Can anyone explain the logic (physics) behind the need to derate at altitide.
To my twisted way of thinking, it is the opposite to what I would have thought.
At altitude, air is less dense, and I would have thought that this would have made it a better insulator - apparently it does not, it is the opposite - why??
Also, there is the issue of different derating requirements between LV and MV. For LV, derating only applies above 2,000 metres, while for MV, derating applies above 1,000 metres - why is this so??
I haven't been able to find a suitable explantion why - any explanation would be appreciated (because for my poor old mind, if you use this logic, a vacuum should be a good conductor).