Test procedures for use of wireless partial discharges instrumentation in HV networks

On-field diagnostic methods based on Partial Discharge (PD) measurements for asset assessment in High Voltage (HV) sectors are experiencing a constant growth in recent years. This rise of interest motivated the research toward faster, reliable and less expensive methods and technologies to perform PD measurements. Recently, a portable instrument based on a wideband antenna sensor, intended for accurate partial discharge measurements, has been developed by the authors. This sensor allows to capture electromagnetic waves in a bandwidth ranging from 0.1-100 MHz as well as the electric field of the AC supply voltage to be used as a phase reference. This approach completely avoid the need of a direct connection with the parts under test, also allowing to perform the measure at a distance, in some cases. The instrument also integrates a digital acquisition units allowing to obtain a Phase Resolved PD (PRPD) pattern in real-time. These features makes this device particularly suitable as a portable instrumentation for on-field operations, especially in on-line tests. The effectiveness of this new approach to PD measurement, as well as the related new possibilities, has been thoroughly studied and assessed. The portable instrument has been characterized through both laboratory and on-site experiments, carried out on different types of HV components (mainly terminations, joints and transformers). The instrument performances were compared to traditional sensing techniques such as capacitive couplers and High Frequency Current Transformers (HFCT). In general a very good agreement was found performing concurrent measurements. Another aim of this research was to study standardised procedures to perform on-line PD measurements when using portable instruments based on electromagnetic sensors, in order to obtain repeatable and reliable results. In this case in fact some factors like position of the sensor, distance from the components, calibration and sequence of operations, need to be evaluated, considering the impact on the measurement results. These experiments and related results are presented and discussed in the paper. © 2014 CIGRE. All rights reserved.