Weathering the storm
Nov 1, 2009 12:00 PM, By Johnny Gonzales
Flywheels light the stage in greening up power protection.
Figure 1. This illustration of a flywheel shows how an electrical input spins the flywheel rotor up to speed, and a standby charge keeps it spinning 24/7.
Select image to enlarge.
Today's broadcasters have a lot to be concerned about. Ratings, programming, budgets, OPEX, ROI, equipment, personnel and a myriad of other things can keep broadcasters up at night. Worrying if the station will go off the air during a power blackout shouldn't be one of them. Armed with uninterruptible power supply (UPS) systems and an engine generator, most broadcasters feel protected against whatever the local utility throws at them or if Mother Nature is in a storm-frenzy fury. However, they might not be as protected as they think. While battery-based systems have been the standard in UPS — due mostly to their low cost — they are in fact the weakest link in providing reliable power protection.
Transmission systems are notoriously difficult to protect against power anomalies because of their sensitivity to even the smallest disruption, yet at the same time, they require high power to feed large transmitters. And now with DTV, the requirement for clean, continuous power has never been greater. Protecting the myriad of master control switchers, transmitters, cameras, amplifiers, editing bays, servers, RAID storage systems and other critical systems has traditionally been handled by battery-based UPS systems. These systems have done a good job in mitigating power interruptions and conditioning “dirty” power. However, broadcast engineers are finding that adding flywheels into the power continuity scheme significantly enhances reliability, increases green initiatives and lowers the total cost of ownership of the UPS system.
UPS batteries are chemically based dc sources. This means that frequent battery maintenance, testing, cooling requirements, weight, toxic and hazardous chemicals, and disposal issues are key concerns. One dead cell in a battery string can render the entire battery bank useless — which is not good when you're depending on the power backup system to perform when you need it most. Every time the batteries are cycled, even for a split second, the more likely they will fail the next time they are called upon.
Clean energy storage
Flywheel technology stores kinetic energy in a quiet, spinning disk to provide a reliable and predictable source of DC power. With recent advances that have made it more compact and able to support higher power applications, flywheel technology has emerged as a reliable, environmentally friendly power protection solution that stores energy mechanically instead of chemically — greatly enhancing dependability.
Figure 2. When used in conjunction with a UPS system, flywheels provide uninterrupted DC ride-through power and voltage stabilization during brief utility power disruptions and brownouts.
Select image to enlarge.
A flywheel system can replace lead-acid batteries and works like a dynamic battery that stores energy kinetically by spinning a mass around an axis. And it is designed for high-power, short-duration applications. Electrical input spins the flywheel rotor up to speed, and a standby charge keeps it spinning 24/7 until called upon to release the stored energy. (See Figure 1.)Technology used in the flywheel allows the flywheel hub — formed from aerospace-grade steel, a high-speed permanent magnet motor/generator and contact-free magnetic bearings — to levitate 100 percent and sustain the rotor during operation. The elimination of bearings for normal operation combined with zero rotor hub metal-to-metal contact eliminates maintenance concerns such as bearing replacements and or oiling/greasing of bearings. Higher reliability and improved availability is the end result. What this means is a more reliable backup power solution. The flywheel can charge and discharge at high rates for countless cycles without degradation throughout its 20-year life — unlike traditional batteries. The amount of energy available and its duration is proportional to its mass and the square of its revolution speed. In the flywheel world, doubling mass doubles energy capacity, but doubling rotational speed quadruples energy capacity: E = KMω
When used in conjunction with a UPS system, flywheels provide uninterrupted DC ride-through power and voltage stabilization during brief utility power disruptions and brownouts, preserving the battery array for only longer-term outages. (See Figure 2.) Most backup generators require six to 10 seconds to come online and to connect with the UPS via the automatic transfer switch. Some flywheel units can provide up to 300kW of instant ride-through power and voltage stabilization for more than 20 seconds (or other combinations of power and time) — more than enough time for the vast majority of electrical disturbances. Flywheel units can be paralleled for additional power capacity, run time and/or redundancy.
Proper sizing
Figure 3. This life cycle cost comparison shows some advantages of flywheel technology over battery systems.
Select image to enlarge.
Depending on the growth of the broadcast station, normally the sizing of UPS systems and flywheels is done based on actual load. Most engineers size the UPS at 30 percent to 40 percent larger than the actual load to allow for growth. Once the UPS is sized, the flywheel needs to be sized to the UPS. All UPS ratings are based on kVA and kW numbers; the rating used for power applications is the kW rating. When this kW number is established, this will be labeled as the full load kW rating. For example: A 275kVA UPS with a power factor (pf) rating or capability of 0.9 results in a 248kW output rating for the UPS (kVA x pf). Real work loading on a UPS is typically 80 percent or less. Our 275kVA example (80 percent loaded) would require 207kW of DC power or support from the flywheel. This is the rating used to size the flywheels to assure proper power rating and proper amount of run time requirement. Most flywheel manufacturers have made it easier to size flywheels by supplying users with run-time charts.
As illustrated in Table 1, using two flywheels of Model 1 will achieve 26.6 seconds of run time, and using two flywheels of Model 2 will achieve 28.6 seconds of run time. In either case, it exceeds the goal of meeting a 20-second run-time requirement as a minimum. This makes for a solution that fits the needs of most broadcast stations.
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