Lightning surge protection standards and testing for electronic products
After long-term in-depth research on the three main forms of lightning strikes: direct lightning, conductive lightning, and induced lightning, people have established the theory of lightning induction and high-voltage counterattack, and clarified the transmission law of high-voltage lightning waves on metal wires. On this basis, people invented lightning arresters with gap series fuses, gapless zinc oxide lightning arresters, and transient overvoltage surge suppressors (TVS). The comprehensive application of these technologies on power and other metal transmission lines effectively prevents the catastrophic damage of conducted lightning strikes to people and the environment.
2. Mechanism and comprehensive protection of lightning surge
Although we have effective protective measures for the catastrophic damage caused by direct and conductive lightning, indirect lightning (such as lightning strikes within or between clouds, or lightning strikes on nearby objects) can still induce surge voltage and current on outdoor overhead lines. In addition, in power plants or switchyards, large switching moments can also induce large surge voltages and currents on the power supply line. The common characteristic of these two types of surges is that their energy is particularly high (compared to energy, electrostatic discharge is in the picojule level, fast pulse group is in the millijoule level, and lightning surge is in the hundreds of joules level, which is several million times the amount of the first two types), but the waveform is relatively slow (in microseconds, while electrostatic and fast pulse group are in the nanosecond level, or even sub nanosecond level), and the repetition frequency is low. The surge referred to in the field of electromagnetic compatibility generally comes from switching transients and lightning transients.
2.1 Switching Transients
The system switching transient is related to the following: main power system switching disturbance, such as the switching of capacitor banks; Minor switch actions or load changes near instruments within the distribution system; Resonant circuits related to switching devices, such as thyristors; Various system faults, such as short circuit and arc fault of equipment group grounding system.
2.2 Lightning transient
The main sources of surge (impulse) voltage generated by lightning are as follows: direct lightning strikes external circuits (outdoor), and the injected large current flows through the grounding resistance or external circuit impedance to generate surge voltage; Indirect lightning strikes that generate induced voltage and current on external conductors inside buildings; The lightning incoming current of nearby direct ground discharge is coupled to the common grounding path of the equipment group grounding system. If there is a lightning protection device, when the protection device acts, the voltage and current may change rapidly and couple to the internal circuit, still generating transient impacts.
Therefore, the surge (impact) protection of electronic devices has become a problem that electronic product designers must face and solve. The relevant surge protection standards and their testing provide a basis and means for determining the compliance of surge (impact) protection design in electronic products.
2.3 Comprehensive protection against lightning surge
In order to effectively ensure that personnel, the environment, and equipment are protected from the hazards of lightning surges, a comprehensive and systematic protection system is needed.
When designing a protection system, the protection area should be divided based on the probability of lightning damage and the sensitivity of the protected object to lightning, and the corresponding lightning protection level and measures should be determined to form a three-dimensional deep (lightning strike) surge protection system.
The protective measures taken based on the characteristics of each partition include:
(1) Lightning arrester (lightning rod, lightning strip, etc.) and its system shall be used at high places outside the building or system to prevent direct lightning strike.
(2) Install a surge device on the transmission conductor entering the building or system to divert lightning energy and prevent conductive lightning strikes.
(3) The method of equipotential bonding to the grounding of buildings or system equipment is used to prevent direct lightning strikes from striking back through grounding.
(4) Adopting multi-level electromagnetic shielding inside buildings or equipment to reduce or limit the generation of induced lightning overvoltage. These shields include building shielding, electronic system equipment room shielding, equipment casing shielding, and signal pipeline shielding.
(5) Overvoltage/overcurrent protectors are used in the transmission channels of external power sources or signals entering the building or system to prevent them from harming the protected objects. That is, overvoltage protectors (such as overvoltage limiters or surge absorbers) are installed in power circuits, signal interfaces, and other circuits. The limiters place the generated overvoltage clamps below the limit value, ensuring that system equipment or components are free from abnormal actions or damage. The setting or selection of overvoltage protectors should be comprehensively and systematically considered based on the importance level of their protection system or the interface mode of the system circuit.
The specific implementation and installation of each part have corresponding standard requirements. As long as the above protective measures meet the corresponding protection standard requirements according to their zoning and location characteristics, a complete modern lightning protection system can be formed, which can effectively ensure that personnel, environment, and equipment are protected from (lightning) surge hazards.
3. Surge (impact) immunity standards and testing for electronic products
3.1 Common lightning protection standards and their application scope
3.1.1 Lightning protection standards for building design
a) GB50057-94 (2000 Revision) "Code for Design of Lightning Protection of Buildings"
Specify the lightning protection design requirements for general buildings, so that buildings can adopt appropriate lightning protection measures according to local conditions to prevent or reduce personal injury and property damage caused by lightning strikes on buildings.
b) GB50174-93 "Code for Design of Lightning Protection in Computer Rooms"
Applicable to the design of electronic computer rooms with a building area greater than or equal to 140 square meters for newly built, renovated, and expanded host rooms on land. This specification does not apply to industrial control computer rooms and microcomputer rooms.
c) IEC1312 "Protection against Lightning Electromagnetic Pulse"
3.1.2 Lightning protection standards for building grounding and installation
a) YD5068-98 "Design Specification for Lightning Protection and Grounding of Mobile Communication Base Stations"
This specification is applicable to the lightning protection and grounding design of new mobile communication base stations. For the lightning protection and grounding design of modified or expanded mobile communication base stations, the modification of lightning protection and grounding technology of existing base stations can also be referred to.
b) YDJ26-89 "Provisional Technical Regulations for Grounding Design of Communication Bureau (Station) (Part of Comprehensive Building)"
This standard specifies the design, installation, inspection, maintenance, and evaluation of lightning protection systems for information systems inside or on top of buildings.
c) YD2011-93 "Design Specification for Lightning Protection and Grounding of Microwave Stations"
d) VDE0185 "Installation Guidelines for Lightning Protection Systems"
3.1.3 Technical standards for lightning protection devices
a) GA173-1998 "Lightning Protection and Security Devices for Computer Information Systems"
The lightning protection device installed in the computer information system should comply with the technical requirements, experimental methods, inspection rules, marking, packaging, transportation, and storage requirements of this standard, and can effectively prevent induced lightning from damaging the protected equipment of the system.
b) IEC61643 SPD Power Supply Lightning Protection Device
Standard, suitable for power lightning protection devices on AC/DC power circuits and equipment, with a rated voltage of 1000VAC or 1500VDC. The power lightning arrester is classified, tested, and applied according to this standard.
c) IEC61644 SPD Communication Network Lightning Protection Device
Standard, suitable for lightning protection devices in communication signal network systems, with built-in overvoltage and overcurrent components and a rated voltage of 1500VAC/DC. The power lightning arrester is classified, tested and applied according to this standard.
d) VDE0675 "Overvoltage Protector"
German standard, applicable to overvoltage discharge protectors (power lightning protectors), suitable for use in power distribution systems with rated AC and DC voltages ranging from 100V to 1000V. The standard specifies classification requirements for lightning protectors.
3.1.4 Technical standards for product lightning protection
a) GB17626.5-1999 Electromagnetic Compatibility Testing and Measurement Techniques - Surge (Impact) Immunity Test
b) YD/T993-1998 "Technical Requirements and Test Methods for Lightning Protection of Telecommunication Terminal Equipment"
c) GB3482-1983 "Lightning Test Methods for Electronic Equipment"
d) GB3483-1983 "Guidelines for Lightning Test of Electronic Equipment"
Below is a brief introduction to the lightning protection (surge) standards for these four products.
3.2 GB17626.5-1999 Standard Testing Requirements
Different electronic and electrical product standards have different requirements for surge (impact) immunity tests, but most of these standards directly or indirectly refer to the national electromagnetic compatibility basic standard GB/T17626.5-1999 (idtIEC61000-4-5:1995): "Electromagnetic Compatibility Testing and Measurement Techniques Surge (Impact) Immunity Test", and conduct tests according to the test methods in it.
3.2.1 Scope of application
Applicable to the response of electrical and electronic equipment to surge (impulse) voltage generated by switching or lightning action at a certain hazardous level when working under specified working conditions. This standard does not test the ability of insulation to withstand high voltage. This standard does not consider direct lightning strikes.
This standard is the basic standard that specifies the classification of test levels and test methods for surge (impact) testing, but does not specify specific criteria for selecting test levels and determining conformity. It is generally not directly applicable to specific product surge (impact) immunity testing and compliance judgment. This standard is generally referred to as a specific product or product cluster standard as its testing method, and the specific selection of testing levels and qualification criteria are specified in the corresponding standards.
3.2.2 Test generator
The characteristics of the signal generator should simulate switching transients and lightning transients as much as possible: if the interference source is on the same line as the port of the tested equipment, such as in a power network (directly coupled), the signal generator can simulate a low impedance source at the port of the tested equipment; If the interference source and the port of the tested device are not in the same line (indirectly coupled), then the signal generator can simulate a high impedance source.
For products used in different occasions and different ports of the product, the parameters of the corresponding analog signal generator are also different due to the different transient waveforms of the corresponding surge (impact). For example, for the AC/DC power supply port and short distance signal circuit/line port, a 1.2/50 µ s (8/20 µ s) combined wave signal generator is usually used (voltage surge wave is formed when the output end of the generator is open circuit; electrical surge wave is formed when the output end of the generator is short circuit), and its waveform diagram is shown in Figure 2-1; For telecommunications ports and long-distance signal circuits/line ports, a 10/700 µ s CCITT compliant test signal generator is typically used.
3.2.3 Test level and signal generator
The test level should be selected based on the installation situation. When testing at higher levels, the test should meet the lower levels listed in the table. For specific products, the selection of test levels is often specified in the corresponding product or product family standards.
Table 2-1 Test Levels
Level open circuit test voltage (± 10%), KV
Note: X is an open level that can be specified in the product requirements
3.2.4 Coupling method
It is recommended to use a matching coupling/decoupling network for AC/DC power lines (only applicable to combined wave signal generators). Capacitive coupling can be used for AC/DC power lines: while connecting to the power decoupling network, the test voltage can also be added in a line to line or line to place manner through capacitive coupling. For unshielded unbalanced I/O lines, capacitive coupling is recommended when it has no impact on the communication function of the line. For unshielded balanced (communication) lines, it is recommended to use gas discharge tubes for coupling.
3.2.5 Source impedance determination
The selection of signal generation source impedance depends on the type of wire, conductor, and line (AC power supply, DC power supply, interconnection, etc.); The length of cables and lines; Application of test voltage (line to line or line to ground). 2 Ω impedance represents the source impedance of the low-voltage power grid; 12 Ω impedance represents the source impedance of the low-voltage power grid to ground; 42 Ω impedance represents the source impedance of all other lines to ground.
3.2.6 Test implementation
The power, signal, and other functional electrical quantities should be used within their rated range and in normal working condition. Select the corresponding test waveform generator, coupling unit, and corresponding signal source internal resistance based on the port type of the EUT to be tested. Place the test equipment under typical working conditions and apply impulse voltage to each port in sequence based on the test equipment port and its combination.
When conducting surge tests on power terminals, the test voltage should be applied at the positive and negative peaks and zero crossing points of the AC voltage waveform. Pulse impact should be applied to the power and signal lines in different combinations of common mode and differential mode states. Perform at least 5 pulse shocks for each combination state. Each combination should be tested for different pulse polarities, with an interval of no less than 1 minute between two pulses.
If higher level testing requirements need to be met, lower level testing should also be conducted at the same time. Only when both requirements are met at the same time can we consider the test to have passed. Different product or product family standards may have specific provisions for the implementation of tests based on the characteristics of the product.
3.3 YD/T993-1998 Standard Test Requirements Overview
YD/T993-1998: "Technical Requirements and Test Methods for Lightning Protection of Telecommunications Terminal Equipment" is a product cluster standard that not only specifies test methods, but also specifies test levels and judgment criteria. It is applicable to lightning protection testing and standard compliance evaluation of telecommunications terminal equipment such as machines, fax machines, modulation demodulators, and multimedia user terminals that are directly connected to balanced pairs through metal wires. It is a mandatory testing standard for mandatory product certification (3C certification) of current telecommunications terminal equipment.
3.3.1 Test items
a) Horizontal test: The test in which an impulse voltage is applied between the input (output) terminals of the signal line or power line of the device under test (EUT)
b) Longitudinal test: The test in which the impulse voltage is applied between the input (output) end of the EUT signal line or power line and the ground.
c) Electrical isolation test with communication network: Impulse voltage is applied between the communication external terminal of the EUT and each of the following components or circuits: the EUT needs to grip or contact non grounded non-conductive or conductive components; Test refers to accessible components and circuits (excluding connector contacts that meet the requirements of telecommunications circuit accessories) as specified in Figure 19 of GB4943 standard; A circuit that connects other devices (excluding signal lines).
3.3.2 Pretreatment of test samples
EUT should be a product that has passed inspection according to relevant standards. Terminals without shock waves should be in a normal load impedance state. For EUTs with remote power supply, the remote power supply should be considered as a component of the test sample, and the impulse voltage is applied through a discharge tube. Turn on the power supply of the EUT and preheat the test sample at the rated working voltage and current for half an hour.
3.3.3 Test voltage and waveform
a) For non exposed environments (without primary protection), the impulse voltage amplitude is:
Lateral test: 1.5kV ± 3%
Longitudinal test: 1.0kV ± 3%
b) For exposure to the environment