Electronics All-in-One For Dummies (For Dummies (Computer/Tech))

Author:Lowe, Doug [Lowe, Doug]
Language: eng
Format: epub
ISBN: 9781119320807
Publisher: Wiley
Published: 2017-01-17T16:00:00+00:00

In other words, power equals voltage times current. A transformer transfers power from the primary coil to the secondary coil. Since the power must stay the same, if the voltage increases, the current must decrease. Likewise, if the voltage decreases, the current must increase.

Transformers are the main reason we use alternating current instead of direct current in large power distribution systems. That’s because when you send large amounts of power over a long distance, it’s much more efficient to send the power in the form of high voltage and low current. That’s why overhead power transmission lines often carry voltages as high as 400,000 VAC. Such high voltages allow the electrical power to be transmitted using much smaller wires than would be required if the same amount of power were transmitted at 120 VAC.

Power distribution systems use large step-up transformers to step voltages generated at power plants up to thousands or hundreds of thousands of volts. Then, as the power gets closer to its final destination (such as your house), a series of step-down transformers drops the voltage down to more manageable levels, until the voltage is dropped to its final level (120 VAC) before it enters your house.

Transformers work only with alternating current. That’s because it’s the change of the magnetic field created by the primary coil that induces voltage in the secondary coil. To create a changing magnetic field, the voltage applied to the primary coil must be constantly changing. Because DC is a steady, fixed voltage, it creates a fixed magnetic field that won’t induce voltage in the secondary coil.

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