Led Lighting Spd Design Installation Guide Page 12 LED Lighting SPD Design & Installation Guide

LED Lighting Surge Protection Modules Design and Installation Guide 2015 Littelfuse LED Lighting SPD Module Design and Installation Guide www.littelfuse.com IEC 61643-11 Temporary Overvoltage (TOV) Test Compared to surge transients, which are short-duration (microseconds) over-voltage disturbances in AC power lines, temporary over-voltages (TOVs) are longer-duration (milliseconds to minutes long) abnormal high voltages affecting the SPD module. TOVs can lead to short-circuited SPD modules and thermal runaway, potentially resulting in a catastrophic fire or explosion of the SPD. Several things can cause TOVs to occur in AC power lines. IEC 61643-11 includes a TOV test in the standard to simulate these possible causes and verify SPD module safety. TOVs are caused by short-circuit faults in the power distribution network and by faults in the low voltage system and the high/medium voltage system. TOV caused by faults in the low voltage system - Line-to-Ground Fault. A single line-to-ground fault at one phase shifts the ground potential at the fault location and generates 1.73 ( 3) over-voltage at another phase line-to-ground in the worst case. The over-voltage condition continues until an over-current device activates to clear the line-to-ground fault, which usually happens in less than five seconds. B A C Neutral = Ground (A) Normal Conditions B A = Ground Line-to-Ground Over-voltage C (B) Fault Conditions Figure 11. Line-to-ground fault in 3-phase electric power system. Over-voltage Testing in UL 1449 and IEC 61643-11 (continued) 12

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