What is the function and principle of a surge protector?
Surge, also known as surge, surge, refers to the peak value that exceeds the stable value instantaneously, including surge voltage and surge current
The surge of the power supply system mainly comes from two reasons: external (thunder and lightning) and internal (start and stop of electrical equipment, failures, etc.). Surge is often characterized by a very short time (the overvoltage caused by lightning is often in the microsecond level, and the overvoltage caused by electrical equipment is often in the millisecond level), but the instantaneous voltage and current are extremely large, which is very likely to affect the electrical equipment and Cables cause harm, so a surge protector is needed to protect them.
Surge Protective Device, English name Surge Protective Device, SPD for short, is an electronic device that provides safety protection for various electronic equipment, instruments and communication lines, and is mainly used to limit overvoltage and discharge surge current. Surge protectors are generally connected in parallel with the equipment to be protected. When an overvoltage is generated, it can have the effect of shunting and limiting voltage. Prevent excessive current and voltage from damaging the equipment.
The core component of the surge protector is an internal non-linear component. According to the difference of non-linear components, surge protectors can be divided into switching type (the core component is mainly a discharge gap) and voltage limiting type (the core component is mainly a varistor).
Although the working principles of the discharge gap and the varistor are different, the basic characteristics are very similar: when there is no overvoltage, their impedance is very high, generally at the megohm level, which is almost equivalent to an open circuit. When an overvoltage occurs, the impedance quickly drops to a few ohms, and the surge current will flow into the ground through the surge protector without entering the equipment. At the same time, because the impedance of the surge protector at this time is very small, its two The voltage is also relatively small, and because it is connected in parallel with the protected device, it prevents the device from withstanding a large surge voltage. This has the effect of draining and limiting pressure
Surge protection device (Surge protection Device) is an indispensable device in the lightning protection of electronic equipment. It used to be called "lightning arrester" or "overvoltage protector" in English abbreviated as SPD. The instantaneous overvoltage into the power line and signal transmission line is limited to the voltage range that the equipment or system can withstand, or strong lightning current is discharged into the ground to protect the protected equipment or system from impact and damage.
The type and structure of the surge protector are different for different purposes, but it should at least contain a non-linear voltage limiting element. The basic components used in surge protectors are: discharge gap, gas-filled discharge tube, varistor, suppression diode, choke coil, etc.
Surge protection process
The standard surge protector will deliver the current from the power socket to multiple electrical and electronic devices plugged into the power board. If a surge or spike occurs and the voltage exceeds the acceptable level, the surge protector will transfer the excess current to the ground of the power outlet.
In the most common surge protectors, there is a component called Metal Oxide Varistor (MOV), which is used to transfer excess voltage. As shown in the figure below, the MOV connects the live wire and the ground wire together.
MOV consists of three parts: in the middle is a metal oxide material, and two semiconductors are connected to the power supply and ground.
These semiconductors have a variable resistance that changes with changes in voltage. When the voltage is lower than a certain value, the movement of electrons in the semiconductor will produce extremely high resistance. Conversely, when the voltage exceeds this specific value, the movement of electrons will change, and the resistance of the semiconductor will be greatly reduced. If the voltage is normal, the MOV will be idle. When the voltage is too high, the MOV can conduct a large amount of current and eliminate the excess voltage.
As the excess current is transferred to the ground wire through the MOV, the live wire voltage will return to normal, causing the resistance of the MOV to increase again rapidly. In this way, the MOV only transfers the surge current, while allowing the standard current to continue to power the equipment connected to the surge protector. For example, the MOV acts like a pressure-sensitive valve, opening only when the pressure is too high.
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