Question

Which is not true for three-phase AC?

• A. The three-phase power supply has three distinct wave cycles.
• B. The voltage of three-phase is 230 V.
• C. The efficiency of three-phase is high compared to single-phase
• D. Three-phase is expensive compared to single-phase

Answer 1

The correct option is B

The voltage of three-phase is 230 V.

Alternating Current (AC)

1. The flow of electric charge that periodically reverses is called an alternate current. AC is cheaper to generate and easy to transmit over long distances at the loss of low energy. The distribution of a load is known as the phase, mainly single phase and three phase AC in different applications.
2. Single-phase power uses one power wire and one neutral wire to complete the simple circuit. Residential applications are usually served by a single-phase AC, were most commonly used for lighting and heating.
3. Three-phase power is a three-wire that uses three power wires, each of them 120 electrical degrees apart. The appliances in commercial and industrial facilities usually use a three-phase supply to get power supply at a steady, constant rate.
4. One key difference between single-phase vs. three-phase is that a three-phase power supply better accommodates higher loads and also three-phase power supply can transmit three times as much power as a single-phase power supply.

Answer

1. Correct answer: Option B
2. Given voltage for three phase AC is $230V$ which wrong. As three phase AC voltage is $415V$.

Incorrect options:

1. Option A - The three-phase power supply has three distinct wave cycles as shown in above diagram.
2. Option C - The efficiency of three-phase is high compared to single-phase because of constant and steady power supply.
3. Option D - Three-phase is expensive compared to single-phase as it has three power loads and commercial supply.

Hence option B is correct.