By Michael Valenti

The power behind thunderstorms can cause problems for industrial facilities where electronic systems that control critical equipment are sensitive to the storms' slight voltage disturbances. These brief voltage sags can disrupt process electronics, resulting in losses in production and costly downtime to recalibrate and restart the equipment. A pilot project funded by Oglethorpe Power Corp. in Tucker, Ga., and the Electric Power Research Institute (EPRI) in Palo Alto, Calif., aims to eliminate the problem by compensating voltage fluctuations with the PQ2000 energy storage system designed by AC Battery Corp. in East Troy, Wis.

The PQ2000 system offsets voltage disturbances caused by storms, thereby preventing costly production-equipment shutdowns.

Oglethorpe Power selected the Brockway Standard Lithograph plant in Homerville, Ga., as the site for the first commercial installation of the PQ2000 system. The lithography facility is a customer of Slash Pine Electric Membership Corp., an electricity-distribution utility served by Oglethorpe Power. The Brockway facility is a prime location to test the power-compensation system because southeast Georgia has one of the highest rates of lightning in the United States; the flat terrain is also susceptible to high winds and hurricanes that can cause power disturbances.

The Homerville plant houses four production lines, each equipped with high-temperature drying ovens, that are used to cure printed metal for can products such as the lion's share of Folger's Coffee cans in the United States as well as paint and brake-fluid cans. Fifteen adjustable-speed drives on the four lines control the printing process.

"We would lose power 30 to 50 times per year due to storms," said Charlie Backus, plant manager at the Homerville facility. "We experienced an average of three motor burnouts per month due to poor-quality electrical service after an outage." The outages also triggered the protective devices that turned off the plant's ovens. Plant workers had to purge the oven systems of gas before relighting them, a 15-minute process for each line.

Backus added that power disturbances were both a safety concern and a productivity issue, because workers had to climb a 20-foot ladder to purge the burners. "We cannot take the chance that someone will eventually get hurt by malfunctioning equipment," he said.

The PQ2000 incorporates an electrical battery system, an electronic selector, and a matching transformer.

The PQ2000 system is designed to continuously monitor the utility voltage provided to a commercial or industrial facility, according to Chuck Ward, an electrical engineer and senior power-quality engineer at Oglethorpe Power who is the project manager of the PQ2000 installation. "Whenever a disturbance is detected, the system switches and picks up the load, isolating itself and the load from the utility system to protect the load from the disturbance. Once the utility system returns to normal, the PQ2000 system switches the load back to the utility."

Speed is of the essence in fulfilling this mission. The PQ2000 can deliver up to 2 megawatts in about one-quarter of a cycle (or 1/240 second) to maintain power to critical equipment. Most power disruptions typically last only a few cycles, so the AC Battery engineers designed the power-storage system to dispense power for up to 10 seconds, ensuring an extra margin of safety.

The self-contained PQ2000 system is installed outdoors in a 30- by 40-foot area. The system contains three major components: the PQ2000; an electronic selector device made by PBI in Roanoke, Va.; and a matching transformer made by Engineered Magnetics Inc. in Rancho Dominguez, Calif. The PQ2000 consists of 48 Delco 1150 truck batteries (which are commercially available and maintenance-free lead-acid batteries), an inverter and bridge, a charger made by Omnion in East Troy, and a hydrogen exhaust system. AC Battery and Omnion designed the monitoring-system software to oversee the PQ2000 system and record the number of times it runs.

A major design challenge for the PQ2000's inaugural commercial installation was reconciling the different results obtained from factory testing and field testing. In the factory, engineers tested the system by using a three-phase breaker on the 480-volt secondary side. The engineers tripped the breaker off to simulate a power disturbance and trigger the PQ2000, and turned the breaker back on to simulate reclosure.

"The system worked just fine under those conditions," Ward said, "but when we installed it at the Brockway plant for field testing, we got different results because we had to pull the single-phase fuses on the distribution circuit in order to simulate power disturbances such as a fuse blowing."

This disparity forced Ward and his colleagues to perform 18 weeks of in-field engineering, including installing and removing relays, replacing the system's discrete logic with programmable logic controllers, and adding programming to make the PQ2000 respond to actual utility disturbances. "We also provided single-phase protection, implemented three-phase voltage sensing, and replaced power-supply wiring," Ward said.

Since its installation on Dec. 3, 1996, the system at the Brockway lithography plant has demonstrated its ability to protect plant operations from various utility disturbances ranging from a voltage sag to a complete outage, up until successful reclosure. "We're not losing synchronization anymore. The PQ2000 brings a lot of stability to the operation," Backus said. The plant manager added that the PQ2000 and other improvements recommended by Slash Pine, such as properly grounded and improved electrical drives, trimmed the Homerville factory's annual electrical budget from a high of $110,000 to $120,000 down to $60,000 to $70,000.

The Brockway Standard Lithograph plant in Homerville, Ga., was chosen to test power-compensation systems because the region is one of the most lightning-prone in the United States.

Ward said the lessons learned from the Brockway project should shorten future PQ2000 installations to one or two weeks. "We are currently working on a second PQ2000 system for another of our industrial customers," he said. In addition, AC Battery engineers have developed a mobile version of the PQ2000 in conjunction with Sandia National Laboratories in Albuquerque, N.M., to demonstrate the transportability of the system at East Coast utilities.

Based on their experiences at the Homerville plant, EPRI and AC Battery will be developing further applications for the PQ2000 system where critical or sensitive power equipment is used. For example, using the system to correct a 2-second power outage can save a semiconductor-manufacturing plant $70,000 in product that would otherwise be lost. The same 2-second interval can cause $600,000 in data-processing losses for a computer center, require weeks of cleanup in a glass plant, or corrupt critical patient data at a hospital.


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