While I cannot explain the double contact wire in the second picture,
the following may help:

Catenary wire is normally kept under tension with weights. Only short
sections of about a quarter mile or so can be kept taut by each set of
weights.

Where you have the transition between the two tensioned sections, you
have short sections of double catenary, where one contact wire goes
up slightly and the other goes down slightly so that the pantograph
transfers from one section to the next. The adjoining sections are,
of course, connected electrically, so the locomotive (or EMU) receives
continuous power from the same source.

This can be seen in the linked photo of a German ICE high-speed line:

http://www.robl.w1.com/Pix-2/I-911558.htm

The tensioning weights are on the second catenary pole on the right.

Sorry this isn't a particularly high-resolution image, but I hope it
helps.

-- Ernest