Amethyst Hydro

Amethyst Hydro had to overcome a string of challenges to complete the company’s 7.6 MW power station near Harihari.

The scheme, commissioned in June, provides a secure and reliable source of electricity for southern Westland and reduces transmission losses to the region.

And it does so from within a Department of Conservation-administered catchment, with technology that enables the scheme to continue operating islanded from the national grid if necessary.

A series of technical and commercial innovations were required to ensure a successful and affordable development.

A low-level weir was used to extract water from the Amethyst River, eliminating the need for a dam and minimising the project’s environmental footprint. Special resonant inverted angle cantilever-mounted screen bars were installed to provide a self-cleaning action.

Helicopters were needed to transport workers and materials to complete weir construction, as the terrain did not allow for the construction of a roadway.

One of the biggest construction challenges was the construction of a small, steep tunnel through uncertain rock conditions with the likelihood of high-pressure water inundation.

Special techniques were developed to prevent explosives being blasted out of drill-holes by the extreme water pressures. Tunnellers worked in wetsuits at times to avoid hyperthermia.

A special extension boom was designed to enable penstocks to be installed in the tunnel, saving the time and expense of installing a rail and craneage system.

Plant

Innovation continued in the design and installation of the turbine and electrical plant.

The New Zealand built and designed six-jet Pelton turbine proved highly efficient, exceeding the 7.2 MW design capacity.

A special deflector governing capability was designed to provide superior frequency regulation, key to enable the plant to operating in an islanded mode.

Likewise, the synchronous generator it is coupled with is designed for fast response and quick de-excitation in the event of a fault.  Specifying a standard slip ring and brush arrangement on the rotor reduced the risk of exciter failure and greatly improved transient voltage response, a critical element when transitioning from synchronous to island modes.

The plant was also designed with black start capability in the event the West Coast is disconnected from the national grid. Special algorithms had to be written to manage the interaction between the spear governors and the deflector governors in such an event.

The Innovation in Energy Award category is sponsored by Gentrack.