Lightning Protection

Completed

Other Power and Storage Technologies(Electricity transmission and distribution)

Applied Research and Development

ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)

Not Cross-cutting

Project Contact
Scottish Hydro Electric Power Distribution plc (SHEPD)

Network Innovation Allowance

Ofgem

01 December 2013

01 October 2017

46 months

£220,000

Power

Scotland

Network Innovation Allowance

Project Contact, Scottish Hydro Electric Power Distribution plc (SHEPD)

1) Understand the behaviour of transmission lines under lightning strike conditions. 2) Determine the alternative techniques to provide lightning protection on transmission lines. 3) Create recommendations for a lightning protection policy for transmission lines. This is intended to inform the further development of SHE Transmission’s lightning protection policy. The project will be successful if it can deliver recommendations to further improve our approach to lightning protection , and more informed decisions on lightning protection options can be made.

Transmission towers require to have a low footing resistance (i.e. the legs of the tower provide earthing), so that if the tower is stuck by lightning, the lightning can travel directly through the tower to the ground without damaging the lines or insulators. Furthermore, transmission towers carry an overhead earth wire as the uppermost wire. The primary purpose of this wire is to protect the conductors and insulators from lightning strikes (being uppermost and grounded it is more attractive to the lightning that the conductors, providing the least resistance path to earth). It is directly connected to the top of each tower to provide a route for lighting to ground through the tower. However, where a tower is not sufficiently earthed (e.g. where a tower is built into rock which typically has a high resistance), it will have a high footing resistance; therefore lightning will not find a route to the ground through the tower and so will tend to travel along the transmission conductors instead. This can overload the conductor causing damage to the conductor and insulators, with the risk of conductor failure and outages. There are a number of potential solutions to this problem, the first would be to provide additional earthing for the tower in the form of copper earthing rods in the ground to lower the footing resistance (to approximately 10 ohms). Where additional earthing has been tried, but the resistance is still too high (i.e. still above 10 ohms), there is a risk of flashovers, where a lightning strike to the shield wire jumps across the conductor causing undesirable effects. To reduce the risk of flashovers damaging conductors or insulators, lightning surge arrestors can be fitted between the phase conductors and the tower. This provides a safe route from the shield wire through the tower and on to the phase wire, without a flashover. However, there is currently not a consistent understanding on how to deploy surge arrestors (e.g. on which phases and which towers), or the extent to which a tower’s resistance should be decreased if a surge arrester is used (i.e. how much costs should be invested in additional copper earthing), or what other methods may be preferred, to enable the identification and optimisation of least-cost mitigation options. Improving the understanding of lightning strikes where towers have high footing resistances, in a variety of scenarios, will help to further inform the decisions on the most cost effective lightning protection methods. To achieve this, the project will: 1) Investigate state-of-the-art of technologies and published work. 2) Develop a comprehensive model for the simulation of issues involved. 3) Verify models with lab and/or field studies.Note : Project Documents may be available via the ENA Smarter Networks Portal using the Website link above

31/08/18