Civil Engineering Reference
In-Depth Information
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Current,
I
Voltage,
E
0
90
°
180
°
270
°
360
°
1 Cycle
-
Fig. 30-1.
Instantaneous power in an AC circuit with coinciding voltage and current waveforms
30-3. When capacitance is greater than inductance, current will lead voltage. The
amount by which the current lags or leads the voltage is expressed as an angle, with
one full cycle being 360
. Power factor is the cosine of this angle and is the ratio of
the active power to the apparent power. Partially loaded induction motors create the
largest reactive demand on most systems, and current tends to lag voltage on most.
1
Useful electrical relationships are shown in Table 30-1.
ENERGY CONSUMPTION IN WATER TREATMENT PLANTS
Energy is a major cost in the waterworks industry. The distribution of energy by
process in water treatment plants of various sizes is presented in Table 30-2. Design
Active Power (i.e.,
V
x
A
xPF), kW
0, Phase Angle
Reactive
Power,
kVAR
Active Power
Apparent Power
= cos 0 = Power Factor
Fig. 30-2.
Power triangle
