Fiona Macnab reports:
Tom Miles, the area manager for East Sussex & Kent at UK Power Networks (UKPN) gave a solid run-through of the ‘Electricity Situation’ at the Annual Parish Meeting on 14th April
Tom looks after 800,000 customers within this region, of which 279 customers sit in the power network between Brightling and the Mountfield Primary Sub-station.
Analysing the detailed list of electricity faults experienced on this line for these 279 people over the year April 2020 to April 2021, in total there were 34 High Voltage interruptions. Tom broke them into the following categories:
- 28 short interruptions with no known cause, known as ‘blips’
- 3 significant damages cause by trees falling
- 1 insulator damage
- 1 de-energised for safety (low line reported)
- 1 Extra High Voltage Fault (5000 customers off)
It’s the blips!
82% of electricity cut outs are caused by unknown ‘blips’. On average these have lasted <10 seconds, or less than the time it takes to fumble around for the candles and remember where the matches were last seen….
Let’s face it, these are also the most annoying too, as every device in the house needs resetting after the loss of power. There is clearly ‘something going on’, Tom explained, as this considerably above levels experienced in other areas. To the point that Tom is directly reporting situation updates to UKPN senior management.
Currently the line between Mountfield and Brightling has a ‘protection mechanism’ at each end. This means any fault between the two cuts out 279 people. These cut outs are designed to ‘clear’ momentary faults by quickly opening/closing 4 times. These 4 on/off tests are the ‘blips’ over the 10 second power break.
If the system still detects a problem after the blips, there is a full power cut out. On-site engineers are then required to diagnose the fault and manually switch the power back on.
So, what is causing the blips? What is the Mountfield – Brightling diagnosis?
Across the UKPN network, tree-related faults are usually between 6% and 15% of all faults. On the Brightling/Mountfield line, the figure is 82%. Some blips may also be vermin-related or old cable terminations, but UKPN believes the number of blips to be more indicative of tree debris flying around and hitting the lines.
Tom explained how the company uses planes fitted with laser scanning devices (LiDAR) to assess the risks along the powerlines. From these surveys, Tom and his team assess the risks from vegetation and create tree-cutting programmes. Surveying the Mountfield Brightling line, UKPN has diagnosed that most of these short interruptions are caused by tree debris hitting the lines. Furthermore, areas along the Mountfield Brightling power line are clearly suffering from Ash Dieback.
Ash Dieback will kill 80% of ash trees. Sadly, the South East is the most affected area. In fact, Sussex & Kent areas saw confirmed infected sites between 2012-2014 (green squares in the Forestry Commission map, which also has reams of further information on Ash Dieback). Not only does this materially change and impact flora and fauna but it also means a lot of falling dead branches (‘blips’) and a lot of falling tall trees (power outages).
Ash trees can be as tall as 35 metres
In the South East, there are 46,000 km of powerlines, carried on 750,000 poles, the distance between the poles called ‘spans’. UKPN, like other electricity providers, are legally obliged to ensure clearance around power lines to 0.8 metres. This results in UKPN cutting back tree vegetation for, on average, 30-35 spans every year for the whole network.
Assessing the 133 spans along the 13km Mountfield Brightling line, UKPN found:
- · 42 have dead or diseased (tall) trees within falling distance of powerlines.
- · 61 need cutting back to give a 5-metre clearance on both sides of the line.
So – What is the Plan?
First, UKPN have done/are doing bespoke surveys of every span between Mountfield and Brightling. More detailed surveys are also needed for 30 of the Ash dieback-affected spans.
Secondly, UKPN are asking landowners for permission to cut back 5-metres clearance, rather than the statutory 0.8metres, and to cut down ALL dead/diseased trees on this circuit outside normal clearance spans.
Thirdly, UKPN are adding two more circuit breakers along the line, so that when there is a ‘blip’, it affects fewer people. Work on the two new circuit-breakers will start in May 2021, if the suppliers can provide the materials needed (so do not pack the candles away just yet). This will lead to some planned outages.
After these are put in place, the line will have 3 key circuit ‘lengths’:
- ·Mountfield → Darwell Wood
- Darwell Wood → South of Brightling Rectory
- South of Brightling Rectory → Gypsum Brightling
UKPN currently has approved £100,000 budget to tackle this plan.
Why is it taking so long?
First, it takes time to discuss the challenges and gain permission from landowners to cut the full 5-metre clearance, who are already tolerantly having the network travelling across their land.
Secondly, cutting 103 Spans compares to a yearly average of 30-35 for the whole network. That said, 26 have been completed so far and UKPN hope to complete another 12 spans needing 5m clearance by end of May 2021.
Third, there is the more ‘normal’ stuff like: Cost, location/style of new circuit breakers, the need for light weather conditions for the tree fellers and, of course, COVID – which has not only affected man-power but has also caused supplier delays.
And in the meantime …
To mitigate problems caused by blips and avoid/minimize device ’resets’ – Tom suggested investigating uninterrupted power supply devices (UPS), which he believes some customers have found useful to ensure continuity over a power cut.
A useful source of information and contact numbers in the event of a problem can be found on the UKPN website in the section ‘about the priority services register’.
The website also has information and options about obtaining compensation for outages. Alternatively, one can view the £100,000 funding as equivalent to £10.54 per person for every time we’ve had to reset the electrics over the last year….
Postscript: Ash Dieback
According to the Woodland Trust website, ash trees make the perfect habitat for a number of different species of flora and fauna. The airy canopy and early leaf fall allow sunlight to reach the woodland floor, providing optimum conditions for wildflowers such as dog violet, wild violets, wild garlic and dog’s mercury. In turn, these support a range of insects such as the rare and threatened high brown fritillary butterfly.Bullfinches eat the ash seeds and woodpeckers, owls, redstarts and nuthatches use the trees for nesting. Because ash trees are so long-lived, they support deadwood specialists such as the lesser stag beetle. Ash is regularly accompanied by a hazel understorey, providing the ideal conditions for dormice. Ash bark is often covered with lichens and mosses. The leaves are an important food plant for the caterpillars of many species of moth, including the coronet, brick, centre-barred sallow and privet hawk-moth.