by Mike Rycroft, Now Media
Cigré, an international professional organisation which focuses on the generation, transmission and distribution of electricity, held its local colloquium recently. A feedback session on the activities of the local activity groups was held on 13 February 2020.
The organisation’s activities are run by study committees, (SC) each of which takes responsibility for a particular aspect. On a national basis, the study committees form regional activity groups (RAGs) to handle items under discussion. SCB2 (overhead lines) and SCD1 (materials and emerging test technologies) recently held a joint colloquium in India, which was attended by local SC B2 and D1 representatives.
Study committee B2 (SCB2)
Cigre South Africa has four active SCB2 working groups. The SC originally covered transmission lines only but has now been expanded to cover distribution lines as well, to fit in with the association’s end-to-end approach.
The technical direction of SCB2 at the moment is:
- Increasing the ampacity of existing lines
- Ensuring reliable lines, improving the reliability of existing lines
- Ensuring environmentally compatible lines
- Assessment of the condition of lines, methods, new tools and materials
- Assessment of the effect of climate change on the network
Presentations and discussions at the colloquium fell into three groups: Design optimisation and new lines; reliability, economics and maintenance; and new materials and products for use on overhead lines.
Topics of particular interest were:
Modern aspects of line design optimisation (deterministic and probabilistic design methods), comparison and experiences. The use of high temperature, low-sag conductors (HTLS) in re-conductored routes, the use of dynamic line ratings in mixed lines, the use of sectional steel poles instead of towers, and the use of fibre-reinforced polymer poles. Tower design remains a lively topic in spite of many years of experience. There is an interest in extending the life of towers by the use of coatings.
In addition to the above concerns is the issue of vandalism and theft, which is prevalent in many developing countries. A study in India on demographics of theft found that mainly young people were involved. A programme in India to pay local communities to protect infrastructure has proved successful.
Unmanned aerial vehicles (UAVs)
There is strong interest in the use of UAVs for inspection of overhead lines. However, many people are unaware of the limitations of such vehicles. There are currently no standards or common procedures and the biggest problem is in analysing the data obtained using UAVs and processing it to get meaningful results.
A Cigré working group (WG), set up to study the subject, is collecting data from members who are using UAVs. The goal is to establish the state of the technology, and to determine what can be reasonably achieved by using them. UAVs tend to be used in distribution networks rather than transmission networks, as there are more distribution networks.
Structures and conductors
Some countries are using fibre composite poles for both distribution and transmission. Sweden for instance, and Australia are using recycled materials in composite poles.
A major concern is the use of bare conductors in overhead lines in countries subject to bush fires. Concern about fire ignition from overhead line conductors is widespread in California, Australia and even Canada. Probability of ignition is normally low (1,5%) but under certain weather conditions can be greater than 30%. Some countries are moving to aerial bundled cable (ABC) for MV and LV distribution.
Affordable overhead lines for Africa remains a concern. Many networks are donor-provided and the standards used are those of the donor country, which leads to a multiplicity of different standards and incompatible networks.
Study committee D1 (SCD1)
The technical focus for SCD1 is:
- Materials and emerging technologies
- Diagnostic techniques and emerging test techniques.
- All insulation types including gas, liquid and solid materials.
The current focus is on:
- Testing monitoring and diagnostics
- Functional properties and degradation of insulation material
- Insulation systems of advanced components
The technical direction of SCD1 ensures that their activities cut across the activities of all other SCs.
Specific items under investigation are:
- Dissolved gas analysis (DGA) in transformers. This is receiving serious attention as present methods appear to be unsatisfactory. DGA is the only non-destructive test that gives the utility access to the supplier under warranty period.
- Solid insulation ageing markers (field experience)
- Functional properties of modern insulating liquids for transformers
- Solid state sensors and chemical measurement of moisture
- Testing methods for wood and composite poles. New testing methods are available that do not require destruction or boring into pole. The WG is to produce TB on the subject.
- Nanomaterials: Research at the University of the Witwatersrand is underway concerning the use of nanomaterials in electrical insulation. Tests have shown that the inclusion of nanomaterials into solid and liquid insulation improves the insulating properties, resulting in the full-scale deployment of nanocomposite insulation technologies. Nanomaterials are being considered as a replacement for crosslinked insulation technology in HV cables.
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