UPS: Power Players
More than ever, facilities rely on critical power supplies for their operations. Gone are the days when facility executives would tolerate occasional and lengthy power interruptions.
As a result, maintenance and engineering managers are under growing pressure to ensure that key components of electrical distribution systems operate efficiently and reliably. Managers are expected to oversee power systems that provide the resilience and reliability of Internet systems. Today’s digital economy requires a 7x24 uptime for all critical equipment.
Although facilities desire such a high level of reliability, it is no small feat to achieve because most facilities are connected to a utility using one electric cable and associated switch gear. Any failure along this path interrupts the flow of power to the load being serviced.
An uninterruptible power system (UPS) can provide power to a facility during both normal and abnormal conditions. Under normal conditions, a UPS supplies electricity to the load using the prime electrical source. But when power from the prime source is outside the acceptable tolerance, the UPS can continue to serve the load without interruption — essential for ensuring smooth facility operations.
Because of this central role, UPS specification, installation and maintenance have become increasingly important issues for managers.
UPS generally fall into two categories:
- A continuous UPS works continually and serves the load, regardless of the condition of normal power source. In other words, the load is not directly connected to normal power but instead is always served by the UPS through its battery bank and inverter system. A battery charger continually charges the UPS battery bank. Some professionals argue that a continuous UPS is the only true UPS system.
- A standby UPS is dormant, as the prime electric supply serves the load under normal conditions. But when power from this prime electric source deviates from a predetermined condition, the UPS automatically disconnects the load from the prime source and begins supplying power. This process takes 1-4 milliseconds — a momentary interruption that generally is not a problem.
A standby UPS virtually meets the needs of most critical loads practically. It is preferable to a continuous UPS, since it costs roughly one-third as much as a continuous UPS, and that is the reason the standby UPS is becoming the most common type in facilities.
When speaking of an abnormal condition in an electrical distribution system, people generally think of a power interruption. But today, power systems are cluttered with other interruptions, including harmonics, transients and electrical noise. Also, power from a utility might undergo significant voltage sags or swells, frequency variations, undervoltages, overvoltages and spikes.
So a UPS not only provides power to critical equipment under during an outage; it also protects them from damage attributed to power quality problems.
Since UPS units play an important role in maintaining a highly reliable power source for facility operations, it is important for managers to specify devices that can monitor the performance and condition of UPS systems.
In recent years, manufacturers have developed advanced technology to assist mangers in monitoring UPS. These devices continually monitor a UPS and provide valuable information on the system’s status, including remaining back-up time, battery test schedule, shutdown software, and broadcast and paging capabilities for predetermined events.
During a power interruption, a UPS can service the critical load as long as its battery bank has an adequate electric charge. To enable a UPS to continue serving the load, managers need to provide an emergency generator to charge this battery bank.
Recently, manufacturers have introduced a new technology, a distributed generation system (DGS), which is designed to improve uptime. In contrast to an emergency generator that is only used as a standby unit, a DGS operates continually. Power generated by a DGS is synchronized with the utility power and connected to the power grid. During a utility outage, the DGS unit can continue to serve the critical loads.
Fierce competition has increased the need for reliable electric power systems in all types of facilities. But most electric power systems were designed and built mainly to serve standard appliances, such as refrigerators, fans and air conditioners, which requires “three-nine” — or 99.9 percent — reliability. Three-nine reliability means that, on average, the power system might experience an eight-hour interruption in a year, which might be acceptable for traditional electric loads.
By contrast, many electrical loads for computers networks and servers now require much higher reliability ranging from a five-nine reliability — 99.999 percent — to seven-nine reliability — 99.99999 percent — levels beyond the reach of many existing power systems.
In other words, these systems can only afford power interruptions of three seconds to five minutes. The reason for this low tolerance in power interruptions is the high cost they can inflict on businesses.
To achieve the higher level of system reliability managers will need to take several steps.
First, if possible, the facility should receive power from two utility substations. This strategy implies that the facility is connected using a double-ended station, where even if one utility source is interrupted, the other feeder can service the load. Second, they will need to add another layer of backup by incorporating a UPS.
To rise to the challenges that the digital economy creates, power system management is a must. To meet these needs, manufacturers have rolled out a new series of products.
Commonly referred to enterprise energy management (EEM) systems, these products collect data on the condition of individual power system components, integrate their performance, and ensure improved uptime. An EEM consists of intelligent devices, communication technologies — including wireless systems and the Internet — and software that link all of these components together.
These components monitor and collect relevant data concerning the status of individual power system elements in one or many facilities. When conditions change to an alarming or critical condition, the EEM can take predetermined steps to ensure higher system uptime.
EEMs give managers the ability to monitor and control electrical power systems for one or more facilities from a central location. They also enable managers take preventive measures to reduce power interruptions, rather than merely reacting to emergencies as they occur. And finally, they gather valuable system data to help managers gather better insights about system conditions in a real-time manner.
The presence of an EEM can assist facilities managers optimize the required maintenance by shifting from preventive to condition maintenance. Since EEM continually collects valuable data on various system parameters, managers can always evaluate the working condition of the power systems.
No matter how reliable an electrical system is or how thoroughly its components — including a UPS — are specified, chances of failure increase rather significantly if system components not adequately maintained. System maintenance is an important prerequisite in minimizing outages, but developing and implementing a maintenance program helps.
First, managers must ensure that technicians periodically check the primary electricity received from utility distribution system components. The weekly inspection process should include checking distribution transformers for appreciable temperature rise and unusual noise, such as high humming or crackling.
The annual maintenance should include a check for loose connections, insulation discoloration and calibrated safety relays. Loose connections should be tightened and relays recalibrated to prevent nuisance trips and failures.
One major cause of system failures is the ambient condition, so managers should ensure that mechanical rooms housing electrical switchgear are cool, dry and properly ventilated.
As for the UPS, technicians should periodically check control systems to make sure they can respond quickly and adequately in case of an actual failure. Since the UPS consists primarily of non-moving electronic parts, the maintenance requirements are minimal, aside from monitoring the UPS conditions.
But the larger potential failure with a UPS relates to the emergency generator that serves it. The generator must be operated under load at least once a week, if possible.
Generator maintenance has two parts. First is inspection of the engine, which often is prone to failure. The second is preventive maintenance, including the manufacturer’s recommended maintenance.
Another critical item is the emergency generator’s transfer switch, since the transfer switch must operate under normal utility power and the emergency generator.
One reason transfer switches must be exercised periodically is to ensure they will operate when needed. This is especially important for mechanical switches, since they can freeze in one position if not operated periodically.
Mohammad Qayoumi is the author of The Metering Guide for Managers published by the Association of Higher Education Facilities Officers (APPA).