How2Day: The Disadvantages of AC Generators

There are two kinds of electricity: AC and DC. Jupiterimages/Photos.com/Getty Images
All electricity is the flow of electrons. There are two kinds of electricity: Alternating Current (AC) and Direct Current (DC). In AC the electrons flow first in one direction, then reverse and flow in the other direction. In DC the electrons flow in one direction only. For some uses like light bulbs, either kind of electricity will work. For some other uses like motors, AC is better. Devices like radios, television and computers, for instance, need DC power.

The conflict between AC and DC goes back to the late 1800's and involves giants like Edison, Tesla and Westinghouse. In those early days, AC emerged superior---especially in terms of power generation and transmission. DC had to be generated near where it was going to be used and at exactly the right voltage. AC could be boosted up to hundreds of thousands of volts (at low amperage) and transmitted for hundreds of miles---before being "transformed" down to exactly the voltage that is needed. In the second half of the 20th century, things changed. It became possible to transmit DC for longer distances than AC---while using simpler systems. Also devices like radios, televisions and computers require DC---unlike earlier systems (lights, motors an electric fences) that required AC. DC also avoids some of the problems associated with AC generation and transmission.

The back-and-forth actions of electrons in AC causes raising and falling magnetic fields. This makes it easy to transform AC into different voltages (transformers need raising and falling magnet fields to work), but it takes a lot of power to create these changing magnet fields. The chief problem with AC generators is that they are generating the wrong kind of electricity. Modern techniques provide ways to transmit DC more economically over very long distances (over 400 miles) than AC---which need boosting substations every 400 miles or less. This is especially critical for applications like undersea cables where substations every 400 miles are impractical.

Because of the way they work, AC generators must produce high currents which causes heating and sparking, which means that AC generators wear out faster than DC generators. The wasted power involved with AC starts at the generator and continues through each transformation of voltage up and down and through the final conversation of AC to DC when the electricity is used for electronic devices. The high currents in the generator and the high voltages in the transmission lines means that AC is more dangerous than DC, too.

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