Ian A. Glover

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.

Measurement of the impulsive noise environment for satellite-mobile radio systems at 1.5 GHz

Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented.

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.

Implementation of herd management systems with wireless sensor networks

The work summarises a study of the data communications requirements for agricultural livestock monitoring applications using wireless sensor networks (WSNs). Several design challenges are identified and analysed in depth based on actual global positioning system positioning data gathered from an actual herd of cattle. A wireless system including antennae diversity together with data downloads optimisation schemes utilising data collector and routers are developed and tested in a working farm environment. Two analysis metrics, connection availability and connection duration, are used to quantify the impact of cattle movement on network connectivity. The major contributions of this study stem from a definition of the communication issues in deploying animal monitoring platforms in free-ranging farm environments and the analysis and optimisation of the wireless data download performance using as the foundation knowledge gained from a series of working farm trials. Additionally, the data download protocols are designed particularly to treat animal movement. The results prove the viability of WSN-based solutions for livestock monitoring applications.

An Advanced SOM Algorithm Applied to Handover Management Within LTE

A novel approach to handover management for Long-Term Evolution (LTE) femtocells is presented. Within LTE, the use of self-organizing networks (SONs) is included as standard, and handover management is one of its use cases. Base stations can autonomously decide whether handover should take place and assign the values of relevant parameters. Due to the limited range of femtocells, handover requires more delicate attention in an indoor scenario to allow for efficient and seamless handover from indoor femtocells to outdoor macrocells. As a result of the complexity of the indoor radio environment, frequent ping-pong handovers between the femtocell and macrocell layers can occur. A novel approach requiring a small amount of additional processing using neural networks is presented. A modified self-organizing map (SOM) is used to allow a femtocell to learn the locations of the indoor environment from where handover requests have occurred and, based on previous experience, decide whether to permit or prohibit these handovers. Once the regions that coincide with unnecessary handovers have been detected, the algorithm can reduce the total number of handovers that occur by up to 70% while still permitting any necessary handover requests to proceed. By reducing the number of handovers, the overall efficiency of the system will improve as the consequence of a reduction in associated but unnecessary signaling. Using machine learning for this task complies with the plug-and-play functionality required from SONs in LTE systems.

Vulnerability of Zigbee to impulsive noise in electricity substations

The vulnerability of Zigbee technology to noise in an electricity substation environment is assessed. Substation noise obtained from a measurement campaign is modelled as a Symmetric α-Stable process. The parameters of the model are estimated from the measurements and the resulting model is used to investigate the likely BER performance of Zigbee technology deployed in a substation.