Question 507Electricity & Electronics - Assistant Engineer

The correct answer is C) The alternator output voltage must be decreased proportionately downward with the frequency decrease. When an alternator is run at a frequency lower than its rated frequency, the output voltage must be decreased proportionately to maintain the correct voltage-to-frequency (V/F) ratio. This is because the V/F ratio is a key parameter that determines the performance and efficiency of the alternator. Decreasing the frequency without decreasing the voltage would result in an increase in the V/F ratio, which could lead to magnetic saturation and other issues. The other options are incorrect because A) increasing the voltage to compensate for frequency decrease is not the correct approach, B) maintaining the rated voltage is not appropriate, and D) running an alternator below 5% of its rated frequency is generally permissible, as long as the voltage is decreased accordingly.