MIL-HDBK-1004/5
2.6.3.4
Rationale of Maximum Cable Lengths. The essential factor in
determining acceptable cable lengths is the 113-volt limitation at the
aircraft interface point. Meet this limitation in the following manner:
a) Permit a steady-state voltage droop to 3,918 volts on the
4,160-volt end of the medium-voltage distribution system. Droop is defined as
the absolute change in voltage between the steady-state no-load condition and
the steady-state full-load condition. This equates to 113 volts on the
low-voltage distribution system or 0.942 per unit volts (using base voltages
of 4,160 volts and 120 volts) at the terminals of the utilization service
assembly.
b) Make up for the low-voltage system droop by compensating for the
low-voltage system's reactance.
Table 3
Frequency Conversion Assembly Parameters
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1. Synchronous Units with Revolving Fields
------------------------------------------------------------------------------
Motor
Power Factor
1.0
0.8
Voltage
460 volts
575 volts
60 hertz
400 hertz
Full load
Synchronous Unit Current
420 amperes
314 amperes
Field current
8.86 amperes
26.7 amperes
Current to bridge air gap
3.9 amperes
17.01 amperes
No Load
Field current
3.8 amperes
14.435 amperes
Current to bridge air gap
3.6 amperes
14.03 amperes
Number of poles
6
40
Full load rating
400 horsepower
312 kVA
Synchronous speed
1,200 rpm
1,200 rpm
2. Transformer
-----------------------------------------------------------------------------
Rating
312 kVA
Voltage
575 to 4,160 volts
1 percent
Reactance
5 percent
Current base
313.3 to 43.3 amperes
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