FOR THE PAST THREE YEARS, BRITISH COLUMBIA TRANSMISSION CORP. (BCTC) has used light detection and ranging (LIDAR) technology to do aerial surveys of the transmission system in British Columbia. This technology allows as-built measurements of the conductor-to-ground and conductor-to-vegetation clearances that are present in an efficient manner.

The conductor position and movement can then be accurately modeled to identify potential encroachments of vegetation that would be experienced under maximum design criteria using line design software. BCTC uses PLS-CADD programming developed by Power Line Systems. A refinement in the PLS-CADD programming has permitted the conductor-to-ground data to be depicted as a series of isolines that represent polygons of equal clearance.

The use of the isoline function in PLS-CADD permits a permanent model to be presented in GIS and used on patrols. This allows areas such as low conductor-to-ground clearance and spans prone to unequal ice loading to be depicted graphically so that they can be reviewed more carefully during regular aerial and ground patrols. Further treatment cycles can be adjusted, taking into account actual growth rates observed in inspections.

These refinements have allowed BCTC to manage vegetation in a more predictable way. BCTC has used the technology on all voltage classes from 69 kV to 500 kV. Given the cost of LIDAR flights, the company has focused primarily on the higher voltage classes because these circuits traverse longer distances over rugged terrain in mountainous British Columbia. In the models, several isolines can be calculated and depicted in the GIS system that can be turned on or off to highlight clearance issues. Many advantages of isoline modeling have become apparent, including:

• Accurate calculation of areas requiring treatment with herbicides allowing for very selective treatments a plus with both the public and regulators.

• Greater ability to develop appropriate compatible uses of the rights of way, such as allowable tree heights in landscaping or Christmas tree farms. In the landscaping of properties on rights of way, the right vegetation in the right place can be determined using the model and working in cooperation with the owner to ensure that vegetation does not become an encroachment problem that must be removed or regularly pruned.

• Allows for better and more accurate understanding of conductor location under load conditions, which ensures that the utility can enforce new NERC regulations on how close vegetation can come to power lines.

BCTC has divided its entire corridor into administrative management units that can be optimized for treatments and monitored year-to-year to observe improvements and efficiencies to its management programs.

For more information contact Thomas Wells, BCTC vegetation program manager, at Thomas.Wells@bctc.com.