Sep 2015
Electricity Distribution
Composite Shell Joint Retrofit Trial
Sep 2015
May 2017
UK Power Networks and London Power Networks
Lynne McDonald
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Network Innovation Allowance
LV & 11kV Networks and Overhead Lines
The project will research the existing market, design, develop, trial and validate a safe, affordable LV branch (T) joint repair solution.

i) Literature Review

The literature review will involve researching the current market locally and internationally to determine what products exist on the market that could be either adopted directly or amended to suit our requirements. Speaking with jointing contractors and UK Power Networks Field Engineers, it is understood that no products as proposed exist anywhere in the UK.

ii) Development and Design

Design and development of a trial run of plastic shells will involve producing a casting model based on LV branch (T) joints which have been replaced. This will be done in conjunction with a molding company and our jointing partners.

iii) Manufacture Trial Run

An initial trial run of five plastic shells will be developed to aid in the off-network testing (summarised in iv below) following which a further manufacture run of 100 are proposed to be rolled out into the on-network trial (summarised in v below).

iv) Off Network Tests

The first run of shells will be utilised in off-network tests. The off-network trials are proposed to test and refine the design prior to a full 100 shell manufacture trial run.

v) On Network Tests

The on network trial will involve installing approximately 80 shells on defective LV joints as identified during the Cable Pit inspection process. The exact number cannot be confirmed at this stage as each location has not yet been enabled to confirm that a shell can be fitted.

vi) Monitor

The repairs will be logged on UK Power Networks’ asset management system. Details will be added against the assets as the repairs are completed. It is also proposed to circulate a directive to all network engineers that the future replacement of any repaired joints will need to be communicated to the project team so that an assessment can be made on the cause of the fault and whether the repair was a contributing factor. It is proposed that a forensic examination of failed joints be carried out on all failed joints to determine the cause of the failure.

vii) Review

Review of the trial will rely on a qualitative analysis as a suitable control group cannot be assigned. Comparing the failure rates of non-defect T-Joints with defective ones would be an unrealistic comparison as would comparing defective joints against one another.

viii) Product Development

Building on vii above, product development will involve liaison with the existing UK Power Networks incumbent shell supplier and developing an approved kit and installation procedure. It is likely that this stage will involve an additional round of design amendments to suit the production process.

This project aims to develop a safe, cost effective alternative to removal and replacement of defective LV branch (T) joints, lowering the unit cost per repair and allowing for more repairs to be carried out under the same budgetary constraints.

The proposal aims to innovate an existing jointing technique which involves encapsulation of joints in resin filled plastic shells.  Where traditionally this approach is only adopted on new joints, the project proposes to adapt this technique to repair existing, defective joints.

The project will be deemed a success if:

  • We can prove retro fitting existing LV branch (T)-Joint and encasing it in resin is a suitable repair option to avoid water ingress into the crutch of a damaged joint (see iv above in method)

  • Field trials of the installed repair do not lead to any faults of the damaged joints

  • A safe, effective, cost efficient repair kit can be developed and implemented across the network on to all future faulty –LV branch (T) Joints.