Reliable power is key to industrial productivity

Pay attention to harmonics
Excessive harmonics in a facility’s power distribution system is a major concern. Due to the ever increasing amount of computer equipment powered by switch-mode power supplies, variable speed drive motor controllers and other non-linear loads, the level of harmonics generated on the facility’s power system can become too high. The level of harmonics should be measured and if too high, steps must be taken to reduce the level. Harmonic levels should be in compliance with IEEE Standard 519-1992. Should harmonic levels exceed the maximum specified levels, excessive current can cause to flow through the building’s wiring, increasing the potential of overheating the wiring, possibly resulting in an electrical fire. Harmonics can cause voltage sags, which increases the current demand of equipment operating in the building. The increase in the equipment’s operating current will result in more heat being generated inside the equipment and shortening its service life. Telecommunications and data cabling are often run close to power cables. If harmonics are above normal tolerances, high frequency harmonics can be induced into phone lines and data cabling. The end result is noisy phone lines and unexplained data lose or data corruption and computer hangs.

Harmonic problems can be treated in three ways: elimination, filtering and cancellation. A major source of harmonics is computer-based, specifically, computer and network equipment. By adding an online topology uninterruptible power supply (UPS) or active power conditioner with input power factor correction (PFC) ahead of the equipment, harmonics are eliminated and the overall power factor is increased. Both devices provide a tightly regulated output voltage irrespective of the input voltage level, reducing the equipment’s internal temperature. The UPS also provides necessary backup power when utility power is lost, prior to backup generators coming online. As the number and type of loads being connected to the facility’s power system is dynamic, harmonic filtering can be difficult to implement. Filtering is best accomplished on a power system having a fixed load as the filter is effective over a limited harmonic frequency range. Should large three-phase loads be the major source of harmonics, a harmonic cancelling transformer may be installed as a solution. This type of transformer has patented built-in electromagnetics technology designed to remove high neutral current and the most harmful harmonics from the 3rd through 21st.

Equipment is only as reliable as its power source
In the industrial environment, large motors, variable speed drives, pumps, robotic equipment, heaters, ovens and other equipment having large instantaneous current demands often generate power problems with other power sensitive CPU-based equipment operating within the same facility. During the startup of the offending equipment, its initial high current demand can cause voltage sags and transients on other power circuits in the same facility. Extreme voltage sags and high voltage transients often cause microprocessor based PLCs, laboratory equipment, computers and data networks to operate unreliably resulting in costly down time. To minimize these problems, wherever possible the sensitive equipment should be powered from a dedicated circuit. Again, installing an active power conditioner or online UPS ahead of the sensitive equipment will eliminate both problems and assure reliable operation.

In hindsight, a lack of foresight becomes painfully obvious and is often costly. In all industries, critical processes rely on key equipment that is only as reliable as its power source. Taking the necessary steps upfront to assure a high level of power quality throughout the industrial facility will minimize lost productivity and profits and in some cases prevent a disaster.

{1} Jon Toiga, Disaster Recovery Planning: Managing Risk and Catastrophe in Information Systems, (Yourdon Press, 1989).

About the author:
Michael A. Stout is vice president of engineering, Falcon Electric, Inc.
Visit: www.falconups.com

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