Question 35

The Correct Answer is D. **Explanation for Option D (Correct):** The device labeled "Man-Auto Sw." (Manual-Automatic Switch) on a typical generator switchboard is a critical control element related to the excitation system and voltage regulation. Its primary purpose is to select the operating mode for the voltage control system. * **Automatic Mode (Auto):** In this position, the switchboard utilizes the Automatic Voltage Regulator (AVR) to maintain a constant terminal voltage by automatically adjusting the generator's field excitation based on feedback (often via a regulator, not shown as a discrete switch). This is the standard operating mode for synchronization and normal operation. * **Manual Mode (Man):** In this position, the AVR is bypassed, and the operator must manually control the generator's field excitation (and thus the output voltage) using a separate manual control device, often a rheostat (like "Man. Volt. Adj. Rheo." mentioned in option C, though not necessarily the exact device being read). Therefore, the function of the "Man-Auto Sw." is definitively **to shift from the automatic voltage regulator to manual voltage control or vice versa.** **Explanation for Incorrect Options:** **A) to supply regulated control power to the switchboard:** This is incorrect. Control power (often DC or a separate AC feed) is supplied by separate transformers or batteries, often through breakers or fuses. The Man-Auto switch selects a control *method*, not the power source itself. **B) to shift the governor control from manual to automatic/zero droop or vice versa:** This is incorrect. Governor control (which manages engine speed and real power/frequency) is entirely separate from voltage regulation (which manages excitation and reactive power). Governor mode selection would be done via a separate switch, typically labeled "Speed Man/Auto," "Isoch/Droop," or similar. **C) to enable the operator to read the field voltage on device "Volt. Reg. Adj. Pot." or device "Man. Volt. Adj. Rheo.":** This is incorrect. The switch's purpose is functional (selecting the control mechanism), not purely informational (selecting which device is monitored). Meters (voltmeters/ammeters) or selector switches (like a V-A-W switch) are used for reading parameters. Furthermore, "Volt. Reg. Adj. Pot." and "Man. Volt. Adj. Rheo." are adjustment controls, not meters themselves.