Looks like a transition between LV overhead lines and LV cable. I suspect either insulation breakdown or a high resistance joint. Either could produce enough heat to ignite the bitumen or similar material in the joint. Since burnt or charred insulating materials are conductive, continued arcing will result. black smoke is also somewhat conductive.

Heat from the burning bitumen and from the arcing ignited the wooden pole. The arc would drop some voltage, unlike a dead short, and limit the current to less than that needed to promptly operate the substation fuses.

Looks like a transition between LV overhead lines and LV cable. I suspect either insulation breakdown or a high resistance joint. Either could produce enough heat to ignite the bitumen or similar material in the joint. Since burnt or charred insulating materials are conductive, continued arcing will result. black smoke is also somewhat conductive.

Heat from the burning bitumen and from the arcing ignited the wooden pole. The arc would drop some voltage, unlike a dead short, and limit the current to less than that needed to promptly operate the substation fuses.