18 INDUSTRIAL SPD 25 kA 20 kA 15 kA 10 kA 0 kA 25 kV 20 kV 15 kV 10 kV 0 kV 0 200 250 100 150 50 300 350 400 t µs Crest current Combined pulse Undefined causes 14% Other causes 41% Overvoltage 45% DAMAGE TO THE ELECTRONICS IN SPD SYSTEMS (OVERVOLTAGE LIMITERS) THESE DAYS, WITH THE EVER-INCREASING USE OF ELECTRICAL EQUIPMENT AND WITH THE EXPONENTIAL INCREASE OF THE LEVEL OF SEMICONDUCTOR INTEGRATION, MORE AND MORE ATTENTION IS GIVEN TO THE PHENOMENA RELATED TO TRANSITORY SURGE VOLTAGE OF ATMOSPHERIC ORIGINS AND SURGE VOLTAGE DUE TO ELECTRICAL SWITCHING ON DISTRIBUTION SYSTEMS BECAUSE OF THE SUBSTANTIAL ECONOMIC DAMAGE THAT THEY CAN CAUSE. THERE IS CONSEQUENTLY A NEED TO ADOPT INCREASINGLY GREATER SAFETY MEASURES INSIDE BUILDING AND SYSTEM INFRASTRUCTURES IN ORDER TO ENSURE THAT THE ELECTRICAL AND ELECTRONIC EQUIPMENT IS NOT DAMAGED AND CAN PROVIDE ITS PERFORMANCE, EVEN IN THE PRESENCE OF INTERFERENCES. THE SPDS, DEPENDING ON THE PARAMETERS OF THE LIGHTING CURRENT PULSE THEY ARE CALLED UPON TO DISCHARGE TO EARTH, ARE TESTED AND THEN CLASSIFIED IN DIFFERENT WAYS. THE IEC 61643-11 ED.1 (2011-03) STANDARD AND THE CORRESPONDING CEI EN 61643-11/A11 STANDARD, ALTHOUGH USING DIFFERENT, BUT SUBSTANTIALLY IDENTICAL DEFINITIONS, DIVIDE THEM UP AS FOLLOWS: IEC 61643-11 (2011-03) CEI EN 61643-11/A11 SPD WAVE FORM DISCHARGE CURRENT COMBINED PULSE Class 1 SPD Type 1 SPD T SPD for lightning current Tested with limp pulse current (10/350 µs) and with the nominal In discharge current (8/20 µs) 10/350 μs limp 25 kA - Class 2 SPD Type 2 SPD T Overvoltage limiter Tested with nominal In discharge current (8/20 µs) and with maximum Imax discharge current (8/20 µs). The Imax, nevertheless, is neither useful nor usable to choose the SPD 8/20 μs limp 20 kA - Class 3 SPD Type 3 SPD T Overvoltage limiter Tested with the combined generator that applies Uoc no-load voltage (1,2/50 µs) and in short circuit a presumed In current (8/20 µs) 1,2/50 μs - 10 kV
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