What is a notable advantage of mercury arc rectifiers over rotary converters?

Mercury arc rectifiers offer several advantages when compared to rotary converters, particularly regarding quiet operation. These rectifiers operate using an arc discharge in mercury vapor, resulting in minimal mechanical noise. This feature is highly beneficial in environments where noise concerns are paramount, such as urban settings or near residential areas.

While the other options present valid considerations in evaluating electrical conversion systems, they do not accurately reflect the primary advantage of mercury arc rectifiers. For instance, while energy efficiency and maintenance requirements may vary depending on specific circumstances and designs, they typically do not outperform rotary converters in those aspects. Additionally, the size of the devices can also depend on the application and configuration, making the claim of reduced size less consistent. However, the notably low noise level is a distinct and valuable characteristic that sets mercury arc rectifiers apart.