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Examoogle • User • info@examoogle.com • EE-2024-8821
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If voltage surge represented by 5/50 µs then at 50 µs value of voltage will be
Zero
Peak
Half of the Peak
None of above
Peak
Quick Summary: A voltage surge or impulse wave is defined by its rise time and tail time. In the notation $T_1 / T_2 \,\mu s$, $T_1$ represents the time to reach the peak value (virtual front time), and $T_2$ represents the time taken for the voltage to decrease to half of its peak value (virtual tail time).
A voltage surge or impulse wave is defined by its rise time and tail time. In the notation T1/T2μs, T1 represents the time to reach the peak value (virtual front time), and T2 represents the time taken for the voltage to decrease to half of its peak value (virtual tail time).
V(t)=V0(e−αt−e−βt) — represents the standard impulse voltage wave equation
The impulse voltage waveform is generated in high-voltage laboratories to simulate lightning surges. The wave rises rapidly to a crest value Vpeak and decays exponentially. By standard international convention (IEC), the tail time T2 is defined as the time interval between the virtual origin and the instant the voltage falls to 50% of the peak amplitude on the tail portion of the wave.
A 5/50μs wave means the virtual front time is 5μs.
The virtual tail time is 50μs.
Standard testing impulse waves are defined by these two parameters to ensure consistency in insulation breakdown testing.
The virtual origin is determined by the intersection of the line through the 30% and 90% points on the front of the wave with the zero axis.
Provides standardized stress testing for high-voltage equipment
Allows simulation of lightning strokes in a controlled laboratory environment
Requires high-cost impulse generators
Extreme precision needed for pulse shaping circuits
Testing transformers for Basic Insulation Level (BIL)
Dielectric strength testing of power cables and switchgear
The 5/50 µs wave is a common standard wave used for lightning impulse testing of electrical equipment.
Option B is incorrect because the peak occurs at T1 (5 µs), not at the tail time.
C is correct — By convention, the second number in the impulse notation denotes the time at which the voltage magnitude decays to 50% of its peak value.
Remember that in lightning impulse notation, the first number is always shorter than the second; if you see a notation like 1.2/50, it is the standard lightning impulse wave.