Safety and reliability of overhead lines
Overhead lines transmit electricity from production center up to the customers.
Overhead line activities
With 25 active Working Groups, Study Committee B2 covers the electrical performance, mechanical behavior and asset management of overhead lines, namely conductors and fittings, towers, foundations, and insulators. New working groups have been launched since the beginning of this year or will be launched soon to address the increased awareness as to the safety of the workers on overhead lines, guidelines for long span crossings, transition facilities between underground and overhead lines as well as corona discharges during rain and its environmental effects to lessen its nuisance effect.
Guidelines for Safety of Overhead Line Construction, Maintenance & Operations
There is a growing expectation to ensure a safe work environment for workers, driven by a combination of economic benefits, legislative compliance, and community values. The design of new transmission line assets should generally consider safe working practices that can be adopted throughout the life of the assets (construction, maintenance and even demolition). On the other hand, existing assets may lack the same measures and require modifications to ensure safety before undertaking routine or corrective maintenance.
Some examples of safety issues that can be encountered are:
- Hazard associated with new technologies/work methods for construction/maintenance (e.g., helicopter methods, drones)
- Installation and commissioning new lines parallel to existing energised lines (electric shock due to induction or proximity to live parts)
- Unstable soil conditions that may lead to collapse of excavations or de-stabilise machines (cranes, elevated work platform vehicles)
- Climbing constraints on older assets not compliant with current personnel access/fall arrest loading criteria
- Working at heights
- Design structures for safety (to eliminate or control hazards)
WG B2.88 began its work at the beginning of this year and its objective is not to develop design/construction engineer or work supervisor into safety specialists, but rather ensure these front-line persons have the awareness, tools and understanding to ensure risks are minimised.
The work will be undertaken in two stages:
- Part 1: Identification of construction/maintenance work hazards/risks
- Part 2: Evaluation of current safety control management practices & recommended guidelines for improved practice
Overhead line long spans and crossings: Design practices and field experience
Although there are numerous long spans in the world, there seems to be a lack of literature that delves into the different design practices and experiences surrounding these spans. Therefore, creating a document that summarizes the various practices and experiences from around the world will allow designers to gain a deeper understanding of the various approaches that can be taken when designing long crossings. This can help them make informed decisions and avoid potential pitfalls that may arise during the design process.
This Working Group is planned to begin its activities next Fall and its aim will be to:
About design:
- Provide guidelines for long crossings with extreme tension, including guidelines for vibration damping and an overview of different vibration damping methods used as well as design considerations for dampers and conductor fittings.
- Examine possible capacity problems, conductor types used, conductor lengths, use of mid-span joints, and conductor design.
About follow-up:
- Provide an overview of inspection methods and intervals as well as maintenance methods used.
- Offer an overview of the expected conductor lifetime.
- Provide recommendations for revitalization (restringing) and prolonging the lifetime of spans.
- Identify sensors and instruments to improve the monitoring of long crossings.
Transition facilities between overhead and underground lines
Many new development networks include underground sections to make the grids compatible with special environmental requests and social demands, close urban areas and their growth, and other facilities; obtain authorizations for the use of new rights-of-way; facilitate their connection to gas insulated substations, etc.
On the other hand, modifications of the existing networks to underground one or more sections of their overhead circuits are also quite frequent, since grid owners must adapt and make them compatible with other developments, land uses and special social claims and needs.
These mixed lines (overhead and underground) have a particular component which deserves special attention: the transition facility which are the meeting point of two network realms, overhead lines and underground cables. The transition facility often suffers from a lack of coordination.
This joint working group between B1 (Insulated cables) and B2 (Overhead lines) will start its activities this Summer and will encompass design, construction and environmental, social and safety issues, leaving maintenance and network operation for a subsequent working group that will start once this one has finished. It will take into consideration inputs from study committees B3 (Substations and electrical installations) and C4 (Power system technical performance), and its technical brochure will contain a detailed description of the transition facilities from a comprehensive point of view, best practices, recommendations, experiences, examples of real facilities and references.
Corona Discharge and its Environmental effects of HV AC and DC Overhead Transmission Lines During Rain
The environmental effects generated by the corona discharge of overhead power lines, especially the audible noise, has become a key factor that restricts the design of power lines. Corona discharge is closely related to weather conditions and rain is the most influential factor.
As the voltage level continues to increase, it is necessary to study corona discharge and its environmental effects of AC and DC overhead power lines during rain and in fair conditions. In the past ten years, great progress has been made in this area. Therefore, it is necessary to summarize the latest research results from various countries.
WG B2.89 proposes to figure out the different AC and DC corona phenomena during rain compared to fair weather conditions, clarify the degree of the variation, and update the existing formulae for predicting audible noise and radio interference, which will provide basic technical support for the development of environmentally friendly overhead power lines.
The work will be coordinated with the WG B2.83 “Mitigation of induced noises by corona activity in overhead AC and DC lines”, which analyzes the different alternatives to reduce audible noise. This new proposal is more detailed and focuses on the corona discharge at different rain conditions comparing it to fair weather conditions. In addition to the audible noise, it also pays attention to corona loss and radio interference.