So if the cable is kinked it follows that the conductor diameter is reduced at this point and therefore the electrical resistance at this localised point will be higher than along the length of the rest of the conductor
High resistance heating at a kink in a cable run is partially caused by a microscopic reduction in the diameter of the cable (in a similar manner to water flowing through a kinked hose). However, the crystalline structure of the conductor is altered as well; (if you repeatedly bend a conductor back and forward it will eventually become more brittle and snap)
Add to this kinks in cable runs are sometimes caused by the cable being inappropriately run, either into tight spaces or trapped between the structure or substructure of a building, (jammed in between a skirting board and a floor board for example). This then further insulates the heated point and can lead to smouldering ignition.
Harmonic, interference may cause interesting effects, as 50Hz is a radio frequency and mains electricity is still EM and will obey all the rules for EM energy. And I am personally very interested in this area; hence my (and my teams) interest in the original programme. But how you look for these in a post fire scene I really don’t know. A starting point we have discussed would be to look for dimmers and possibly IT transmission devices in the mains circuitry? More research needed methinks.
