January_1968 — Page 42

ANNUAL FLOW

1000 MILLION GALLONS

30

27

24

21

181

15

12

ON

LO

W

X OBSERVED DATA

Highland Catchment

Best-fit line for observed data

x 1962-63

x1961-62

X

1960-61 1965-66

X

1964-65

DISCHARGE — M. G. D.

N

1000

~

100

6

<

2

8

% Time discharge equalled or exceeded

% Volume passing at flows in

excess of given discharge

101

1963-64

0

10

20

30

40

50

60

70%

20

40

60

80 100 120 140

AVERAGE CATCHMENT RAINFALL INCHES

-

Fig. 3:4. Average catchment rainfall inches

reversing the process and injecting extra energy into the rotor. A special feature of the N-S motor is the use of small auxiliary windings to over- come sparking on the commutator and allow the use of fixed brush-gear.

The auxiliary windings lie in the bottom of the slots and are connected to the same segments as the main motor windings; their function is to absorb the energy that would normal- ly be dissipated by sparking and transfer it by transformer action to groups of main windings not under- going commutation.

Starting is direct-on-line, the great- est starting current being twice the normal maximum running current. The speed/torque characteristic of a pump is favourable for starting, as the full torque is not required until the speed builds up. Pumps will nor- mally be started at the slowest speed; once this is attained the speed will be increased according to the duty.

The three booster units are similar in arrangement to the main units but work at a fixed speed and each de- liver a nominal 12.5 m.g.d. against 250 ft. head.

The motors for all the pumps are connected to the incoming supply through metal-clad switchgear having a rupturing capacity of 250 MVA. The busbars are air-insulated and single-break oil circuit-breakers are mounted on withdrawable carriages for ease of maintenance. The switch- gear is situated in a separate room to reduce the risk of damage to other equipment in case of fire.

―

Control

Reduced catchment -- allowing for diversions direct to Plover Cove 13,232 Acres.

Fig. 3:5. Indus flow duration and distribution curves

The pumps will ordinarily be con- trolled automatically from the river level through "No-flote" electrodes. Assuming that the suction pond has been drawn right down, no pumps will operate until the level has built up to the lowest "start" electrode. One pump will then start at the slow- est speed. If the flow is low, so that the quantity pumped is greater than the flow, the level will fall again until the "stop" electrode is uncovered and the cycle will then be repeated,

The frequency of starts will be

greatest when the flow equals half the capacity of a pump and the storage between the levels of the "stop" and "start" electrodes must be sufficient to limit starts to about one per hour. If the river flow is greater than the out- put of one pump, the level will con- tinue to rise until the "start" electrode for the second pump is covered, and

so on.

When an additional pump is brought into operation, it is first run up to the speed of the pumps already working and then the speed of all pumps is raised automatically

to

5565

Fig. 3:6. Fabridam at Tai Po

Far East Architect & Builder January, 1963