Surge protection device, also called lightning protection device, is an electronic device that provides security protection for various electronic devices, instrumentation, and communication lines. When a sudden current or voltage is suddenly generated in the electrical circuit or communication line due to external interference, the surge protector can conduct the shunt in a very short time, thereby avoiding the damage of the surge to other equipment in the circuit.
Surge protector basic components
1. Discharge gap (also known as protective gap): It is generally composed of two metal bars exposed to the air in a certain gap, one of which is the power supply line L1 or neutral line (N) of the required protection equipment. Connected, another metal rod is connected to the grounding wire (PE). When transient over-voltage strikes, the gap is broken down and a part of the over-voltage charge is led into the earth to prevent the voltage on the protected equipment from rising. The distance between two metal rods of such a discharge gap can be adjusted as required, the structure is relatively simple, and the arc extinction performance is poor when the disadvantages are eliminated. The improved discharge gap is an angular gap, and its arc extinguishing function is better than the former, and it is extinguished by the action of the electric force F of the loop and the rise of the hot gas flow.
2. Gas discharge tube: It is composed of a pair of cold cathode plates that are separated from each other and are enclosed in a glass tube or ceramic tube filled with a certain inert gas (Ar). In order to increase the trigger probability of the discharge tube, there is also a triggering agent in the discharge tube. This type of gas-filled discharge tube has two types of diodes and three types of electrodes. The technical parameters of the gas discharge tube are: DC discharge voltage Udc; impulse discharge voltage Up (Usually, Up≈(2~3)Udc; power frequency) Withstand current In; Impact withstand current Ip; Insulation resistance R (>109Ω); Inter-electrode capacitance (1-5PF)
The gas discharge tube can be used under DC and AC conditions, and its selected DC discharge voltage Udc is as follows: Use under DC conditions: Udc≥1.8U0 (U0 is the DC voltage for normal operation of the line)
Use under AC conditions: Udc≥1.44Un (Un is the AC voltage rms for normal operation of the line)
3. Varistor: It is a metal oxide semiconductor nonlinear resistor with ZnO as its main component. When the voltage across its terminals reaches a certain value, the resistor is very sensitive to voltage. Its working principle is equivalent to the series and parallel of multiple semiconductor PNs. The varistors are characterized by good nonlinearity (I=coefficient α in CUα), high through-flow capacity (～2KA/cm2), low normal leakage current (10-7 to 10-6A), low residual voltage (depending on In the varistor operating voltage and flow capacity), the instantaneous over-voltage response time is fast (~10-8s), no freewheeling.
The technical parameters of varistors are: varistor voltage (ie, switching voltage) UN, reference voltage Ulma, residual voltage Ures, residual voltage ratio K (K=Ures/UN), maximum flow capacity Imax, leakage current, response time .
Varistor use conditions are: varistor voltage: UN ≥ [(√ 2 × 1.2) / 0.7] U0 (U0 is the rated voltage of the power frequency)
Minimum reference voltage: Ulma ≥ (1.8 ~ 2) Uac (used under DC conditions)
Ulma ≥ (2.2 ~ 2.5) Uac (used under AC conditions, Uac is AC working voltage)
The maximum reference voltage of the varistor should be determined by the withstand voltage of the protected electronic device. The residual voltage of the varistor should be lower than the level of the damage voltage of the protected electronic device, ie, (Ulma)max≤Ub/K. Where K is the residual pressure ratio, Ub is the loss voltage of the protected equipment.
4. Suppression Diode: The Suppression Diode has a clamp voltage limiting function. It operates in the reverse breakdown region. Because it has the advantages of low clamping voltage and fast response, it is particularly suitable for use as the end of a multi-stage protection circuit. Several protection elements. Suppression diode volt-ampere characteristics in the breakdown region can be expressed by the following formula: I = CUα, where α is a nonlinear coefficient, for the Zener diode α = 7 ~ 9, in the avalanche diode α = 5 ~ 7.
Surge protector basic components
1. Discharge gap (also known as protective gap): It is generally composed of two metal bars exposed to the air in a certain gap, one of which is the power supply line L1 or neutral line (N) of the required protection equipment. Connected, another metal rod is connected to the grounding wire (PE). When transient over-voltage strikes, the gap is broken down and a part of the over-voltage charge is led into the earth to prevent the voltage on the protected equipment from rising. The distance between two metal rods of such a discharge gap can be adjusted as required, the structure is relatively simple, and the arc extinction performance is poor when the disadvantages are eliminated. The improved discharge gap is an angular gap, and its arc extinguishing function is better than the former, and it is extinguished by the action of the electric force F of the loop and the rise of the hot gas flow.
2. Gas discharge tube: It is composed of a pair of cold cathode plates that are separated from each other and are enclosed in a glass tube or ceramic tube filled with a certain inert gas (Ar). In order to increase the trigger probability of the discharge tube, there is also a triggering agent in the discharge tube. This type of gas-filled discharge tube has two types of diodes and three types of electrodes. The technical parameters of the gas discharge tube are: DC discharge voltage Udc; impulse discharge voltage Up (Usually, Up≈(2~3)Udc; power frequency) Withstand current In; Impact withstand current Ip; Insulation resistance R (>109Ω); Inter-electrode capacitance (1-5PF)
The gas discharge tube can be used under DC and AC conditions, and its selected DC discharge voltage Udc is as follows: Use under DC conditions: Udc≥1.8U0 (U0 is the DC voltage for normal operation of the line)
Use under AC conditions: Udc≥1.44Un (Un is the AC voltage rms for normal operation of the line)
3. Varistor: It is a metal oxide semiconductor nonlinear resistor with ZnO as its main component. When the voltage across its terminals reaches a certain value, the resistor is very sensitive to voltage. Its working principle is equivalent to the series and parallel of multiple semiconductor PNs. The varistors are characterized by good nonlinearity (I=coefficient α in CUα), high through-flow capacity (～2KA/cm2), low normal leakage current (10-7 to 10-6A), low residual voltage (depending on In the varistor operating voltage and flow capacity), the instantaneous over-voltage response time is fast (~10-8s), no freewheeling.
The technical parameters of varistors are: varistor voltage (ie, switching voltage) UN, reference voltage Ulma, residual voltage Ures, residual voltage ratio K (K=Ures/UN), maximum flow capacity Imax, leakage current, response time .
Varistor use conditions are: varistor voltage: UN ≥ [(√ 2 × 1.2) / 0.7] U0 (U0 is the rated voltage of the power frequency)
Minimum reference voltage: Ulma ≥ (1.8 ~ 2) Uac (used under DC conditions)
Ulma ≥ (2.2 ~ 2.5) Uac (used under AC conditions, Uac is AC working voltage)
The maximum reference voltage of the varistor should be determined by the withstand voltage of the protected electronic device. The residual voltage of the varistor should be lower than the level of the damage voltage of the protected electronic device, ie, (Ulma)max≤Ub/K. Where K is the residual pressure ratio, Ub is the loss voltage of the protected equipment.
4. Suppression Diode: The Suppression Diode has a clamp voltage limiting function. It operates in the reverse breakdown region. Because it has the advantages of low clamping voltage and fast response, it is particularly suitable for use as the end of a multi-stage protection circuit. Several protection elements. Suppression diode volt-ampere characteristics in the breakdown region can be expressed by the following formula: I = CUα, where α is a nonlinear coefficient, for the Zener diode α = 7 ~ 9, in the avalanche diode α = 5 ~ 7.
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