductor so it is inferred undoubtedly that every signal received by the sensor is just the result of electromagnetic radiation from a source. However, when the antenna is settled close to an HV conductor, although the capacitances are negligible, the voltage involved in this process is high enough to induce significant capacitive voltage on the antenna’s plates. Therefore, the UHF sensor would not be a pure antenna that only receives some electromagnetic waves, because it is intentionally located near HV equipment, and consequently, its capacitive features play a role in receiving the induced voltage. In this article, these in-circuit effects are investigated in the time domain and in the form of phase resolved PD (PRPD) patterns. In addition, some methods for compensation of adverse capacitive features of the antenna are presented. Also in this article, wave propagation features of PD signals emitted to the surrounding space are studied. It is shown that the shape of PD signals received by the antenna, in the form of a damped exponential signal, is due to the reflection of electromagnetic waves from the surface of the antenna and the nearby conductors. This might provide a new approach for future work on PD signals through the nonconventional UHF method.