Generation and suppression of surges

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This post was last edited by sdwfsgyykai on 2019-3-26 08:04. Surges refer to sudden, intense pulses in a circuit that exceed stable values, including transient overvoltages and overcurrents. In electronic devices, surges refer primarily to strong pulses that occur within one millionth of a second when the power supply is turned on, or pulses generated as a result of external electromagnetic interference affecting the circuit. Today, Junhe Electronics will analyze with you the generation and suppression of surges. I. Causes of surge generation There are many reasons for the occurrence of surges, which can be mainly divided into external and internal causes. (1) External causes: The main external cause is the overvoltage generated by lightning current. During a lightning discharge, extremely high overvoltages are generated within a 2-kilometer radius around the point of impact. Studies have shown that the transient overvoltages caused by lightning can reach up to 20,000 volts, while the transient overcurrents can reach up to 10,000 amperes; surges resulting from such external factors account for 20% of all such cases. Its main manifestations are as follows: 1. Direct lightning strikes buildings on the ground; due to the enormous energy released in an instant, the destructive force is extremely high, resulting in high transient overvoltages and overcurrents in electrical power systems and wiring. The surges caused by direct lightning strikes are the most severe incidents; especially when lightning hits an overhead power line near the user’s connection point, the voltage can rise to hundreds of thousands of volts. The lightning current can travel along the power lines for a distance of one kilometer or more, with peak currents in the vicinity of the strike point reaching 100 kA or more. But this probability is low. 2. Induced lightning: The lightning strike generates a strongly varying electromagnetic field with high speeds; the electric field emitted by the lightning acts on conductors, inducing very high overvoltages. Indirect lightning strikes and internal surges occur with relatively high frequency, and the majority of damage to electrical equipment is related to them. Therefore, the key to surge protection for power supplies is the absorption and suppression of this surge energy. 2. Internal causes: The internal causes of surges are related to the start-up and shutdown of devices within the power supply system, as well as faults in the operation of the power supply network. Within a power system, changes in system parameters occur due to internal conditions such as circuit breaker operations, the addition or removal of loads, or system failures. These changes give rise to transitional processes of electromagnetic energy conversion or transmission within the system, resulting in overvoltages within it. II. Hazards caused by surges Surges are common in power supply and distribution systems, and the hazards they pose cannot be ignored. The main ones include: (1) Cumulative hazards – Repeated exposure to surges leads to a decline in equipment performance, equipment failures, and a shortened lifespan, which in turn results in data loss and a reduced capacity for safe operation. The main manifestations are as follows: 1. Voltage fluctuations ； 2. The machinery will automatically stop or start ； 3. Electrical equipment has its service life shortened due to faults, resets, or voltage issues... (II) Catastrophic damage: If transient overvoltages exceed the equipment’s tolerance limits, it will result in complete damage to the equipment, leading to shutdowns, production interruptions, and significant losses such as the inability to recover data. The main manifestations are as follows: 1. The motor often needs to be replaced or rewound ； 2. Voltage breakdown of semiconductor devices ； 3. Damage to the metalized surface layer of components ； 4. Damage to the printed circuits or contact points on the printed circuit board ； 5. Damage to silicon components, thyristors… III. Measures for suppressing surges Surges pose numerous hazards; the most effective protection measure currently available is to install surge protectors in the circuits. Since the energy of lightning strikes is extremely large, it is necessary to dissipate this energy gradually into the ground through a staged discharge process. This is divided into four levels: (I) First-level surge protection. The first-level surge protection serves to prevent surge voltages from passing directly from the LPZ0 zone into the LPZ1 zone, limiting surge voltages ranging from tens of thousands to hundreds of thousands of volts to 2500–3000 V. It can handle direct lightning current, as well as the large amounts of energy generated when power transmission lines are struck by lightning. The first-stage surge protector (KSP-25KA/350) selected by Junhe Electronics is capable of withstanding lightning impulses of 10/350μs and 100KA; the technical specification here is that the lightning current rating is 100KA or higher (10/350μs) ； The residual voltage should not exceed 2.5 KV ； The response time is less than or equal to 100 ns. (II) Secondary surge protection: The secondary surge protection device is designed to protect against the residual voltage from the previous stage of lightning protection devices, as well as against induced lightning strikes within the area. When a large amount of energy from a lightning strike is absorbed by the previous stage, a portion of this energy – which can still be quite substantial for the equipment or the third stage of lightning protection devices – is transmitted forward, and it is the secondary surge protector that is needed to absorb this additional energy. At the same time, the transmission lines passing through the first-level surge protector can also be exposed to lightning-induced electromagnetic pulse radiation, LEMP. When the length of the lines is sufficient, the energy from lightning becomes substantial, requiring a second-level surge protector to further discharge this lightning energy. The second-level surge protector (KSP-80KA) selected by Junhe Electronics is used in the circuits of the power distribution cabinets. This type of protector provides full-mode protection for phase-to-neutral, phase-to-ground, and neutral-to-ground connections. Its key technical specifications include a lightning current rating of 40KA or more (8/20μs) ； The residual voltage peak shall not exceed 1000V ； The response time is no more than 25 ns. (III) Third-level surge protection: The third level of surge protection serves as the ultimate means of protecting equipment, reducing the residual surge voltage to below 1000V so that the energy of the surges does not cause damage to the equipment. The third-level surge protector (KSP-40KA) selected by Junhe Electronics – which is installed at the AC power inlet of electronic information equipment as a lightning protection device for the power supply at the third level – should be a series-connected voltage-limiting type power supply lightning protector, with a lightning current carrying capacity of not less than 10KA. (IV) Fourth-level surge protection: Fourth-level surge protection is determined based on the voltage tolerance level of the equipment to be protected. If two levels of lightning protection are sufficient to keep the voltage below the equipment’s tolerance level, then only two levels of protection are needed. If the equipment’s voltage tolerance level is low, four or even more levels of protection may be required. Junhe Electronics’ fourth-level surge protection uses power lightning protection sockets (KS-CP-42N and KS-CP-10A-10A), with a lightning current carrying capacity of not less than 5KA. In summary, the power supply lines have achieved a very high level of safety through four stages of protection. The surge protectors in the wiring are vulnerable components that require regular inspection and maintenance to ensure their proper functioning, thereby safeguarding the safety of the power supply lines and equipment.