I. Portugues

Radiometric location of partial discharge sources on energized high-Voltage plant

Partial discharges (PD) generate wideband radio frequency interference and, consequently, can be detected using radio receiving equipment. Due to the advances in ultra-high-speed sampling equipment, it is possible to accurately measure the propagation of the PD wavefront as it passes through a 4 element antenna array. From these measurements, the three-dimensional position of the PD source can be calculated using an iterative algorithm. The locating equipment is suitable for use within the vicinity of energized high-voltage plant and can locate sources up to 15 m from the array. Results are presented showing the location ability of the equipment under laboratory and field conditions. A significant advantage is the ability to detect PD sources in energized plant without the need for outages or electrical connections.

RF-Based Partial Discharge Early Warning System for Air-Insulated Substations

Partial discharges (PDs) generate wideband radio-frequency interference which can be used for noninvasive monitoring of discharges. This paper presents a novel method based on this principle for PD monitoring of substations. The significant advantage of this method lies in the ability to detect PD sources in energized equipment anywhere within a substation compound during normal operating conditions. The results obtained from the prototypes installed in the U.K. and U.S. substations are reported. Results include correlation with apparent charge and daily recordings obtained before, during, and after the failure of a 132-kV current transformer and 69-kV voltage transformer.

A nonintrusive partial discharge measurement system based on RF technology

Conventional electrical measurements of PD are performed with detectors connected to the plant. This paper describes research conducted in conjunction with the National Grid Company and the radiocommunications agency for the radiometric detection of partial discharge sources via a novel noncontact digital method. The equipment uses an antenna sensor and reference voltage inputs which are directly sampled at 2.5 GHz. Results for hv laboratory tests involving air, SF6 and oil discharges are presented. The results include the waveform, average frequency spectrum and pulse count distribution. A proposal is made for the characterisation of the recorded impulses from these different breakdown effects based on analysis of the spectra and pulse count distributions.

Partial discharge investigation of a power transformer using wireless wideband radio-frequency measurements

The remote detection of a transformer internal partial discharge (PD) has been demonstrated using mobile wideband radio-frequency receiving equipment. The PD is externally detectable due to coupling within the transformer tank, causing impulsive signals to be radiated from external connections. A wideband direction-finding technique using a four-antenna array has shown the source of the radiation to be the tertiary winding connections; the radiated impulse has characteristics typical of this method of emission. No other external site of radiation from the transformer was detected. Due to the lack of coupling to the primary and secondary windings, it is believed that the PD is present between the tertiary windings and the core.

The influence of personal computer processing modes on line current harmonics

The influence of the personal computer processing mode on the generation of line current harmonics has been investigated using a university library building containing over 370 PCs. The harmonics were monitored from the building switchboard using purpose-designed hardware. The PCs were set to execute four types of processing mode: idle, numerical processing, floppy, and hard disk accesses. The results recorded were indicative of harmonics caused by the PC box only, and secondary effects of harmonic production caused by distorted supply voltages were avoided. The results show that hard disk accesses cause the highest level of harmonic production affecting the 3rd and 5th components. Harmonic attenuation was very apparent when comparing the results between a single PC and 124 PCs connected to the same supply phase. However, attenuation and diversity effects due to changes in loading level on the PC power supply were not as predicted, showing an increase in harmonic generation with line current RMS level.

Estimation of Impulsive Noise in an Electricity Substation

Measurements of impulsive noise in a 400/275/132-kV electricity substation are presented. The measurements are made with three antennas having overlapping bands covering the range 100 MHz-6 GHz. This range includes those bands relevant to modern wireless local area network and wireless personal area network technologies (e.g., IEEE 802.11a/b/g and IEEE 802.15.1/4), which, if proved to be sufficiently robust in the presence of impulsive noise, could play a useful role in substation monitoring and control. Impulsive events are extracted from the measured data using the wavelet packet transform, and the statistical distributions of pulse rate, pulse amplitude, pulse duration, and pulse rise time are presented. An unexpected quasi-periodic component of the noise is observed.

Remote diagnosis of overhead line insulation defects

High voltage insulation defects cause partial discharges (PD) which can be detected through the reception of radiated radio frequency (rf) impulses. The paper describes a method of detecting insulation defects on overhead lines using vehicle mounted rf measuring equipment. The equipment is based on a 4 antenna array that is directly sampled using digital equipment with a bandwidth of 1 GHz. The results are analysed by firstly estimating the time delays apparent between the 4 antennas. Secondly, using the time delays, bearing and RMS time delay error information is calculated that allows identification of the PD source. The equipment has been tested in the field on a 132 kV overhead line defect that was initially reported to a radio spectrum management agency. The results show that equipment has the sensitivity to identify the defective insulator string.

Performance of Zigbee in Electricity Supply Substations

A study to assess the impact of partial discharge on the performance of ZigBee equipment in high voltage electricity supply substations is described. The character of partial discharge and ZigBee technology are both briefly reviewed. A field trial system developed for deployment in a 400 kV air insulted substation is described in detail and some preliminary proof-of-system results are presented.

An Investigation into Electromagnetic Radiation due to Partial Discharges in High Voltage Equipment

Measuring partial discharge (PD) activity in high voltage plant is a well established technique use to monitor insulation integrity. A partial discharge is a surge of electrons within a dielectric normally caused by insulation degradation or overstressing. This movement of electrons creates electromagnetic radiation. This paper studies the propagation characteristics of this radiation by considering a current transformer as an example. Initial simulations based on the finite difference time domain technique have been conducted. The results obtained have been used together with laboratory experiments to compare and expand the simulations. This paper describes these experiments and draws its conclusions based on their comparison.

Laboratory Assessment of WLAN Performance Degradation in the Presence of Impulsive Noise

A laboratory test to assess the impact of impulsive noise on the performance of WLAN equipment is described. The test is put in the context of a larger programme of work to assess the performance and reliability of wireless equipment subject to partial discharge noise in high voltage electricity supply substations. The character of partial discharge and WLAN technology are briefly reviewed. The laboratory test methodology is reported and some preliminary results are presented. A related forthcoming field-trial for tests of WLAN equipment in a 275/400 kV air-insulated substation is briefly described.