Have you have considered the power potential of the human body? What about the energy stored in a raindrop? In this article I discuss five strange methods that could one day become an integral way that civilization generates electricity.
Principle of operation of transformers can be easily understood from this article. Basic working principle of the transformer is mentioned very clearly and briefly
Buchholz relay is a type of protection relay universally used on all oil immersed transformers having rating more than 500 kVA. From this article its principle and working can be understood.