75 Hz uninterruptible power supply for the Apollo high voltage direct current transmission terminal

The original power supply to the high voltage direct current (HVDC) converter bridges used in the Apollo terminal, is via motor generator sets. The frequency of the output voltage is 75 Hz, making it a special application. The availability and reliability of the motor generator sets have reduced due to its age, impacting the safe and reliable operation of the HVDC scheme. Uninterruptible power supplies (UPSs) were installed to replace the motor generator sets. The application of the UPSs is unique due to the 75 Hz output voltage criteria.