1、 Lightning protection zoning

1. What is lightning protection zoning?

According to the definition of lightning protection zoning in IEC61312-1:

Lightning Protection Zone LPZ0A (Zone 0A)

All objects in this area may be directly struck by lightning, and the electromagnetic field generated by lightning in this area can propagate freely without attenuation.

Lightning protection zone LPZ0B (0B zone)

All objects in this area are within the protection range of the lightning arrester and will not be directly struck by lightning. However, the electromagnetic field generated by lightning in this area can freely propagate without attenuation due to the lack of shielding devices.

Lightning Protection Zone LPZ1 (Zone 1)

The objects in this area will not be directly struck by lightning due to being inside the building, and the current flowing through each conductor is smaller than that in LPZ0B area. The lightning electromagnetic field in this area may attenuate (the lightning electromagnetic field may not be consistent with LPZ0A and LPZ0B areas), depending on the shielding measures.

Subsequent lightning protection zone LPZ2 (zone 2, etc.)

When further reduction of lightning current and electromagnetic field is required, subsequent lightning protection zones should be introduced, and the required conditions for subsequent lightning protection zones should be selected according to the environment required by the system to be protected.

The installation locations of different levels of lightning arresters in the interval are different. B-level, C-level, and D-level can withstand direct lightning strikes without attenuation. Zone 0A may be affected by direct lightning strikes without attenuation. Zone 0B will not be affected by direct lightning strikes. Surge lightning arresters in Zone 1 will not be affected by direct lightning strikes at the junction between Zone 0 and Zone 1, and at the junction between Zone 2 and other important equipment in Zone 1 will not be further attenuated by direct lightning strikes.

2. What is the graded protection for lightning protection?

IEC61312 defines the protection zones for lightning protection. According to the requirements of the protection zones, corresponding lightning arresters need to be installed at the junction of each zone. B-level (i.e. level) lightning arresters should be installed at the junction of LPZ0B zone and LPZ1 zone, C-level (i.e. level 2) lightning arresters should be installed at the junction of LPZ1 zone and LPZ2 zone, and D-level (i.e. level 3) lightning arresters should be installed at the front end of equipment in LPZ2 zone. Its working principle is to use graded lightning arresters to release the energy induced by lightning layer by layer, gradually reducing the surge voltage and protecting the user end equipment.

According to the requirements of VDE 0675 for the protection level of B-level, C-level, and D-level lightning arresters, the installation level of lightning arresters is B-level power lightning arrester<4KVIC level power lightning arrester<2.5KVIID level power lightning arrester<1.5KVIII

That is to say, Class B surge is installed in Zone AB, Class C is installed in Zone 1, and Class D is installed in Zone 2

Selection method for upper switch or fuse of surge protector:

Determine the breaking current C of the switch or fuse based on the high fuse strength A of the surge protector and the high supply current B of the connected distribution line.

Determination method:

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 when C<a is not installed, style="box sizing: border box;" c is less than b or when c<a is not installed

The parameters for surge protection are specified in the international standard IEC. 8/20uS is a waveform that mimics lightning current. The specific meaning is that the time it takes for the waveform to reach the peak is 8us, and the time it takes to drop from the peak to half the wave (half of the peak) is 20us

2、 What is the classification of lightning protection levels? I often hear people say that A-level protection, B-level protection, C-level protection, and how to distinguish them based on large flow rates. Also, what is the concept of nominal voltage and current!

Grade A: Imax=120KA or above

B-level: Imax=80KA or above

C-level: Imax=40KA or above

D-level: Imax=20KA or above

3、 The principle of lightning protection device. The lightning protection device (surge protector) is actually a varistor with high pass and low resistance characteristics. When the power grid operates at a voltage not exceeding the maximum continuous operating voltage, there is a high resistance state between the two electrodes. If the voltage between two electrodes in the power grid exceeds the ignition voltage due to lightning strikes or overvoltage operations, the gap is broken down and the overvoltage energy is released through arc discharge. After the shock wave, the arc will be extinguished by the arc extinguishing system composed of arc segments and extinguishing chambers, and restored to a high resistance state to protect the system. (Function of Surge Protector)

If the surge protector itself malfunctions, it will remain connected for a long time, causing a short circuit in the power/system. At this time, the front-end circuit breaker or fuse needs to cut off the grounding circuit in a timely manner to ensure the normal operation of the circuit. (Function of circuit breaker or fuse in front of surge protector)

So how can this circuit breaker or fuse distinguish whether the short circuit is caused by lightning strike (referred to as A) or damage to the surge protector itself (referred to as B)? Because if A is identified as B, the circuit breaker will disconnect and the main circuit will be burned out. Conversely, if B is identified as A, the main circuit will continue to be short circuited and the circuit will be burned out.

All your questions can be summarized, as long as you understand the principle of installing a fuse in the front of the lightning arrester, you will be able to understand it!

The lightning arrester we use to prevent lightning is not actually a high-energy self mine that can destroy everything, but an induced lightning with high peak voltage, high current, and very short time. A fuse needs to meet certain conditions to melt, which is energy accumulation. Transient lightning strikes obviously do not melt the fuse when the lightning arrester is working. Because of the fuse, neither A nor B will burn out the circuit, but only cause the fuse to break, thus safely disconnecting the circuit from the ground.

You asked how to identify how the lightning arrester was damaged. I have a simple but not very accurate method:

A、 There may be burn marks on the lightning arrester or the circuit connected to the lightning arrester

B、 There are no such traces.

4、 Surge protector lightning protection level

Due to the enormous energy of lightning strikes, it is necessary to gradually release the lightning energy to the ground through a graded discharge method. Grade I lightning protection devices can discharge direct lightning current or the huge energy conducted when power transmission lines are directly struck by lightning. For places where direct lightning strikes may occur, Class-I lightning protection must be carried out. The second level lightning arrester is a protective device for the residual voltage of the previous level lightning arrester and the induced lightning strikes in the area. When a large amount of lightning energy is absorbed by the previous level lightning arrester, there is still a considerable amount of energy that can be conducted to the equipment or the third level lightning arrester, which needs to be further absorbed by the second level lightning arrester. At the same time, the transmission line passing through the level lightning arrester will also induce electromagnetic pulse radiation LEMP from lightning strikes. When the line is long enough, the energy of induced lightning becomes large enough, and a second level lightning arrester is needed to further discharge the lightning strike energy. The third level lightning arrester is used to protect LEMP and residual lightning energy passing through the second level lightning arrester.

1. Level protection

The purpose is to prevent surge voltage from directly conducting from LPZ0 zone into LPZ1 zone, and to limit surge voltage of tens of thousands to hundreds of thousands of volts to 2500-3000V.

The power lightning arrester installed on the low-voltage side of the household power transformer should be a three-phase voltage switch type power lightning arrester as a level protection, and its lightning current should not be less than 60KA. This level of power lightning arrester should be a large capacity power lightning arrester connected between each phase and the ground of the user's power supply system inlet. Generally, this level of power lightning arrester is required to have a large impulse capacity of at least 100KA per phase and a limited voltage of less than 1500V. It is called a Class I power lightning arrester. These electromagnetic lightning arresters are designed to withstand high currents from lightning and induced lightning strikes, as well as attract high-energy surges, and can divert a large amount of surge current to the ground. They only provide medium level protection by limiting the voltage (when the surge current flows through the power lightning arrester, the high voltage appearing on the line is called the limiting voltage), because Class I protectors mainly absorb large surge currents, and they alone cannot fully protect sensitive electrical equipment inside the power supply system.

The level power lightning arrester can prevent lightning waves of 10/350 μ s and 100KA, meeting the high protection standards specified by IEC. The technical reference is: lightning current greater than or equal to 100KA (10/350 μ s); The residual voltage value is not greater than 2.5KV; the response time is less than or equal to 100ns.

2. Second level protection

The purpose is to further limit the residual surge voltage of the lightning arrester to 1500-2000V and implement equipotential connection for LPZ1-LP52.

When the power lightning arrester for the output of the distribution cabinet line is used as the second level protection, it should be a voltage limiting power lightning arrester with a lightning current capacity of not less than 20KA. It should be installed at the branch distribution point that supplies power to important or sensitive electrical equipment. These power lightning arresters have a more complete absorption of residual surge energy passing through the surge arrester at the user's power supply inlet, and have excellent suppression effect on transient overvoltage. The power lightning arrester used in this area requires a large impulse capacity of 45kA or more per phase, and the required limiting voltage should be less than 1200V, which is called a Class II power lightning arrester. The second level protection of the power supply system for general users can meet the requirements for the operation of electrical equipment.

The second level power lightning arrester adopts Class C protector for full mode protection of phase to medium, phase to ground, and medium to ground. The main technical parameters are: lightning current capacity greater than or equal to 40KA (8/20 μ s); The peak residual voltage shall not exceed 1000V; the response time shall not exceed 25ns.

3. Third level protection

The purpose is to ultimately protect the equipment by reducing the residual surge voltage to within 1000V, so that the energy of the surge can damage the equipment.

The power lightning arrester installed at the input end of the AC power supply of electronic information equipment should be a series voltage limiting power lightning arrester as the third level protection, and its lightning current capacity should not be less than 10KA.

The rear line of defense can be achieved by using a built-in power lightning arrester in the internal power supply of the electrical equipment to completely eliminate small transient overvoltages. The power lightning arrester used in this area requires a large surge capacity of 20KA per phase or lower, and the required limiting voltage should be less than 1000V. For some particularly important or sensitive electronic devices, it is necessary to have third level protection, which can also protect the electrical equipment from transient overvoltage generated within the system.

For rectifier power supplies used in microwave communication equipment, mobile station communication equipment, and radar equipment, it is advisable to select DC power supply lightning arresters adapted to the working voltage as the final protection according to the protection needs of their working voltage.

4. Level 4 and above protection

According to the withstand voltage level of the protected equipment, if two-level lightning protection can limit the voltage below the equipment's withstand voltage level, only two-level protection is needed. If the equipment's withstand voltage level is low, four or even more levels of protection may be required. The lightning current capacity of the fourth level protection should not be less than 5KA.

5、 Installation methods and requirements for surge protectors

Surge protector HYC1 is installed using a 35MM standard rail

For fixed HYC1, the following steps should be followed for routine installation:

1) Determine the discharge current path

2) Mark the wires that cause additional voltage drops at the device terminals.

3) To avoid unnecessary induction loops, the PE conductor of each device should be labeled,

4) Establish an equipotential connection between the device and HYC1.

5) To carry out multi-level HYC1 energy coordination

In order to limit the inductive coupling between the protected and unprotected equipment parts after installation, certain measurements are required. By separating the induction source from the sacrificial circuit, selecting the loop angle, and limiting the closed loop area, mutual inductance can be reduced. When the current carrying component wire is part of the closed loop, the proximity of this wire to the circuit reduces the loop and induced voltage.

Generally speaking, it is better to separate the protected and unprotected wires, and they should be separated from the grounding wire. At the same time, necessary measurements should be taken to avoid transient orthogonal coupling between power cables and communication cables.

HYC1 grounding wire diameter selection:

Data cable: required to be larger than 2.5mm2; When the length exceeds 0.5 meters, it is required to be greater than 4mm2. YD/T5098-1998。

Power cord: When the cross-sectional area of the phase line is S ≤ 16mm2, use S for the ground wire; when the cross-sectional area of the phase line is 16mm2 ≤ S ≤ 35mm2, use 16mm2 for the ground wire; When the cross-sectional area of the phase line S is ≥ 35mm2, the ground wire requires S/2; Article 2.2.9 of GB 50054