Final answer:
The firing angle controls when an electronic switch conducts in an AC circuit and influences input power and power factor. Improving the power factor, which expresses efficiency of the power use, is better for motor output than increasing voltage. At resonance, the power factor and efficiency are maximized, indicating the importance of designing motors to operate at this point.
Step-by-step explanation:
The firing angle in an AC power circuit controls the phase at which an electronic switch starts conducting. This angle directly influences the input power and the power factor of the system. The power factor, which is the cosine of the phase difference between voltage and current, ranges from -1 to 1. A power factor of 1 indicates perfect alignment in phase between current and voltage, which means power is used most efficiently.
In motor applications where the motor has a power factor significantly less than 1, improving the power factor would be a more efficient method to increase the motor's output than merely increasing the input voltage. Increased power factor leads to reduced phase difference, minimizing losses incurred due to reactive power. Boosting the input voltage, without addressing the phase shift, can lead to reduced efficiency and higher energy costs over time.
At resonance in an RLC circuit, the power factor is highest, which means that both the current and efficiency are maximized, providing significantly greater power as compared to operating at off-resonance frequencies. Hence, optimizing a motor for resonance, where the power factor is 1, is critical for achieving maximum efficiency.