The HS2 OLE was built to a higher standard than most of the UK's installations. No Headspans, closer pylons and higher tension. I've not heard of any problems with the GWML OLE today, - yes the one that so many said was gold plated and completely unnecessary! Still it was engineered by a Swiss company so that speaks for itself.
I've always known about the GE's ex-1500VDC OLE sagging because it is fixed lengths with no tension adjustment. But Simon Calder made me think by saying (for the benefit of lay listeners) that OLE was fitted with pulley systems and weights to maintain a roughly constant tension. He went on to say that some of these weight systems are ending up with the weights bottoming out meaning that any additional expansion in the wires causes sagging. So there will no doubt be a review of the range of temperatures that the tension compensators can cope with as climate change heralds mor days like this. Does anybody know if the Tensorex units being put into new installations have a wide enough range to cope with extremes in the future?