What role does a surge protector play in a power distribution circuit? What is its principle of action?

The surge protector limits the atmospheric overvoltage (lightning and lightning strike) in the power grid to no more than the impulse withstand voltage that various equipment and power distribution devices can withstand.
The essence of the surger is a semiconductor varistor device, and the resistance depends on the terminal voltage of the surger.
When the terminal voltage is less than the trigger voltage Up of the protector, the resistance of the protector is very high (greater than 1 megohm), and only a small leakage current (less than 1 mA) flows; When the voltage reaches its trigger voltage Up, the resistance suddenly decreases to only a few ohms, so that a large inrush current passes through, and the overvoltage suddenly drops and then becomes high resistance in a short period of time.
The normal leakage current of the surger is very small, but the leakage current will increase with the increase of the number of lightning strikes.