Power Distribution

The transformer’s ability to step a.c. voltage up or down with ease gives a.c. an advantage unmatched by d.c. in the realm of power distribution. When transmitting electrical power over long distances, it is far more efficient to do so with stepped-up voltage and stepped-down currents, then step the voltage back down and the current back up for industry, business, or consumer use.

If you have forgotten why a high voltage is good for power distribution, recall that:

$$\begin{aligned}P_{\text{loss}} &= IV \\ &= I^{2}R \end{aligned}$$

Power loss can be reduced by minimizing I and R. Reducing the resistance R requires very thick cables which are heavy and expensive. The better choice will be to reduce I by employing step-up transformers to increase the transmission voltage and reduce the current. This will reduce the energy loss due to Joule heating.

Transformer technology has made long-range electric power distribution practical. Without the ability to efficiently step voltage up and down, it would be cost-prohibitive to construct power systems for anything but close-range (within a few kilometres at most) use.

As useful as transformers are, they only work with a.c., not d.c. We need changing magnetic fields, and direct current can only produce steady magnetic fields, so transformers simply will not work with direct current. Direct current may be interrupted (pulsed) through the primary winding of a transformer to create a changing magnetic field, but pulsed d.c. is not that different from a.c. Hence, why go through the hassle when a.c. is available. This is why a.c. finds such widespread application in power-systems.

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