Parangana Mini-Hydro Project

Grid-connected, distributed generation, renewables

The site

The Parangana Dam was built in 1968 as part of the Mersey Forth Power Development.
It diverts the water of the Mersey River into the Forth River valley. The Dam itself is a 53 m high rockfill dam with a clay core.

The dam has an emergency-dewatering outlet built into the 6.5 m diameter conduit that was originally the dam's diversion facility.This outlet consists of a 2.5 m diameter butterfly valve with a pipe leading to a 2.2 m diameter removable domed bulkhead about 7 m downstream from it. An off-take between the valve and the dome leads to a 0.6 m hollow jet valve that is used for riparian releases. There is also a similar 0.2 m diameter outlet.

These valves are about 60 m upstream of the conduit's outlet. At the outlet the conduit transitions into a concrete discharge chute 43 m long. A control house is situated next to the transition point.

Water discharge

In 1999 Hydro Tasmania agreed with the Department of Primary Industries Water and Environment (DPIWE) that it would increase the riparian discharge from Parangana Dam, in order to maintain a minimum `environmental' flow of 2.0 m 3 /sec in the Mersey River at Liena, some 8 km downstream.

Technology

A power station (Mini-Hydro Plant) with an installed capacity of 0.85 MW has been constructed next to the existing control house. The domed bulkhead was modified to include a 1.2 m diameter off-take, and a 1.2 m diameter penstock mounted on the left side of the conduit which then leads 60 m to the power station.

The power station is mounted on a steel platform that is supported from the chute invert on steel legs. It contains a vertical axis Francis turbine directly coupled to a 850 kW induction generator.Turbine discharge is directly into the chute.

A new butterfly valve has been installed just upstream of the turbine. A simple steel-framed building on top of the platform, with a removable roof, houses the valve, turbine and generator.

The existing control house accommodates the combined switch/control cubicle and a hydraulic power pack. No modifi cations to existing concrete structures were necessary. The transformer and switchgear are situated in a fenced yard approximately 10 m from the control house, and power fed at 22 kV to connect to the nearest Aurora feeder, about 500 m away.

Energy output

The plant output supplies the local community in the Mersey Valley via a 22 kV Aurora feeder. The mini-hydro has also been accredited under the Australian Greenpower scheme.

This allows the output to earn an additional premium as it is sold as a Green Power product on the mainland, to retail customers willing to pay extra for renewable energy.