As the name implies is beyond the normal operating voltage of the instantaneous overvoltage, known as transient pulse voltage, transient overvoltage, sudden wave or surge, etc., is a short-lived current, voltage fluctuations in the circuit, in the circuit usually lasts for about one millionth of a second of a violent pulse.
220 v circuit system in a sustained instant (millionths of a second) of 5KV or 10KV voltage fluctuations, that is, for the surge or transient overcharge.
Surge also refers to a voltage change in which the RMS value of the grid output voltage is greater than 110% of the rated value, and its duration is from one weekly wave (20ms) to several weekly waves.
I. Generation of power surges
There are two types: external power surges and internal power surges.
External surge: the most important source of lightning;
1, lightning surge overvoltage
Lightning surge caused by lightning is the most hazardous, in the lightning discharge, lightning strike as the center of the 1.5 ~ 2KM range, are likely to produce dangerous overvoltage. Lightning caused (external) surge is characterized by a single-phase pulse type with huge energy. The voltage of an external surge can rise rapidly from a few hundred volts to 20KV in a few microseconds and can be transmitted over considerable distances. According to ANSI/IEEE C62.41-1991 description, the instantaneous surge can be as high as 20KV, and the instantaneous current can be up to 10KA. according to the statistics, the surge outside the system mainly comes from lightning and other system impacts, which accounts for about 20%.
(1) induction lightning surge over-voltage: lightning strike lightning generated by high-speed changes in the electromagnetic field, the lightning radiation of the electric field on the conductor, the induction of a very high over-voltage, this type of over-voltage has a very steep leading edge and rapid decay.
(2) direct lightning surge overvoltage: direct lightning on the grid, due to the instantaneous energy is huge, extremely destructive, there is no one device can protect the direct lightning.
(3) lightning conductive surge overvoltage: by the distant overhead line conduction, due to the equipment connected to the power grid has a different overvoltage suppression ability, so the conductive overvoltage energy with the extension of the line and weakened.
(4) oscillating surge overvoltage: the power line equivalent of an inductor, and the earth and the presence of distributed capacitance between the adjacent metal objects, constituting a parallel resonant circuit, in the TT, TN power supply system, when a single-phase grounding fault occurs at the moment, due to the high-frequency components of the resonance, the line produces a very high over-voltage, the main damage to the secondary instrumentation.
Direct lightning strikes are the most serious events, especially if the lightning strike hits an overhead transmission line near the customer's inlet. During these events, the overhead transmission line voltage will rise to hundreds of thousands of volts, often causing insulation flashover (flashover is the phenomenon of discharging along the surface of a solid insulator when the gas or liquid dielectric surrounding the solid insulator is pierced). Lightning current is transmitted over a distance of one kilometer or more on a power line, and the peak current near the point of lightning strike can be 100kA or more. The current in the low voltage line at the customer's inlet can reach 5kA to 10kA per phase, and in areas with high lightning activity, power facilities may be subject to several direct lightning strikes per year causing severe lightning currents. In areas with high lightning activity, power facilities may experience several direct lightning strikes per year, resulting in severe lightning currents. These events are rare when power is supplied by underground power cables or in areas where lightning activity is infrequent.
Power surge protection focuses on the absorption and suppression of this part of the surge energy.
Internal surge: the source is the switching operation in the grid, inductive loads start and stop, power supply network operation faults, etc. overvoltage generated in the power lines.
Operating surge overvoltage
Inside the power system, due to the operation of the circuit breaker, load input and removal or system faults and other internal state changes within the system, and the system parameters change, which caused by the power of the internal electromagnetic energy conversion or transmission of the transition process, will be overvoltage within the system. The surge within the system mainly comes from the impact of the electrical load within the system, accounting for about 80%. The causes of internal overvoltage in the power system can be broadly divided into:
(1) the input and removal of large loads of electricity;
(2) the input and removal of inductive loads;
(3) the input and removal of power factor compensation capacitors
(4) short-circuit faults
Power supply system due to the start and stop of high-power equipment, line faults, casting and cutting action and frequency conversion. Failure, casting and cutting action and the operation of frequency conversion equipment, etc., will bring internal surge, to the power equipment to bring adverse effects. Especially computers, communications and other microelectronic equipment to bring a fatal impact. Even if there is no permanent damage to the equipment, such as nuclear power plants, medical systems, large factory automation systems, securities trading systems, telecommunication bureau switches, network hubs and other system operation anomalies and stoppages can bring very serious consequences.
Research has found that 88% of power surges on low-voltage power lines are generated by equipment inside buildings, such as: air conditioners, elevators, welding machines, air compressors and other inductive loads.
Two, the surge phenomenon
From the phenomenon of:
1, flying arc: in the damaged parts leaving obvious traces of arc;
2, corona: on the surface of the insulator, there are obvious traces of erosion, eroded parts of the insulation is reduced;
3, control circuits, such as the IC and other components of the damage;
4, the general Electronic equipment, household appliances, rectifier components, voltage regulator components are damaged;
5, ground faults caused by equipment charged (single-phase grounding): cause equipment phase-to-phase short circuit (motor phase-to-phase short circuit).
Three, the harm of the surge
Mainly divided into two kinds: catastrophic harm and cumulative harm.
Catastrophic hazards: a surge voltage exceeds the equipment's ability to withstand, the equipment is completely destroyed or greatly reduced life.
The insulation voltage of a motor is usually 2 times the normal working voltage plus about 1000V, so a 220V motor has an insulation voltage of 1500 V. A surge of electricity constantly strikes the insulation of the motor, causing the insulation to be pierced.
Cumulative Hazard: The cumulative effect of multiple small surges results in degradation of semiconductor device performance, equipment failure, and shortened lifespan, leading to shutdowns or reduced productivity.
According to statistics
In China: 63% of electrical products with problems under warranty are due to power surges.
Four, surge protection
Surge protection to be implemented in a graded manner, and ultimately achieve the purpose of perfect protection of power distribution systems and electronic equipment. Graded implementation of surge protection is the first step of the surge environment is categorized.
The classification of the surge environment is based on the strength and frequency of the surge. Internationally, the surge environment is generally divided into three categories
(1) Category C: refers to the outdoor as well as the incoming main switch, these parts are prone to stronger lightning surges, the specific location includes: the meter and the distribution panel between the line, the overhead line between the building, connected to the underground cable underground;
(2) Category B: refers to the location of the connection line between the environment of the C category is shorter, as well as the lighting system in large buildings, these locations include: meters and distribution panels, the overhead line between buildings, connecting the underground cable;
(2) Category B: refers to the location of the shorter connection line between the environment of the C category, as well as large Lighting systems in buildings, these locations can be generated by lightning as well as internal electrical switching, the surge generated by lightning is attenuated by the distribution line, has been attenuated a little more than the surge in the environment of class C;
(3) Class A: refers to the room power outlets and the terminals of the longer distribution line; the longer means more than 10 meters away from the location of the B class provisions of the power outlets, the Or away from the location of the class C provisions of more than 20 meters of power outlets, these locations of the surge is mainly the surge voltage generated by the internal electrical switch.
In accordance with the recommendations of the Institute of Electrical and Electronics Engineers (IEEE), surge protection should be implemented in a graded manner, the grading method corresponds to the classification of surge environments:
The first level: in the entry of the distribution cabinet, to eliminate the surge generated by outdoor lightning, to prevent the huge surge energy from entering the house;
The second level: in the distribution system of the switchboard at the distribution system, which serves two purposes, one is to further attenuate the residual voltage of the first level. One is to further attenuate the residual surge energy of the first level, and the other is to eliminate the surge generated by the internal electrical switch;
Third level: installed in the sensitive electronic equipment at the power supply into the line, to provide complete protection for electronic equipment.
The purpose of the graded protection is twofold: one is to attenuate lightning surges step by step, and the other is to eliminate surges generated when internal loads are switched on and off.
Reference:
1. Surge
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2. Surge
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