Backup Generators, UPS Systems Provide Power in an Outage

By James Piper, P.E.  
OTHER PARTS OF THIS ARTICLEPt. 1: This PagePt. 2: Maintenance of Switchgear and Backup Power Systems

Facility managers are under increasing pressure to provide a reliable, stable supply of electricity under a wide range of operating conditions. Systems and processes have steadily grown less tolerant of power disturbances. What once might have been considered to be little more than a minor inconvenience, today could result in major disruptions and losses to the facility and its occupants.

The problem for facility managers is that in spite of their best efforts, power disturbances will occur. While some may be the result of problems within the facility itself, most are due to events that are outside of the facility and therefore beyond the control of the facility manager. Faults in the utility's distribution system, voltage spikes, voltage sags, brownouts, and blackouts can all cause interference or interruption in service.

Facility managers have multiple tools at their disposal when looking for ways to improve the reliability of their electrical power system. For large facilities with critical operations, redundant electrical supplies offer one level of protection. Battery powered units with built-in inverters can offer short-term protection for smaller loads. But for most applications, the most commonly applied means of improving the reliability of a facility's electrical supply is the backup generator. And for those facilities with loads that cannot tolerate even a momentary loss of power, or that require a clean, stable source of power, there is the UPS system.

Often overlooked in the push to install these items is the necessary supporting switchgear that ensures that the systems will function properly when needed. Equally overlooked are the requirements that these systems and components have for ongoing maintenance. Improved power reliability is not the result of a one-time investment. Improved reliability comes only as a result of an ongoing effort.

It is important to note the some facilities, such as health care facilities, have specific requirements for power reliability systems that must be followed.

Backup Generator

The natural gas, propane, or diesel generator is the most widely used alternative source of power in facilities today. Its ability to provide continuous power as long as it has a supply of fuel makes it well-suited for providing both long- and short-term backup power.

Most generator-based systems are designed to automatically provide power to designated loads in the event of an interruption in service. When power is lost, the generator automatically starts. Once the generator comes up to speed, a switch automatically transfers the load from utility power to the output of the generator. Depending on the size of the generator, this transfer typically takes place in 30 seconds or less. Once utility company power is restored, the load is transferred back and the generator shuts down.

While generator systems are very reliable, they are not maintenance-free. If the systems are to perform as needed, when needed, they must have regularly scheduled maintenance.

One of the most important maintenance tasks that can be performed with generator-based systems is the regular exercising of the entire system. Once each week or two, depending on the size of the generator and the nature of the loads it must supply, generators should be started and run for at least 30 minutes. To fully test the entire system, the generators should be run under load — ideally the load that it would normally power. By operating the system under load for 30 minutes, the generator is tested along with its starting system, cooling system, and all switchgear required to supply power to the loads.

In addition to the program of regular exercising, there are a number of other routine maintenance tasks that must be performed. The batteries used to start the generator should be checked monthly. Each time the generator is run or exercised, the fuel supply should be inspected to determine how much is present and to ensure that it is free of contamination. Additionally, the generator's cooling and exhaust systems should be inspected once each month.

The UPS System

While generators offer long-term protection in the event of an interruption of service, they cannot offer protection against many of the common faults in power systems. That level of protection can be achieved only with an uninterruptible power supply (UPS). While there are several different configurations for UPS systems, the most commonly used is the online system.

The online UPS has three major components: a charger/rectifier, storage batteries and a power inverter. Incoming alternating current from the utility company enters the charger/rectifier where it is converted to direct current. This direct current charges the batteries and supplies power to the inverter which converts the direct current back to alternating current. In systems designed to power loads during extended outages, a generator is typically connected to the batteries.

The UPS system offers the advantage of supplying power to the loads continuously, no matter what happens to the utility power. But the benefits of the UPS go beyond its ability to continuously supply power. The process of taking alternating current from the utility and converting it to direct current, then back to alternating current, eliminates practically all power disturbances, including transients, noise, and voltage fluctuations.

UPS systems, like generators, are only as reliable as the maintenance that is performed on them. For example, most systems use lead acid batteries to supply power during service interruptions and while the generator is getting up to speed. These batteries require regular inspections to ensure that all cable connections are free of corrosion and are properly torqued. Electrolyte level within the batteries must be kept at the proper height to prevent damage to the batteries. Batteries must also be tested every six months to check for capacity loss.

Other components in the UPS system require less maintenance, but still should be inspected on a regular basis to ensure that they are free of dust that might result in overheating and that all connections are properly torqued.

Continue Reading: Power Reliability

Backup Generators, UPS Systems Provide Power in an Outage

Maintenance of Switchgear and Backup Power Systems

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  posted on 6/29/2010   Article Use Policy

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