Military-grade MIL-COTS UPS meets the unique demands of heavy industries

Military-grade MIL-COTS UPS meets the unique demands of heavy industries

MIL-COTS online UPSs provide double conversion online power conditioning and battery backup protection for difficult heavy industrial applications

BY MICHAEL STOUT
Vice President of Engineering
Falcon Electric
www.falconups.com

In many heavy industrial applications the diversity of environmental factors that can render a computer-grade online uninterruptible power supply (UPS) inoperable is only exceeded by the number and magnitude of power-quality problems that are encountered. Most online UPS products have been designed for installation in a fixed location and protected environment with a controlled temperature range of 0 to 40C. They will provide many years of reliable operation when installed in a laboratory, office or computer room environment, and their price is very attractive. However, many heavy industrial UPS applications demand that the UPS be installed in an environment more like a battlefield than a computer room. They are often subjected to higher levels of shock and vibration, airborne contamination, and wider operational temperature extremes, in addition to having to provide clean computer-grade output power while operating from extremely polluted power sources. Military-grade commercial-off-the-shelf (MIL-COTS) online UPS products can provide a viable solution in meeting the demanding requirement of heavy industrial applications. The following is a brief discussion of problems associated with these applications as they relate to the design and construction of a high-grade MIL-COTS online UPS.

The first area we will look at is the UPS’s ability to withstand shock and vibration. The Department of Defense has issued MIL-STD 810 that details the manufacturing and performance guidelines specifying allowable parts and environmental condition ranges in which mobile equipment and computers must operate to meet compliance. In addition, the Army requires mobile-based equipment to pass the Munson Road Test. A MIL-COTS UPS sold to the military will have been tested to various levels of these standards providing an added level of assurance as to their suitability for use in harsh heavy industrial environments.

Mobile applications

An online UPS intended for use in an industrial mobile environment must be specifically designed to withstand continuous low-frequency vibration and repetitive high-G shock.

A UPS incorporates high mass, circuit-board-mounted components such as transformers, power components, heat sinks, and batteries. To assure reliability, the UPS must be specifically designed for use in this environment. Chassis sheetmetal gauge, circuit board material, component mounting, and mechanical design must be to a higher level than found in standard computer-grade UPS products. Typical industrial applications having this type of vibration profile include mobile medical laboratories, mobile television news or film production vans, mobile law enforcement command and control vehicles, and mobile forensics labs.

Fig. 1: Typical on-line UPS design topology

Should the mobile platform include an element that creates additional high frequency vibration unsecured low mass components may be adversely affected. In military applications this type of vibration profile is typically found in aircraft applications. Furthermore, special attention must be paid to mechanical design and the securing of key components to prevent lead fatigue and internal damage. A brief list of industrial applications having both low- and high-frequency vibration profiles includes: aircraft installations, mining machines, mobile power generation platforms, and oil and gas drilling rigs.

The next area of concern is airborne contaminants. The typical online UPS requires an adequate amount of forced airflow to cool internal heat sinks and components. This is usually accomplished by using cooling fans that pull cool air from the outside of the UPS enclosure, over the critical internal components and exhausts the heated air back to the outside. Computer-grade UPS units are designed to operate in a contaminant-free environment. As such, they do not have any method of filtering the air or preventing contaminates from collecting on circuit board and component lead surfaces. Ingesting small amounts of non-conductive dust into the UPS is typically not a problem and expected. However, in heavy industrial applications the amount and types of contaminants can be substantial. For example, inside sewage and water treatment plants, corrosive gases are often present. These gases damage the copper circuit traces on unprotected circuit boards, leading to premature failure. Many MIL-COTS UPSs have an additional thick layer of protective conformal coating applied over their entire circuit board and component surfaces. This coating acts as a barrier against contaminants and adds to the overall life of the UPS. In severely contaminated environments, conformal coatings may not provide the level of protection needed. Filters are impractical, as they would have to be cleaned or replaced hourly. These applications require the UPS be installed inside a sealed NEMA 4X enclosure.

NEMA 4x enclosures can present cooling problems for the UPS as cool outside air is excluded from the enclosure. Most computer-grade UPSs have an operational temperature range of 0° to 40°C. Special design considerations must be implemented to assure the higher operational temperature limit is not exceeded. Again, MIL-COTS UPSs have an advantage as they have been designed to operate reliably over much wider temperature ranges. A typical MIL-COTS UPS has an operational temperature range of –30° to 65°C. Further, special wide temperature range batteries are configured with the UPS. Good examples of high contaminant industries requiring the UPS be installed into a NEMA 4X enclosure are refineries, land based and offshore gas and oil rigs, machining facilities, and bakeries.

A wide operational temperature range is a real asset in industrial applications where it is not desirable to use a NEMA enclosure. For many applications, an online UPS must be located where heating and air conditioning are not available. The UPS must survive the wide temperature extremes of the local environment. Outdoor locations include gas and oil well sites, tollbooths, foundries, mills, communications transmitters, and repeater sites. Indoor applications include food processing, mining, power generation, farming, and warehousing.

Power-related problems are one of the leading causes of lost productivity in an industrial environment. Heavy industry often has some of the harshest and most destructive power problems. These include long-term low- and high-voltage conditions, high-voltage transients, harmonics, high level of common-mode noise, and frequent momentary and sustained outages. These problems are present due to high level localized power pollution being created within the facility by other high power demand equipment operating from the facility’s power system. Voltage sags or equipment damaging high voltage transients are caused by the starting and stopping of large motors, compressors, and hydraulic pumps, for example. To meet military objectives, MIL-COTS online UPSs are designed to operate reliably from harsh power sources while regenerating a clean sinewave AC power. Often the military requires battery backup periods lasting for several hours. To meet this requirement the MIL-COTS online UPS and associated battery options have specifically been designed to support long-term power outages.

MIL-COTS online UPSs are a viable option to providing the benefits of double conversion online power conditioning and battery-backup protection for difficult heavy industrial applications. They will give years of service in environments where computer-grade UPS products will fail within a few months or not operate at all. They are the best investment for long-term reliability and productivity. ■