Optical sensor to provide early warning of power-line defects

A new application of optical sensing technology could prevent costly rail delays caused by the breakdown of overhead power lines.

It is hoped the technology will form the basis of an early-warning system to detect defects before they escalate and cause major failures — a problem known as ‘dewirement’.

In June this year the London-Norwich rail line made headlines for major train delays, reportedly resulting from the 30ºC+ temperatures causing powers lines to sag.

‘You can get all sorts of strange effects on power lines,’ said Prof Ken Grattan of City University who is leading the project. ‘You can get sagging in the winter with snow and you get it in the summer with heat, so it’s potentially problematic.’

Grattan and colleague Prof Tong Sun have received £102,000 in funding from the EPSRC collaboration fund to develop a prototype sensor system with industrial partners.

The team, which specialises in building sensors for industry, developed a novel fibre-optic sensor design for attachment to the pantographs — the ‘coat hanger-like’ structures that collect power for trains from overhead lines. The sensors will measure the critical strain and temperature parameters of the power lines as they run along the wires.

‘An enormous advantage you get with an optical system is that you can use it very easily in the context of high voltages — you don’t have to worry about isolating them in the same way you would for conventional electronic-type sensors.’

Grattan said another advantage of the optical sensors is that they are ’highly compatible’ with being buried in the carbon connecting surface of the pentograms, allowing the system to effectively ‘run in the background’.

‘There’s a danger of ending up with too much data and what you can do with this [system] is make measurements as and when you need them. You can make static measurements, you can make dynamic measurements, but the key thing is to look at the situation to measure and signal when there is a potential problem.’

The City Collaborative Transport Hub, the university’s interdisciplinary network on transport challenges, will play an important role in the research, with hub advisor and rail expert Prof David Johnson bringing crucial links with industry. These include manufacturers Brecknell Willis and Morganite Electrical Carbon, which will provide staff hours and resources, as well as Network Rail and the Rail Safety and Standards Board.

‘Our aim is to convince railway engineers that this offers the right sort of scheme for measurement and we’ll work with them to refine the system and create it in such a way that’s useful in the long term,’ Grattan said.