SPDis an indispensable device in the lightning protection of electronic equipment. Its function is to limit the instantaneous overvoltage entering the power line and signal transmission line within the voltage range that the equipment or system can withstand, or to discharge the strong lightning current into the ground. , to protect the protected equipment or system from shock.
By working principle
According to its working principle, SPD can be divided into voltage switching type, voltage limiting type and combination type.
⑴ voltage switching SPD. It presents high impedance when there is no transient overvoltage. Once it responds to lightning transient overvoltage, its impedance suddenly changes to low impedance, allowing lightning current to pass through, also known as “short-circuit switch SPD”.
⑵ pressure limiting type SPD. When there is no instantaneous overvoltage, it is high impedance, but with the increase of surge current and voltage, its impedance will continue to decrease, and its current-voltage characteristic is strongly nonlinear, sometimes called “clamp-type SPD”.
(3) Combined SPD. It is composed of voltage switching type components and voltage limiting type components, which can display the characteristics of voltage switching type or voltage limiting type or both, which depends on the characteristics of the applied voltage.
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The components of a SPD The SPD chiefly consists of (see Fig.1): 1) one or more nonlinear components: the live part (varistor, gas discharge tube, etc.); 2) a thermal protective device (internal disconnector) which protects it from thermal runaway at end of life (SPD with varistor); 3) an indicator which indicates end of life of […]
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