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Plant management: improved power factor and new control system reduce plant's utility bills.

Engineers at the Borden Proponite plastics processing plant in North Andover, Mass., were becoming increasingly concerned about rising utility costs, and frustrated over their inability to monitor how much and where electricity was being used. Monthly utility bills ran as high as $200,000, of which approximately $15,000 resulted from avoidable kVA demand costs. In addition to power factor penalties, engineers were concerned about harmonic problems (caused by the large number of high-horsepower variable speed DC drives) that threatened to shut down production equipment.

The [250,000-ft.sup.10] plant, which employs 250 people, manufactures large rolls of heat-sealable plastic film that are sold primarily to the flexible packaging industry; it also manufactures polypropylene film for the coverting and graphic arts industries.

The plant operates 24 hrs/day on four rotating shifts. Unscheduled downtime can result in the loss of thousands of dollars per hour.

"Because of our low power factor, we were billed based on kVA demand, but the only way we knew our power factor was low was by relying on the utilities' measurements and by analyzing our monthly bills," noted Bill Young, of the plant's project engineering group. "We had no way to verify what they claimed because we didn't have the necessary equipment to monitor our electrical usage," he said.

"Every month, our accounting department would question the high cost of the electrical bill, and grudgingly pay it. We decided it was time to update our electric system and make it more efficient."

Electrotek Concepts, a consulting firm specializing in power quality analysis, was hired to take on-site measurements of harmonics, voltages, and load distribution. This information, along with transformer data, previous utility bills, and an electrical layout of the utilities distribution system, was used to create a computer model that could better characterize harmonic levesl and develop a filter system design.

At the time, the plant had no power factor correction equipment. Engineers were concerned that the addition of capacitors would increase harmonic levels and potentially damage DC drive equipment. An analysis of the distribution system indicated that installation of static power factor correction equipment would not be the ideal solution; instead, harmonic filtering, with some controls for switching the banks incrementally, would be necessary.

On the basis of Electrotek's recommendations, a combination of capacitors and inductors--configured as harmonic filters--was installed. As a result, the power factor improved dramatically--from between 0.67 and 0.72 to more than 0.93.

"Our electrical bills showed our power factor had improved and our demand charges were now based on kW demand instead of kVA demand," Young said.

Installation of Borden's power factor correction began in July 1990. Because of the company's 24-hr/day operation, equipment was installed during scheduled maintenance shutdowns. Square D 2000-amp Bolt-Loc switches were installed on each of the five substations and used as main disconnects for the harmonic filter systems.

Until the summer of 1990, the company had only rudimentary instrumentation equipment on four of its five 2500 kVA substations; the fifth substation had no instrumentation equipment. At the individual substations, plant personnel could read only voltage and current values. To obtain more detailed information required that someone go into the substation to clamp meters on live busbars.

"To use portable equipment on live high voltage/high amperage systems is not preferred from a safety standpoint," Young noted. "But we really didn't have any choice, because our substations were not set up with meters to give us the required readings."

In conjunction with the decision to install harmonic filters, the company decided to install a new, permanent power monitoring system that would provide real-time, system-wide electrical information on a continual basis. The firm chose PowerLogic, a system developed and manufactured by the Square D Co.

"With utility rates continuing to rise, we felt we needed to do something to monitor our electrical usage," Young said. "The new monitoring system would also enable us to verify the effectiveness of the new harmonic filter system design by allowing us to get accurate harmonic readings.

"The analysis the consultants did gave us only a one-time reading. We wanted to look at harmonics and long-term trending ourselves. Now we have a system that allows us to get a wide variety of information any time we want."

In addition to purchasing PowerLogic circuit monitors for each substation, Borden Proponite purchased Square D's System Manager software, which integrates real-time circuit information collected from circuit monitors and organizes it in a simple, usable format.

Circuit monitors were retrofitted to the existing CTs and PTs (current transformers and potential transformers), and communication cables were fed back to Young's desk, where he now has continuous access to such metering information as power factor and demand kW. Figure 1 shows the wiring by which the circuit monitors are typically connected to a power system.

The Waveform Capture feature of the circuit monitors provides waveform data from all three phases of current and voltage for a given substation. With the data, Young can obtain a measurement of total harmonic distortion at the substation; he can also verify that the harmonic filters are operating properly.

"The new monitoring system provides us with several advantages," Young said. "We have a safer system because we don't have to send people into live substations to get readings. It's much more convenient than our old system. The PowerLogic units at the substations give us complete information for day-to-day operations, and, for more detailed reports, we can use the System Manager software.

"The scale on our old meters was not nearly as precise and accurate as the readings we get from the new circuit monitors."

Young believes the system will increase reliability and help troubleshoot problems by providing access to more than 70 monitored values, including time and dates, temperature indication, minimum/maximum history, and energy management alarms.

"With access to this type of information, we can see dangerous trends developing, or, in the case of problems, look back at the historical data to help analyze what went wrong," he said.

"If the local utility puts additional capacitors on the line that cause problems, with PowerLogic we can analyze the change in the amount of our harmonic distortion."

The PowerLogic system indicates the percentage of capacity that is being used. History of demand current, by phase, can be used to make informed decisions on where to add new loads and, when spare capacity already exists, where to avoid unnecessary expenditures for new power equipment.

Plots of information over time are easily produced. Trending of demand levels, energy usage, and equipment loading can be generated to help manage equipment loading and aid in maintenance. Real power history can be charted over a range of hours or days, thus providing the user with a trend chart. In the event of a system problem, the user has access to all pertinent system data--a feature that allows for quick diagnosis and return to service.

Should the need arise, SY/MAX programmable logic controllers (PLCs) can be integrated into the system, permitting automation of transfer, load shedding, and load sequencing functions.

"Up until recently, we were flirting with problems that could have shut down our production lines," Young said. "If that had happened, it would have been extremely difficult to determine what caused our problems.

"If you are upgrading your electrical system, it makes sense to install a monitoring system. It's economical and so sophisticated that it provides us with a wealth of information that was not available in the past. It allows us to monitor electrical facilities closely, and should help us detect and avoid problems before critical loads begin to malfunction and electrical failures occur."

Don McComas, product marketing engineer of the firm's PowerLogic business, says that although other companies manufacture systems for power monitoring and control, the PowerLogic system offers various unique capabilities. Among them are a SY/NET local area network (LAN), which permits high-speed communication and allows many users to gain access to information from circuit monitors (see Fig. 2).

"Typically, power monitoring systems are limited to a single computer to control the system. But in our system, many computers have access to the information on the network and can either monitor or monitor and control. In response to a user request, the circuit monitor can perform a waveform capture of its metered circuit, sampling 256 points pwer wave over four cycles. By creating a waveform representation of the metered circuit, the system allows users to obtain information on factors relative to power quality of the circuit, such as crest factor, total harmonic distortion, and spectral analysis of the waveform."

For control applications, PLCs monitor data stored in the memory of the circuit monitor. "If a PLC reads a low voltage on any phase, it can be programmed to trip a breaker to protect a motor," McComas continues. "Or, if the power factor drops below a predetermined level, the PLC can add capacitance to the system by turning on banks of capacitors, functioning as a power factor correction system."
COPYRIGHT 1991 Society of Plastics Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Borden Proponite
Author:Rickey, Don
Publication:Plastics Engineering
Date:Nov 1, 1991
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