131.What is generator purging?

During Power generation, Generators radiate enormous heat. Hence the Generator casing needs to be cooled. Hydrogen gas is used for fillling the Generator casing as it is most effective. However, H2 will easily react with air (O2) unless it is >98% pure. In order to ensure that there are no entrapped air in the Gen casing,the casing is first purged with Nitrogen gas as N2 is an inert gas.Subsequently, the N2 gas is displaced with H2 and purity maintained > 98%.