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Advantages of Three Phase System Over Single Phase System

Advantages of 3-Phase Power over Single Phase Power System

A three phase power generation, transmission and distribution system is very common around the world due to solid advantages over single phase and other multiphases systems.

Single Phase System

The sinusoidal alternating voltage having a specific time period and frequency generated by a single winding alternator as source voltage is known as a single phase supply system. A circuit fed up by these voltages is known as a single phase AC circuit. In other words, A circuit contains on single alternating current and voltage is identified as 1-Φ circuit.  

Three Phase System

A system contains more than one phase known as a polyphase or multiphase system. A 3-Φ system contains three phases having a uniform frequency where a fixed angle of 120° exists between the source voltages generated by the alternator having three windings. Similarly, there is a 90° angle difference between the two phases in a two phase supply system.

Difference Between Single Phase and Three Phase Power Supply

Key Advantages of 3-Φ System over a 1-Φ System

A poly phase or three phase power supply has the following advantages over a single phase power supply system.

  1. To transmit a specific power over a specific distance at a given rated voltage, a three phase system needs less conductor material as compared to the single phase system.
  2. The size of a three phase system operated machine is less than the machine operated at single phase voltage having the same output rating.
  3. In a three phase power supply system, the less voltage drop occurs from source to the load points,
  4. A three phase supply produces uniform rotating magnetic field therefore,  three phase motors are simpler in construction, small in size and can be started automatically with smooth operation.
  5. A polyphase system produces power at a constant rate in the load.
  6. A three phase system can transmit more power as compared to a single phase system.
  7. The efficiency of three phase operated devices and appliances is higher than the single phase operated machines.
  8. Three phase machines are less costly and more efficient.
  9. A three phase system provides constant power while a single phase system provides pulsating power which leads to a smooth and vibration free operation of a 3-Φ machine as compared to the 1-Φ machines with noise and vibration.
  10. The output rating of machines can be increased by increasing the number of phases in a system.
  11. A three phase machine having the same rating occupies less space as compared to the single phase machine.
  12. A single phase supply can be obtained from three phase supply to run the 1-phase machines. A three phase machine can’t be operated on single phase supply voltage.
  13. A three phase supply can be easily converted to a single phase supply while a complex system is needed to convert the single phase supply into a three phase supply system
  14. If a fault occurs on a single phase line, the whole system will have to shut down. In case of three phase single line fault, the other two lines provide the power supply to other single phase load points connected to them.
  15. A polyphase or three phase motor provides uniform torque while single phase motors (expect commutator motors) provides pulsating torque.
  16. Three phase motors  are self started while single phase motors can’t be started automatically.
  17. If the frame size of a three phase alternator, motor or transformer is the same like a single phase motor, alternator or transformer,  the output of three phase machines would be higher than that of a single phase machine.
  18. A polyphase alternator can be easily paired and run in parallel operation as compared to single phase alternators having the pulsating armature reaction.
  19. The ripple factor in DC rectified voltage from 3-Φ supply is 4% while the ripple factor in DC rectified voltage from 1-Φ supply is 48%. Hence, the cost of converter for  DC rectified from 3-Φ supply is less than the converter used for rectified DC voltage from 1-Φ supply due to the less number of filters used in 3-Φ supply system rectification.
  20. Three phase motors have better power factor as compared to single phase motors.

Related Post: Difference Between Single Phase & Three Phase Induction Motor

The following figures shows the uniform power produced at unity power factor by a three phase power supply where the power produced by a single phase machine is pulsating.

The above explanation shows why a three phase power supply system is more efficient, convenient, economical, and reliable as compared to the single phase power supply system. Due to the above mentioned advantages of three phase system over a single phase system, most of the countries around the world opted for it instead of single phase or other multiphases systems.

Uniform Power in 3-Φ System in Resistive Circuit at Unity Power Factor - Three Phase Waveforms Single Phase Power supply Waveforms - Pulsating Power


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