On the morning of March 20, 2006 cyclone Larry crossed the coastline of tropical Far North Queensland, Australia. The eye of the cyclone passed directly over the township of Innisfail, traveling west. Although the 8000 residents of Innisfail have experienced tropical cyclones before, it was reported that Larry was the most severe cyclone to hit the coast of Queensland since 1931. Figure 1 shows the path of Cyclone Larry.

While the devastation to northeast coastal communities caused by Tropical Cyclone Larry remains deeply etched in the minds of all Australians, the disaster was proof of Powerlink Queensland's capability and efficiency in restoring its transmission network, along with the commitment and expertise of the staff.

The intensity of the cyclonic winds battered the township and the countryside over an area extending hundreds of kilometers in all directions. Wind speeds were reported in excess of 220 km/h (137 mph) with gusts exceeding 300 km/h (186 mph), leaving in its wake a trail of destroyed homes and buildings, flattened crops, stripped vegetation and damaged infrastructure. The scene confronting Powerlink's emergency manager on the following day was overwhelming devastation.

DAMAGE TO THE TRANSMISSION NETWORK

The cyclone's effect on the electricity network began to register at around 5 a.m., when the high winds and flying debris forced the first of Powerlink's 132-kV lines out of service. In a sequence of trips on the 132-kV network, bulk electricity supply was cut to Cardwell, Tully, Innisfail, Kareeya and Kamerunga substations. Figure 2 shows Powerlink's 275-kV and 132-kV transmission network in North Queensland.

Despite the network performing to design, in the cyclone aftermath, seven 132-kV transmission lines, spanning more than 300 km (186 miles), were out of service. These were mostly double-circuit transmission lines where both circuits had tripped due to wind-carried vegetation and fallen trees, particularly where the lines passed through World Heritage rainforests. In that locale, five high-voltage substations were out of service as the cyclonic winds had totally collapsed five steel transmission towers and badly damaged another two towers (Fig. 3).

This damage was the worst ever sustained by Powerlink's transmission network. Fortunately, there was no substantial damage to the high-voltage substations, with supervisory control and data acquisition (SCADA) operating normally from all but one of the substations directly after the cyclone.

Where tower failures had occurred, there was extensive damage to the ACSR conductors. The aluminum strands were cut mainly due to abrasion against tower steel work, but the steel strands remained intact, a factor that may have prevented the possible cascade failure of additional towers.

Due to the damage to Powerlink's transmission network and very extensive damage to the local distribution network, more than 140,000 customers in the area stretching 200 km (124 miles) along the coast and up to 60 km (37 miles) inland were without power supply.

EMERGENCY MANAGEMENT RESPONSE

In preparation for the cyclone's potential impact, Powerlink's Corporate Emergency Management Team was mobilized, placing field crews on standby and establishing communication channels with outside agencies. Following the cyclone, Powerlink's emergency manager's first actions were to oversee the assessment of network damage and the extent of power interruptions to customers, as well as verify the safety and well-being of all staff in the area.

It was critical that the electricity supply be restored quickly to the devastated areas to power essential services such as water supply and sewerage, and to facilitate the cyclone-relief efforts. Together with Ergon Energy, the local electricity distributor, and Powerlink's maintenance-services provider in regional Queensland, the emergency-management plans were immediately implemented. Thus began a highly coordinated restoration effort to return the electricity network to service.

On the afternoon after the cyclone hit, once the extent of the damage and the impact on customers were realized, Powerlink's emergency and corporate communication managers relocated to Cairns. This provided a local base from which to manage the response to the emergency situation, liaise with key agencies and stakeholders, and manage the communication with affected communities.

Transmission line field crews from across Queensland were quickly transported to the affected areas to assess the damage, diagnose the problems and begin on-ground works, working all the while in very wet conditions. Faced with poor visibility due to low clouds, heavy rain and local flooding that prevented inspection by helicopter or vehicle, crews were forced, at times, to resort to entering the Wet Tropics Rainforest on foot to assess and repair the damage to the transmission lines. From dawn until dusk, they undertook the difficult and painstaking task of inspecting some 800 transmission towers and 300 km of transmission line to locate and remove cyclone-carried debris and fallen trees, and to repair broken phase and earth conductors.

Behind the scenes, Powerlink's operational staff coordinated the switching and earthing of the faulted lines and substations so that work could proceed safely. They also commenced planning the progressive safe restoration to service of the transmission lines and substations following completion of repairs.

By the second day, two transmission lines along the more easily accessible coastal plains had been returned to service enabling power to be restored to four substations and helping to restore supplies to the cyclone-devastated communities. Restoration of supply to the fifth substation, at Innisfail, took a further two days, as both 132-kV transmission lines supplying Innisfail had collapsed transmission towers

AIRLIFT REDUCES RESTORATION TIME

One of the 132-kV transmission lines supplying Innisfail had a collapsed tower in a flooded cane field near Babinda. After considering options such as a temporary wood-pole diversion or erecting Lindsey emergency-restoration towers, it was decided to use a fully erected spare lattice steel tower available in Townsville, 200 km from Babinda, as the tower foundations were still serviceable. Transmission crews from Brisbane, 1600 km (995 miles) away, were relocated to Townsville and Babinda to undertake the repair work.

The relentless wet weather made ground work difficult, and flooded rivers blocked road transport of the spare transmission tower from Townsville. Faced with these obstacles, Powerlink worked through the multi-agency Counter Disaster Committee to obtain assistance from the Australian Defence Force to airlift the tower from Townsville to Babinda. A Defence Force Chinook helicopter transported the 32-m (105-ft) high, 4-ton steel tower in just 1.5 hours (Fig. 4).

Providing heavy-vehicle access to the failed tower site also posed a logistical challenge as the tower position was a water-logged cane field, some 400 m (1310 ft) from an all-weather road. Working again through the Counter Disaster Committee, the State Department of Main Roads constructed a suitable heavy-vehicle temporary-access track using 2000 tons of gravel, which allowed the required 48-ton crane to cross the flooded field to erect the replacement tower. This replacement tower was delivered to the site three days after the cyclone, and on day four, Powerlink staff erected the tower onto the straightened stubs, completed the fit out and reinstatement of the conductors, and re-energized the line. This was the first time Powerlink had used a helicopter to transport a complete tower in these conditions, and it was a very successful operation. More importantly, it enabled the restoration of bulk electricity supply to Innisfail quickly by avoiding the delays that would have been caused by road transport attempting to navigate flooded rivers and roads.

Bulk electricity supply had been fully restored to the cyclone-devastated communities of Far North Queensland within five days. Only one 132-kV line remained out of service: the Kareeya to Innisfail circuit, an aged line that had sustained severe damage, including four collapsed towers and further damage deep within a rugged rain-forested region where access by field crews was still not possible.

SECOND-PHASE RESTORATION EFFORT

With the bulk electricity supply restored to Innisfail, after replacement of the collapsed tower at Babinda, the Innisfail area was being supplied over a double-circuit transmission line that had both circuits previously paralleled to operate as a single circuit. This single-circuit means of supply was considered unreliable in an area known to be prone to storms and lightning. Additional restoration works, therefore, were critical to improve the security of supply to this area.

Within six days after the cyclone hit, a plan had been approved to provide a second 132-kV transmission circuit by separating the paralleled circuits on this 80-km (50-mile) transmission line and reconfiguring substation bays at Woree and Innisfail substations, along with appropriate changes to protection and telecommunications systems.

The challenge, however, was to avoid outages to the transmission line, as this would interrupt all electricity supplies to the Innisfail community and hamper the cyclone relief efforts. Specialized live-line stringing techniques were employed to install temporary conductors over the live 132-kV bus bar at Woree Substation, and protection and telecommunication changes were made with the line energized wherever possible. Ergon Energy field staff undertook line-connection works at the substations.

While most of this complex reconfiguration was undertaken with the existing line in service, the final circuit alterations required a 4-hour supply interruption to the Innisfail community to enable the seven final steps to be performed simultaneously. To minimize the impact on the community, the outage was scheduled to begin at dawn on Sunday, so an open and comprehensive communication campaign detailing the need for the outage provided advance notice to the community. Careful planning and work scheduling minimized the outage duration, and emergency generators were deployed to supply essential loads in Innisfail. The works were completed successfully within the predicted time frame, providing Innisfail with a more secure and reliable electricity supply, as the town's citizens faced the challenge of rebuilding after Cyclone Larry.

THE AFTERMATH

Powerlink's response to Cyclone Larry is a striking example of the innovation and dedication that lies at the heart of the utility's approach to managing and operating the transmission network. Within two weeks of the devastating cyclone, Powerlink's 132-kV network in North Queensland was restored, with the exception of the Kareeya to Innisfail transmission line.

Powerlink's response to the cyclone earned the praise of individuals and organizations, including the Queensland government and General Peter Cosgrove, who took leadership of the government's cyclone restoration efforts. The effectiveness of this response reinforces the value of having comprehensive corporate emergency-response procedures in place and the importance of regular training exercises in these procedures.

A full review of our response to Cyclone Larry was carried out and identified Powerlink's strengths and some opportunities for improving procedures. Among the strengths in the emergency response were:

• Strong relationship with Ergon Energy, Powerlink's maintenance service provider in the region

• Cooperative interaction with other key organizations

• Effective scheduling of the restoration works

• Establishing a local base for all the emergency and communication managers

• Drawing on the knowledge and expertise of locally based staff

• Availability of highly skilled staff on short notice to support the Corporate Emergency Management Team.

The performance of Powerlink's staff in managing the restoration efforts was strongly supported by the cooperative assistance and efforts of other organizations involved in the cyclone response, including the State Department of Emergency Services, State Department of Main Roads, the Australian Defence Force and Ergon Energy.

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Simon Bartlett is currently Powerlink's COO and was the emergency manager for Cyclone Larry. He is also a director of ElectraNet SA, the South Australian Electricity Transmission Utility, which is 41% owned by Powerlink. His 34-year career in power generation and electricity transmission includes roles in Queensland, Switzerland, England and Canada. He holds B.Sc and BE degrees, and is a fellow of Engineers Australia, the Australian Institute of Company Directors and the Australian Academy of Technological Sciences and Engineering. He received the prestigious Technical Committee Award in 2002 for his contributions to CIGRÉ, as well as a commendation from the Australian prime minister and the Queensland premier for outstanding leadership during the Cyclone Larry restorations. sbartlett@powerlink.com.au