How does Buchholz Relay work in a transformer?

Generally it magnetically coupled electrical current small gap between two winding but cannot see through our eyes and also based on winding turns, number of turn,on it classified as stepup transformer and stepdown transformer n1/n2=v1/v2=i2/i1
above is condition for what about current and voltage relationship while transformer operates
More disadvantages due to its interns noise effect the which connected you other circuit for power supply but no other way to step up or step down the voltage our required voltage
It is big problem For eee students how to replace transformer