Power Line Modelling

POWER LINE MODELLING

Growth and an increasing dependence on power means continuing development in power generation and distribution is a necessity. Distributing power to more places and in higher volumes involves lengthy design measures and massive investment. At the outset of a new route design or line upgrade project accurate topographical data is extremely important in ensuring the design provides for the highest efficiency. While each individual project will have varying requirements the common issue remains how to capture data over often expansive areas in a timely manner.

LiDAR
The swath width for a single LiDAR pass is determined by the flying height and scan settings. For modelling an existing line it is beneficial to fly lower to achieve reflections of the conductors, so the swath width will be in the order of 100m to 200m. For a proposed route flying higher allows a swath width anywhere from 400m to 2,500m across. The wider swath enables sufficient terrain data to aid the design of access roads or allow for variations and making improvements in the proposed route.

The RGB imagery captured with the integrated digital camera is developed into 8 bit per channel Tiff format images and using the POS data and LiDAR ground points is rectified to produce high resolution orthophotography.

Products
The primary objective of the LiDAR survey is to generate a digital terrain model (DTM) with sufficient point density and accuracy. A common specification might be an absolute vertical accuracy of +/- 0.15m (1 sigma confidence, clear even ground areas) and point density of 1pt/sqm (clear areas). From the DTM further products can be generated, including a grid DTM or DEM, a TIN or contours. The data is then supplied in a file format suitable for import directly into CAD, GIS or dedicated line design software. Wide area or localised calculations can be made including the generation of cross-sections, while 3D visualisation and view-shed analysis can be undertaken by integrating the above-ground data and orthophotography.

Applications
NZ Aerial Mapping has undertaken both existing line and proposed route surveys with extremely positive results. Using their Optech sensor relative vertical accuracies of +/- 0.05m (1 sigma confidence) have been consistently achieved and absolute accuracies of up to +/- 0.1m. The surveys have been over a range of environments including steep, bush covered land often inaccessible by foot which has further demonstrated LiDAR to be superior to alternative data collection techniques, such as ground survey or photogrammetric mapping.

For existing line surveys it is important to measure the climatic conditions during LiDAR acquisition, predominantly temperature, air pressure and wind characteristics which all have an affect on the conductor's catenary. Modelling the catenary more precisely means more informed assessment of the suitability of current span lengths and the design of higher or newly located poles or towers. The survey will also help identify situations where there is new vegetation encroachment or insufficient terrain clearance possibly caused by gradual changes in pole location.

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