What adjustment would be necessary for a generator that is running below the desired speed?

When a generator is running below the desired speed, it's crucial to focus on its running speed for adjustment. The running speed of a generator directly affects its output frequency and power generation capabilities. If the generator is not running at the required speed, it cannot function efficiently, leading to insufficient power production or unstable operations.

In practice, increasing the running speed will help achieve the desired output characteristics, such as voltage and frequency stability. This adjustment may involve mechanically increasing the speed of the engine that drives the generator or configuring the electrical setup to enhance the generator's performance.

The other choices, while related to generator functionality, do not directly address the issue of the generator's operational speed. Voltage adjustments might stabilize the output but won’t resolve the fundamental problem of insufficient running speed. Gain adjustments pertain to the responsiveness of controls rather than the speed itself. Idle speed is a separate consideration and typically refers to the minimum operational speed before the generator can start producing power effectively. Therefore, focusing on the running speed is the most effective approach to remedying the low-speed issue.