What term describes three sinusoidal voltages that have equal frequency and magnitude, and are phase-displaced by 120 degrees?

The term that describes three sinusoidal voltages with equal frequency and magnitude that are phase-displaced by 120 degrees is known as balanced three-phase voltages. In a balanced three-phase system, each phase voltage is equal in magnitude and frequency, while the phase angle differs by 120 degrees, ensuring that the system operates efficiently and with consistent power delivery.

This configuration is widely used in power generation and distribution because it allows for more effective energy transmission over long distances and provides a smoother and more constant power supply. The balance in the voltages ensures that the load is evenly distributed across the phases, minimizing losses and improving the reliability of the electrical system.

In contrast, single-phase voltages involve only one sinusoidal voltage wave, lacking the advantages offered by multiple phases. Unequal phase voltages would imply that the phases have different magnitudes or frequencies, resulting in an imbalanced load that can lead to inefficiencies. Inverted phase voltages suggest a phase shift that is more than 180 degrees which does not fit the context of balanced voltages. Thus, the definition of balanced three-phase voltages aligns precisely with the characteristics outlined in the question.