Advantages of Three-Phase System

Electrical power is generated, transmitted and distributed in the form of 3-phase power because it has the following advantages over the single phase system −

• The three phase power has a constant magnitude while the power in single phase system is the function of supply frequency i.e. pulsates from zero to maximum value at twice the supply frequency. It can be seen from the following equations,

1 − phase power,

$$p=\frac{V_{m}I_{m}}{2}-\frac{V_{m}I_{m}}{2}\cos2\omega\:t$$

3 − phase power,

$$p=\sqrt{3}(V_{L}I_{L}\cos\varphi)$$

• In the 3-phase system, a rotating magnetic field can be created in stationary windings, whereas this cannot be done in a single phase system.

• For the same rating, three phase machines (like motors, generators etc.) are smaller and simpler in construction as compared to single phase machines. Therefore, the overall cost of a three phase machine is less than that of a 1-phase machine.

• To transmit the same amount of power over certain distance at a given voltage, the three phase system requires less (or 3/4) of the weight of copper (conductor material) than that required by the single phase system.

• The voltage regulation of three phase transmission lines is better than that of 1-phase line.

• A single phase load can by supplied by a three phase system but, the converse is not true.

• The DC supply obtained from the rectification of 3-phase supply has only 4% ripples whereas DC obtained from the 1-phase supply has 48.2% ripples. Therefore, the less filter requirements for the DC obtained from the 3-phase supply as compared to 1- phase supply which reduces the cost of converter.

Hence, a three phase system is more efficient, economical and convenient as compared to the 1-phase system.