Characterization of Cavity PD and Corona Under Impulse Voltage

Abstract

Understanding the phenomenon of Partial Discharge (PD) under impulse voltage is essential to improving the reliability of High Voltage (HV) equipment. PD in HV equipment can cause severe insulation deterioration, resulting in breakdown, production loss, and high repair costs. HV equipment insulation can fail due to PD activities initiated by impulse voltages, such as lightning strikes and switch- ing operations, which are inevitable phenomena. The latter has been exacerbated by load-shedding switching operations in South Africa. PD detection technology is well developed under Alternating Current (AC) frequency voltage conditions. However, there is inadequate knowledge of the detection and interpretation of PD in non-power frequencies. The challenge in PD measurements is to detect PD during the impulse voltage due to the overlaps between the test impulse voltage and the PD frequencies. In the present work, PD characteristics in cavity PD and corona discharges are studied using a developed balanced PD detection circuit to detect PD current pulses e!ectively. A balanced PD detection circuit e!ectively separates interferences induced by the impulse voltage from PD current pulses. The experimental results showed a distinctive characteristic of the cavity PD with main and reverse discharges located respectively during the rise-time and fall-time phases of the applied lightning impulse voltage. In contrast, positive and negative corona discharges are observed only in the rise-time part of the applied lightning impulse voltage. MATLAB ® Simulink® is also used to simulate cavity PD and corona discharges under lightning impulse voltage, and the characteristics of the PD pulses correlate with the experimental results. The experimental circuit and the simulation model can be developed and used as a standardized PD measure- ment technique under non-power frequencies.