In Hong Kong, everything that touches upon the reliability of electricity supply is usually a matter of great public interest. Over half of the several million people living in the multitude of high-rise buildings one finds across Kowloon and Hong Kong Island occupy apartments located higher than the 15th floor. This means that any disturbance of electricity effectively prevents a great many people from leaving or returning to their homes. As a result, one of the top priorities at the territory’s major electricity supplier – CLP Power – has been doing whatever is necessary to ensure uninterrupted power supply. For example, one of the recent past investment efforts towards this goal was a program of installing line arresters on many of the exposed towers along the utility’s 132 kV and 400 kV overhead networks. CLP Power has also begun employing more effective maintenance strategies so that higher pollution levels being experienced in Hong Kong do not result in outages triggered by insulator flashover.This past INMR article discussed the various considerations involved in CLP Power’s decision to adopt helicopter washing as a major maintenance tool for insulators.
The process of finding a better way to clean insulators on the CLP overhead network began about 15 years ago. At the time, the area’s growing pollution problem had already come to be viewed with concern even though its severity was less than at present. This pollution comes not only from the sea but also includes airborne ash from nearby coal-fired power plants in China as well as factory emissions originating from the heavily-industrialized south-eastern Provinces. Outages triggered by pollution have been a recurrent problem on Chinese power networks, including in nearby Shenzhen, and have been a major factor in the growing application of composite insulators in that country.
At CLP Power, however, which relies almost exclusively on glass and porcelain for its HV lines, replacing existing insulation with composite types was not considered economically feasible. On top of this, engineers apparently still had reservations about the long-term performance of such insulators – all the more so since the utility once experienced a brittle fracture failure of a composite line post.
Therefore, washing insulators was still regarded as the preferred method to deal with the growing pollution problem. The major issue to resolve was whether or not this work could now be done more efficiently by using helicopters. Evaluating the possible use of helicopters for washing of insulators was made all the more important since it coincided with a growing interest at CLP Power to increasingly rely on helicopters for conducting other maintenance activities such as replacing spacers and dampers or for carrying out periodic line inspections.
According to the former Team Leader for this assessment program, the evaluation process included several steps, beginning with visits to a number of Australian utilities which had experience with helicopter-based washing of insulators. This was followed up by collecting relevant background information on the subject from the Helicopter Association (HAI) – an international organization representing helicopter manufacturers, operators and utility users.
Alternative business justification models were then considered by the Assessment Team from the point of view of the comparative costs of helicopter versus ground-based cleaning of insulators. Up until then, insulator cleaning at CLP Power involved truck-based maintenance crews climbing towers and cleaning insulators on de-energized circuits by hand. Due to the dense mountainous terrain, these workers were often forced to walk long distances carrying cleaning equipment and supplies. This process was not always productive because of issues of fatigue and occasional injuries to personnel from dog bite and bee sting.
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