At high-speed, the series resistance for the stator windings of an older AC motor is typically:

In older AC motors, particularly at high-speed operation, the series resistance for the stator windings is typically minimized to reduce losses and improve efficiency. As the speed of the motor increases, the effective resistance in the circuit becomes a critical factor in maintaining performance.

When the series resistance is at a minimum, it allows for maximum current flow through the windings, thereby enhancing the motor’s capability to reach and sustain high speeds. This effectively translates into better operational efficiency and performance. The design of such older AC motors often emphasizes lower resistance to optimize the function of the stator windings in conjunction with the rotor, ensuring that they can handle the demands of high-speed applications.

The other options suggest either maximum resistance, which would hinder performance due to excessive voltage drops across the windings, or intermediate and variable resistances, which do not accurately represent the typical behavior observed in older AC motor designs under high-speed conditions. These factors reinforce the understanding that at high speeds, maintaining minimum series resistance is crucial for optimal motor operation.