Answer / aariz ali

1)impedence relay is used for transmission lines protrction and diffrential relay is used for alternator protection.
also you can give their operational dirrerence.
2)ans: transformers, circuit breakers, isolators , realys etc ETC....
3)ans: the main difference is of the arc quenching medium which is only used in circuit breakers but not in isolator.
4) ans: air blast, vaccum, sf6, oil circuit breakers.
5)ans: SF6 medium is most commonly used because:
-sf6 gas is non inflammable so there is no any risk of fire in these ckt breakers.
-sf6 has high dielectric strenght so these breakers have short arcing time
- due to enclosed circuit these breakers have no moisture problem.
-small noise
etc etc.

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