Advantages of three phase system
•Three phase system give study output and power delivered is constant. In single phase system power delivered is pulsating.
•The output of three phase machine is greater than single phase machine of same size.
•Three phase induction motors are self starting. Single phase motor are not self starting.
•We can obtain single phase supply from three phase but three phase supply cannot be obtained from single phase.
•For transmission of three phase system conducting material required is less as compared to single phase system for given volt ampere and voltage rating.
•Efficiency of 3 phase motor is more as compared to single phase motor.
•Parallel operation of three phase alternator is simpler as compared to single phase alternator.
•Power to weight ratio of three phase alternator is high as compared to single phase alternator which reduces the cost for generating same amount of power.
Advantages of Polyphase circuit over Single phase circuit: i) Three-phase transmission is more economical than single-phase transmission. It requires less copper material. ii) Parallel operation of 3-phase alternators is easier than that of single-phase alternators. iii) Single-phase loads can be connected along with 3-ph loads in a 3-ph system. iv) Instead of pulsating power of single-phase supply, constant power is obtained in 3-phase system. v) Three-phase induction motors are self-starting. They have high efficiency, better power factor and uniform torque. vi) The power rating of 3-phase machine is higher than that of 1-phase machine of the same size. vii) The size of 3-phase machine is smaller than that of 1-phase machine of the same power rating. viii) Three-phase supply produces a rotating magnetic field in 3-phase rotating machines which gives uniform torque and less noise.