Transmission Corridor Management Part III

This is the third edition of our series on transmission corridor management using LIDAR.As detailed in the first two articles, transmission corridor management comprises a number of tasks. The two that are of particular interest to LIDAR operators are Line Rerating and Vegetation management.

Line rerating is the process of analyzing existing transmission lines with respect to the amount of current the line can carry under certain ambient conditions (primarily temperature). The rerating may indicate that a line can carry less or more current than its original (build-to) design capacity. Lowering the rating is obviously a safety issue. Increasing the rating (the real desire of the transmission line operator) allows the operator to service a heavier load without building out new lines. The majority of line rerating analysis is performed using a product called PLS-CADD from Madison, Wisconsin-based Power Line Systems.

Transmission Vegetation Management (TVM) is the process of controlling the hazards of lines touching or arcing over to objects that would cause a fault. This is primarily vegetation or the ground. The general idea is to measure existing vegetation as well as line location and model so-called grow-in and fall-in vegetation. This information is passed on to a vegetation management function of the transmission line operator (either in-house or out sourced). The process is governed by NERC FAC-003. The FAC requires a dynamic model in which the line is swung through its physical limits for analyzing behavior in high wind conditions (termed blowout).

The LIDAR industry was energized (pun intended) by the now widely cited NERC Alert of 7 October 2010. It is important to note that the NERC Alert does not mandate the use of LIDAR. However, the fact that it is cited will drive a lot of transmission line owner/operators toward this solution since non-compliance carries stiff financial penalties.

This presents two areas of opportunity for LIDAR collection and processing companies. While it should be obvious that line rerating and vegetation management use much the same data, we are told by companies already doing this sort of work that they tend to still be treated separately by the transmission line owner/operators.

Lets first consider TVM. The general idea is that the transmission line owner/operator or a contractor receives data, on a cyclic basis (i.e. annually), that provides sufficient information for their TVM program. Quite interestingly, there is no industry best practices nor data exchange specifications for the data content passed from the LIDAR processor to the transmission vegetation management system. The data exchange is typically negotiated on a contract by contract basis.

The minimum information needed for TVM are simply geocoded polygons that indicate the vegetation areas that must be remediated. One level above this are data sets containing other hazards such as ground and structures (e.g. buildings in the right of way). Beyond this (and really outside the scope of TVM) are hazards from crossing wires (e.g. other wires crossing through the right of way (inferring the heights of vehicles that might traverse the road/rails/rivers).

A TVM program that uses a computerized dispatch system (as opposed to simple electronic documents graphically indicating hazards) will generally accept a richer input data set. This set can include polygons that contain extended attributes such as biomass estimates, wire locations, ortho photos, tower locations and so forth.

The ideal opportunity for LIDAR operators is to establish long term relationships with transmission line operators. We have seen several LIDAR operators offering services priced on a per right of way corridor mile that are five year subscription services that deliver annual data. These sorts of arrangements should reduce the cost both to the LIDAR provider as well as the transmission line operator. That said, the transmission line operators should be extremely careful to avoid proprietary solutions. This is a rapidly evolving technology and where certain functions will land in the cost optimized systems is yet to be determined. GeoCue Corporation has initiated work to draft an open specification to make it easier to identify the data types and formats for exchange and prevent vendor lock-in.

In the next edition, we will explore some of the details of collecting and processing LIDAR data for TVM