⒈ Discharge gap (also known as protection gap):
It is generally composed of two metal rods exposed to the air separated by a certain gap. One of the metal rods is connected to the power phase line L1 or neutral line (N) of the required protection equipment, and the other metal rod is connected to the grounding line ( PE) is connected, when the instantaneous overvoltage strikes, the gap is broken down, and a part of the overvoltage charge is introduced into the ground, avoiding the voltage rise on the protected equipment. The distance between the two metal rods in the discharge gap can be adjusted as required, and the structure is relatively simple, but the disadvantage is that the arc extinguishing performance is poor. The improved discharge gap is an angular gap, and its arc extinguishing function is better than the former. It relies on the action of the electric power F of the circuit and the rising action of the hot air flow to extinguish the arc.
⒉ Gas discharge tube:
It consists of a pair of cold cathode plates separated from each other and enclosed in a glass tube or ceramic tube filled with a certain inert gas (Ar). In order to improve the triggering probability of the discharge tube, there is also a triggering aid in the discharge tube. This gas-charged discharge tube has a two-pole type and a three-pole type.
The technical parameters of the gas discharge tube mainly include: DC discharge voltage Udc; impulse discharge voltage Up (usually Up ≈ (2~3) Udc; power frequency withstand current In; impulse withstand current Ip; insulation resistance R (>109Ω) ); capacitance between electrodes (1-5PF)
The gas discharge tube can be used under DC and AC conditions, and the selected DC discharge voltage Udc is as follows: Use under DC conditions: Udc≥1.8U0 (U0 is the DC voltage for the normal operation of the line)
Use under AC conditions: U dc≥1.44Un (Un is the rms value of the AC voltage for the line to work normally)
⒊ Varistor:
It is a metal oxide semiconductor nonlinear resistor with ZnO as the main component. When the voltage acting on both ends reaches a certain value, the resistance is very sensitive to the voltage. Its working principle is equivalent to the series-parallel connection of multiple semiconductor P-Ns. Varistors are characterized by good nonlinear characteristics (non-linear coefficient α in I=CUα), large current capacity (~2KA/cm2), small normal leakage current (10-7~10-6A), and low residual voltage (depending on Due to the working voltage and current capacity of the varistor), the response time to instantaneous overvoltage is fast (~10-8s), and there is no freewheeling.
The technical parameters of varistor mainly include: varistor voltage (ie switching voltage) UN, reference voltage Ulma; residual voltage Ures; residual voltage ratio K (K=Ures/UN); maximum current capacity Imax; leakage current; response time .
The use conditions of the varistor are: varistor voltage: UN≥[(√2×1.2)/0.7]U0 (U0 is the rated voltage of the power frequency power supply)
Minimum reference voltage: Ulma≥(1.8～2)Uac (used under DC condition)
Ulma≥(2.2～2.5)Uac (used under AC conditions, Uac is the AC working voltage)
The maximum reference voltage of the varistor should be determined by the withstand voltage of the protected electronic equipment, and the residual voltage of the varistor should be lower than the loss voltage level of the protected electronic equipment, that is (Ulma) max≤Ub/K, the upper In the formula, K is the residual voltage ratio, and Ub is the loss voltage of the protected equipment.
⒋Suppression diode:
The suppressor diode has the function of clamping and limiting voltage. It works in the reverse breakdown region. Because of its low clamping voltage and fast response, it is especially suitable for use as the last-level protection element in multi-level protection circuits. The volt-ampere characteristics of the suppression diode in the breakdown region can be expressed by the following formula: I=CUα, where α is the nonlinear coefficient, for Zener diode α=7～9, in avalanche diode α=5～7.
Technical Parameters of Suppressor Diodes
The breakdown voltage refers to the breakdown voltage under the specified reverse breakdown current (usually lma), which is generally in the range of 2.9V to 4.7V for the rated breakdown voltage of the Zener diode, while the rated breakdown voltage of the avalanche diode is in the range of 2.9V to 4.7V. The breakdown voltage 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 it passes a large current with a specified waveform.
(3) Pulse power: It refers to the product of the maximum clamping voltage at both ends of the tube and the equivalent value of the current in the tube under the specified current waveform (such as 10/1000μs).
⑷Reverse displacement voltage: It refers to the maximum voltage that can be applied to both ends of the tube in the reverse leakage area, and the tube should not break down under this voltage. This reverse displacement voltage should be significantly higher than the peak value of the maximum operating voltage of the protected electronic system, that is, it cannot be in a weak conduction state when the system is operating normally.
⑸ Maximum leakage current: It refers to the maximum reverse current flowing in the tube under the action of reverse displacement voltage.
⑹Response time: 10-11s
⒌ Choke coil: The choke coil is a common mode interference suppression device with a ferrite core. It consists of two coils of the same size and the same number of turns wound symmetrically on the same ferrite toroidal core. , to form a four-terminal device, it has a suppressing effect on the common mode signal showing a large inductance, but has little effect on the differential mode signal showing a small leakage inductance. The use of choke coils in balanced lines can effectively suppress common mode interference signals (such as lightning interference), but has no effect on differential mode signals normally transmitted by the line.
