Utility providers deploy kilometres long conductors and transmission lines to provide electricity to cities. Their network can consist of thousands of pylons that bridge spans of transmission wires to avoid power loss. Since the transmission lines pass forests, vegetation can grow close to the energised lines. Therefore, utility companies need to design effective vegetation techniques to ensure the safety of their assets and the forest.
Although asset failures resulting from vegetation have become easier to manage, it’s not enough that we discuss management methods in theory. We must venture beyond our textbooks and expand our focus to industry examples to understand how leading utilities used cutting edge technology to prevent them.
Power and Water and their Vegetation Management Plan
In Australia, the Power and Water Corporation designed an Asset Management Plan to control and manage the vegetation in the proximity of their power lines and critical power network facilities located in the Northern Territory. Power and Water framed its rationale into three terms:
- Short Term (0 to 2 years)
Starting detailed maintenance and capital works based on current asset conditions. Plan execution within the current financial year.
- Medium Term (2 to 5 years)
Designing strategies according to performance trends and health indicators in the 2019 to 2024 regulatory period.
- Long term (5 to 10 years)
Conducting qualitative articulation of the expected long-term outcomes in the 2024 to 2029 regulatory period.
Power and Water hires service providers for their vegetation maintenance. However, the northern territory is considered remote and requires significant investment for immobilisation. Service providers are willing to work but at an increased premium. Travel to sites and their accommodations can be up to 1500 km, increasing time and additional cost.
The vegetation work plan is recorded and stored in PowerWater’s ERP software, Maximo. Power and Water also used LiDAR quickly to assess vegetation clearance from their power lines network and designed tree trimming standards.
In urban areas, conductor span lengths are short, with an average of 40m; hence conductor sag and sway is lower. However, in rural areas (Northern Territory), conductor span lengths are about 100m on average, leading to high sag and sway. Therefore, the service providers need to trim the vegetation in less than 12 months.
PowerWater also directed service providers to maintain the following minimum clearance distances for all overhead power lines and poles for all types of conductors to ensure zero instances of vegetation touching the energised power lines to avoid asset failures and power outages. Here are the trimming standards PowerWater use:
|Insulated Low Voltage||0.5m|
|HV Aerial Bundled Cable||1.0m|
The Greek way of taking care of vegetations
Constructing transmission is a work of public interest in Greece as the utility companies use expropriation to acquire land to construct, safely operate and maintain power lines. In 1957, Greece issued tree trimming guidelines before constructing power lines in Cretes and Rhodes.
Hellenic Electricity Distribution Network Operator S.A is responsible for clearing vegetation around power lines.
Even when all trees inside the ROW corridor pose a hazard to power lines, leading to equipment failures. However, authorities excluded olive and fruit trees because their maximum height is lower than the clearance guidelines.
Usually, HEDNO’s personnel, such as linemen, trim the trees as they are familiar with working around transmission lines. However, HEDNO also hires external contractors when additional equipment is required to clear vegetation to avoid asset failures.
In Greece, the Government or HEDNO does not own the trees. If trimming leads to the tree’s death, the owner is compensated.
The Greek law also requires utility providers to clear all vegetation from connection points to minimise the risk of wildfires in the fire danger period from May to October. Clearing large areas is assigned to external contractors, such as in Crete and Rhodes which have 287 and 117 towers (terminal, transpositional, and tension) respectively.
Greece takes exceptional care of forests as well as private and agricultural land by banning the use of herbicides to get rid of vegetation to avoid electrical equipment failures. Therefore, most work happens through manual labour as workers use grass cutters and pickaxes. Manual labour is slow, and the time taken to restore power results in lost revenue.
The Greeks designed the tree trimming guidelines for the environment, not utility companies. As a result, utility providers must bear high costs and risks while clearing vegetation around the transmission system.
BC Hydro get help from helicopters
British Columbia Hydro has 18,000 circuit kilometres of transmission lines, which range from 69 kV to 500 kV, with generating capacity of 11,500MW. However, to keep things safe for their crews and assets, BC Hydro required estimations or field measurements of trees to understand how much they would have to compromise on their clearance zone if a tree fell to ensure no equipment failures.
BC Hydro decided to combine two technologies; LiDAR and PLS-CADD.
Since 1995, BC Hydro has been using Power Line Systems’ computer program to identify vegetation around their conductor clearance thresholds.
Vegetation management field personnel now had to work from the ground and take helicopters equipped with LiDAR scanners to scan their clearance lines.
BC Hydro approached Power Line Systems in late 2002. It requested a new management program to design better PLS-CADD features, exclusively used to conduct vegetation clearance analysis by utilising the vegetation points supplied by LiDAR scanners. After vegetation experts from both sides discussed the possibilities, both companies agreed that PLS-CADD could include the following abilities:
- Identifying grow-in vegetation violations.
- Identifying trees that could compromise clearance lines if they fall.
- Presenting the above two results in an easily understandable manner for field crews.
Power Line Systems designed these new features for BC Hydro as part of their PLS-CADD. During testing, BC Hydro assumed that they could simply merge the LiDAR vegetation data with the new features and conduct a vegetation clearance analysis. It worked perfectly for small sections, but the LiDAR data overwhelmed their computer’s memory for longer lengths, causing the system to crash.
Afterwards, BC Hydro decided to collaborate with Terra Remote Sensing, its LiDAR supplier, to reduce the data volume to make it manageable for PLS-CADD while retaining accurate essential points of the vegetation canopy. TRS decided to remove all vegetation points that were lower than 1.0m.
BC Hydro also upgraded the RAM of their computer for better asset performance management before combining the new LiDAR data with PLS-CADD to run their desired vegetation clearance analyses without crashes.
The combination of LiDAR/PLS-CADD gave more reliable, economical and safer vegetation management to BC Hydro by eliminating human errors.
Effective vegetation management is a critical success factor for all utility providers. Apline’s Aptimize can easily integrate datasets including LiDAR and satellite imagery to give you a clear picture of what’s growing around your power lines and when you need to trim the trees to keep everyone safe.