Ensuring a reliable and secure transmission of electricity for customers on the North and South of New Zealand

Hitachi Energy has been selected by Transpower to replace the bushings on the converter transformers at both ends of the HVDC Pole 2 inter-island link, which balances energy demand between the North and South Islands, to ensure a reliable and secure supply of electricity for another 30 years. 

Pole 2 is one of two HVDC poles that make up the inter-island link and was installed in 1991 (the other Pole – Pole 3 – was commissioned in 2013). 

Currently circa 60% of power generation in NZ is provided by the South Island hydro schemes - a 350kV high voltage direct current link connects Haywards Converter Station on the North Island to Benmore Converter Station located on the South Island.

The converter transformers of Pole 2 are undergoing a half-life refurbishment program after 30 years in service. The replacement of the bushings is logistically a complex project given the size of the converter transformer bushings as well as the intrinsic nature of the HVDC Pole 2 to New Zealand’s energy supply. The largest DC transformer bushing is circa 6 meters long, 0.8 meters wide and weigh 1,000 kilograms.

A special outage will be scheduled by Transpower each year for the next 3 years, for Hitachi Energy to progressively exchange the bushings on the eight converter transformers at either end of the HVDC Pole 2 link. There are six active converter transformers and 2 spare converter transformers.

Hitachi Energy in New Zealand will install and commission the bushings via its Grid Integration operations team.

Hitachi Energy in Sweden will design, engineer and manufacture the converter transformer bushings utilizing the latest technology of Resin Impregnated Paper (RIP) Bushings. Existing bushings are oil impregnated. Prototypes of the DC bushings will be manufactured and sent off for type testing in European laboratories prior to the manufacture of the actual replacement bushings.

The project is part of the program to enable Transpower to continue to meet its targets for security and reliability of supply, set by the Commerce Commission in NZ.