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Power protection in industrial settings.

Power protection contains special challenges unique to the plant engineer or industrial facilities manager. The first, challenge is accepting the reality that there is a need for adequate power protection in a plant setting - process control equipment is just as prone to power-related shutdowns and downtime disruptions as are data processing computers. In fact, a study was once conducted that showed a slight power interruption of just 16 milliseconds can cause shutdown of a computer system, and the same holds true for industrial electronics. A microprocessor in a control system is just as sensitive as one in an office computer.

The presence of dirty power is just as widespread in a factory environment as in an office building. The poor and inconsistent quality of incoming utility lines has been well documented, and process control electronics are very sensitive to power sags, surges and even those millisecond-long power interruptions. (Many users think of outages only in terms of several minutes or hours, but that's not the case; interruptions occur much more frequently, yet they are so brief that people often are not aware of them.)

The factory environment itself is also just as likely to create internal power surges and sags, as electric motors and other heavy equipment place momentary draws or surges through a facility's power system. And, there are processes in a factory that are just as critical as in the data center, such as rollers or other rotating type load processes that can't stop for a moment, when even a momentary ten-second disruption while a generator comes on line is too long.

As PCs, distributed control systems (DCS) and programmable logic controllers (PLC) move to the factory floor with greater frequency, they in turn are controlling more and more mission-critical applications and require UPS (uninterruptible power supply) protection.

One misconception sometimes heard among industrial users of power is a tendency to assume a factory power system has some inherent "ride through" capability not present in office environments. That's obviously not the case. Before purchasing any power protection equipment, UPS manufacturers recommend pre-site analysis of power conditions in that site in order to determine accurately the level of power problems and likely internal causes that could be isolated.

Configurations unique to industrial environments

While the electrical system design for a UPS is similar in either an office or factory, there are two areas that are different in an industrial setting. For example, it's common in older manufacturing environments to find corner grounded or ungrounded delta utility configurations, which is outside of the standard wye configuration typically used in commercial building design.

If the UPS isn't designed for an industrial application, these delta utility configurations can create grounding issues, isolation issues, noise and operational problems. For instance, it could cause the UPS to sense that the utility feed has moved out of range and begin to draw down batteries.

Another industrial UPS design issue has to do with unusually long distribution runs. In a manufacturing setting protected by centralized UPS systems, the UPS can be at one end, while loads are as far away as 50-200 feet. In this case you must account for voltage drop and cabling size issues. You've also introduced other uncertainties to power protection - long cables can be cut or damaged by maintenance personnel, or noise is more easily introduced to the line through long cables. Shorter cables avoid these variables.

Does the factory require a special UPS design?

Having said how similarly vulnerable either an office or industrial environment is, we do recognize that offices and factories are different and at times can require special design considerations for electrical and support systems. But this doesn't require that we always design LIPS equipment differently. Other companies may say that a special UPS topology is uniquely required for industrial power protection. The way the UPS is built - how voltage and frequency are regulated, what specific filtration is present, etc. - affects its effectivity in an industrial setting more than the topology. A variety of topologies can be recommended based not on the application, but on the power range required (certain topologies are more effective at lower kVA ranges, and others are best for larger kVA needs).

General recommendations call for different maintenance routines for the industrial environment - changing air filters more frequently, checking power connections more often, etc. There is a basic rule of nature that whenever you install almost any type of equipment in a harsher environment - industrial or factories certainly apply here - the equipment will experience higher wear and tear and a potentially shorter life.

Temperature extremes

One other special industrial consideration mentioned occasionally is the need to extend temperature operating ranges of UPSs. Today's commercial UPS is designed to operate in a 0-40 [degrees] C temperature range, with 25 [degrees] C (77 [degrees] F) as the optimum temperature. If temperatures in a facility are chronically above this level, the UPS can still operate, but derating may be required. Note, though, that while a UPS can operate at above 40 [degrees], to say 50 [degrees] C, battery life is reduced by one-half from this increase. There's no doubt that an industrial environment does play a role in battery life, and the realities of physics and chemistry make this inescapable.

It is generally recommended that if the UPS will be sitting out in the manufacturing area, where the temperature may exceed the optimum UPS operating range, the UPS should be housed in an enclosure that has air conditioning and air filtration capabilities in order to keep the UPS running under ideal conditions.

Considering solutions for power protection

The first question usually centers around determining what level of power protection is needed - a power conditioner or a LIPS, and what's the difference between them.

First, there's a tremendous amount of confusion over the term power conditioner, and what encompasses a power conditioner. Is it providing voltage regulation, frequency regulation or isolation? Or is it just providing filtering? Appropriately used, a power conditioner is something that regulates, filters and provides isolation.

Simply put, an on-line UPS then provides all the features of a power conditioner - correctly defined - and in addition provides battery back-up in the event of an interruption of power, no matter whether that interruption is in milliseconds or several minutes in duration.

When should one be used over the others?

The answer is both application-driven and consequence-oriented. If a power outage - defined as even a millisecond in duration - would lead to downtime or crashes of a system critical to your operation, then a UPS is required equipment, If a customer purchases a power conditioning system, then the customer is saying that either his or her site is not prone to outages or significant disruptions, or if there are outages, that process can stand to be interrupted with minimal or no damage to the process or electronic equipment.

The decision also has to do with the site location; downtown electric utility grids in large cities that are fed by multiple utility feeds are very reliable, and often a power conditioner without battery back-up is sufficient. However, if your industrial site as at the end of an electrical distribution line in a remote area, your exposure is greater.

The distinction is blurring

Recently, as UPS technology has advanced, many UPSs today offer both constant, on-line power conditioning and battery back-up combined into one unit. There is less of a price difference today between power conditioners and UPSs, so therefore the decision to purchase a UPS-level of protection has become an easier and more obvious choice.

Integration issues

Integration issues include a growth plan for the individual power protection unit and the facility in general. Increases in power capacity need to be planned for when purchasing any type of power protection or conditioning equipment. Users should consider how the UPS is mounted, either rack-mounted or on the floor. Do they prefer a centralized or distributed UPS approach? In other words, one central 300 kVA UPS, or several individual 50 kVA units? How much battery time is required? Does a particular station need X number of minutes to finish a batch process or complete a cycle before shutdown? When do you continue to purchase additional battery cabinets, and when is it more economical to install a diesel generator in conjunction with a UPS for extended outages? And, finally, what communication and LAN network is being installed in the facility, and what connectivity to other computer systems in general are needed? As companies seek to collect and integrate statistical process information more widely, connectivity issues become more critical, even for power monitoring operations.
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Author:Nacke, Brad
Publication:Rubber World
Geographic Code:1USA
Date:Mar 1, 1999
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