MIL-HDBK-1004/5
e)
The location of the filter in the system;
f)
The effect of other utilization service assemblies;
g)
The length of the 4,160-volt feeder cable.
6.7
Example of a Resonant Frequency Analysis. Resonant frequencies and
the resulting THD were analyzed for the two cases shown on Figure A-41. The
results of the computer study are given in Table A-7 which indicates that one
filter element reduces the system THD of Case 2, the two-rectifier load, from
5.4 percent to 3.5 percent. For Case 1, the one-rectifier load, the reduction
still exceeds the 5 percent limitation and additional analyses must be made.
Table A-7
Resonant Frequencies and Harmonic Voltages
______________________________________________________________________________
Case
Parallel
Series
Parallel
Series
______________________________________________________________________________
1
550
3,200
3,720
3,950
2
740
3,050
3,600
4,100
------------------------------------------------------------------------------
Harmonic Voltage Magnitudes
3
5
7
9
11
13
THD
------------------------------------------------------------------------------
Case
First Filter Section Per-Unit Volts
------------------------------------------------------------------------------
1
0.70
0.84
1.60
0.44
0.72
0.14
2
0.09
0.32
1.52
0.61
1.05
0.50
------------------------------------------------------------------------------
Condition
Percent Volts
------------------------------------------------------------------------------
Unfiltered
0.2
5.0
2.0
0.1
0.5
0.2
5.4
Case - 1
0.14
4.2
3.2
0.04
0.36
0.03
5.3
Case - 2
0.02
1.6
3.0
0.06
0.53
0.10
3.5
______________________________________________________________________________
76
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