Advantages of 3 Phase Over Single Phase System
A three - phase system features three live conductors, supplying 440V power to large consumers. In contrast, a single - phase system has only one live conductor and is mainly used for domestic applications. Here are the key advantages of a three - phase system over a single - phase system:
Higher Rating
The rating, or output, of a three - phase machine is approximately 1.5 times that of a single - phase machine of the same size.
Constant Power
In single - phase circuits, the power delivered is pulsating. Even when voltage and current are in phase, the power drops to zero twice per cycle. However, in a polyphase system, when the loads are balanced, the power delivered remains almost constant.
Power Transmission Economics
To transmit the same amount of power over a fixed distance at a given voltage, a three - phase system requires only 75% of the conducting material weight needed by a single - phase system.
Superiority of 3 - Phase Induction Motors
Three - phase induction motors have a wide range of industrial applications due to the following benefits:
Three - phase induction motors are self - starting, while single - phase induction motors are not. A single - phase motor lacks starting torque and thus requires auxiliary means to initiate operation.
Three - phase induction motors have a higher power factor and efficiency compared to single - phase induction motors.
Size and Weight of Alternator
A three - phase alternator is smaller in size and lighter in weight than a single - phase alternator.
Requirement of Copper and Aluminium
The three - phase system demands less copper and aluminium for the transmission system than a single - phase transmission system.
Frequency of Vibration
In a three - phase motor, the vibration frequency is lower than in a single - phase motor. This is because in a single - phase system, the transferred power is a function of current and fluctuates constantly.
Dependency
A single - phase load can be effectively powered by a three - phase system, but a three - phase system cannot rely on or be powered by a single - phase system.
Torque
A three - phase system generates a uniform or constant torque, whereas a single - phase system produces a pulsating torque.
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