The following are the main advantages of three-phase system over single-phase system:
- Constant power: In single-phase circuits, the power delivered is pulsating. Even when the voltage and current are in phase, the power is zero twice in each cycle. While in polyphase system, power delivered is almost constant when the loads are balanced.
- High rating: The rating (output) of a three-phase machine is nearly 1.5 times the rating (output) of a single-phase machine of the same size.
- Power transmission economics: To transmit the same amount of power over a fixed distance at a given voltage, three-phase system requires only 75% of the weight of conducting material as required by single-phase system.
- Superiority of three-phase induction motors: The three-phase induction motors have widespread field of applications in the industries because of the following advantages:
- Three-phase induction motors are self-starting, whereas single-phase induction motors have no starting torque without using auxiliary means.
- Three-phase induction motors have higher power factor and efficiency than that of single-phase induction motors.
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