I wired a circuit as depicted below:
And it caused my miner to explode. Note that the LV transformer is connected to a pump and has no way to get power to generate a MV current to destroy my miner, I was just using it as a switch to turn off my pump.
The way you wired it appears incorrect. The high-side of the transfo is pointing into copper cables, which is nonsense because copper cables would melt on anything but LV either way.
As well, apllying any sort of redstone to the transfo will cause it to blow up whatever is connected to the long copper wire (and the copper wire itself, too).
To be honest your setup doesn't make much sense at all. Unless you intend to blow up the world, then it's perfect 
What he's saying is taht the pump, which isn't a power source, blew up the stuff. I guess when you flick teh switch, there must be some small number of EU as buffer stored in teh transformer, which get sent teh otehr way, blowing it up? IS there currently a good way to make a switch?
Transformers store a small amount of power which when red-stoned they can send the other way causing a surge.
You could try this and see if it works.
Incoming(LV)->Trans1->Out(MV)->Trans2(MV)->Out(LV)
When Trans2 is switched even if it was to try send a MV pulse backwards Trans1 could handle it because it hits the MV face
