How and Why to Monitor Power

Quantity, Quality, and Reliability of This Expensive Raw Material Can Make or Break Your Plant's Bottom Line

By Rich Merritt

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The utility found that the underground feeder was undersized before it entered the facility. "Using the EP Web software with the integral billing module, we were able to determine that the higher demand caused by the undersized feeder cost the facility millions of dollars in overcharges. This information was provided to the utility and an adjustment was received."

(Redundant Power Allows 'Live Maintenance' of IS Segments)

Perhaps your utility will help you monitor power. Georgia Power, Atlanta, offers EnergyDirect.com, an online tool that its business customers can use to analyze and track their current and historical energy use and billing information. The standard package is free, and allows businesses to track energy costs; correlate energy usage with production data, changes in operations, or weather; forecast energy costs for the next year; and spot increased energy usage by faulty equipment.

What a Waste

The other side of the energy question is, are you using power efficiently? As John Havener, energy czar at Pavilion Technologies.

That's a lot of systems to monitor. What uses the most power? "Motors are by far the biggest consumer of electrical power at our site," reports Michael LaRocca, senior process control specialist at Solutia, Sauget, Ill. "Electric heaters for a particular unit operation are second."

The Dept. of Energy agrees. "Over 13.5 million electric motors of 1 hp or greater convert electricity into work in U.S. industrial process operations. Industry spends over $33 billion annually for electricity dedicated to electric motor-driven systems," says a 1998 DOE report. "Because nearly 70% of all electricity used in industry is consumed by some type of motor-driven system, increases in the energy efficiency of existing motor systems will lead to dramatic nationwide energy savings."

Installing efficient motors is one way to save money. Table I shows how much energy electric motors can consume, and Table II summarizes the results of a DOE program where more efficient motors were installed. (See www.oit.doe.gov/bestpractices/motors for more information on the DOE program.)

There are dozens of other ways to save energy in a plant. At Cargill Salt, an Energy Team of workers and supervisors was formed to identify conservation measures. Eric Hoegger, refinery project engineer, says changing lighting systems, installing manual on/off light switches, and a reduction in air pressure throughout the plant helped cut power consumption. Lighting changes alone saved $24,000 per year, he says. Other changes included work practices and moving loads to off-peak hours. Overall, Cargill reduced power consumption by 42% and shaved its peak demand by 52%.

Clearly, if you want to eliminate the energy villains in your plant, you need a plan.

(The Energy Internet, Part 1)

What to Monitor

Several companies will be happy to do an energy program for you. They will analyze your plant, make recommendations, and install the necessary equipment. For example, if you hire Rockwell Automation's Energy Consulting Services to optimize your plant, here's what they will do:

  • Tariff Analysis: Using information compiled from energy bills, energy tariffs, and electrical supplier contracts, Rockwell's analysts will identify alternative methods to reduce energy costs, such as aggregating multiple meters or evaluating new supplier, delivery, and tariff options. In other words, they analyze how you are paying for electric service now, and see if they can renegotiate with that supplier or find an alternate source. This may or may not be something you can do yourself.
  • Power Quality Studies: Rockwell measures and monitors incoming power to determine the causes of voltage excursions, momentary power losses, phase reversals, and harmonics. They determine the correlation between power quality, premature equipment failures, and the cause and frequency of plant shutdowns. Now this is definitely something you can do yourself. Mark Liemiller, director of marketing at Power Distribution Systems at Siemens, says new power monitors are available to make most of the necessary measurements; then they put the information in a form that is usable. "These can be very basic or quite elaborate devices that monitor and display critical power data," says Liemiller. Table III summarizes the major variables Liemiller says you should be monitoring.
  • Plant Energy Audits: Rockwell determines energy consumption patterns in the plant, and identifies equipment and processes that should be modified to reduce power consumption. Again, this is within your grasp. Once you make the necessary power measurements, a host of software is readily available to analyze the data and make recommendations.

The approach seems to work. For example, at Chevron's refinery in Richmond, Calif., Rockwell's energy analysis showed that two pumps in the diesel hydrotreater were oversized, sometimes operating at 40% below their best efficiency points. Chevron installed new medium-voltage drives on a 2,250 hp primary feed pump and 700 hp product pump and saved $330,000 per year.

Monitor Thyself

Engineers have monitored power for decades. "Before the microprocessor revolution, power system engineers recognized three classes of instruments," says Reaz Tajaii, a staff engineer in Power Systems Engineering at Square D. These include digital fault recorders, which obtain oscillograms of fault currents and voltages to evaluate the effect of voltage sags and to construct sequences of events; transient recorders and oscilloscopes, which capture oscillatory and impulsive voltage transients; and power monitors, which report steady-state currents and voltages and provide basic energy and power calculations.

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