Thursday, June 22, 2017
Three Phase System Advantages
In modern power generation, transportation, distribution we use poly-phase system over single phase system.In poly-phase AC system it might be two , three or more individual circuits, operate at same frequency, their voltages and currents are out of phase from one another.But when it comes to practical scenario three phase system considered as poly-phase system.It is most reliable and efficient compared to all poly phase systems.Single phase system has some limitations and drawbacks so it's been replaced by three-phase system.Here we listed out major reasons why 3 phase/poly-phase system is better than single phase system.
Advantages of polyphase systems over single phase systems are
1. A polyphase/3 phase transmission line requires less conductor material than a single phase line for transmitting the same amount power at the same voltage.2. For a given frame size a polyphase/3 phase machine gives a higher output than a single-phase machine. For example output of a 3-phase motor is 1.5 times the output of single-phase motor of same size.
3. Polyphase/3 phase motors have a uniform torque where most of the single-phase motors have a pulsating torque.
4. Polyphase/3 phase induction motors are self-starting and are more efficient. On the other hand single-phase induction motors are not self-starting and are less efficient.
6. Per unit of output. the polyphase/3 phase machine is very much cheaper.
7. Power factor of a single-phase motor is lower than that of polyphase motor of the same rating.
8. Rotating field can be set up by passing polyphase current through stationary coils.
9. Parallel operation of polypahse alternators is simple as compared to that of single-phase alternators because of pulsating reaction in single-phase alternator.
It has been found that the above advantages are best realized in the case of three-phase systems.Consequently, the electric power is generated and transmitted in the form of three-phase system.
Final Points :
| Single Phase Supply | Three Phase supply |
| power delivered is pulsating | Power delivered is constant |
| Single Phase induction motors are not self starting as it does not have starting torque. | Three phase induction motors are self starting. |
| Parallel operation is not easy. | Parallel Operation is easy. |
| Efficiency of single phase motor is lesser. | High efficiency. |
| Single phase motors have pulsating torque. | Three phase motors have uniform torque. |
| Single phase motors have lower power factor. | Three phase motors have higher power factor. |
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