PCC staff regularly contribute to industry conferences. Recently published technical papers are provided here.
We thank the Electricity Engineers' Association (EEA) for approval to publish papers presented at their conferences.
Mike Boardman, Dave Elder, EEA 2013
Historically, transmission towers were only climbed to repair or replace hardware or light members.
In recent years, formal condition assessment programmes have been introduced, whereby towers are climbed and inspected on an8 yearly cycle. This increased the amount of tower climbing considerably but it was not until tower painting of the galvanized lattice steel towers started in earnest in the mid 1990s that the numbers of workers on towers grew enormously.
The tower painting process includes a number of climbing operations including the initial assessment for painting, a number of quality assurance inspections, a final practical completion inspection and future defect liability inspections. Some of these inspections could be carried out using unmanned aerial vehicles (UAVs)
Unmanned aerial vehicles or drones have been developing in the last few years at an exponential rate. In the case of electric propulsion vehicles the advent of lighter lithium polymer power packs has helped increase payload sizes and flight duration.
The selection process for a suitable platform and accompanying recording/image capture equipment for the intended role was in itself an exhaustive exercise. Some of the aspects that were considered included the equipment cost, availability, durability, payload capacity and power consumption/flight duration.
There is a large number of helicopter type UAVs in operation around the world, with numerous configurations from single rotor (traditional helicopter style) through to multiple (up to 9) rotor platforms. The flight control systems range from a simple radio control through to complex multi facet arrangements with GPS, navigation and autonomous flight capability.
With the development of UAVs, aviation regulatory authorities have difficulty keeping up. Whilst there are no formal requirements in place currently, the company decided that working with the New Zealand Civil Aviation Authority (CAA) was essential, however it was an arduous task to finally obtain CAA approval.
Several examples of condition assessment survey work were carried out using the Cyberquad on transmission structures. There are considerable benefits of having a platform Operator (Pilot) and payload Operator who are both qualified inspectors and condition assessment specialists with many years industry experience.
Wal Marshall, EEA 2011
This paper examines the problems with the dual lanyard attachment method, and explains why permanent wire type fall-arrest systems have much better safety outcomes.
Wal Marshall, EEA 2000
To a background of change internationally, and increasing attention from OSH, the industry is re-examining the safety of traditional free climbing of power line structures.
Of the available attachment methods for towers, trials show the dual lanyard technique is the most practical. However this method comes with some significant disadvantages, not the least of which is an increased injury hazard due to added complexity.
A detailed study has shown there are no known cases of a properly trained line worker falling from a tower while using permanent climbing steps, over an estimated 3.3 million structure ascents. This makes the climb / descend process an extraordinary safe work activity. It also introduces the great difficulty that any change to current practice may impact adversely.
However falls are continuing to occur during “positioning” on the structure, and when attaching at the work position.
Therefore a partial attachment policy with the following general characteristics has been recommended for transmission line towers:
- Climbing workers to be fully trained and tested for competency.
- Workers not climbing or descending on permanent climbing steps, to be attached at all times when above 3m from ground level.
- Prior to free climbing, a risk assessment process is to be followed to determine if there are special circumstances, which elevate climbing fall risk. If the risk is significantly higher than normal, attachment would then be mandatory.
The position with regards to climbing poles is to be the subject of a separate EEA study.
Wal Marshall, EEA 2009
During 2008 the author was engaged by the Icelandic Consulting company Efla to act as consultant for a condition assessment trial project on a 220 kV transmission line in Iceland. The trial project was jointly funded by the Icelandic transmission company Landsnett, and the Norwegian national grid transmission company Statnett.
The objective of the work was to:
- Introduce a detailed condition assessment methodology to the two client companies and trial it on an actual line.
- Undertake a predictive modelling analysis on the results to see what the future work and cost profile was for the line.
The work was undertaken from October to November 2008. The author travelled to Iceland to help set up the trial and brief Landsnett and Statnett engineers. A final report was completed late December 2008.
Wal Marshall, EEA 2008
Part A of this paper examines the ability of preservative injection systems to increase the service life of driven timber piles.
Part B of this paper looks at methods to achieve a bond between the external and internal earthing systems.
Mike Boardman, EEA 2008
The World Corrosion Organisation (WCO) places the worldwide annual cost of corrosion at US$1.8 trillion per annum, some 3% of the world’s GDP. The estimated cost of corrosion in the United States electrical power industry in 1998 was US$15.4 billion, representing about 7.9% of the cost of electricity to their consumers.
About 20% or US$3 billion of the corrosion costs were considered avoidable.
Whilst the issue of corrosion is generally understood within New Zealand industry, it is often disregarded or acknowledged to be an inherent problem with metals generally. If the avoidable cost of corrosion is established throughout the electricity industry it would help the participants to better manage their assets and benefit from longer-term cost savings.
Wal Marshall, Mike Boardman, EEA 2009
New Zealand’s transmission and distribution system relies heavily on line and substation support structures constructed using millions of tonnes of hot dipped galvanized steel. It collectively represents an industry investment worth billions of dollars. All this investment has a finite life before rusting sets in. With the average asset age now exceeding 40 years and some structures over 80 years old, zinc protection applied decades ago is now heavily depleted in many locations.
Every day hundreds of kilograms of galvanising corrodes away and is not replaced. Obviously this cannot continue forever and eventually these assets will have to be maintained or, they will have to be replaced. Either way, maintenance is set to become a growing and costly issue for the industry and a ramping up of maintenance and/or capital replacement budgets to cope is already inevitable unless reliability is to decline.
In considering the maintenance of galvanised structures, the industry has essentially three choices: It can maintain proactively, it can maintain reactively or it can replace. Depending on the circumstances of particular assets, each option has its proper place. The challenge facing the industry is to ensure that its asset management selects the correct choice for each situation. Unfortunately this rarely happens and the outcome is usually higher long-term costs; much higher in many cases.
The objective of this paper is to show that for most assets, the proactive maintenance option produces by far the lowest long-term cost; yet this is the least adopted option. This paper asks why that is and whether the industry should be adopting a more coordinated approach given the very large and growing sums involved.
Wal Marshall, Presentation to Iceland Grid Co 2009
The presentation examines the New Zealand experience of managing the maintenance of transmission lines using condition assessment and computer data analysis.
As lines age they not only deteriorate but become increasingly diverse in condition and construction, and the task of managing maintenance becomes evermore complex.
Maintenance must be able to manage diversity; detailed condition-assessment data is essential to enable sound forward planning in diverse systems without loss of reliability.
A computerised line model can give you a view of where you are going, and the costs, allow you to optimize your maintenance management to achieve the reliability and cost targets you want, allow you to value your assets consistently, and plan future resourcing.