Question of the week: Power is usually transmitted over long distances as altern

Question

Question of the week:

Power is usually transmitted over long distances as alternating current (AC). The reason for this is that AC transformers can easily be used to "step-up" the voltage for transmission, and then "step-down" to supply to residences, whereas DC transformers are complicated and costly. Why is it preferable to transmit at high voltage (typically the frequency used is 60 Hz)? For very long distances the conducting cables actually start to gain a significant capacitance (for example, a typical copper 5 mile long cable would have a capacitance of 2.4 microFarad), which adds to the total impedance. In order to minimize the reactance of the above transmission cable, what would you have to do?

Explanation / Answer

Power P = VIcos(theta). V voltage, I current and cos (Theta) power factor.

Transmission loss is directly proportional to square of current at constant impedance. If we made the value of current (I) is less than one, then square will become more small and the value of power loss is very less.

The power factor cos(theta) is the phase angle between emf and electric current it depends on the ratio of Resistance and Impedance. If the frequence is more capacitive reactance is less, hence the impedence is less.

If the power factor is reduced then also the transmission loss of energy decreases. Hence a high voltage gives low current and less powr loss. Hence AC is transmitted.

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