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Working principle of 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 role of surge protector

　　 Surge, (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 function of the surge protector is to limit the instantaneous overvoltage that penetrates into the power line and signal transmission line within the voltage range that the equipment or system can withstand, or to discharge powerful lightning currents into the ground to protect the protected equipment or system from Damaged by impact.

　　 The type and structure of a 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.

The function and principle of surge protector

1. The classification of SPD: 1. According to the working principle: 

1. Switch type: Its working principle is that when there is no instantaneous overvoltage, it presents a high impedance, but once it responds to the lightning instantaneous overvoltage, its impedance suddenly changes to a low value, allowing the lightning current to pass. When used as such devices, the devices include: discharge gap, gas discharge tube, thyristor, etc.

2. Voltage-limiting type: Its working principle is high resistance when there is no instantaneous overvoltage, but its impedance will continue to decrease with the increase of surge current and voltage, and its current and voltage characteristics are strongly nonlinear. The devices used for such devices are: zinc oxide, varistors, suppressor diodes, avalanche diodes, etc. 3. Shunt type or choke type

Shunt type: It is connected in parallel with the protected equipment, which presents a low impedance to the lightning pulse, and presents a high impedance to the normal operating frequency.

Choke type: It is connected in series with the equipment to be protected, which presents high impedance to lightning pulses, and presents low impedance to normal operating frequencies.

The devices used as such devices include: choke coils, high-pass filters, low-pass filters, 1/4-wavelength crowbars, etc.

According to the purpose: (1) Power protector: AC power protector, DC power protector, switching power protector, etc. (2) Signal protector: low-frequency signal protector, high-frequency signal protector, antenna feeder protector, etc.

2. The basic components and working principles of SPD: 1. Discharge gap (also called protection gap):

It is generally composed of two metal rods exposed to the air with a certain gap between them. One of the metal rods is connected to the power phase line L1 or neutral line of the required protection equipment, and the other metal rod is connected to the grounding line. When the transient overvoltage strikes, the gap is broken down, and a part of the overvoltage charge is introduced into the ground, avoiding the voltage increase on the protected equipment. The distance between the two metal rods of the discharge gap can be adjusted as required, and the structure is relatively simple, and its shortcomings are poor arc extinguishing performance. The improved discharge gap is an angular gap. Its arc extinguishing function is better than the former. It is a surge protector that extinguishes the arc due to the effect of the electric power F of the circuit and the rising effect of the hot air flow. It is also called a lightning arrester. , Is an electronic device that provides safety protection for various electronic equipment, instruments, and communication lines. When a spike current or voltage is suddenly generated in the electrical circuit or communication circuit due to external interference, the surge protector can conduct and shunt in a very short time, so as to prevent the surge from damaging other equipment in the circuit.

Surge protector, suitable for AC 50/60HZ, rated voltage 220V to 380V power supply system, to protect indirect lightning and direct lightning effects or other transient overvoltage surges, suitable for households, tertiary industry and industry Field surge protection requirements. Surge protector design principle, characteristics, application scope

Design principle

In the most common surge protectors, there is a component called a Metal Oxide Varistor (MOV), which is used to transfer excess voltage.

The MOV is composed of three parts: In the middle is a metal oxide material, and two semiconductors are connected to the power supply and the ground.

These semiconductors have variable resistances that change 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 the specified 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 via 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.

Another common surge protection device is a gas discharge tube. The role of these gas discharge tubes is the same as the MOV-they transfer excess current from the live wire to the ground wire, which is achieved by using an inert gas as a conductor between the two wires. When the voltage is in a certain range, the composition of the gas determines that it is a poor conductor. If the voltage surges and exceeds this range, the intensity of the current will be sufficient to ionize the gas, making the gas discharge tube a very good conductor. It conducts current to the ground wire until the voltage returns to a normal level, and then it becomes a poor conductor.

Both of these methods use parallel circuit design-excess voltage flows from a standard circuit into another circuit. There are several types of surge protector products that use series circuit designs to suppress surges-instead of shunting excess current to another line, they reduce the amount of electricity flowing through the live wire. Basically, these suppressors store electrical energy when they detect high voltages, and then gradually release them. The company that makes the protector explained that this method can provide better protection because it reacts faster and does not shunt to the ground, but on the other hand, this shunt may interfere with the building’s electrical system.

Suppressor diode: Suppressor diode has the function of clamping and limiting voltage. It works in the reverse breakdown zone. Because of its low clamping voltage and fast action response, it is especially suitable for the last few stages of multi-stage protection circuits. Protection components. The volt-ampere characteristics of the suppression diode in the breakdown zone can be expressed by the following formula: I=CUα, where α is the nonlinear coefficient, for the Zener diode α=7-9, and for the avalanche diode α=5-7.

Ø The technical parameters of suppression diodes mainly include:

(1) Rated breakdown voltage, which refers to the breakdown voltage under a specified reverse breakdown current (usually lma), which is generally within the range of 2.9V～4.7V for Zener diodes, while avalanche The rated breakdown voltage of the diode is often in the range of 5.6V to 200V.

(2) Maximum clamping voltage: It refers to the highest voltage that appears at both ends of the tube when a large current with a specified waveform is passed.

(3) Pulse power: It refers to the product of the maximum clamping voltage at both ends of the tube and the equivalent current in the tube under the specified current waveform (such as 10/1000μs).

(4) Reverse displacement voltage: It refers to the maximum voltage that can be applied to both ends of the tube in the reverse leakage zone, and the tube should not be broken down under this voltage. The reverse displacement voltage should be significantly higher than the peak operating voltage of the protected electronic system, that is, it cannot be in a weak conduction state when the system is operating normally.

(5) Maximum leakage current: It refers to the maximum reverse current flowing in the tube under the action of reverse displacement voltage.

(6) Response time: 10-11us

As an auxiliary component, some surge protectors are also equipped with built-in fuses. The fuse is a kind of resistor, when the current is lower than a certain standard, its conductivity is very good. Conversely, when the current exceeds the acceptable standard, the heat generated by the resistor will blow the fuse, thereby cutting off the circuit. If the MOV cannot suppress the surge, the excessive current will blow the fuse to protect the connected equipment. The fuse can only be used once and needs to be replaced once it blows.

Ø The SPD front-end fuse should be installed according to the parameters of the arrester manufacturer.

If the manufacturer does not stipulate, the general selection principle:

According to (the maximum fuse strength A of the surge protector) and (the maximum power supply current B of the connected distribution line) to determine (the breaking current C of the switch or the fuse).

How to determine:

When: B>A, C is less than or equal to A

When: B=A, C is less than A or C is not installed

When: B<A, C is less than B or C is not installed

Some surge protectors have line adjustment systems to filter out “line noise” and reduce current fluctuations. The system structure of this basic surge protector is very simple. The live wire is connected to the power board socket through the toroidal choke coil. The choke coil is just a ring made of magnetic material with a wire wrapped around it-a basic electromagnet. The up and down fluctuations of the current flowing in the live wire will charge the electromagnet, causing it to emit electromagnetic energy, thereby eliminating the small fluctuations in the current. This “regulated” current is more stable and can make the power supply current of the computer (or other electronic equipment) smoother.

In electronic design, surge mainly refers to the strong pulse generated at the moment the power supply (only mainly refers to the power supply) just turned on. Due to the nonlinearity of the circuit itself, there may be higher pulses than the power supply itself; or due to the power supply or circuit Other parts of the interference by itself or external spikes are called surges. It is very likely that the circuit will burn out at the moment of a surge, such as PN junction capacitor breakdown, resistance blown, and so on. The surge protection is a protection circuit that uses non-linear components to be sensitive to high frequency (surge). The simple and commonly used ones are parallel large and small capacitors and series inductances.

Classification of surge protectors (SPD)

According to the working principle:

(1) Switch type: Its working principle is that it presents high impedance when there is no instantaneous overvoltage, but once it responds to the lightning instantaneous overvoltage, its impedance suddenly changes to a low value, allowing lightning current to pass. When used as such devices, the devices include: discharge gap, gas discharge tube, thyristor, etc.

(2) Voltage-limiting type: Its working principle is high resistance when there is no instantaneous overvoltage, but its impedance will continue to decrease with the increase of surge current and voltage, and its current and voltage characteristics are strongly nonlinear. The devices used for such devices are: zinc oxide, varistors, suppressor diodes, avalanche diodes, etc.

(3) Shunt type or choke type

Shunt type: in parallel with the protected equipment, it presents a low impedance to the lightning pulse, and presents a high impedance to the normal operating frequency.

Choke type: It is connected in series with the equipment to be protected, which presents high impedance to lightning pulses, and presents low impedance to normal operating frequencies. The devices used for such devices are: choke coils, high-pass filters, low-pass filters, 1/4 wavelength short-circuit devices, etc.