A. S. Ayub

Online condition monitoring of partial discharge in HV underground cables

Partial discharges are symptomatic of many degradation phenomena in power cables and can cause further deterioration of the insulation in many cases. The partial discharges may be detected by using online and offline techniques. However, offline techniques have a significant disadvantage in that they require the cables to be taken out of circuit. Hence, electricity supply companies prefer the use of online techniques. The downside is that online techniques have their own disadvantages e.g. interference, ambiguity of partial discharge location, and sensor optimisation difficulties. The paper provides an overview of the current state of the art in partial discharge detection and location and also suggests how some of the disadvantages of online detection and location might be overcome.

External lightning protection system for wind turbine blades — preliminary aerodynamic results

In general, there are three components making up a lightning protection system for wind turbines. These are the receptors, the down conductor and the grounding grid. Receptors and down conductors are usually found in the more recent wind turbine blades and where the down conductors are normally installed on the internal side of the blade. Consequently, the blades are vulnerable to damage and burn resulting from lightning strikes. The authors believe that a system with an external down conductor is likely to reduce the risk of damage when compared to the system having an internal down conductor. One could envisage an external down conductor would look similar to the one installed on a building or an aircraft. However, external down conductors may compromise the aerodynamic performance of the turbine blades. This paper reports the effect of external down conductors on the pressure coefficient distribution around the turbine blade. The blade profile (aerofoil) used is according to NACA 4418. Numerical simulations, using computational fluid dynamics (CFD), were conducted on an aerofoil without and with external down conductors of 1mm thickness. The k-ε turbulence model that is incorporated in COMSOL Multiphysics (CFD Module) was used for the simulation and the wind speed and angle of attack used was 5 m/s and 5° respectively. The preliminary results show that the degradation on aerodynamic properties may not be too significant and these indicate that external down conductor arrangement could be considered.

Lightning protection of wind turbine blades — An alternative approach

This paper is a review of the lightning protection of wind turbine blades in terms of on the layout and location of the down conductor system. Generally, the down conductors of a lightning protection system for wind turbine blades may be installed inside the blade or outside the blade. However, the internal down conductor approach has become a common practice for blade manufacturers. This is presumably due to the preference for the aerodynamic properties of the blades to be maintained. However, by having an internal down conductor, other problems occur (e.g. blade disintegration, burn due to the impact of lightning strikes). This paper discusses the possibility that an external down conductor might be more advantageous and concludes with some recommendations.