Wivenhoe pumped storage hydraulic transient study
Client: Tarong Energy
Location: Queensland, Australia
Date: May - June 2010
Studying hydraulic transients for safe and effective pumped storage hydropower.
Wivenhoe Power Station is a pumped storage hydroelectric station located near Ipswich in south-east Queensland. The power station consists of two 250 MW Francis turbines and two 207 m3/s pumps. The maximum static head for normal operation is 117.5 m. Twin high-pressure tunnels convey water between the upper storage, split-yard reservoir, and the lower storage, Lake Wivenhoe.
As part of a general review of the operation of the power and pump station, Entura was commissioned to conduct a hydraulic transient study to review the pressure surges that could occur in the conduit system if a pump tripped or in case of a sudden loss of turbine load. Fully investigating hydraulic transients, or pressure surges, in turbines, pumps and pipelines is vital as these pressures can cause significant damage to valuable infrastructure.
The Wivenhoe Power Station is located on the edge of Lake Wivenhoe and has short conventional draft tubes and suction conduits. The tunnels consist of a 91 m long by 8.5 m diameter concrete-lined upper section and a 260 m long by 6.8 m diameter steel-lined lower section. A steel bifurcation exists in each of the tunnels at their lower end to connect with both the pumps and turbines in the power station.
Entura developed hydraulic transient models of one of the conduit systems using Hytran transient software. Two models were developed for turbine operation, one with the turbine modelled as a valve and the other with the turbine modelled with full turbine and governor characteristics. One model was developed for pump operation. The models were satisfactorily calibrated against a 312 MW turbine load rejection and a pump shutdown test.
Entura’s hydraulic transient model study showed that the maximum hydraulic transients or pressure surges induced in the conduit system during a turbine emergency shutdown or a pump shutdown were lower than the manufacturer’s guaranteed maximum pressure. The maximum turbine over speed was found to be equal to the manufacturer’s guaranteed value.
These outcomes confirm that the Wivenhoe station can safely operate into the future without risk of excessive pressure surges or excessive unit speeds that could have damaged the plant or in worst case caused a catastrophic failure.