What are the different uses of different types of surge protective devices?
The types and structures of surge protective devices vary according to different purposes, but they should at least contain a non-linear voltage limiting element. The basic components used in the surge protector are: discharge gap, gas discharge tube, varistor, suppression diode, choke coil, etc.
I. classification of SPD:
1. According to the working principle, the surge protector is divided into:
(1) switch type: its working principle is that it presents high impedance when there is no instantaneous over-voltage, but when it responds to lightning instantaneous over-voltage, its impedance changes to low value, allowing lightning current to pass through. The devices used for such devices include: discharge gap, gas discharge tube, thyristor, etc.
(2) voltage limiting type: its working principle is high resistance when there is no instantaneous over-voltage, but its impedance will decrease with the increase of surge current and voltage, and its current and voltage characteristics are strongly nonlinear. The devices used for such devices include: zinc oxide, varistor, suppression diode, avalanche diode, etc.
(3) shunt type or choke type
Shunt type: in parallel with the protected equipment, it presents low impedance for lightning impulse and high impedance for normal working frequency.
Choke type: in series with the protected equipment, it has high impedance for lightning impulse and low impedance for normal working frequency.
The devices used for this kind of device are: choke coil, high pass filter, low pass filter, 1 / 4 wavelength short circuit, etc.
2. The type and structure of surge protector are different according to different purposes, but it should at least contain a non-linear voltage limiting element. The basic components used in the surge protector are: discharge gap, gas discharge tube, varistor, suppression diode, choke coil, etc. By purpose:
(1) power protector: AC power protector, DC power protector, switching power protector, etc.
(2) signal protector: low frequency signal protector, high frequency signal protector, antenna feeder protector, etc.
There are two types of surge sources: external and internal. The main source of external surge is lightning. The other source is over-voltage generated by switching operation in power grid. Internal surge: it is found that 88% of the surge on the low-voltage power line is generated by the internal equipment of the building, such as air conditioning, elevator, welding machine, air compressor and other inductive loads. According to statistics, in the United States, the direct losses caused by power surge to various industries, such as shutdown, time loss, equipment maintenance and premature replacement of equipment, are up to 26 billion US dollars per year. In China, according to relevant statistics, 63% of the electrical products with problems during the warranty period are caused by power surge.