Protection analysis of lightning surge generator

1. Test standards for electronic equipment lightning waves
The national standard  of the lightning waves of electronic equipment is GB/T17626.5 (equivalent to international standard IEC61000-4-5). The standard is mainly to simulate the various situations produced by indirect lightning strikes:
(1) Lightning strike the middle and external lines, and a large amount of current flows into the external line or ground resistance, which causes the interference voltage.
(2) Indirect lightning strikes (such as light strikes between clouds or in -cloud) feel the voltage and current on the external line.
(3) Lightning strike lines are close to objects, and the powerful electromagnetic fields established around them can feel the voltage on the external line.
(4) Lightning strikes the neighboring ground, and the ground current is introduced when it is through the public grounding system.

In addition to simulating lightning strikes, the standards also simulate the substation and other occasions, and the interference introduced due to the switching action (causes voltage transient when switching), such as:
(1) The interference generated during the switching of the main power system (such as the switching of the capacitor group).
(2) The same grid is interference when the smaller switch near the device is beating.
(3) Switch to the crystal tube equipment with a resonant line.
(4) Various systematic faults, such as short circuit and flying arc failure between equipment grounding networks or grounding systems.

The standard describes two different waveform generators: one is the waveform that is induced by lightning strikes on the power line; the other is the waveforms that are induced on the communication line.

How does a surge generator work?
The SG61000-5 surge generator provides a common basis for evaluating the resistance of power cords and internal connectors of different equipment to high energy transient interference caused by natural lightning surge induction and large capacity load switching. It fully meets the IEC 61000-4-5, EN61000-4-5 and GB/T17626.5 standards.

Both lines belong to the air rack line, but the impedance of the lines is different: the waveforms generated on the power line are relatively narrower (50uS), and the frontier should be steeped (1.2US); and the induction on the communication line is induced. The emergence of the waves is wider, but the forefront should be slower. Later, we mainly analyze the circuit with the waveforms produced by lightning strikes on the power line, and also briefly introduced the lightning protection technology of communication circuit.

2. The working principle of simulating lightning wave surge pulse generation circuit

The picture above shows the surge voltage generated by the induction of lightning electric shock to the power distribution equipment. Or the lightning current of the lightning current passed through the anti -high voltage pulse generated circuit generated by the lightning current through the public ground resistance.
The single pulse energy of 4KV is 100J

In the figure, Cs is an energy storage capacitor (about 10UF, which is equivalent to Leiyun capacitance); Us is a high -voltage power supply; Rc is a charging resistor; Rs is the pulse duration to form resistance (the discharge curve forms resistance); Rm is the resistance matching resistance Ls as the The current rises to form an inductance. The lightning and anti -bang resistance test has different parameter requirements for different products. The parameters in the figure above can be slightly changed according to product standard requirements.

Basic parameters requirements:
(1) Open output voltage: 0.5 ~ 6kV, divided into 5 level output, the last level is determined by the user and the manufacturer;
(2) Short -circuit output current: 0.25 ～ 2KA, for different levels of tests;
(3) Internal resistance: 2 ohm, additional resistance 10, 12, 40, 42 ohms, for other different levels of trials;
(4)Waves output polarity: positive/negative; when the wave output is synchronized with the power supply, the phase is 0 to 360 degrees;
(5) Repeat frequency: At least once every minute.

The harsh level of the thunderbolt rushing resistance test is divided into level 5:
Level 1: Good protection environment;
level 2: There is a certain protection environment;
level 3: ordinary electromagnetic harassment environment, special installation requirements for equipment, such as industrial workplace;
level 4: environment that is severely harassed. For example, civil air -rack lines, unprecedented high -voltage substations.
Class X: It is determined by the user and the manufacturer.

The 18uF capacitor in the figure can be different according to the harsh level, and the selection value can be different, but after a certain value, it is basically not much meaningful.

10 ohm resistance and 9uF capacitors can be selected differently according to the harsh level. It doesn’t make much sense.

The main parameters:
(1) DC breakdown voltage. This value is determined by the voltage value of a low -rise rate (dv/dt = 100V/s).
(2) Intellectual (or wave) breakdown voltage. It represents the dynamic characteristics of the discharge tube, and the voltage value of the rising rate is the voltage value of DV/DT = 1KV/uS.
(3) Named impact discharge current. The rated discharge current of 8/20uS waveform (8uS, half -peak duration of 20uS) is usually discharged 10 times.
(4) Standard discharge current. Through the rated valid value of the 50Hz AC current, the time for each discharge is 1s and the discharge is 10 times.
(5) The maximum single impact release current. For a single maximum discharge current for 8/20US current waves.
(6) Frequent current value of work. For a single maximum discharge current for 8/20uS current waves. For 50Hz AC power, it can withstand the valid value of the maximum current of 9 consecutive weeks.
(7) Insulation resistance. For a single maximum discharge current for 8/20uS current waves. For 50Hz AC power, it can withstand the valid value of the maximum current of 9 consecutive weeks.
(8) Capacity. The capacitance between the discharge tube is generally between 2 and 10pF, which is the smallest of all transient interference absorption devices.

Example of ultra -high wave voltage suppression circuit
Example 1

The figure above is a electrical principle diagram that can resist stronger thunderbolt pouring pulse voltage. In the figure: G1 and G2 are gas discharge pipes, which are mainly used to suppress high -voltage co -modulus pouring pulse. It has the ability to suppress; VR is a pressure -sensitive resistance, which is mainly used to suppress high -voltage differential modular wave pulse. After G1, G2, and VR suppression, the amplitude and energy of co -mode and differential waves are greatly reduced.

The breakdown voltage of G1 and G2 can be selected 1000Vp ~ 3000Vp. The voltage of VR is generally 1.7 times the maximum value of the industrial frequency voltage.
After the breakdown of G1, G2, the follow -up current will be generated. Be sure to add a fuse to prevent the short circuit of the subsequent current.

Example 2

Two voltage -sensitive resistance VR1, VR2, and a discharge tube G3 have been added. The main purpose is to strengthen the suppression of the voltage of the covaruance. Due to the leakage current of the voltage resistance, the general electronic products are strict with the leakage current (less than that of the leakage current (less than that 0.7mAp), so a discharge pipe G3 is added to the picture, which makes the current circuit’s leakage current equal to 0. The breakdown voltage of G3 is far less than the breakdown voltage of G1 and G2. After the G3 isolates the leakage, the breakdown voltage of the voltage resistance VR1 or VR2 can be selected as low accordingly and cause a strong inhibitory effect.

The connection of various lightning protection devices
The installation sequence of lightning protection devices cannot be made wrong. The discharge tube must be at the forefront, followed by waves to inhibit inductor and pressure -sensitive resistance (or discharge tube), and then the semiconductor TVS gates or X capacitors and Y capacitors.

The SG61000-5 fully automatic surge generator (also called lightning surge immunity test, combination wave generator, surge current generator/surge voltage generator, combined surge voltage and current generator) . 

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