The correct operation of surge arresters under lightning and switching transient conditions requires that grounding be effective at high frequencies as well as at power system frequency. Effective high frequency grounding also limits the electrocution risk to substation personnel due to transient ground potential rise. This article assesses the performance of high frequency electrodes at typical lightning impulse current magnitudes. The enhancement of such electrodes by addition of bonded horizontal arms in cross and star arrangement is also investigated. The effective impulse resistances for electrodes having lengths up to 4.8 m are calculated over a range of impulse current magnitudes at the same location. The results obtained indicate that, for low impulse current magnitudes, the preionization electrode's resistance (R $_{1}$ ) falls with increasing rod length, a behavior reflected in the measured dc resistance. The presence of horizontal enhancement was found to reduce R $_{1}$ in all cases. The occurrence of soil ionization in the immediate vicinity of the electrode resulted in a reduced postionization resistance (R $_{2}$ ) at higher currents, tending toward a common asymptotic value independent of both the length of the rod and the presence of electrode enhancements. The observed behavior is supported by numerical simulation of electric field and current density distributions, indicating that the high current performance of a grounding rod is heavily influenced by soil ionization and breakdown in high-field regions at the electrode extremities.

Respiration-related changes in the complex impedance were obtained on the thorax in three volunteers. The real part of the image clearly showed the lungs as regions of increased conductivity on expiration. The imaginary part of the image, reflecting changes in the ratio of permittivity to conductivity, showed a central negative region surrounded by a positive region extending to the periphery of the lungs. These features may be due to movement of the diaphragm and liver within the sensitive volume during respiration.

This paper presents the development of a new methodology for the simulation of power line communication (PLC) within the popular electromagnetic transients programme-alternative transients programme (EMTP-ATP). As a first application, the comparative performance of the emerging orthogonal frequency division multiplexing (OFDM) based Prime and G3-PLC narrowband standards is investigated. Models of both standards have been created within the EMTP-ATP and simulations performed using frequency-dependent line models and realistic transformer models as terminations. It is observed that both standards are severely affected by the highly frequency selective nature of the Medium Voltage (MV) power line channel and a more considered choice of OFDM parameters may be necessary for optimal performance on MV networks.

This paper investigates the possible options for achieving a substantial reduction in a substation footprint using air-insulated switchgear as a more environmentally-friendly alternative to gas-insulated substations that use SF₆ gas. Adopting a new approach to surge arrester location and numbers, International Electrotechnical Commission (IEC) minimum clearances can be successfully selected instead of the maximum clearances as currently adopted by many utilities, as is the case in the UK. In addition, innovative alternative compact busbar arrangements using vertical and delta configurations have been proposed by the authors. A further opportunity for compaction is offered by the application of compact and integrated technology offered from several manufacturers. The full overvoltage control within the entire substation under any surge condition is a key aspect of the feasibility of this type of substation. This work demonstrates that the new design option can be an attractive alternative for future substation configuration with minimum footprint.

This paper reports the results of a parametric study on the characteristics of electromagnetic (EM) waves propagated due to surface- and cavity-type partial discharges (PD) in materials using the finite-difference time domain (FDTD) method. First, the EM waves emitted by such discharges in material samples were measured using a broadband aperture antenna. The measurements showed that the frequency range of the measured signals lay within the ultra-high frequency (UHF) range, suggesting that by carefully choosing the UHF antenna characteristics and its location it might be possible to apply this method to characterize the PD-emitted waves; and hence, to potentially use it to detect and monitor PD defects. In this context, the FDTD simulations were used here to simulate the experimental set-up and examine the propagation characteristics of EM waves emitted by such discharges under uniform and non-uniform test electrode configurations. Using an approximation of the exciting PD current pulses, the electromagnetic field components and the voltage signals captured on a simulated monopole sensor were computed in the time domain at various locations. To explore the limits of the application of the UHF method for detecting these PD types, a parametric study was carried out to clarify how the captured signals are influenced by the PD intensity, the frequency content of the exciting PD pulse, the type of insulation material, the dimensions and the position of the UHF antenna. One of the challenges that needs further investigation is the accurate simulation of the actual PD current pulse produced by such discharges, and hence its frequency content, as there is limited or no measured data available. The results showed that while the amplitude of the captured EM signals increase with the PD intensity, no appreciable signal is detected when the PD pulse width is higher than about 4ns, which may not occur often in unbounded air insulated systems. Equally important is the location and orientation of the UHF sensor—the results showed improved sensitivity when the sensor is vertically polarized and placed in close proximity in the lateral direction with reference to the discharge path.