It looks to me as if the catenery wire broke close to the footbridge and dropped both ends onto the roofs of the coaches causing the arcing etc. The stresses on the overhead line then caused a further failure close to the photographer who then decided they'd seen enough!
This appears to be a low-voltage DC tram type system - possibly 1,500 volts?
Very surprising that the current wasn't cut off by any protective devices in the supply.