Electromagnetic nuisance comes from the following sources:
(1) Lightning strikes. Lightning causes an inrush current of up to 100 kA with a rise time of only a few microseconds. This inrush current may induce a very high surge voltage in the building's electrical system, and if the building is struck directly by lightning, the resulting nuisance will be even greater.
(2) high-voltage power equipment harassment. High-rise building substations are generally located in the building, high-voltage transmission lines and transformer magnetic leakage are very strong source of nuisance, the spectrum is mainly distributed in the medium and short-wave frequency band, 30 MHz or less.
(3) power switching operations. The switching circuit process causes strong current pulses and short-term voltage dips, which all form a disturbance on the power grid.
(4) inverter, dimmer switch and other energy-saving devices, such as energy-saving devices are thyristors or similar electronic devices as the core of the equipment, they work on the power grid will produce high harmonic interference. Especially in a large number of such equipment and no corresponding harmonic inhibition measures, high harmonics will reach a very serious degree.
(5) Grid voltage fluctuation. Large-capacity load starting, stopping, causing instantaneous rise and fall of the grid voltage. The instantaneous imbalance of each phase voltage will lead to voltage waveform distortion, resulting in the generation of high harmonics, whose spectrum is low, but the energy is huge.
(6) digital circuit devices. Including computers, program-controlled switches, equipment, automatic control systems, field controllers and so on. Because the switching process of electronic circuits triggers rapid pulse current changes, their spectrum exists from tens of hertz to hundreds of megahertz.
(7) high-frequency oscillation circuit. Including transmitters, receivers and clock principal oscillators and other oscillating circuits of the fundamental frequency and its harmonics, the frequency from tens of kilohertz to hundreds of megahertz.
(8) Rectifiers and starters for gas discharge lamps and fluorescent lamps. They all produce electromagnetic nuisance to the power grid and the surrounding space.
(9) Household and office appliances. Which series excitation motor commutator, electronic controllers, timers, etc. will produce electromagnetic interference on the power grid and the surrounding space, the interference spectrum from tens of thousands of hertz to hundreds of megahertz. The switching operation of electrical appliances will form a heh-niki-heh sound (refers to the switching of electrical equipment caused by the radio similar to the heh-niki-heh sound) of the interference. www.diangon.com
(10) power tools. Electromagnetic interference can be generated by the commutator of a series-excited motor in power tools used in buildings.
(11) industrial, scientific and medical radio frequency equipment. Refers to hospitals, science and technology exhibition halls in those who may be 150 kHz - 400 GHz band of radio interference caused by equipment, including induction heating, microwave heating, high-frequency welding, scientific research instruments, high-frequency medical equipment, etc., a wide range of spectral distribution.
(12) Motor vehicles. Commercial buildings are generally equipped with garages, motor vehicles in the driving process by the spark discharge of the ignition device and electromagnetic interference, its frequency is mainly in the television band and ultra-short-wave communication band range.