Keeping Alabama Public Television's (ABT) sensitive digital production and transmitting systems up and running during the unpredictable storms we experience here in Alabama is a constant challenge, as Hurricane Katrina demonstrated. As a publicly funded station, we also have the responsibility to broadcast emergencies, so we take extra precautions to assure that our transmitter and associated electronic systems are up and running, despite the state of the incoming electricity.
In our Dozier, AL, facility, our transmitter is a solid-state Harris Platinum 4kW VHF. We have five, two-way repeaters and a 1kW NOAA weather transmitter. Our facility also has 20 tons of air conditioning, so keeping all these systems up and running is always my top priority.
In looking at our power protection solution, we wanted to make sure that the systems we put in place would have enough power backup with the highest reliability available. In my research, I contacted several other broadcast engineers to see what they were doing for power backup. They confirmed my concern about uninterruptible power systems' (UPSs) dependence on lead acid-batteries; you never know if you have enough battery capacity, and the charge state of the batteries is always in question.
According to the Electric Power Research Institute (EPRI), “Batteries are the primary field failure problem with UPS systems.” Predicting when one battery in a string of dozens will fail is next to impossible, even with regular testing and frequent individual battery replacements. Batteries have a limited number of discharge cycles they can provide during their expected life. I found out through my research that every time the batteries are used (cycled), even for a split second, the more likely it is they will fail the next time they are called upon. Even testing the batteries shortens battery life, and just one cell in a battery string can render the entire battery bank useless.
Seamless backup power
This information led to our decision to pair up a 160kVA three-phase UPS with a 215kW flywheel system — instead of using batteries — that could provide a reliable “ride-through to generator” function. We chose a VYCON VDC flywheel system that is fully compatible with UPS of leading manufacturers.
Operating as a mechanical battery, the flywheel stores kinetic energy in a rotating mass and converts it back into electrical energy when backup power is needed to support critical loads. The flywheel system provides ride-through time to bridge over to the generator for continued power during long-term grid-power outages.
During a power event — usually attributed to our local storms — the flywheel provides backup power seamlessly and instantaneously to our transmission equipment. If the power outage is longer than a couple of minutes, the flywheel will automatically and gracefully hand off to our backup engine-generator. It's important to note that according to the EPRI, 80 percent of all utility power anomalies/disturbances last less than two seconds, and 98 percent last less than 10 seconds. In the real world, the flywheel energy storage system has plenty of time — up to a couple of minutes — to gracefully hand-off to the broadcast facility's generator.
Since we installed the three-phase UPS along with the flywheel, we have been completely protected against power outages, which we experience here about twice a month. The flywheel system has operated flawlessly, and we're saving considerable money and resources by using a flywheel that requires no bearing replacement and has a 20-year life.
We also needed a system that could accommodate a 208V output. Other flywheel systems we looked at have a 480V output, which wouldn't fit our needs. The VYCON VDC has a 480/208 voltage configuration, which was perfect for us. This technology will not only give us the uptime we require, but also will save ABT money by providing clean, reliable power for 15 to 20 years compared to the typical battery-driven technology life cycle of three to four years.
We're ready for the next power outage. It's not a matter of if — just when.
Windell Wood is director of engineering for Alabama Public Television.
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