POWER TRANSMISSION

One of the most multifaceted, and important, problems facing engineers is power:
transmission.
Generators produce large voltages and currents at a power plant, say from turbines
driven by falling water. The problem: getting the electricity from the plant to the homes,
businesses, and other facilities that need it. This process involves the use of long wire
transmission lines. Also needed are transformers to change the voltages to higher or
lower values.
A radio transmitter produces a high-frequency alternating current. The problem:
getting the power to be radiated by the antenna, located some distance from the transmitter.
This involves the use of a radio-frequency transmission line. The most common
type is coaxial cable. Two-wire line is also sometimes used. At ultra-high and microwave
frequencies, another kind of transmission line, known as a waveguide, is often employed.
The overriding concern in any power-transmission system is minimizing the loss.
Power wastage occurs almost entirely as heat in the line conductors and dielectric, and
in objects near the line. Some loss can also take the form of unwanted electromagnetic
radiation from a transmission line.
In an ideal transmission line, all of the power is VA power; that is, it is in the form of
an alternating current in the conductors and an alternating voltage between them.
It is undesirable to have power in a transmission line exist in the form of true power.
This translates either into heat loss in the line, radiation loss, or both. The place for true
power dissipation is in the load, such as electrical appliances or radio antennas. Any
true power in a transmission line represents power that can’t be used by the load, because
it doesn’t show up there.