Power Bridging Strategies

For years now, the increasing demand for backup power has been a major issue for both consumers and electricians because voltage surges can bring an entire home or office to a standstill. Today, the mission is to bridge the downtime during a switching transition by carrying the critical load away from a failing power source to a stable alternate source immediately. As a result, several new bridging products have been introduced to the marketplace, that use lead-acid batteries, low- and high-speed flywheels and ultra capacitors.

Lead-acid batteries are the cheapest and most popular option, but they have a shorter life-span than other alternatives for short-term storage. These batteries must be kept at 25 degrees Celsius because higher temperatures shorten their life and lower temperatures reduce the capacity. Lead-acid batteries should be stored in temperature-controlled environments to preserve the life of the battery. With proper storage, these batteries should last more than seven years.

On the other hand, flywheels have a longer cycle life because power is provided from the normal source via an open transfer switch. SatCon is one company that designs low-speed flywheels, while Beacon manufactures more high-speed products. Flywheels are charged and then discharged, using a generator. These units have enough stored energy to encounter voltage sags and momentary service interruptions. Computer and manufacturing facilities often use flywheels to enable backup generators to be up and running within five to 10 seconds.

Ultra-capacitors, which can also be charged more quickly than batteries, are most popular for very short-term applications where voltage sags last only a few seconds. Although their initial cost is about 10 times more than lead-acid batteries, their advantage is much greater, having a cycle life that is much better than lead-acid batteries, yielding about five times the power capability and longer life. Ultra-capacitors have a high tolerance for temperature and are more efficient during the charge/discharge cycle. The only real disadvantage of the ultra-capacitor is cost, but for short-term applications, they are cost competitive due to their higher power density. As more are used, their cost will, in turn, come down and they will compete with lead-acid batteries for long-term applications.

For those on a tighter budget, uninterrupted power supply (UPS) offers three systems. The off-line or standby technology is a cost-effective approach for small stand-alone applications like PCs and peripherals. With this type of unit, the power comes directly from the A/C outlet until the voltage fails. When this happens, a battery-powered inverter turns on to continue the power supply while the UPS provides protection from surges.

Similar to the standby system, line-interactive technology provides highly effective power conditioning and UPS backup. But, unlike the off-line unit, this one provides an automatic voltage boost when the power goes down, without accessing the batteries. In areas where power outages are infrequent, but there are often power fluctuations, this system is ideal.

An on-line alternative provides the highest level of power protection, conditioning and UPS available. Using double conversion technology, the UPS changes the incoming alternate current to direct current, then conditions it to eliminate noise or surges, and converts it to AC before it exits the UPS. Since the power runs continuously through the inverter, there is no transfer or switching time to battery mode in the event of a blackout.

UPSs provide a “clean” source of power, eliminating noise that can cause interruptions in operations or data loss. They provide batteries for backup power to a system in the event of a power outage to enable time to safely save all open files and to shut down the system until normal power can be restored. Several hours of work can be lost due to a momentary brownout where the AC power supply slumps to a level under 100 volts, which can crash a computer before the work can be saved to a disk. Generally speaking, power surges often accompany brownouts as the power rebounds to normal. Brownouts often pass unnoticed when a UPS is used as part of a necessary power protection system.

“There are several new technologies coming on board now to bridge the gap for standby power,” said Terry Chandler, director of engineering for Power Quality, Inc. “The old way was to have a backup system with 15 to 30 minutes of battery time. The new way to do it takes 15 or 30 seconds to start the generator, but there is a time in between where there is a gap. The technology of storing energy is changing and so is the cost of battery backup systems. They have come down dramatically. Since September 11, I think it has reinforced to people the need for backup power. Most businesses are not operable without computers, and today they realize the need for battery backup.”

In addition, fuel-free backup power systems are now available and can be installed indoors, require low maintenance and produce no noise, smoke or emissions. If the power went out right now, would you be able to operate systems without interruption that are critical to your home or business needs? Every hospital has a generator that will turn on when the electricity goes off, but do they have a backup battery to bridge the 15- to 30-second gap needed to start the unit? For those on life-support systems, this is obviously a critical situation. Business operations will not stop because of a power failure and valuable data is not lost.

With the increased use of local area networks, offices are becoming more and more susceptible to power issues. Because most files are stored on networks on one high-speed file server, a simple brownout could affect several users at a time. The recent increase in digital phone system use makes them vulnerable to power problems, as many businesses are now conducting all their business over the phone.

Even though no facility has perfect power quality, the electric company tries to supply your home or office with a steady source of maximum current electricity. If the supply does not contain a stable voltage, frequency and source of maximum current, there is a power quality problem. Many people once believed that poor power quality has no cost as long as there are no obvious manifestations like breakers being tripped, equipment being burned or issues in production operations.

Poor power quality does affect electronic and motor loads, which can become damaged and create the largest cost to repair. Voltage and frequency variations can cause problems with both loads. A weak current limits these power loads, overheats an operation and leads to premature failure. Motors are the biggest victims of poor power quality. Once a motor fails, it is generally repaired or replaced but more often than not, the cause of the failure is not diagnosed. Because of poor power quality, the lifetime of a motor can be cut in half.

The popular ElectroFlow system economically optimizes power quality and Electenergy Technologies Inc. (ETI) promises electricity savings of up to 34 percent without any disruption to equipment or machinery. According to ETI, it stabilizes voltage supplied to the load, reducing heat generation in motors and balancing the load over three phases, reducing negative voltage sequences and circulating currents.

Electric utilities have been monitoring their power lines for decades in an effort to prevent electrical disturbances. The result ensures compatibility between equipment and the electrical environment. “Generators were just not cutting it as a solution to power interruptions,” said Tom Key, vice president of technology for the Electric Power Research Institute. “They weren’t up and running quick enough. With that reality, there was a need to bridge that gap. The problems with bridging the system is people are finding it too expensive; they are replacing batteries and they are getting more protection than they need.”

According to C.J. Meiser, product line manager for management and monitoring solutions at American Power Conversion, over the last two years, remote monitoring of backup power solutions has become something that power customers are now looking into.

“Customers were losing IT staff and being asked to provide higher levels of availability when many times it wasn’t their specialty. In the past six to nine months, we have seen an increased demand for our application that monitors a UPS system, checks for battery loads, etc. It’s set up to alert the reseller. What used to happen is that when systems went down, they would call into a help desk to find out why the UPS was not working, only to discover it was because of a bad battery,” he said. “Now, the reseller can dispatch people to take care of it. They are able to tell 60 days before it happens if the battery is bad. The information is then sent to the reseller and they can dispatch a person to replace the battery before the problem happens. Resellers love to provide additional margins, so this has become a really hot topic.”

Only incandescent light bulbs and resistive heating elements demand perfect power while most other loads impose their own demands on the available electrical supply. Because of this, the demand of all inductive loads is for an unusual type of current. Resistive loads demand their current at the same time in each cycle, as the voltage is available.

Bridging power applications, stabilizing voltage and providing regulation for short-term energy solutions requires high-quality electric power. These systems with power bridging components use a fast-acting storage system to bridge the gap when slower starting, long-term systems are unable to do so. While there are many short-term bridging power products available, storage technologies that can provide immediate response with longer life are needed. EC

SPEED is a freelance writer based in Weymouth, Mass. She can be reached at 617.529.2676 or kkspeed@aol.com.

About the Author

Kellie K. Speed

Freelance Writer
Kellie Speed is a freelance writer based in Weymouth, Mass. She can be reached at 617.529.2676 or kkspeed@aol.com .

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