What is a basic definition of a 3 phase system?

A basic definition of a three-phase system is one that is energized by three equal alternating voltages. In a three-phase system, the three voltages are sinusoidal and equally spaced in phase angle, typically by 120 degrees apart. This configuration allows for a more efficient and balanced distribution of electrical power, which reduces the overall amount of electricity needed to transmit the same amount of energy when compared to single-phase systems. The three-phase system's ability to provide continuous power and its increased voltage stability are crucial in industrial and commercial applications for driving heavy machinery and equipment.

The other options present scenarios that do not accurately describe a three-phase system. Energizing a system with four alternating voltages does not conform to the three-phase structure. Utilizing different frequencies or requiring multiple transformers also does not define the fundamental nature of a three-phase power system, which is based on the generation and distribution of three equal voltages.