TRANSMISSION AND DISTRIBUTION

Structure Lifting System Allows Upgrading of Lines While Energized

Since its development in 1996, 13 utilities in Canada and the United States have used the lifting system to raise tangent structures an additional 3 to 20 feet on thousands of poles, thus increasing ground line clearances and line capacity without taking the line out of service.

The lifting system underwent extensive testing with the help of Public Service Company of New Mexico (PNM) in Albuquerque, NM in 1997. PNM has since employed the system in upgrading 300 miles of 345kV line and 170 miles of 230kV line. Additional plans are under way to raise their 115kV H-frame lines as well.

TransAlta Corporation raised thirty-five 230 kV H-frames and several 161 kV single pole structures an additional 6 feet in 1999. Upgrading the lines while energized allowed crews to work safely and quickly, completing an average of 2.5 structures per day without interruption of service.

The system can cost 50 per cent less than the cost of installing taller poles and less than 25 per cent of complete structure replacement. In addition to the material cost savings, utilities have realized considerable savings by keeping the lines in service during installation. A recent 345kV structure lifting project for Central Maine Power is estimated to have saved the utility more than 50 million dollars during the project because the line was kept in service. Now with the additional line clearance, the capacity is increased, generating more revenue from the line. The utility claims "a very short pay back on our capital investment."

The structure lifting system uses a patented procedure and materials in which steel members are driven next to or bolted to the existing poles. The poles are cut completely through and the structure is lifted using hydraulic cylinders attached to the poles above and below the cut.

After the structure is raised to the desired height (from 3 to 20 feet), cross bolts are installed to permanently secure the steel members to the poles. Protective shields are then installed to cover the gap between pole ends.

The lifting system is available in three configurations which can either:

• raise the structure;
• raise and reinforce; or
• raise, reinforce and reclassify.

As already strained American and Canadian power grids become increasingly overburdened, the need for increased capacity will increase dramatically. This structure lifting system is sure to play a significant role in strengthening the grid and helping utilities bring their lines up to code safely and efficiently.