Lightning impulse high voltage test

[MissP.25_5]

Hello, I am posting this here becase this is not a homework, it;s just something I need to know.
Please tell me what these two waveforms mean? I know that they're both lightning impulse waveform but what is the difference between those two, what gives them their shapes?

 

[davenn]

where did you get these waveform images from?
have you got some references ?

cheers
Dave

 

[berkeman]

Hello, I am posting this here becase this is not a homework, it;s just something I need to know.
Please tell me what these two waveforms mean? I know that they're both lightning impulse waveform but what is the difference between those two, what gives them their shapes?

The first looks like a standard "Combo Wave" waveform used in Surge testing (which simulates lightning strikes to AC Mains supply lines leading to equipment). The standard test is EN 61000-4-5. I don't recognize the 2nd waveform...