IN Brief:
- SSEN Transmission is replacing two end-of-life 132kV circuits between Redmoss and Clayhills substations in Aberdeen.
- Water ingress and duct defects have prevented installation of the final section, requiring targeted excavation and repair.
- The scheme replaces 10km of cable in total and will retire the last gas-filled circuits on Aberdeen’s 132kV ring.
SSEN Transmission is carrying out further remedial work on its Redmoss to Clayhills underground cable replacement in Aberdeen after water ingress in existing ducts prevented installation of the final section of new 132kV cable.
The project is replacing two circuits between Redmoss Substation on Langdykes Road and Clayhills Substation on South College Street. The route is approximately 5km long, giving a total of around 10km of replacement cable across the two circuits forming part of Aberdeen’s 132kV ring network.
Existing underground ducts are being reused wherever their condition permits, reducing the amount of completely new excavation required through the city. That approach has limited disruption along much of the route, but it leaves part of the installation programme dependent on civil infrastructure built for the previous generation of high-voltage cables.
Engineers encountered water entering the duct system between the Millburn Street excavation and Clayhills Substation while preparing the remaining cable section. The ingress has prevented the final pull, forcing the project team to suspend cable installation while the affected duct is located and repaired.
Pressure testing, tracer-gas surveys, and sectional testing have already been used to investigate the route. Those methods did not establish the precise defect location, leaving targeted excavation as the next practical step.
Work will progress in sections from the existing excavation at Millburn Street and South College Street towards Clayhills. Each exposed part of the duct can be inspected, repaired or replaced where required, retested, and reinstated before the team advances further along the route.
South College Street is scheduled to close between Riverside Roundabout and Wellington Place from 7 September until 18 December. The programme may change if excavation uncovers additional defects or weather and site conditions delay the repair work.
The road closure is the visible consequence of a problem whose engineering significance sits below ground. The existing Redmoss–Clayhills circuits are approaching the end of their operating lives and are the final gas-filled cables remaining on Aberdeen’s 132kV ring.
Replacing them forms part of a wider renewal programme intended to remove ageing cable technology and restore the two circuits using modern equipment. Completion will depend on resolving the civil defect before the remaining cable can be installed, jointed, tested, and energised.
Gas-filled high-voltage cables can operate for decades, but ageing systems require increasingly careful asset management as joints, sealing arrangements, insulation, and auxiliary equipment move further through their service lives. Replacement decisions have to account for condition, system importance, fault history, maintenance demands, and the ability to secure outages without compromising network operation.
Urban cable schemes add a second set of constraints because new electrical infrastructure has to share limited underground space with water, drainage, telecommunications, gas, and other utilities. Road access, traffic management, working-room restrictions, and reinstatement standards can become as influential on programme timing as the cable installation itself.
Reusing an established duct route avoids creating an entirely new corridor, but Aberdeen demonstrates the risk attached to that decision. Existing ducts can contain water, deformation, debris, structural damage, or obstructions that were of limited consequence to the previous cable yet prevent installation of a new one.
High-voltage cable pulls operate within defined mechanical limits. Excessive tension, restricted bends, damaged ducts, or uncontrolled friction can damage the cable sheath or insulation before the circuit has ever been energised, so forcing the final section through a compromised route would exchange a construction delay for a potential long-term reliability problem.
The water ingress must therefore be treated as a cable-system issue rather than merely a drainage nuisance. Until the duct route is dry, structurally suitable, and proven clear, the final section cannot be installed with the level of control expected for an asset intended to remain in service for decades.
Once the defect has been repaired, SSEN still has several electrical stages to complete. The final cable has to be pulled into position, the remaining high-voltage joint constructed, the circuit tested, and the completed installation accepted before re-energisation.
Ferryhill Road is expected to require a further closure of around four weeks after the duct problem is resolved so that the final installation, jointing, and reinstatement can proceed. The civil fault-finding programme therefore sits directly on the critical path for electrical completion.
Balfour Beatty is working with SSEN Transmission on construction, while Aberdeen City Council is coordinating the associated road-access arrangements. That combination is typical of urban transmission work, where network engineering has to be delivered alongside local transport management and other public infrastructure.
The two substations form part of Aberdeen’s 132kV ring, an arrangement intended to provide alternative routes for power flows and planned maintenance. The resilience offered by a ring still depends on individual circuits remaining serviceable, making replacement of ageing sections important to the flexibility of the wider network.
The current difficulty is relatively localised, but its effect on the programme is substantial. Most of the 10km cable replacement has progressed, yet one defective section of reused duct has stopped completion of the final circuit and added months of civil work.
The remaining sequence is now straightforward in definition, if less so underground: locate the source of the ingress, repair the duct, complete the final cable pull and joint, prove the circuit electrically, and return it to service. Only then can Aberdeen’s last gas-filled 132kV ring cables be retired and the replacement programme closed.
