When does a servomotor operate?

A servomotor operates when the control field is energized because this energization allows the motor to receive commands from a controller. This process initiates the precise movement and positioning that are characteristic of servomotors. Servomotors are designed to respond to control signals by adjusting their position or speed in a controlled manner, which is only possible when the control field is active.

The other options do not accurately represent the operational requirements of a servomotor. For instance, while battery charge or thermal overload conditions might be relevant to other types of motors or systems, they do not directly pertain to the core functioning of a servomotor. Additionally, being connected to three-phase power is specific to three-phase motors rather than servomotors, which can often operate with other types of power configurations depending on their design.