Power Control

Updated: 6/28/2025 Words: 0 words Reading time: 0 minutes

Components used for power control include relays, switches, voltage regulators, etc. These components can be used for power switching, voltage regulation, circuit protection, and other functions to ensure stable operation of power systems.

Direct Current and Alternating Current

Before we start understanding specific components, let's first review direct current and alternating current.

Direct current (DC) is current that flows in a constant direction, or current with constant polarity voltage. DC is current generated by batteries, which have clear positive and negative terminals, or charge generated by rubbing certain types of materials.

Some power sources can naturally produce voltage with alternating polarity, where positive and negative polarity reverse over time. For example, rotating motor generators. Whether as voltage polarity switching or as current switching direction back and forth, this form of "electricity" is called alternating current (AC).

The battery symbol on the left in the diagram below is the universal symbol for a DC voltage source, and the circle with wavy lines on the right is the universal symbol for an AC voltage source.

Working Principle of Generators

Whether DC or AC generators, they are based on Faraday's law of electromagnetic induction, which states that changes in magnetic fields cause the generation of electric fields.

DC Generators

In DC generators, coils are mounted on a shaft while magnets are fixed on both sides. By continuously rotating the coil, induced electromotive force in the same direction is obtained.

AC Generators

In AC generators, magnets are mounted on a shaft while coils are fixed on both sides. When magnets continuously rotate, induced electromotive force with continuously reversing polarity is generated in the coils. If a load is connected, this reversing voltage polarity will produce reversing current direction in the circuit.

The faster the generator shaft rotates, the faster the magnets rotate, and the higher the frequency at which the generated AC voltage and current switch directions in a given time.

DC generators require brushes and commutators to work, which produce sparks and heat during high-speed operation, making them unsuitable for high-power applications. AC generators don't have this problem, so more efficient electric generators and power distribution systems can be built than with DC.

Transformers

If two coils are placed together, the magnetic field changes produced by one coil will cause the other coil to generate voltage. This phenomenon is called mutual inductance effect.

As shown in the diagram below, if we energize one mutual inductance coil with AC, the other coil will also generate AC voltage. This device is called a transformer.

Transformers can step up or step down voltage from the supply coil to the non-supply coil. But they can only be used with AC. Because the mutual inductance phenomenon depends on changing magnetic fields, and direct current (DC) can only produce stable magnetic fields, transformers cannot be used with DC.

The ability of transformers to easily step up and step down AC voltage provides AC with unparalleled advantages. In long-distance power transmission, first increasing voltage and decreasing current ensures that power can be transmitted with smaller diameter high-voltage conductors, reducing power loss; then decreasing voltage and increasing current for industrial, commercial, or consumer use is much more efficient.