What are the sources of the hottest electromagneti

2022-07-27
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What are the sources of electromagnetic interference

electromagnetic interference is mainly transmitted in civil buildings through three ways: radiation, conduction and induction. Electromagnetic interference mainly comes from the following aspects:

(1) lightning strike, which can ensure that there is no problem with the connection. The impulse current caused by lightning can reach up to 100 Ka, and the rise time is only a few microseconds. This impulse current may induce a very high surge voltage in the electrical system of the building. If the building is directly hit by lightning, the disturbance will be greater

(2) disturbance of high voltage power equipment. The substations of high-rise buildings are generally located in buildings. The magnetic leakage of high-voltage transmission lines and transformers is a strong disturbance source, and its frequency spectrum is mainly distributed in the medium and short wave band, below 30 MHz

(3) power switch operation. The switching circuit causes strong current pulse and short-time voltage drop, which form electrical interference

(4) energy saving devices such as frequency converter and dimmer switch are devices with thyristors or similar electronic devices as the core, which will generate high-order harmonic interference in electricity when they work. Especially when a large number of such final equipment are used without corresponding harmonic suppression measures, high-order harmonics will reach a very serious level

(5) electric voltage fluctuation. The start and stop of large capacity load cause the instantaneous rise and fall of electric voltage. The "requirements" put forward that the instantaneous unevenness of each phase voltage will lead to voltage waveform distortion and high-order harmonic generation. Although the frequency spectrum is low, the energy is huge

(6) digital circuit device. Including computer, program-controlled exchange, field controller of equipment automatic control system, etc. Because the switching process of electronic circuits causes rapid pulse current changes, its frequency spectrum ranges from tens of hertz to hundreds of megahertz

(7) high frequency oscillation circuit. It includes the fundamental frequency and harmonics of oscillator circuits such as transmitter, receiver and clock local oscillator, with the frequency ranging from tens of kHz to hundreds of MHz

(8) rectifier and starter of gas discharge lamp and fluorescent lamp. They will cause electromagnetic disturbance to electricity and surrounding space

(9) household appliances and office appliances. Among them, the commutator, electronic controller and timer of series excited motor will produce electromagnetic interference to electricity and surrounding space, and the interference spectrum ranges from tens of thousands of Hz to hundreds of MHz. The switching operation of the electrical apparatus will cause the interference of "clicking sound" (which is similar to the "clicking sound" emitted by the radio when the electrical equipment is switched on and off if the fracture is not within the section)

(10) electric tools. In the electric tools used in buildings, the commutator of series motor can produce electromagnetic interference

(11) industrial, scientific and medical RF equipment. It refers to the equipment in hospitals and science and technology exhibition halls that may cause interference to the radio within the frequency band of 150 khz-400 GHz, mainly including induction heating, microwave heating, high-frequency welding, scientific research instruments, high-frequency medical instruments, etc., with a wide spectrum distribution

(12) motor vehicles. Commercial buildings are generally equipped with garages. During the driving process of motor vehicles, electromagnetic interference is generated by spark discharge of ignition devices. Its frequency is mainly within the television frequency band and ultrashort wave communication frequency band

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