TM
5-811-1/AFJMAN
32-1080
SINLE LINE DIAGRAM
VECTOR DIAGRAMS
ASSUMED UTILITY RATES
CALCULATIONS
Losses - I2R
Energy charge
2
= [(2042 - 186 ) amperes] x 5 miles x 3 conductors x 0.278 ohms per mile
-
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.035 per kWh= 29.27 kw
Power factor
Line loss savings = 29.27 kW x 0.6 load factor x 4,000 hours x
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.035clause credit
= 59 a year
= 0.001 times value
in percent that
Power factor savings (increase 82 percent to 90 percent)
power factor (pf)
= 4,000 kW x 0.6 load factor x 4,000 hours x
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.035 x [0.001 x 8]is raised above a
= .690 a year
stipulated amount.
Total Savings = 59 + ,690 = 49 a Year
us Army Corps of Engineers
Figure 5-3. Average Energy Savings Example.
(3) Existing feeders. Circuit capability will be
miles will provide a sufficiently accurate determi-
nation. For instance, taking the value for aerial
determined by measuring loads over a suitable
No. 4/0 AWG copper at 25 kV or 29.2 megavolt-
period of time. Where such information is unavail-
ampere-miles and multiplying by (35/25)2 gives a
able, knowledge of the station maximum demand
value of 57.2 megavolt-ampere-miles which is al-
and overall transformer capacity can permit deter-
most the value given in table 5-1. For under-
mining an installation's demand factor on the
ground circuits, where proximity effects apply, a
basis of overall connected transformer capacity.
greater variation will be encountered, but esti-
Circuit capability can be roughly evaluated by
mated demand loads are probably within the same
totaling the transformers connected to the feeder
accuracy range.
and applying this factor; however, this method is
(2) New feeders. For new installations, with
too inaccurate as a basis for justifying new feeders
estimated demands based on requirements covered
or adding large loads.
b. Automatic circuit reclosers. Chapter 4 covers
in chapter 2 and estimated feeder lengths based on
the site plan, a determination of circuit require-
provision of reclosing relays on outgoing feeder
ments can be made. Feeders will be large enough
circuit breakers at a main electric supply station.
Where a reclosing relay on a station circuit
to allow a growth factor of 25 percent of the design
maximum demand.
breaker does not provide a protective zone which
5-5
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