Siemens Energy has received an order from Wellington-based Transpower New Zealand Limited, the national grid operator, to modernize and increase the capacity of the existing high-voltage direct-current (HVDC) link between the country’s North and South Island.

For the “Inter Island Connector Pole 3" HVDC project Siemens will supply two turnkey converter stations and replace the aging converters with advanced light-triggered thyristor valves. The investment volume for the overall project is EUR327 million. Siemens’ share accounts for approximately half. The aim is to raise the capacity of the existing HVDC system in increments over the next few years from 700 MW to 1400 MW. This is intended to ensure reliable power supply with minimal losses and to further stabilize New Zealand’s grid. Siemens will complete modernization and expansion of the HVDC system by late 2013.

In the course of the multistage conversion and uprating of New Zealand’s over 570-km-long HVDC link – of which 40 km are a subsea cable link across the Cook Strait – Siemens will replace the aging converter technology (mercury arc rectifiers) with advanced light-triggered thyristor valves. This will involve the installation of two 700-MW turnkey converter stations in the two HVDC substations at Haywards, located north of Wellington, and Benmore on South Island. Siemens will also expand the 220-kV outdoor switchyards of the two substations and replace the existing instrumentation and controls of part of the system with Simatic TDC, the latest generation of its HVDC instrumentation & controls. It is planned to increase the capacity of the HVDC link to 1000 MW by 2012, 1200 MW by 2014 and 1400 MW by 2017.

Siemens will also supply a static reactive-power compensation system based on its new SVC Plus (Static Var Compensator) technology for grid stabilization. It will be installed in the Haywards substation and operate with innovative voltage-sourced converter (VSC) technology, and can be continuously controlled with the aid of insulated-gate bipolar transistors (IGBTs). The scope of supply also includes the converter transformers, smoothing reactors, protection and I&C systems, and AC and DC filters.

The HVDC system in New Zealand is the second power transmission project that Siemens has won in the region. The first project was the “Basslink” high-voltage direct-current link between Tasmania and the Australian mainland. Both sides benefit from the 290-km-long 500-MW subsea cable link: Tasmania, whose power generation is almost exclusively hydro-based, exports “green electricity” to meet peak load demand in the state of Victoria. In periods of drought when the water level in Tasmania’s reservoirs is low, the island’s base-load power demand can be met with electricity imported from the mainland.