What defines three-phase power?

• A. A system with three alternating currents with a phase difference of 90 degrees
• B. A system that operates on a single alternating current
• C. A polyphase system with three alternating currents having a phase difference of 120 degrees
• D. A system that distributes power only in direct current

Answer: (C)

Three-phase power is defined as a polyphase system that utilizes three alternating currents, each separated by a phase difference of 120 degrees. This configuration allows for a continuous and balanced power delivery, which is particularly efficient and effective for industrial and commercial applications.

The reason for the 120-degree phase difference is that it ensures that the power delivery is constant and avoids the fluctuations that can occur in a single-phase system. In a three-phase system, there are always multiple phases that can provide power, resulting in a smoother and more consistent flow of electricity. This reduces the size of conductors needed for distribution, improves the reliability of the power supply, and allows for the use of smaller and more efficient motors and other electrical equipment.

The other choices do not correctly define three-phase power. For example, the option mentioning a phase difference of 90 degrees is characteristic of a two-phase system, and a single alternating current does not represent the concept of three-phase power. A system distributing only direct current entirely misrepresents three-phase power, which inherently relies on alternating current.