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In recent years, a system loss of 2% to 3% would be
accepted in trade for lower system component costs. Today, these initial
component costs must be very carefully weighed against a higher long term
system operating cost.
Depending on the local price of electricity, it is
probably more worthwhile now to spend more initially on the system to get
components that will have minimal operating losses.
The range of losses in power system equipment at full
load is summarized below:
Outdoor circuit breakers 0.002% - 0.015%
Medium voltage switchgear 0.005% - 0.02%
Transformers 0.4% -1.9%
Load break switches 0.003% - 0.025%
Bus way 0.05% - 0.50%
Low voltage switchgear 0.13% - 0.34%
Motor control centers 0.01% - 0.40%
Cable 1% - 4%
Motors
1-10 HP 14% -35%
10-200 HP 6%-12%
200-1500 HP 4% - 7%
Static variable speed drives 6%-15%
Capacitors 0.5%-2%
Lighting 3% - 9%
The component with the greatest percentage of loss
that is a part of the power distribution system is the cable. Conductor
current carrying capacity or 'ampacity' is determined by the maximum
operating temperature that its insulation can with-stand.
The heat that produces the conductor temperature rise
is caused by the wattage loss in the conductor. Both aluminum and copper
conductors can be obtained. Aluminum has a higher electrical resistance
than copper, so aluminum wire has a lower current rating than copper wire
of the same size since its higher resistance generates more heat. Thus,
the maximum operating temperature of the conductor is reached with lower
current. To carry the same amount of current, the aluminum conductor must
be larger. The appropriate size of each conductor and its initial cost
should be considered when selecting the type to be used. |
