Pentadyne's VSSDC

Broadcast engineers in Louisiana know firsthand the demands of keeping sensitive digital production and transmitting systems up and running. Weather-related issues are a constant threat, as Hurricane Katrina demonstrated in August 2005. Baton Rouge-based WBRZ-TV was experiencing problems with its backup power set-up. The double-conversion 50kVA battery-based UPS system had been replaced just two years before and already suffered from battery cell failures in a number of strings. Subjected to the impact of numerous voltage sags and temperature extremes in a technical room with no air conditioning, the batteries of the existing UPS degraded quickly, requiring regular replacement of failed cells.

The backup power system was critical because it supported the station's 24-hour newsroom equipment and corporate data center. It became necessary to take action and find a better solution.

The solution

In the station's search for a reliable and proven solution to upgrade its backup-power set-up, it was determined that a new 50kVA UPS paired with a Pentadyne VSSDC (Voltage Support Solution) DC flywheel power system was the answer. The system is fully compatible with UPS systems from leading manufacturers. A flywheel power system operates as a mechanical battery. It is an electro-mechanical device that stores kinetic energy in a rotating mass with the capability to convert it back into electrical energy when backup power is needed to support critical loads.

The flywheel provides ride-through time to bridge over to backup generators for continued power during long-term grid-power outages. It serves as a quiet, low-maintenance, space-saving alternative to service-intensive batteries for UPS systems. Compared with traditional battery-based UPS systems, the flywheel dramatically reduces UPS costs while improving UPS system reliability.

Longer battery life

Because the two-year-old battery pack had recently undergone service, most of it could still be used; it was then retained as part of the backup power set-up. In parallel with batteries, the flywheel power system provides battery protection by taking care of short disturbances and preserving battery capacity for longer disturbances. Only the power disturbances lasting longer than the flywheel's ride-through time use energy from the UPS's battery bank.

The system serves as an effective means of isolating chemical battery strings from more than 98 percent of power disturbances. Calling on batteries less often — while minimizing the number of battery charge/discharge cycles — has a direct effect because battery usage decreases battery life. This configuration consequently extends the battery's life expectation while improving UPS system reliability.

Easy installation

Once the design was finalized, the station's director of engineering and operations set the start-up time of the new backup power installation. With all the equipment in place, the installers performed an initial start-up procedure on each piece of equipment. They connected the original battery pack to the DC bus, and adjusted the flywheel settings so that the system discharged completely before the batteries would be called upon.

The flywheel is rated for 160kW for 12.5 seconds. However, with only 50kVA on the UPS output, the discharge duration lasts about one minute — well in excess of the 10 to 12 seconds needed to start and synchronize the generator.


WBRZ-TV had been struggling with its aging battery-based system for years, unaware that there was a better alternative available. The station initially retained the battery pack and used the system in parallel with the flywheel.

During Hurricane Katrina, Pentadyne Power's VSSDC flywheel power system played a key role in keeping WBRZ-TV on-air, providing uninterrupted, vitally important, around-the-clock TV news coverage.

Now that station engineers have built up their confidence in the system, the battery strings are simply removed as they fail. Soon the station will be relying solely on the flywheel system to ride through to the generator during grid disturbances or when a transfer to the generator is manually initiated as storms approach.

Clyde Pierce is the director of engineering and operations for WBRZ-TV.