High voltage transmission line back in service following flood damage

30 March 2020

Transpower, the owner and operator of the National Grid, has recommissioned the high voltage electricity transmission line partly washed out due to the Rangitata River flooding prior to Christmas.

On 7 December, the Rangitata River in South Canterbury burst its banks causing extensive damage to surrounding areas including to nine high voltage transmission towers on the Roxburgh–Islington 220 kV transmission line.

Since then a dedicated project team has been working to design and install a temporary line section, by April to ensure a full security of supply to the upper South Island prior to winter. 

“Without this line, and with higher demand as we head into winter, any outage of another line could have resulted in outages to some areas in the upper South Island,” said Mark Ryall, Transpower’s General Manager Grid Delivery.

The temporary section of line includes 11 pole structures strung with new conductor (ie wire). Due to its temporary nature, including Transpower’s ability to source materials and build it as quickly as possible, the line does have a slightly lower operational capacity to the original line.  However, this is not expected to impact on supply security.

Work continues on designing and building the permanent solution (steel lattice towers) which will eventually replace the temporary pole line to return the line to full capacity. 

“We expect to have the permanent line section completed and commissioned by spring this year.” Mr Ryall said.