Overview
National Grid Electricity Transmission (NGET) asked RW to investigate engineered solutions for sealing transformer oil leaks—an issue faced globally across transmission and distribution networks. Both M3Spray and M3Cast, assessed from proof of concept through laboratory validation and M3Spray was taken forward to pilot demonstrations on representative assets, while the leak was flowing. The objective was to develop viable methods for sealing both weeping leaks and higher-flow leaks, without the need to remove the oil which would shorten outage criticality and time to make a repair.
Problem Statement
Transformer oil leaks occur on flanges, connections and radiator banks, often in constrained access environments. Leak rates vary widely, from minor weeps to higher-flow radiator leaks. The engineering challenge included ensuring:
- effective alloy placement on the leak path
- no contamination of the oil
- containment of the spray so as not to be deposited on critical components
- successful application on dissimilar materials
- deployment under real world access limitations
- application for leaks with operating temperatures up to 65°C
Methodology
Laboratory Development
Initial testing evaluated both M3Spray and M3Cast across representative geometries, including flanges and elbow joints. Both technologies achieved successful leak mitigation, with M3Cast and M3Spray achieving >99% leak mitigation against a dripping oil leak. Oil quality testing showed no alloy ingress in oil or filters through repeated applications in laboratory environments. Temperature and pressure cycling demonstrated that pressure variation had limited impact on seal performance, while thermal cycling imposed a greater effect on collar performance than spray – thus M3Spray was selected to be taken forward for leaks from large, flanged connections and radiator banks.
Leaking flanged connections
Following extensive lab testing, it was concluded that the positioning of the alloy was the most important parameter and therefore a robotic solution was developed in additional to the manually applied solution, intended to bring accuracy and repeatability.
Radiator Leak Development
High-flow radiator leaks required additional tooling development. Heated end effectors enabling the spray to be deployed at different angles to overcome access issues in constrained geometries. Testing demonstrated that a flowing radiator leak at 330 ml/min could be completely sealed when alloy aim was correct. Cases where sealing was reduced were directly linked to misaimed alloy delivery, identifying a key variable for continued optimisation. Minimal surface preparation (removal of loose rust and paint only) was sufficient for sealing.
Pilot Deployment
A large flanged lid was selected for the pilot using both manual and robotic deployment. The robotic method successfully deposited alloy through preplanned or manually taught paths, although site space constraints limited full automation benefits. Pilot results showed successful mitigation of leak paths, with secondary leakage occurring only from out of scope fasteners. The seal is being monitored for performance over time.
Outcomes
The combined programme demonstrated that:
- M3Spray is a viable leak sealing technology across representative transformer oil leak scenarios
- High-flow leaks on radiator banks can be sealed with minimal surface preparation
- Leak mitigation on flanged connections can translate from the laboratory and into the operating environment of a substation
Next Steps
Work has continued on improving the manual application, including overcoming access constraints and improving applicability to a wide range of geometries and leaks. Residual work will focus on answering remaining technical questions, which once resolved, the technology will be positioned for transition into supporting the transformer fleet reduce leakage.
