Vegetation is a significant source of outages for many utilities. In some regions from one quarter to one half of all outages can be ascribed to vegetation. Vegetation encroachment initiated the massive North American northeastern outage of 2003. It is so critical for utility operations that some utilities have a vice president responsible for vegetation management. It can be costly for utilities to identify areas of high risk vegetation encroachment. Scheduling and routing crews to prune the trees that require attention is often sub-optimal adding to the cost of vegetation management. Optimizing these processes can produce significant benefits in the form of fewer outages and reduced costs. At Distributech 2018 Pedro Lemes, and engineer at Energisa (Brazil) described an innovative project which used high resolution satellite imagery to optimize vegetation management. Energisa is the sixth largest Brazilian power utility with 6.6 million customers.
Vegetation is the source of many outages at Energisa and the budget for vegetation management represents a significant proportion of its operating budget. To reduce the number of outages due to vegetation and the costs of vegetation management, Energisa initiated a project to develop a tool that would allow it to identify and map high risk areas for vegetation encroachment and secondly to optimize routes and crew allocation for tree pruning. The objective of the project was to decrease the number of outages due to vegetation encroachment, reduce vegetation management costs especially third-party firms hired to identify risk areas for vegetation encroachment, reduce the level of risk associated with vegetation near power lines, and to bring more IT into operations at Energisa.
The project innovated in using satellite imagery together with GIS data to solve the problem of identifying high risk areas for vegetation encroachment in a distribution grid. By analyzing satellite imagery it was possible to distinguish vegetation from other objects, to differentiate trees from grass and bushes, measure the height of trees, and using GIS data to measure the distance between trees and poles and cables. Energisa contracted with Airbus Pléiades to provide 50-cm resolution, colour, orthorectified as well as near infrared (NIR) imagery. The contract with Airbus specified that all imagery supplied to Energisa had 15% or less clouds. The imagery enabled identification of vegetation using the RGB and near infrared (NIR) bands. In addition Pleiades provides high-resolution stereo imagery enabling generating digital surface and terrain models. Trees heights could be determined by comparing surface and terrain models. Trees were separated from other vegetation by a minimum height threshold. Even when there were many trees together, it was possible to separately identify individual trees. NDVI (Normalized Difference Vegetation Index) was used to differentiate between vegetation and other objects and to distinguish healthy and diseased trees. Coconut palms were the most challenging because of the lack of a central crown. Energisa's GIS provided the location of line segments, switches, poles and structures. Based on the information derived from the two sources it was possible to calculate the distance between trees and cables and identify high risk areas of vegetation encroachment.
The second part of the project involved developing a pruning management system to optimize pruning. Once the risk areas had been identified, based on the available budget, team locations, the desired level of risk and the cost of pruning a tree, the algorithm was able to determine an optimized route and schedule for pruning operations for each team. The algorithm was sufficiently robust to be able to be applied to a neighbourhood or an entire city.
Nowadays there is a plethora of satellite imagery with resolution as high as a foot and a frequency of several times a day. One company is now imaging the entire landmass of the Earth every day. Satellite imagery is becoming increasingly competitive which is lowering the cost of imagery. Energisa's creative use of satellite imagery and another innovative application that uses satellite-based radar interferometry to detect subsidence, which often can be sourced to a water leak, are two examples demonstrating how satellite imagery can be applied by innovative utilities to improve performance and reduce costs.