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Disclaimer: I'm not experienced in many phyiscal nor electrical terms and I have no idea where to ask this question elsewhere. I'd be open for a move request if needed.

Today when using public transport in switzerland I noticed something odd. All trians emitted a lot of sparks where they met the electrical supply line. Seen in different train stations on different trains. enter image description here (Image not from today, just as example)
I never noticed even in rain. The only difference from other days was the temperature.

Time / Date: 7:15 - 7:40, January 16th
Sky: Still dark, not cloudy
Temperature: -2°C
Humidity: 92%
Last snow / rain: The day before yesterday

Can these conditions cause an entire train network to emit sparks? If so why? Is there another possible explinations?

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The Swiss Federal Railways explained that very same phenomenon in a (German) newspaper article from 2013.

The basic idea is that the cold weather leads to a thin layer of ice forming on the overhead wires. The Swiss rail electrification system works with a voltage $15kV$, which is easily enough to lead to an electric arc between the engine collector and the wires.

On a side note, looking at the arcs directly is not advisable, due to the high light intensity. This effect was (still is) used for movie projectors and high intensity searchlights.

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    $\begingroup$ As an additional warning, the arcs are likely to contain UV radiation which can damage the eyes. $\endgroup$
    – my2cts
    Commented Jan 16, 2019 at 11:39

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