25 February 2020

Advantages of three-phase system over single phase systems

The main advantages of 3 phase system compared to a single-phase system:

  • The output of 3 phase machine is always greater than a single-phase machine of the same size.
  • The three-phase system gives a steady output.
  • For a given frame size a polyphase machine gives a higher output than the use of a single-phase machine.
  • The power factor of single-phase machines are poor compared to three-phase machines.
  • 3 phase motor will have uniform torque whereas single phase motor will have pulsating torque.
  • Single-phase systems can be obtained from the three-phase supply system, vice versa is not possible.
  • Polyphase systems can set up a rotating magnetic field in stationary windings.
  • The parallel operation of a three-phase generator will be simple as compared to single-phase generators because of pulsating reaction in a single-phase generator.
  • The power delivered is constant. In the single-phase circuit, the power delivered is pulsating and objectionable for many applications.
  • For transmission of electrical power, a three-phase supply requires less copper or some less conducting material than that use of a single-phase system, for a given voltage compare and voltage rating.
  • Single-phase machines are not self-starting machines, on the other hand, three-phase machines are self-starting due to the rotating magnetic field.
  • For a while in use a three-phase system, converting systems like rectifiers the DC voltage waveform becomes smoother with the increase in the number of phases of the system. 
  • In polyphase induction motors are self-starting and are more efficient while in single-phase motor has no starting torque and require an auxiliary means for starting.
  • Three-phase motors are very robust, cheap, smaller, provide a steadier output and require little maintenance compared with single-phase motors.