1. Lightning protection zone
1. What is lightning protection zone?
According to the definition of IEC61312-1 lightning protection zone:
Lightning protection zone LPZ0A (Zone 0A)
All objects in the area may be struck by direct lightning, and the electromagnetic field generated by lightning in the area can propagate freely without attenuation.
Lightning protection zone LPZ0B (Zone 0B)
Objects in this area are within the protection range of the air-termination device and will not be struck by direct lightning. However, because there is no shielding device for the lightning electromagnetic field in this area, the electromagnetic field generated by lightning can also propagate freely without attenuation.
Lightning Protection Zone LPZ1 (Zone 1)
Since the objects in this area are in the building, they will not be struck by direct lightning. The current flowing through the conductors is smaller than that in the LPZ0B area. The lightning electromagnetic field in this area may attenuate (the lightning electromagnetic field may not be consistent with the LPZ0A and LPZ0B areas). Depends on shielding measures.
Follow-up lightning protection zone LPZ2 (Zone 2, etc.)
When it is necessary to further reduce the lightning current and electromagnetic field, the follow-up lightning protection zone should be introduced, and the requirements of the follow-up lightning protection zone should be selected according to the environment required by the system to be protected.
The installation position of lightning arresters of different levels in the interval is different. Level B, Level C, and Level D can be subjected to direct lightning strikes without attenuation. Zone 0A may suffer from direct lightning strikes without attenuation. Zone 0B will not suffer direct lightning strikes. The front-end of important equipment at the junction between Zone 1 and Zone 2 will not be directly attenuated by lightning.
2. What is the graded protection of lightning protection?
IEC61312 defines the lightning protection zone. According to the requirements of the protection zone, the corresponding lightning protection device needs to be installed at the junction of each zone, and the B-level (that is, the first level) protection is installed at the junction of LPZ0B and LPZ1. For mine devices, install C-level (ie, second-level) lightning protection devices at the junction of LPZ1 and LPZ2 areas, and install D-level (ie, third-level) lightning protectors at the front end of the equipment in LPZ2 area. Its working principle is to use hierarchical lightning protection devices to discharge the energy induced by lightning layer by layer, and to reduce the surge voltage step by step, thereby protecting the user equipment.
According to the requirements of VDE 0675 for the protection level of B, C, D three-level lightning protection device, the protection level of the lightning protection device is the installation level of the B power lightning protection device<4KVIC power supply lightning protection device<2.5KVIID power supply lightning protection device< 1.5KVIII
In other words, Class B surge is installed in Zone AB, Class C is installed in Zone 1, Class D is installed in Zone 2
Selection method of the upper switch or fuse of the surge protector:
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 fuse).
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 not installed C<a style="box-sizing: border-box;" c is less than b or not installed c
The parameters of surge protection are stipulated in the international standard IEC. 8/20uS is a waveform that imitates the lightning current. The specific meaning is that the time for the waveform to reach the peak is 8us, and the time from the peak to the half wave (half of the peak) It is 20us.
2. What is the classification of lightning protection levels? I often hear people say that A-level protection, B-level protection, and C-level protection are distinguished by the maximum flow rate, and what is the concept of nominal voltage and current!
Class A: Imax=120KA or more
Class B: Imax=80KA or more
Class C: Imax=40KA or more
Class D: Imax=20KA or more
3. The principle of lightning protection. The lightning protector (surge protector) is actually a varistor, which has the characteristics of high pass and low resistance. When the grid is running under the condition of not exceeding the maximum continuous operating voltage, there is a high resistance state between the two electrodes. If the voltage between the two electrodes exceeds the ignition voltage due to lightning strikes or operating overvoltages, the gap will be broken down and the overvoltage energy will be released through arc discharge. After the shock wave, the arc will be extinguished by the arc extinguishing system composed of the arc splitter and the arc extinguishing chamber, and it will be restored to a high resistance state to protect the system. (The role of surge protector)
If the surge protector itself fails, it will be turned on for a long time, causing a short circuit of the power supply/system. At this time, the front-end circuit breaker or fuse is required to cut off the ground loop in time to ensure the normal operation of the loop. (The function of the circuit breaker or fuse in front of the surge protector)
So how does this circuit breaker or fuse distinguish whether it is a short circuit caused by a lightning strike (referred to as A) or a short circuit caused by the damage of the surge protector itself (referred to as B), because if A is distinguished as B, the circuit breaker opens, The main circuit will be burned. On the contrary, if B is identified as A, the main circuit will continue to be short-circuited and the circuit will be burned.
All your questions can be summed up as long as you understand the principle of installing a fuse in the front of the lightning arrester!
The lightning protection device we use is not actually a lightning that can destroy everything with a lot of energy, but an induced lightning with high voltage peaks, large currents, and a very short time. The fuse must meet certain conditions to be blown, that is, energy accumulation. It is obvious that transient lightning strikes will not blow the fuse when the lightning protection device is working. Because of the fuse, no matter what you call A or B, you will not burn the circuit, but just let the fuse open, so that the circuit and the ground are safely disconnected.
You asked above how to distinguish how the lightning protector is damaged. I have a very simple but not very accurate method:
A. There will be burn marks on the lightning protection device or the circuit connected to the lightning protection device
B. There is no such trace.
Fourth, the lightning protection level of surge (surge) protectors
Since the energy of lightning strikes is very huge, it is necessary to gradually discharge the energy of lightning strikes to the ground through a hierarchical discharge method. The first-level lightning protection device can discharge direct lightning current, or discharge the huge energy conducted when the power transmission line is directly struck by lightning. For places where direct lightning strikes may occur, CLASS-I lightning protection must be carried out. The second-level lightning protection device is a protection device for the residual voltage of the front-level lightning protection device and the induced lightning strikes in the area. When the front-level lightning strike energy absorption occurs, there is still a part of the equipment or the third-level lightning protection device. It is quite a huge amount of energy that will be transmitted, and it needs to be further absorbed by the second-level lightning protection device. At the same time, the transmission line passing through the first-level lightning protection device will also induce the lightning electromagnetic pulse radiation LEMP. When the line is long enough, the energy of the induced lightning becomes large enough, and the second-level lightning protection device is required to further discharge the lightning energy. The third-level lightning protection device protects LEMP and the residual lightning energy passing through the second-level lightning protection device.
1. The first level of protection
The purpose is to prevent the surge voltage from being directly conducted from the LPZ0 zone into the LPZ1 zone, and to limit the surge voltage of tens of thousands to hundreds of thousands of volts to 2500-3000V.
The power surge protector installed on the low-voltage side of the home power transformer should be a three-phase voltage switch-type power surge protector as the first level of protection, and its lightning flow rate should not be less than 60KA. This level of power surge protector should be a large-capacity power surge protector connected between each phase of the incoming line of the user's power supply system and the ground. It is generally required that this class of power supply lightning protection device has a maximum impact capacity of more than 100KA per phase, and the required limit voltage is less than 1500V, which is called CLASS I power supply lightning protection device. These electromagnetic lightning protection devices are specially designed to withstand the large currents of lightning and induced lightning and to attract high-energy surges, which can shunt large amounts of surge currents to the ground. They only provide limited voltage (when the impulse current flows through the power surge protector, the maximum voltage appearing on the line is called the limit voltage) is medium-level protection, because CLASS I protectors mainly absorb large surge currents. They cannot completely protect the sensitive electrical equipment inside the power supply system.
The first-level power lightning arrester can prevent 10/350μs, 100KA lightning wave, and reach the highest protection standard stipulated by IEC. The technical reference is: the lightning flow rate is greater than or equal to 100KA (10/350μs); the residual voltage value is not greater than 2.5KV; the response time is less than or equal to 100ns.
2. The second level of protection
The purpose is to further limit the value of the residual surge voltage through the first-stage lightning arrester to 1500-2000V, and implement equipotential connection for LPZ1-LPZ2.
The power surge protector output from the distribution cabinet circuit should be a voltage-limiting power surge protector as the second level of protection, and its lightning current capacity should not be less than 20KA. It should be installed in the substation that supplies power to important or sensitive electrical equipment. Road distribution office. These power supply lightning arresters can better absorb the residual surge energy that has passed through the surge arrester at the user's power supply entrance, and have an excellent suppression effect on transient overvoltage. The power surge protector used here requires a maximum impact capacity of 45kA or more per phase, and the required limit voltage should be less than 1200V, which is called a CLASS II power surge protector. The general user power supply system can achieve the second-level protection to meet the requirements of the operation of electrical equipment.
The second-level power lightning arrester adopts class C protector for phase-center, phase-ground and middle-ground full mode protection. The main technical parameters are: lightning current capacity is greater than or equal to 40KA (8/20μs); residual voltage The peak value is not more than 1000V; the response time is not more than 25ns.
3. The third level of protection
The purpose is to ultimately protect the equipment by reducing the value of the residual surge voltage to within 1000V, so that the surge energy can damage the equipment.
The power surge protector installed at the incoming end of the AC power supply of electronic information equipment should be a series voltage-limiting power surge protector as the third level of protection, and its lightning current capacity should not be less than 10KA.
The last line of defense can use a built-in power lightning arrester in the internal power supply of the electrical equipment to achieve the purpose of completely eliminating the tiny transient overvoltage. The power surge protector used here requires a maximum impact capacity of 20KA or less per phase, and the required limit voltage should be less than 1000V. For some particularly important or particularly sensitive electronic equipment, it is necessary to have the third level of protection, and it can also protect the electrical equipment from the transient overvoltage generated inside the system.
For the rectified power supplies used in microwave communication equipment, mobile station communication equipment and radar equipment, it is advisable to select a DC power supply lightning protector 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 levels of lightning protection can limit the voltage to be lower than the equipment’s withstand voltage level, only two levels of protection are needed. If the equipment’s withstand voltage level is low, four levels or even More levels of protection. The lightning current capacity of the fourth level protection should not be less than 5KA.
5. Installation methods and requirements of surge protectors
Surge protector HYC1 adopts 35MM standard rail installation
For fixed HYC1, the following steps should be followed for conventional installation:
1) Determine the discharge current path
2) Mark the wire that causes the extra voltage drop at the terminal of the device.
3) To avoid unnecessary induction loops, the PE conductor of each device should be marked,
4) Establish an equipotential connection between the equipment and HYC1.
5) To carry out multi-level HYC1 energy coordination
In order to limit the inductive coupling between the protected part and the unprotected part of the equipment after installation, certain measurements are required. Mutual inductance can be reduced through the separation of the inductive source and the sacrificial circuit, the choice of the loop angle, and the limitation of the closed loop area. When the current-carrying component wire is part of the closed loop, the loop and induced voltage are reduced due to the proximity of the wire to the circuit.
Generally speaking, it is better to separate the protected wire from the unprotected wire, and it should be separated from the ground wire. At the same time, in order to avoid transient orthogonal coupling between power cables and communication cables, necessary measurements should be made.
HYC1 ground wire diameter selection:
Data cable: It is required to be greater than 2.5mm2; when the length exceeds 0.5m, it is required to be greater than 4mm2. YD/T5098-1998.
Power cord: when the cross-sectional area of the phase wire is S≤16mm2, the ground wire uses S; when the cross-sectional area of the phase wire is 16mm2≤S≤35mm2, the ground wire uses 16mm2; when the cross-sectional area of the phase wire S≥35mm2, the ground wire requires S/2; GB 50054 Article 2.2.9
