Americas Generators

Backup Generators, UPS Systems Provide Power in an Outage

by GoPower 28. May 2014 04:47

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.

The electrical switchgear that connects the backup generator or the UPS system to the facility's loads forms the backbone of the power system. With the UPS system, the loads are connected to distribution panels that are wired to the output of the system. Loads in generator-based systems are connected to distribution panels that are wired to an automatic transfer switch. Utility power is normally connected to the loads through the transfer switch. When utility power is interrupted and the generator is producing power, the switch automatically transfers the load to the output of the generator. When utility power is restored, the switch automatically transfers the load back to the utility.

Electrical switchgear typically is a long-life, low-maintenance item. Because it is reliable and does not require much maintenance, it is the most overlooked component in the system. A malfunction in the switchgear, however, can prevent an otherwise perfectly operating system from coming online. Additionally, malfunctions within the switchgear can result in damage to the switchgear itself.

Most damage to electrical switchgear is caused by a combination of water, dust, high humidity levels and vibration. Moisture and dust combine to form an insulating layer on surfaces, reducing heat transfer from the components and increasing component operating temperatures. Similarly, moisture and dust coat components, restricting their movement and causing excessive wear. Vibrations can cause terminations to come loose.

At least once each year, all switches, disconnects, and circuit breakers should be exercised to verify that they are not binding. At the same time, all contacts and connections within the system should be inspected for pitting, discoloration and tightness.

Avoiding Common Pitfalls

Backup power systems are very reliable, and good maintenance practices can keep them that way for a long time. And while the systems may be fully automatic, they do require some careful planning during installation and once the systems become operational.

For example, during a prolonged power outage, it will be necessary to arrange for fuel deliveries for propane gas and diesel generators. Contracts with suppliers should be set up ahead of time with guaranteed delivery schedules. If a facility manager waits until the generator is already running to figure out how fuel is going to be supplied to the unit, maintenance personnel may be forced to shuttle fuel in five gallon cans, a practice that is unsafe and unreliable.

Care must be taken when planning the location of a backup power system. Generators are noisy units that create vibrations and give off exhaust fumes. Units must be located in such a way that they do not interfere with operations, yet are fairly close to the facility's power distribution panels so that they can be tied in relatively easily.

UPS systems also must be carefully sited. These systems and their batteries generate large quantities of heat under normal operation. Without adequate ventilation, a buildup of heat will shorten the lives of the batteries and other components. Good ventilation is also required to prevent a buildup of hydrogen gas, which is a normal byproduct of the battery charging process.

In addition, it's important to make certain that all required loads are properly connected to the system. Over time, power requirements within the facility change. New loads are added while old ones are removed or relocated. At least once each year, the facility should be reviewed for backup power requirements. Failing to do so may result in a perfectly operating backup power system that is not connected to the required loads.

Power outages can occur at any time. As a result, personnel who are most familiar with how to operate and monitor the backup power system may not be on-site at the time of the outage. Therefore it is essential to have well written procedures detailing what should be done in the event of an outage. These procedures must cover everything from what to do if the system does not start to how to monitor the health of the system while it is operating.

James Piper, PhD, PE, is a writer and consultant who has more than 35 years of experience in facilities management. He is a contributing editor for Building Operating Management.

Comments (1) -

GenPower Corp United States
6/1/2014 4:03:34 PM #

Great article. Generator reliability is the best policy since our Grid is old and ready to fail every time the wind blows.

Comments are closed

Blog Links