& Power Factor
Lets look at the energy savings associated with the cable from the previous example in the "Transformer Capacity" section, which was 1,000 feet long, delivering 1,400 kW of power at 13,800 volts and a Power Factor of 0.7.
Since Power is the product of Volts, Amps, Power Factor and the constant 1.73 (for 3 phase circuits), then the current flow in the cable is 83 amps. If we correct the power factor at the transformer from 0.7 to 0.9, the current flow in the cable drops to 65 amps.
In piping systems, the pipe-wall friction creates pressure drops and thus energy losses associated with higher flow rates. In electrical systems, the resistance of the cable creates voltage drops and thus energy losses associated with the higher flow. The heating loss in the cable is:
Heat Loss in Watts = Amps x Amps x Resistance, and a typical resistance for a cable used in this application would be .1 ohm per 1,000 feet.
So the heat loss at a .7 power factor is 689 Watts and the heat loss at .9 Power Factor is 417 Watts. This cable consumes 272 Watts to carry that Reactive Current. That would be approximately $350 per year at 15 cents per kWH.
So.....Beware of spending large capital sums in the name of "Energy Savings".