Measurement Of Partial Discharge Activity Research Articles

Partial discharges within two spherical voids in an epoxy resin

A void in a dielectric insulation material may exist due to imperfection in the insulation manufacturing or long term stressing. Voids have been identified as one of the common sources of partial discharge (PD) activity within an insulation system, such as in cable insulation and power transformers. Therefore, it is important to study PD phenomenon within void cavities in insulation. In this work, a model of PD activity within two spherical voids in a homogeneous dielectric material has been developed using finite element analysis software to study the parameters affecting PD behaviour. The parameters that have been taken into account are the void surface conductivity, electron generation rate and the inception and extinction fields. Measurements of PD activity within two spherical voids in an epoxy resin under ac sinusoidal applied voltage have also been performed. The simulation results have been compared with the measurement data to validate the model and to identify the parameters affecting PD behaviour. Comparison between measurements of PD activity within single and two voids in a dielectric material have also been made to observe the difference of the results under both conditions.

UHF and current pulse measurements of partial discharge activity in mineral oil

Investigations are reported into a range of defects causing partial discharge (PD) activity in high-voltage oil-insulated equipment. The aim is to explore the relationship between radiated ultra-high frequency (UHF) signals and electric charge in a PD current pulse for PD sources in oil insulation. Experiments are performed under high-voltage AC conditions using electrode configurations that included a sharp protrusion, a bad contact, and a free metallic particle. A broadband current transformer is used to measure the PD current pulses with the UHF signals being detected using a pair of sensors mounted inside a metal tank surrounding the PD sources. Current pulses and UHF signals were recorded simultaneously using an oscilloscope with a bandwidth of 3 GHz. The level of correlation between the energy of the radiated UHF signals and the charge content of PD pulses is shown to vary depending on the defect type. Polarity-dependent UHF spectral content and ratio of UHF signal energies measured at the two sensors are shown to exhibit characteristics dependent on the discharge behaviour. These results and the analysis procedures introduced will contribute to the development of effective UHF monitoring systems for oil-insulated high-voltage plant.

Degradation and breakdown of mica under partial discharge stressing

Given the increasingly sophisticated tools available to acquire, store and process partial discharge measurements, it is imperative that the mechanisms of partial discharge degradation and the factors influencing the nature, form, extent and rate of degradation are elucidated. This will permit correlation among the measurements of partial discharge activity and the prevalent degradation in the practical situation. Only by these means will the ultimate peal, i.e. the prediction of remnant life of plant insulating systems through partial discharge measurement, be realised. The paper reports the results from the initial stage of an extensive investigation of the partial discharge degradation of mica. Ruby-muscovite and amber-phlogopite have been subjected to axial partial discharge stressing under AC, both polarities of DC and both polarities of impulse electrical stress. Two gaseous atmospheres, air and nitrogen, have been utilised to determine the degradation mechanism(s) involved. A mechanism of discharge degradation is hypothesised, based on the effects of bombardment by energetic particles and chemical interaction with gaseous discharge by-products.

Partial discharge. IX. PD in gas-insulated substations-fundamental considerations

For pt.VIII see ibid., vol.7, no.5, p.9 et seq. (1991). The physical aspects of partial discharge (PD) in SF/sub 6/ gas-insulated substations (GIS) are reviewed. The orientation is toward present and developing techniques for evaluating defects in solid and gaseous insulation systems on the basis of PD measurement. Standard evaluation methods provide an indication of PD in GIS, but cannot quantitatively determine the type and size of defect. Statistical analysis of PD activity, together with physical models for the various types of discharge and defects, provides the basis for more advanced interpretation. Measurements of PD activity that do not require an absolute calibration are of greatest utility. >