How plausible is it for electrical panels to explode etc? (is it possible that dangerous power can occur [I hope so ; )]? ; are high TL wires made of superconducting material that may or may not burn?)
Certain electrical components can
and do explode. Circuit breakers are one really good example: any electrician with a brain pushes those switches with a broom-handle after the work is done.
I wasn't present when it happened, but I did see the damage of a 460v breaker panel that blew at work.
Very scarey, and now I don't flip breakers on by hand even at home. While I was on vacation they had over a week with no power, waiting for a new one to be manufactured and shipped in.
Another example of electrical equipment that can explode: DC generators. I don't know exactly what conditions are necessary.
Apparently, EMP has that effect on various kinds of electrical equipment. Basically, metal wires themselves will explode if a massive current heats them up to the point of vaporization. EMP from a nearby (1 km) nuke can generate 10000+ volts per cm of wire and amperage out the yang.

<boom>
True superconducting wires would not themselves generate voltage due to EMP, since true superconducting materials repel a magnetic field. However, any room-temperature material will more likely be a pseudo-superconductor which has exceedingly low electrical resistance and only partial immunity to magnetic inductance current.
In either case, any part of the system that does not use superconducting material can generate current from EMP and dump it into the superconducting circuitry, which heats up and degrades its properties and then becomes vulnerable to any secondary EMPs (you can bet advanced nukes of the future will be designed to generate secondary pulses).