Scottish and Southern Electricity Networks Transmission and InterBolt: Overhead conductor line sag measurement

Scottish and Southern Electricity Networks Transmission (SSEN-T) used the Innovate UK Innovation Exchange’s programme to find a solution to monitor overhead conductor lines for sagging. From 21 credible technologies which were found through the competition, SSEN-T have chosen to trial InterBolt’s high accuracy bolt load monitors, which can detect any increased mass of the conductor line in real time, delivering improvements in network resilience and operational efficiency.

Posted on: 15/12/2023
An example of an overhead line sagging due to ice build up - Image credit: SSEN-T
An example of an overhead line sagging due to ice build up - Image credit: SSEN-T

Scottish and Southern Electricity Networks Transmission (SSEN-T) is the owner of the high voltage electricity assets in the north of Scotland, including the 132kV, 275kV and 400kV electricity network. Whilst operating in the north of Scotland, SSEN-T faces some of the most extreme weather conditions in the UK. During winter periods temperatures can drop as low as -30°C with wind speeds up to 110 mph. Such weather conditions can result in thick, dense ice forming on the overhead lines, causing them to sag under the weight of the accrued ice.

Recently a 132kV overhead line has been fitted with ACCC conductors, which are high-temperature low-sag conductors. However, subsequent design studies have indicated that the conductor will sag to an unacceptable level due to ice build-up. This may present a hazard to third parties and/or require additional manpower as a result of potential outages. These conductors and transmission towers can be in hard to access locations which may require staff to walk long distances over difficult and often mountainous terrain to address issues.

The ideal operating height of such lines typically around is 6 – 7 metres above ground level, however under iced conditions ground clearance can reduce to as little as a few metres with the potential for serious issues to occur.

To control this risk, SSEN-T has previously installed an indirect monitoring system aimed at detecting weather conditions leading to ice build-up and sending a notice when these conditions are present. This system has proved unreliable, producing a high number of false alarms, requiring interpretation of photos to discern if a potential risk is occurring and therefore costing significant staff time.


SSEN-T was supported by Innovate UK Innovation Exchange to find an improved monitoring system that could directly determine any issues of conductor line sagging, eliminating the false alarms and need for interpretation.


This challenge attracted 21 high-quality entries with 6 solution providers progressing to the second round and presenting to SSEN-T management and subject matter experts. Ultimately, InterBolt’s intelligent load-sensing bolts were chosen by SSEN-T as the winning solution.

An InterBolt high accuracy and low-cost bolt load sensor embedded into a bolt - Image credit: InterBolt
An InterBolt high accuracy and low-cost bolt load sensor embedded into a bolt - Image credit: InterBolt

InterBolt’s technology consists of wireless, battery-powered and internet-of-things enabled bolts with embedded measurement of the elongation of the fastener. This allows for real time, remote bolt load measurements which eliminate the need for manual inspection.

In this scenario, as ice accrues on an overhead line, the mass of the line will increase, and hence the load on a bolt fastening the power line to a tower will increase. Therefore, through remote monitoring of the bolt load, if an increase in baseline bolt load is observed through periods of inclement weather, SSEN-T can deduce that there is ice accrual on the line.


SSEN-T and InterBolt have agreed terms and are busy preparing for a live network trial over the 2023/2024 winter period, which will run alongside other technology assessments by SSEN-T. Early estimates from SSEN-T suggest that if successful, a full roll out of InterBolt’s technology could deliver considerable savings in operational efficiency as well as improving network resilience in extreme conditions.

Innovate UK Innovation Exchange (iX) has been invaluable in connecting us with problem holders in industries where we don’t typically operate. The initial application process was extremely straightforward and the secondary pitching phase worked well with good engagement with the client and prompt feedback. The result was a contract for a technology trial with a view for wide scale roll out of the technology. I’m certain we wouldn’t be in this position if it wasn’t for the Innovate UK Innovation Exchange (iX) programme.

– Jack Hughleigh, Founder & CTO, Interbolt

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Innovate UK Innovation Exchange is a cross-sector programme supporting innovation transfer by matching industry challenges to innovative companies from other sectors. It does this by putting large businesses with technical needs in contact with companies who have the right innovative solutions, for faster development of novel solutions.


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