In the past year Transpower achieved its lowest rate of sulphur hexafluoride (SF6) emissions. The absolute weight of gas lost to the atmosphere was also an all-time low.
The gas, used globally in high-voltage circuit breakers and switch gear, has unique electrical insulation and arc interruption properties. But its global warming potential is 22,800 times that of carbon dioxide.
SF6 emissions are the single largest contributor to Transpower’s total carbon footprint – 49 per cent in the year ended June 30, 2014.
Transpower is trialling development of alternatives to the use of SF6 in its equipment. But in the meantime it is working to reduce leaks from its equipment and handling errors.
The company established an SF6 reduction working group in 2005. Since then it has reduced its SF6 emissions to the equivalent of 4.93 tonnes of CO2, a 21.6 per cent reduction.
Emissions have fallen every year and last year reached 0.48 per cent of Transpower’s total installed capacity, an all-time low and less than the targeted 0.8 per cent. Absolute emissions were also an all-time low at 216 kg.
Transpower has reduced its emissions despite the increased quantities of SF6 in the company’s equipment.
This has been achieved through on-going development of a range of techniques, including the use of an SF6 camera to identify leaks early and more accurate testing and storage devices, and having replacement components readily available for prompt repairs.
The company ensures competency training of personnel handing SF6 gas, has improved its specifications and has worked with manufacturers to improve SF6 sealing in its equipment.
Additionally, Transpower and its contractors have developed improved procedures and equipment that minimises the potential for SF6 handling losses when certain procedures are carried out.
The main causes of leaks are poor equipment design and assembly and premature ageing of seals due to New Zealand’s harsh environment.
Transpower now prioritises the rapid repair of circuit breaker leaks and aims to replace or repair any leaking units before their fourth top-up of SF6. That programme not only reduces emissions, but it has also improved safety, reliability and cost effectiveness by reducing repeat visits and the number of outages.
Transpower says equipment makers are developing circuit breakers with a vacuum interrupter or with CO2 as an alternative to SF6, but currently only at lower voltages.
In 2013 Transpower installed one of the first 66 kV vacuum circuit breakers at its Islington substation as a trial of the technology.
The Environmental Initiative of the Year award category is sponsored by Transfield Worley Power Services