Civil Engineering Reference
In-Depth Information
Table 7.2
Voltage drops and losses for different cases shown in Fig.
7.11
Z1 (cable 4
150 mm
2
;92m)
R1
¼
0.0034
Ω
X1
¼
0.0014
Ω
Z2 (bus duct 252 mm
2
; 150 m)
R2
¼
0.0129
Ω
X2
¼
0.0196
Ω
Z3 (bus duct 252 mm
2
; 112 m)
R3
¼
0.0096
Ω
X3
¼
0.0146
Ω
RT 0.0073
Ω
XT 0.0073
Ω
Three-phase voltage
380 V, 50 Hz
P
,
Q
in point (1)
Case 1
Case 2
Case 3
Case 4
Load power
P
,
Q
P
(W)
260,000
260,000
459,200
459,200
Q
(var)
300,000
125,000
529,840
220,770
φ¼
atan(
Q
/
P
) (rad)
0.86
0.45
0.86
0.45
Power factor cos
φ
0.65
0.90
0.65
0.90
Power losses PL (W)
7,967
4,207
24,852
13,124
Line voltage drop
ΔV
(V)
10.758
7.396
19.000
13.063
Energy losses working hours (h/year)
3,000
3,000
3,000
3,000
Losses (kWh/year)
23,902
12,622
74,556
39,372
Energy saving
Case 1-Case 2 (kWh/year)
11,280
Case 3-Case 4 (kWh/year)
35,184
Capacitor power
Case 1-Case 2 (kvar)
175
Case 3-Case 4 (kvar)
309
In all cases, Tables
7.2
and
7.3
shows the annual energy losses and potential energy
saving if capacitors are installed as in Case 2 and Case 4. The power of the capacitors
needed is also provided for these cases, so as to evaluate the investment. The cost of
the capacitors alone represents a small part of the total investment which is determined
mainly by installation costs dependent onmany factors, such as the state of the electric
line and related equipment and the distribution of loads along the line.
Economic evaluations for Case 2 and Case 4 are given in Table
19.4
.
Example 2
Compare the energy consumption of a microwave and a thermal dryer
system in the textile industry.
An example is given here of a microwave heating system used for drying in the
textile industry.
The drying line processes 250 kg/h of dry cotton cops for 6,000 h per year.
The cotton entering the line has a water content equal to 250 % by dry weight; that
means 875 kg/h of total weight entering the line of which 625 kg/h is water.
The water content must be reduced to 8 % by dry weight at the end of the process
