MIL-HDBK-1004/5
Throughout this study one 75-kVA utilization service assembly
(200-ampere capacity) is assumed to supply one 100-ampere 0.8-power-factor
unit load. When the transformer is loaded with two unit loads, i,e, its full
capacity, the results of this study can be related by dividing the maximum
allowable number of utilization service assemblies indicated by two.
Examples of calculations for determining the maximum number of
utilization service assemblies are given below:
For a 40,000-foot feeder cable: 0.0583
=
2.1 = two
(1 - 0.9726)
For a 10,000-foot feeder cable:
0.0583
=
5.6 = five
(1 - 0.9896)
Although Table A-1 shows distribution feeders up to 40,000 feet in
length, economics dictates that the 400-Hz medium-voltage distribution systems
must be designed to have feeder lengths not greater than 15,000 feet.
Table A-1
Feeder-Cable Length Versus Loads (1)
______________________________________________________________________________
Cable Length
Bus 3
Number of
No-Load
Feet
Per-Unit volts (2)
Unit Loads (3)
Volts 1-n (4)
______________________________________________________________________________
40,000
0.9775
One
117.3
0.9551
Two
114.6
(5)
0.9325
Three
111.9
30,000
0.9832
One
118.0
0.9664
Two
116.0
0.9496
Three
115.0
25,000
0.986
One
118.3
0.972
Two
116.6
0.958
Three
115.0
0.9391
Four
112.7
20,000
0.0889
One
118.7
0.9778
Two
117.3
0.9667
Three
116
0.9556
Four
114.7
0.9445
Five
113.3
0.9334
Six
112
15,000
0.9917
One
119
0.9834
Two
118
0.9751
Three
117
0.9668
Four
116
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