Summary
Utilities worldwide have been moving away from oil-impregnated paper cables due to the challenges of operating and maintaining these systems and general perception that the dielectric liquid presents an environmental risk. Many of these systems have been in service for approximately forty years, which is often regarded as the baseline lifetime for these cable systems. In particular, pipe-type cable has seen global production reduced to just one manufacturer in North America causing utilities still using these systems to regard pipe-type cable as a security risk due to the limited diversity of supply. Some utilities still have a significant investment in these systems, and the logistics to design and construct an entirely new system with extruded cable, in particular cross-linked polyethylene (XLPE), takes time and presents a significant cost. With most underground transmission, the civil infrastructure represents 60-80% of the new circuit cost, and the civil construction involves the greatest obstacles for approval. Utilities can realize significant cost savings if the pipe-type cable route and civil infrastructure can be re-used, essentially keeping the same terminal points, retaining the circuit route, and utilizing the installed cable pipe and splice vaults for a new cable system.
Read more Read lessEven if limited modifications are required to accommodate, for example, new configurations of terminations or extending splice vaults, substantial cost savings can be realized, and utilities may benefit by avoiding long delays and costly efforts to permit an entirely new project.
However, retrofitting a pipe-type cable pipe with XLPE-insulated cables presents many challenges that must be addressed. Decommissioning the existing pipe-type cable pressurization equipment can be difficult. Verifying the integrity of the cable pipe to confirm it can receive new cable and support the cable for the anticipated life of the system requires special procedures. Preparing the pipe by cleaning to receive new XLPE cable is also of great concern since there is limited background regarding the impacts of common dielectric liquids on XLPE cable components, in particular the cable jacket; required cleanliness is not well-defined by current industry practice. Cable pipe inspection is an element of a retrofit project, even when considering replacing existing pipe-type cable with new pipe-type cable; facilitating repairs to the cable pipe is far more difficult with power cables inside, so the interval after the old cable is removed but before new cable is introduced is critical to make any repairs that are needed to the existing pipe infrastructure. The ultimate challenge for retrofit is maintaining or improving the existing circuit rating understanding that typical insulation thicknesses for XLPE cable, even when using EHV-grade compounds, are greater than that of paper-insulated cables of the same voltage when considering constraints of installed pipe sizes.
This paper describes and discusses the many challenges to XLPE retrofit applications for pipetype cable and identifies a specific case study where a utility retrofit three existing 115 kV pipetype cable systems with XLPE-insulated cable.
Additional informations
| Publication type | Session Materials |
|---|---|
| Reference | B1_10679_2026 |
| Publication year | |
| Publisher | CIGRE |
| Country | United States of America |
| Study committees | |
| File size | 3 MB |
| Price for non member | 30 € |
| Price for member | 30 € |
Authors
BASCOM III Earle {Rusty} C. - Electrical Consulting Engineers, P.C., United States of America; SMITH Alec - National Grid, United States of America; ASHKOURI Sinan - National Grid, United States of America; WALL Phyllis - National Grid, United States of America; AL-SIBAI Eyad - National Grid, United States of America
Keywords
Transmission - XLPE - Retrofit - Pipe-Type - HPFF - Replacement - Life Cycle
