Alternating current is a current in which the directions of the current alternate with time.
AC voltage is defined as follows
Household appliances are used by converting alternating current to direct current voltage, but the reason why they are sent from the power plant by alternating current instead of direct current is that the transmission cost is lower.
Since electric power is proportional to the square of voltage, high voltage is more efficient to obtain high voltage, so I want to handle high voltage as much as possible, but on the other hand, high voltage cannot be used as household electric power.
The voltage should be low before it comes to the household outlet. At that time, it is cheaper to step down from AC to AC than to step down from DC to DC (AC -> AC requires a coil and diode, but DC -> DC requires a switching function by a transistor).
The effective value is the "DC current voltage value equivalent to the same power as in AC", but the reason why it is higher than the average value is that the power is proportional to the square of the voltage, so the voltage amplitude is large.
This is because the area has a great influence on the power.
＜How to calculate the effective value of a saw-shaped waveform＞
If the waveform is saw-shaped or not an accurate sine wave, the effective value can be calculated using the following formula. This is Root Mean Square.
■Alternating Current
The operation of alternating current changes depending on the characteristics of the circuit to which the voltage is connected (the direction of the current does not change periodically).
The current when the resistor, coil, and capacitor are connected is as follows.
■AC power
Apparent power is sent from the power source.
However, not all are consumed in the circuit.
The power actually consumed by the circuit is called Active power, and the power returned without being consumed by the circuit is called Reactive power.
In addition, AC power can be expressed on the complex plane as shown below, which makes it easier to calculate AC power.
■Principle of alternating current generation
Alternating current is generated using the principle of electromagnetic induction. Electromagnetic induction is a phenomenon in which magnetic flux is generated by moving the coil and magnet closer to each other, and when magnetic flux is generated, electric current is generated.
Then, the magnet is rotated as shown below, and the direction of the magnetic field lines is switched quickly and alternately to generate an alternating current.
＜Three-phase alternating current＞
As shown below, the current can be taken out efficiently by arranging the coils with the phase shifted by 120 degrees.
Turning the magnet in the center is the power from others, and in the case of automobiles, it is the engine that turns the alternator, and in the case of thermal power plants, it is the turbine that is turned by steam.
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