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Examoogle • User • info@examoogle.com • EE-2024-8821
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A traveling wave 400 ∕ 1 ∕ 50 means crest value of
400 V with rise time of 1/50 s
400 kV with rise time 1 s and fall time 50 s
400 kV with rise time 1 μs and fall time 50 μs
400 MV with rise time 1 μs and fall time 50 μs
400 kV with rise time 1 μs and fall time 50 μs
In power system engineering, standard lightning impulse voltage wave shapes are defined by the notation 'A / B / C', where 'A' represents the crest voltage in kV, 'B' represents the front (rise) time in μs, and 'C' represents the time to half-value (fall time) in μs.
In power system engineering, standard lightning impulse voltage wave shapes are defined by the notation 'A / B / C', where 'A' represents the crest voltage in kV, 'B' represents the front (rise) time in μs, and 'C' represents the time to half-value (fall time) in μs.
Tf=1.25×(t90−t10) — Formula for virtual front time calculation
V(t)=Vp(e−αt−e−βt) — Basic mathematical representation of an impulse wave
The wave 400/1/50 represents an impulse test wave. The front time (1 μs) is the time taken by the wave to rise from 10% to 90% of its peak value, adjusted by a factor (1.25). The time to half-value (50 μs) is the duration between the virtual origin and the instant on the tail where the voltage falls to 50% of the peak value.
The standard lightning impulse wave is defined as 1.2/50 μs by IS and IEC standards.
The crest voltage is always expressed in kilovolts (kV).
Rise time is measured from 10% to 90% of the peak value.
Fall time is the time taken to reach 50% of the crest value on the wave tail.
Provides a standardized method for insulation testing.
Simulates transient overvoltages caused by lightning strikes.
Requires high-voltage impulse generators for simulation.
Does not account for switching surge wave shapes which have longer durations.
Testing of power transformer insulation.
Calibration of surge arresters and insulators.
The notation represents the voltage magnitude followed by the geometric properties of the wave shape.
Option A is incorrect because the unit is kV, not V, and the time unit is μs, not seconds.
Option B is incorrect due to incorrect units for the wave shape timings.
Option D is incorrect because the crest value magnitude (400 MV) is physically unrealistic for standard testing.
C is correct — The notation 400/1/50 indicates 400 kV peak amplitude, 1 μs rise time, and 50 μs fall time to 50% peak.
Always remember that in power system transients, the time units are almost exclusively in microseconds (μs) for lightning impulses and milliseconds (ms) for switching surges.