Simon's post #12 above is on the right track.
In the old magnetos the armature has the low tension generating coils wound on the armature. The high tension windings were wound over the top of the generator windings. When the points open the field in the LT indings collapses and a high voltage is induced in the HT windings and fed to the plugs. Most old magnetos were classed as rotating armature with the magnets static, built into the magneto body. Some magnetos were rotating magnet with (you've guessed it) the magnet going round and the coils static. I guess that most people know the above. (Anyone still awake?)
O.K. I am not an electronics expert (or an expert of any sort come to that) but in
very simplistic terms the new BT-H, like any magneto has a low tension generator section. In this instance the magnets are rotating. The HT winding section is the HT coil or coils mounted external to the body. Between the LT section and the HT section there are some electronics involved to rectify this output and charge capacitors to output maybe 400 Volts. (The elctronics are encapsulated and are inside the BT-H body or sometimes mounted externally.) There is a rotating magnet on an arm that passes over a coil to produce a trigger pulse. This pulse is fed to an RC circuit. (RC time circuit is a capacitor being charged through a resistor. The more pulses the sooner it charges to a given voltage.) When the voltage in the RC circuit reaches a threshold voltage a circuit dumps the 400 Volt charge stored in the capacitors mentioned earlier through the HT coils.
Phew!
Re: "mechanical maintenance in a Nuclear Power Station" I know very little about nuclear power stations. The closest I got was over 50 years ago when I worked for a company where we made a few stainless steel parts for Hinkley Point (B?) power station. Youngest daughter works for the Nuclear Decommissioning Agency in Cumbria. She probably knows more than me.
Re: "Every day's a school day". Late in my working life I moved from engineering to teaching. For 10 years
I certainly learnt something every day. Not sure if the kids learnt much.