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(Solved): The Poatina Power Station is part of the Great Lake Power Scheme. It houses six Siemens generators c ...
The Poatina Power Station is part of the Great Lake Power
Scheme. It houses six Siemens generators coupled to Pelton
turbines. When the station was commissioned in 1966 there
were only five turbines. The sixth was added in 1977. Between
2007 and 2010 number 1, 4 and 5 machines were upgraded
under a program to modernise the ageing plant. The station is
underground on the northern side of the lake with its machine
hall 150 metres below the surface.
Water from yingina / Great Lake travels through a 5.6
kilometre-long headrace tunnel to a single, hydraulically
operated hilltop valve. A 105 metre-long, steel lined
penstock tunnel leads to the penstock tunnel portal. Water
is then carried via a 1.8 kilometre-long surface penstock
to a 150 metre vertical shaft leading to the underground
penstock distributor.
The penstock distributor has six branches, each feeds an
isolating valve inside the power station which is bolted
directly to the main turbine inlet valves. The rated head for
the station is 758 metres.
Once it leaves the turbines the water is discharged along a
4 kilometre tailrace tunnel exiting at Palmers River. Poatina
supplies irrigation water to the Cressy-Longford Irrigation
Scheme and Macquarie Irrigation with minimum required
flows set for the summer period.
The station output is fed to TasNetworks’ transmission
grid via underground circuit breakers to two 16 kV/110 kV
and four 16 kV/220 kV generator transformers located in
the switchyard above. Poatina’s positioning in the network
means it feeds into the Palmerston switchyard, which is on
the main North-South transmission corridor.: Fast facts
Scheme: Great Lake - South Esk
Year commissioned: 1966/1977
Power station structure: Underground dimensions:
• 91 m long x 14 m wide and
26 m high excavation
It houses generating sets with
assembly bay and services bay
and with a vertical busbar/
lift shaft to a surface control
building and transformer yard.
Static head: 835 m
Generating set: Six vertical shaft generating
sets:
• Five Boving 51.6 MW of
which three are upgraded
Andritz turbines
• One Fuji 54.5 MW four
nozzle spear Pelton.
All units are capable of
operating at over 60 MW.
Turbines directly coupled to
a 3-phase, 50 Hz, 62.5 MVA
synchronous generator and
with provisions for synchronous
compensator operation.
Turbine manufacturer: 2 Boving, 3 Andritz, 1 Fuji
Generator manufacturer: Siemens
Rated head: 758 m
Rated output: 62.5 MVA
Rated discharge: 9 m3/s
Power factor: 0.8
Rated speed: 600 rev/min
Rated voltage: 16 k ; please solve this
Using the Poatina Power Station Fact Sheet provided on the MEC4104 StudyDesk as your reference for technical specifications; for the Fuji Pelton turbine: (a) assume and justify a bucket turning angle, and calculate the bucket efficiency; (b) calculate the velocity and diameter of the jets; (c) calculate the average radius of the Pelton wheel; (d) deduce the head loss in the system upstream of the turbine; and (e) compare and contrast the net head at the turbine with the rated head of the facility. A financial asset manager has conducted a brief survey of the turbines used by Hydro Tasmania across their 25 hydroelectric sites and has summarised their findings in Table 1. Based on this analysis, this manager has found that the Francis turbines produce the most energy per turbine asset and are the most numerous turbine type. Therefore, this manager wants to transition all sites to Francis turbine technology. (f) As lead engineer for Hydro Tasmania, you are required to respond to this manager's request via written memo (or similar). Ensure that your response: (1) identifies any logic flaws in the manager's analysis; (2) communicates technical information in a clear and accessible manner; and (3) is professional. You will need to make clear and justifiable engineering assumptions in your analysis for all or some of the elements of this task.