Alternating current refers to the voltage or current whose magnitude and direction change periodically (or frequency). It can also be understood that alternating current has no fixed positive and negative poles, and current will flow into the ground and upward from the ground.

Advantages of AC power supply: the alternator has no brush, more stable structure and longer service life. Through the transformer, the voltage can be easily stepped up and down, which is convenient for high voltage transmission, thus reducing the power loss. By embedding the neutral line (using grounding capacitance), transmission lines are reduced and so on.

The mains frequency in China is 50HZ (periodically changing) and the voltage is 220v v.