Due to DC arc extinguishing current has no natural zero-crossing point, so, DC arc can only been extinguished by forced zero-crossing-over.

由于直流熄弧电流不存在自然的过零点，因此必须强制过零才能熄灭直流电弧。

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Before crossing that road, trucks stocks could be forced to slow down.

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Andy Swallowe, crossing patrol service manager, said "imposed austerity measures" forced the council to "think outside the box" to maintain services.

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