not "painful" but i would hazard a guess "carrier" for the "peiner" part. the "masten" part is pretty self explanitory and obvious. many things can be deduced from context. that is how we first learn to speak as infants. and it still often works, if not always reliably, with things we have some insight as to the context of as adults. (peiner, sounds in my mind close to panner, like the side baskets on bicycles, or somularly mounted arraingemtens for carrying things, thus in this example, and still only guessing from context, a catenary mast that "caries" the live and messanger (the wire the live wire is suspended from) wires, without feeding, terminating or otherwise altering them or their function)
Something from the German wikipedia: Peiner Träger GmbH Peiner Träger Namensgeber ist der in Fachkreisen weltweit bekannte Peiner Träger. Es handelt sich um einen parallelflanschigen Breitflanschträger, der 1914 durch das Unternehmen entwickelt und patentiert wurde.
Obviously this pylon was developped in the German town Peine.
Most of the other cat masts on the DLS are named according to their structure type (flat, ladder, pole etc) so I was expecting 'peine' to be something structural.
Calling it a 'carrier mast' seems a bit redundant because all catenary masts carry the catenary.
But if 'peiner' refers to a place, company or a person (the inventor?), then I should not change it because there really is no translation.