Steel Fabricator Reduces Voltage Sags with S&C PureWave AVC

Continuous process industries cannot afford downtime -- no matter what the end product is, production delays cost money. One brief voltage sag can cost millions of dollars in downtime, lost productivity, and damaged or scrapped product.

(PRWEB) August 7, 2003 -- The Challenge: Steel Fabricator Needed to Reduce Voltage Sags to Keep on Rolling. A steel fabrication facility in east Texas specializes in the manufacture of pipe for the petroleum industry. Their process reduces steel ingots to pipe-wall thickness. Huge rollers are required to exert the tremendous force needed to flatten the ingots. Depending on the size of the ingot and the desired pipe wall, either their 2Hi" or 4Hi" rolling mill is used. The 2Hi" mill has two rollers each on the top and bottom, the 4Hi" mill has four rollers each on the top and bottom.

A few years ago, the facility removed the older motor-generator sets in their rolling mills and replaced them with variable-speed drive motors. Current surges were then experienced when ingots entered the 2Hi" mill. These current surges caused voltage sags of up to 8% on the 13.8-kV bus of the facilitys East Mill motor room. In addition to causing nuisance tripping of other motors connected to the bus, the entire facility experienced poor power factor. With a peak reactive power demand of close to 11 MVAR, the need for VAR compensation was evident.

Sizing Up the Options
Several different technologies were evaluated for providing the necessary VAR compensation, including:

Fixed capacitors. Although the least costly to install, this solution was less than ideal. There would be ongoing losses associated with the capacitors always being in the circuit. Further, the fixed capacitors would be unable to handle large swings in reactive power associated with the variety of mill motors.

An inverter-based compensator. This solution would certainly be capable of handling the large swings in reactive power, but would be very costly.

A capacitor-based compensator. This solution would also be capable of handling large swings in reactive power but would be significantly less expensive than an inverter-based compensator.

A 5000-kVAR S&C PureWave AVC Adaptive VAR Compensator was chosen for the application. It offered a 2½-year payback time, compared to a 6½-year payback time for the inverter-based solution. And its compact size permitted the device to be installed as close as possible to the 2Hi" rolling mill, providing reactive power exactly where it is needed.

Remarkable Results
The PureWave AVC, installed and commissioned in January 2000, has performed extremely well  exceeding all customer acceptance criteria. Voltage variation on the 13.8-kV bus is now maintained within ±3.2% of nominal, and power factor is now typically above 92% (way above the 85% power factor value which had been specified). The equipment runs at lower temperatures, and the total voltage and current harmonic distortion are now less than 10% and 5%, respectively.

The fabrication facility is now evaluating additional reactive compensation measures, and has requested that S&C perform a site study.

S&C Electric Company, headquartered in Chicago, IL, specializes in the development and manufacture of innovative products and services for the electric power industry. S&C's family of PureWave® Power Quality Systems have been installed at critical-process facilities worldwide to deliver reliable protection from the power quality problems that can disrupt operation. Information about S&C is available at www.sandc.com/PQ/PR.

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