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Planning is a prerequisite for good power management

By Jack Smith

June 2012

During the last week of April, I had the privilege of attending a press event where a major manufacturer introduced its latest generator set. Attending the event reminded me about power management - actually, more about the big picture than the nuts and bolts. This column will present a brief overview of power management concepts when incorporating generator sets.

Where do generators fit?

Where do generators fit?

Again, looking at the big picture, the answer is, "It depends." Some facilities don't need a generator because relying on the utility is adequate for the business model of some companies. Many power outages are short - from a few seconds to a few minutes. Although it may be inconvenient, losing power isn't devastating to some businesses, such as those that are not highly automated.

However, data centers, hospitals, and process plants are a few examples of facilities that require electrical power without interruption. Obviously, it's possible for electrical power from the utility to have some interruptions, even though they may be very infrequent. Therefore, the companies most affected by power outages must plan accordingly. Planning is a prerequisite for good power management.

Whether legally required or part of a business/operational model, generators provide the power that's missing if (when) the utility fails. Generators are necessary for those applications that can't tolerate power outages. For some types of facilities the National Electrical Code (NEC) requires an electrical power source, or sources, to be available in case utility power fails. NEC Article 700 covers emergency systems, Article 701 covers legally-required standby systems, and Article 702 covers optional standby systems. (Specific details and definitions aren't covered in this column, as the focus is on power management.)

However, a few explanations may be helpful in understanding how generators fit into the power management discussion. The terms emergency standby rating, prime-rated power, and continuous power rating are based on generator capacity, load factor, and nameplate ratings, according to ISO-8528-1: Reciprocating Internal Combustion Engine-Driven Alternating Current Generating Sets.

Emergency standby rating is the maximum power output capacity of a generator supplying facility power to a variable load if the utility fails. Typically, ISO-8528-1 limits the 24-hour average output to 70 percent of nameplate emergency standby rating.

A prime-rated power generator is available for an unlimited number of hours per year to supply power to a variable load. However, the average load factor must not exceed 70 percent of the nameplate rating.

A continuous power rating is applicable in situations where the generator provides primary power because of the unavailability of utility power. In this case, the generator supplies a constant 100 percent of rated load without the limitation of hours per year.

Many times (but not always), the same model generator can be used in all of these scenarios. What's different is the way that manufacturers rate - or derate - the generator. Another consideration is the difference between full load and partial load. This may sound like a specifications or ratings game. Actually, it's not a game, and it's fully legitimate. Manufacturers and users must understand each other when it comes to a generator's application and/or intended use.

Managing power and costs

In any facility - whether commercial, industrial, or municipal - electrical distribution requirements are determined by the types of loads connected to it. Conversely, load characteristics determine how a facility's electrical distribution system behaves.

The concept that drives - or should drive - power management involves finding ways to economize in order to combat rising energy costs. For example, identifying and replacing inefficient loads such as power-hungry lighting; using variable-frequency drives with large electrical motors instead of starting them across the line; and shifting and/or staggering equipment starting times (especially compressors, pumps, and HVAC systems) away from peak demand periods are strategic ways of managing power usage. Also, using smart metering and submetering can help facilities identify power usage peaks.

Implementing a "formal" energy management plan can incorporate all of these efforts. However, a good way to make the most of a formal energy management plan is to start with an energy audit. Engineering firms that specialize in energy audits can help with this by identifying energy-saving opportunities that will have the most impact.

Part of a power management plan is to explain how electrical demand charges are calculated and applied. Understanding the "business" side of electrical demand can help facilities best apply the technical and engineering strategies that save energy and money.

So what about generators? In addition to being there if the utility fails, generators can be used for peak shaving during periods of high demand charges. However, generator system first cost and cost of operation - as well as the cost of downtime - must factor into the cost-effectiveness equation.

Maintenance should also figure into those costs. Equipment that monitors, controls, and manages electrical power must perform flawlessly to protect the facility's investment. A great way to do that is to use top-notch measurement tools such as Fluke power quality analyzers, digital multimeters (DMMs), clamp meters, infrared cameras and thermal cameras, and vibration testers to keep facility equipment in tip-top shape.

Until next time, keep standing on "Solid Ground."