M.D. Judd

Simultaneous measurement of partial discharges using IEC60270 and radio-frequency techniques

Partial discharge (PD) measurement is an established condition monitoring technique used to facilitate the detection of incipient faults in high voltage electrical insulation systems such as gas-insulated switchgear and power transformers. By simultaneously recording partial discharge using both the IEC60270 apparent charge measurement technique and the more recent Radio Frequency method, which measures the energy radiated from the discharge, it is thought that more information can be gained about the nature of the PD source. Combined measurement has been carried out on various common PD source topologies recreated under laboratory conditions using PD test cells in a range of insulating media including SF6, oil and epoxy resin. Test cell geometries include floating electrodes, free particles and protrusions. By plotting apparent charge against the energy of the RF signal for a large number of PD pulses, the relationship between the two techniques can be quantified for a given test configuration. It has been found that the correlation between the two techniques produces characteristic patterns specific to each defect type. It is envisioned that combined RF/IEC measurements will contribute to a more widespread acceptance of the RF technique in terms of its ability to quantify PD severity by relating the RF energy to the more widely accepted IEC60270 pC level.

Frequency distribution of RF energy from PD sources and its application in combined RF and IEC60270 measurements

Using an integrated measurement system, partial discharge activity has been recorded simultaneously in terms of radiated energy and IEC60270 apparent charge. Correlation between these two quantities can yield important information regarding the shape of the underlying PD pulse. It is proposed that this new measurement strategy can be further enhanced by additionally calculating the relative spectral energies of the measured RF signals. The spectral energies of radiated RF PD pulses vary depending of the topology of the defect source and therefore may serve to enhance the quality of diagnostic information. Results indicate that the frequency distribution of RF energy measured simultaneously along with apparent charge could prove useful as an additional means of defect identification and characterisation.

Application of UHF diagnostics to detect PD during power transformer acceptance tests

Different diagnostic techniques are currently available for on-line insulation condition assessment of power transformers. Amongst these techniques a relatively new technique for detecting partial discharges (PD) in the ultra high frequency range of the spectrum is also introduced. The UHF technique has been recently presented in the field of transformer diagnostics, and although it is under development it shows great potential for on-line detection, recognition and location of PD activity. This paper describes the practical application of the UHF technique on two new identical 90 MVA, 150 kV power transformers. Both transformers are equipped with four external UHF sensors. Initially, injection measurements were performed to investigate the effects experienced by UHF signals when propagating through the transformer. Moreover, software developed to model the propagation of UHF signals inside the transformer tank was tested in its application to these specific transformers. The results obtained during the both the induced voltage test, as well as during the PD acceptance test in the factory are described. The practical experiences related in this paper provide further insight into the application of UHF PD monitoring techniques to power transformers

Managing Remote Online Partial Discharge Data

The volume of data produced by existing partial discharge monitoring systems is often too large for engineers to examine in detail, leading to data being ignored and useful indicators of health being missed. The case study reported in this paper recorded 21thinspace839 events around an HVDC reactor over a six-day period. We estimate that it takes 1 min to check whether an event requires detailed study, leading to over two man-months of effort to locate important events in a dataset of this size. Additionally, online monitoring data are stored onsite, and may require an engineers visit for collection. This paper presents an approach to remote partial discharge monitoring, supported by automated data interpretation and prioritization, which enables engineers to remotely find and download important data. Results from the case study are used to illustrate these concepts.

UHF and IEC60270 correlation analysis of radiated frequency band measurements on resin insulation void samples

Partial discharge (PD) measurement is an established condition monitoring technique used to assess the deterioration of high voltage insulation systems such as power transformers and gas-insulated switchgear. Two popular monitoring techniques employ radiated RF measurements and conventional apparent charge measurements according to the IEC60270 Standard. Recent research has shown that combining simultaneous radiated RF with IEC60270 measurements of PD events appears to provide additional information to assist in the discrimination of specific insulation faults. This paper aims to show for sample voids in resin that the frequency content of the radiated RF signals can be used as an additional discriminatory feature for simultaneous RF and IEC60270 measurements in identifying PD produced by single and multiple resin voids under electrical stress.

A simple metric for assessing the severity of partial discharge activity based on time-sequence analysis-discharge level patterns

This paper introduces a partial discharge (PD) severity metric, S, based on the evaluation of time-sequence PD data capture and resulting Time-Sequence-Analysis Discharge (TSAD) level distributions. Basically based on an IEC60270 measurement technique, each PD event is time stamped and the discharge level noted. By evaluating the time differences between a previous and subsequent discharge, a 3D plot of time-sequence activity and discharge levels can be produced. From these parameters a measurement of severity, which takes into account dynamic or instantaneous variations in both the time of occurrence and the level of discharge, rather than using standard repetition rate techniques, can be formulated. The idea is to provide a measure of the severity of PD activity for potentially measuring the state of insulation within an item of plant. This severity measure is evaluated for a simple point-plane geometry in

Analysis of PD in voids using correlation plots of RF radiated energy and apparent charge

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Suggestions to augment the IEC60270 partial discharge standard in relation to radiated electromagnetic energy

as a function of gap distance and applied high voltage. The results show that as the partial discharge activity increases, the severity measure also increases. The importance of future investigations, quantifications and evaluations of the robustness, sensitivity and importance of such a severity measurement, as well as comparing it with typical repetition rate assessment techniques, and other monitoring techniques, are also very briefly discussed.

Differentiating between partial discharge sources using envelope comparison of ultra-high-frequency signals

Partial discharges (PD) have been successfully recorded measuring both the simultaneous RF radiated energy and the apparent charge according to the IEC60270 Standard. From the measurements, correlation graphs are plotted. The correlation graphs provide an insight into the dynamics of the related current pulses associated with the discharge geometry. This paper makes attempts to quantify mathematically the RF energy and apparent charge correlation curves and clusters arising from specifically made resin void samples. A comparative analysis of multiple void samples with free particle in oil samples prove that the correlation depends on a number of factors such as the number of voids and the influence of multiple radiating sources.

Identification of simultaneously active partial discharge sources using combined radio frequency and IEC60270 measurement

The IEC60270 standard has become the key reference for general measurement of partial discharge (PD) in high voltage. This paper discusses the need to include reference to radiated emissions within this standard alongside the additional PD detection techniques outlined in the Annex. The paper suggests that the Annex should in the future also make reference to combined simultaneous IEC60270 and RF measurement systems allowing traditional apparent charge measurements to be complimented by knowledge of the radiated signals. The issues of RF calibration through the deployment of a combined measurement system are also discussed as well as the potential of a combined apparent charge and RF system to help further identify basic PD fault types.