Human error and faulty maintenance work have been blamed for an incident in the Northern Territory where gas was inadvertently cut off to Darwin’s largest gas power station, triggering a Northern Territory blackout that left tens of thousands without power.
Almost 50,000 Northern Territory residents were left without power for a period of four hours in November last year after gas supplies to the Channel Island Power Station were accidentally cut off.
The loss of 138MW of electricity supply had a snowball effect through the Darwin-Katharine grid, because it triggered frequency disruptions that caused a significant number of feeders to trip, forcing the grid operator to “load-shed” to restore stability to the grid. That resulted in more than 60 per cent of households losing power.
The Northern Territory government released the results of investigations into the incident, including from both the territory’s Power and Water Commission and the Utilities Commission, on Thursday.
An investigation into the cause of the accident undertaken by APA Group, one of the territory’s main gas suppliers, attributed the outage to faulty maintenance work.
APA Group said that maintenance undertaken on a supply valve had inadvertently wired controls the wrong way around, causing control systems to send incorrect signals that cut off supplies of gas to the power station.
“The cables for the solenoid valves had been incorrectly labelled in a previous package of work. This led to the contractor technician installing the cable for the open solenoid into the closed solenoid and the electrical work passing the visual inspection,” APA’s report found.
“When the SCADA sent a ‘confirm position’ signal, the solenoid valve of the heater that was meant to be open, closed. At this point the other heater was also closed. This resulted in a loss of gas supply to Channel Island Power Station (CIPS) Units 1-7.”
In its own investigation of the incident, the Northern Territory Power and Water Corporation recommended that the APA Group be required to provide more information to system operators about maintenance work with the potential to disrupt gas supplies.
Power and Water said that while it was notified of the works undertaken by APA Group, it was unaware of the extent to which it could impact gas supplies.
“The Territory Generation Channel Island operations team was aware of the APA works; however, were not notified of any risks associated with the works. Power and Water’s System Control was not aware of works being undertaken at Channel Island, therefore, no risk notification was in place to manage a possible contingency,” the Power and Water Corporation’s report says.
“In order to prevent or to reduce the impact of similar incidents occurring, the existing arrangements between APA and Power and Water will be reviewed to include the requirement for APA to notify Power and Water of the works conducted on its metering stations or gas pipelines that pose a risk to the gas supply.”
The Power and Water Corporation also recommended that the coordination of media and communications between the territory’s main energy companies, including Power and Water Corporation, Territory Generation and Jacana Energy, be improved to ensure households are able to receive reliable information during such emergencies.
The Northern Territory government said welcomed the results of the investigations, labelling the outage “unacceptable”.
“Hardworking Territorians, families and businesses deserve stable, reliable and affordable power,” Northern Territory minister for essential services, Eva Lawler, said.
“The power-outage which occurred on 18 November 2020 and affected Darwin to Katherine power users was unacceptable and put down to human error from our third party supplier. These issues have been identified and processes have been put in place to make sure this incident does not happen again.”
“During the course of the outage there were over 35,000 visits to Power and Water’s outage web page, which is equivalent to a six month period of business-as-usual. The team also responded to 3,552 phone calls, 226 emails and 406 Facebook messages during the course of the outage.”
“I want to thank the dedicated and hardworking staff of Territory Generation and Power and Water Corporation for their efforts to restore power after the outage,” Lawler added.
The findings follow a blackout in Alice Springs in 2019, that saw 12,000 customers lose power and ultimately resulted in the sacking of the heads of two of the territory’s key energy companies.