Environmental Engineering Reference
In-Depth Information
D1
D2
FIGURE 3.7
Basic concept of using ratio of total conduit distance to head distance. The ratio should be less
than or equal to 10:1; 1:1 is optimal. D1 is the conductor distance and D2 is the head distance.
Water conduit sizing has a direct connection to the starting time of a PHES
unit. The starting time for a unit should be between 1 and 2.4 seconds and
not exceed 2.5 seconds.
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The water starting time of a hydro facility is the time
required for the water to move through the conduits to the turbo machinery.
This may be calculated by summing the lengths of constant diameter sections
of conduits times the velocity of the fluid in that section, over a gravitational
constant times the net head. This calculation
9
is expressed as
W
=
∑
(3.4)
T
LV/gh
where T
w
= water starting time, L = length of constant diameter section of
water conduit, V = average flow velocity in a related section of L, g = gravi-
tational constant, and h = net head. Mechanical starting time is the time
required for the turbo machinery to reach rotational speed and begin electri-
cal operation.
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Tm= (WR
2
× n
2
)/(1,620,000 × P)
(3.5)
where T
m
= mechanical starting time, WR
2
= product of weight of revolv-
ing parts (shaft turbine runner and generator rotor) and the square of their
radius of gyration, n = rotational speed of turbine and generator for a direct
connected synchronous generator, and P = turbine full gate capacity (hp).
The mechanical starting time over the water starting time (T
m
/T
w
) measures
unit stability. If a PHES unit is expected to follow load or variable generation
for integration and provide frequency regulation, the ratio of T
m
/T
w
should
be equal to or greater than 5.
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Draft Tube
Where a reaction turbine is used, a draft tube is necessary and is designed
simultaneously with the pump turbine. The draft tube takes water from the
