Power Watch: Monitoring and Metering

Power monitors track power usage to verify billing and create an effective strategy for consumption and conservation. In the future, they will become even more useful with the implementation of enticing conservation incentives such as load shedding, peak shaving and alternative rate structures.

09/01/2001


Power monitors track power usage to verify billing and create an effective strategy for consumption and conservation. In the future, they will become even more useful with the implementation of enticing conservation incentives such as load shedding, peak shaving and alternative rate structures.

Monitoring allows users to establish criteria and substantiate usage patterns during negotiations for favorable rates. Monitors also give users the ability to investigate the cause of a power problem. Poor power quality can shorten equipment life, leading to failure and costly downtime. Monitoring can identify which general area of the system or which specific pieces of equipment are generating unwanted levels of harmonic distortion. Once this is identified, corrective action can be taken: installing line reactors to add impedance, adding active filters to cancel harmful harmonics or employing phase shifting to neutralize harmonics.

Since cost and reliability always come into play, monitoring assists in utilizing the full capacity of equipment and systems by providing the information needed to avoid premature changeouts and upgrades of switchboards, motor-control centers and panelboards. Power monitoring provides early notification of degrading electrical systems, equipment or cables, allowing corrective action to be taken in time to avoid costly downtime (planned vs. forced outage). Fault recording capabilities provide helpful information for quick, accurate troubleshooting.

Users Reports

Typical of user responses is that of Daniel J. Willard, P.E., senior electrical engineer in the power and utilities engineering department at Coors Brewery, Golden, Colo. His company uses power monitors mainly for load analysis: "We want to make sure we are not exceeding the ampacities of the switchgear, circuit breakers and feeders," says Willard. "We also use the demand information from the monitors to plan future growth, design new substations and reassign loads as necessary." Coors officials keep an eye on harmonic distortion. Engineers measure the power system's harmonic content before and after any electrical additions or modifications and take any necessary corrective action.

Agilent Technologies of Palo Alto, Calif., uses power monitoring for power and load management, and also to help in troubleshooting. While power monitors don't necessarily solve the problem, they can provide valuable information that expedites reaching the problem's root. Company spokesman Steve Sauer calls power monitoring "very effective in determining causes of power problems, and helpful in allocating resources to repair problems and avoid future troubles."

Lead electrical engineer Gary Bolin adds that Agilent's monitoring system has helped in determining whether special filtering systems must be added to the site. On one occasion, Agilent's engineers were able to avoid an unplanned shutdown when the metering system pointed out a potential system overload, leading them to offload critical equipment to alternate power sources. Agilent's future plans include using power monitoring to document future energy and demand-cost savings associated with a new utility center.

Agilent uses a facility-wide networked system that gives the firm the continuous data needed to calculate billing information for on-site customers and divisions, and the trending information needed to allocate long-term resources. Large-scale systems also give users like Agilent the tools they need for comprehensive energy planning and management.

Targeted Data

Regardless of the type or scale of the system, six electrical parameters are consistently the target of power monitoring:

  • Voltage (sags and swells).

  • Current (demand and phase-to-phase balance).

  • Usage (in kilowatt-hours).

  • Power factor.

  • Harmonic distortion (current and voltage).

  • Fault recording.

Asked whether they believe their power monitoring systems have been cost-effective, all but one person interviewed answered a resounding "Yes." (The single "No" was from someone who had installed a high-tech system that far exceeded his needs.) Some respondents cited financial savings that resulted from an early alert to a potential problem, allowing the prevention of a serious expense. Every person indicated that, regardless of financial impact, some level of power monitoring is useful.

The benefits of power monitoring aren't always anticipated. For example, one project involved justifying the addition of new loads to a large data-processing center with a load demand of more than 2 MW. A couple of years earlier, a custom power-monitoring system was created for this facility that continuously captured voltage and current waveforms, breaker status, uninterruptible power supply operating status and battery voltages and low-speed data from RTDs, humidity sensors, and watt and VAR transducers.

When it came time to add new loads, calculations indicated that the system was already overloaded, with code-connected demand greatly exceeding the system's rating. Fortunately, actual trending data were available from the monitor demonstrating to the building department that the new loads could be safely added.

An additional unanticipated benefit was provided when the utility's grid began experiencing power-quality issues. Suspicion fell on the data-processing facility—one of the largest users—in the belief that it was polluting the system with harmonic distortion. The power monitoring system provided data that exonerated the end-user.

Is State-of-the-art Needed?

If power monitoring provides so many benefits, is new equipment needed? Advances over the past few years may be worth considering, although there might be a few systems to avoid. The essential question is: How much monitoring is the right amount?

Intoxicated by whizbang technologies, engineers are sometimes inclined to give clients the most up-to-date and powerful equipment. The impulse must be tempered, of course, by common sense and budget constraints. It boils down to what is really needed.

In many cases, the answer is still a fairly conservative application of short-term monitoring using portable meters and monitors. This applies to the most critical and sophisticated facilities as well, including a sensitive Department of Defense installation and several large-scale data centers. Sophisticated monitors have a central role in effective predictive maintenance, which is key to preserving productivity. These systems compare data against preset performance parameters to alert facilities staff to slipping performance.

The industrial sector is in the vanguard in applying permanent, networked systems. Industrial power users have a greater vested interest in watching their power use closely, because power cost and reliability figure directly into manufacturing cost and productivity. The additional cost of a sophistical centralized power-monitoring system is a smaller piece of the pie, comparatively speaking, except for commercial users like data centers with 150 or greater watts per square foot.

Trends in power monitoring at industrial sites parallel today's organizational structures of smaller staffs and outsourced support. Centralized monitoring systems work well for organizations with fewer personnel available to monitor equipment or when a single site is responsible for monitoring several others. Systems that serve increasingly diverse industrial campuses are becoming more common. It's not unusual for an industrial site to house several operations with discrete cost centers—or even several companies. Trending data can be used for load analysis, enabling the campus to plan for future electrical growth or to assign usage to different buildings or organizations at the site. Many industrial users like the centralized system's ability to track not only electrical power but also other items such as volumetric gas flow.

Consulting engineers are joining manufacturers and vendors in offering power-monitoring services, which can be a great deal for smaller clients who may not have the resources for a permanent system, but can benefit from having someone keep an eye on electricity-use levels and optimize power usage. It's also a great opportunity for engineers to develop long-term relationships with clients.

Technology Marches On

Both as complex networked systems and simple hand-held devices, power monitors have come a long way. Older meters were difficult to configure and produced only hard-copy output. Today's high-end monitoring systems:

  • Incorporate microprocessors.

  • Are easily linked together.

  • Have TCP/IP Ethernet network capabilities.

  • Use e-mail, pagers or modems to instantly alert personnel to alarm or trouble conditions.

  • Can communicate via telephone, fiber-optic cable and even cellular phones and radios.

  • Can use the Internet for remote viewing and analysis.

Even basic field instruments have become easier to program, install and use—and they do more than just record data. A typical unit might be portable, offering multiple channels, significant memory and an easy-to-use computer interface for set-up. It might be operated by either battery or line power. Collected data might be downloaded via modem to be analyzed, graphed or imported into spreadsheets.

Many manufacturers are working to expand monitoring systems' communication capabilities. Some are developing Web-based total energy-management systems. One is planning Web-based services featuring software upgrades and equipment leases with maintenance and warranty plans. This type of arrangement will give users the opportunity to test-drive a complete, up-to-date system, allowing them to evaluate the benefits of that system before purchasing it outright.

Trying out a power monitor before purchasing it can make the difference in system satisfaction. They're not "one size fits all." High-level capabilities that serve one user's needs may prove worthless—even detrimental—to another. For example, some high-tech systems require specialized factory training, which may present a problem for companies with limited personnel resources or high turnover rates. Advanced systems simply may be more than a user wants or needs. Each user should carefully evaluate power-monitoring systems based on current and anticipated needs.

In the era of electric utility deregulation, power monitoring and metering has become an especially important tool for facilities that not only want to closely watch power usage but also for assessing the possibilities of on-site power installations. An effective system can help facility managers plan for the future. But be careful not to exceed the needs of the facility.

Often the consulting engineer plays an important role in specifying monitoring equipment and must have a firm understanding of the issues at hand, as well as the user's budget and true objectives. Users not convinced of the benefits may hesitate to install power metering and monitoring equipment in their facilities, shying away from the added cost. Again, the consulting engineer can help the user to select equipment that provides the necessary function at a cost which is comfortable, perhaps starting small (portable monitors, which are cheaper and easier to operate) and working up to a more complex, permanently installed system.

Whatever role engineer plays, there are many new consulting opportunities opening up that shouldn't be missed.

From Pure Power, Fall 2001.



Harmonics at Deep-Well Pump Stations

An investigation was performed to confirm that electrical noise at various deep-well pump stations was caused by harmonics and to recommend measures to correct the problem. A site visit was prompted by the complaints of neighboring residents, underscoring the special concerns about locating large electrical equipment in dense urban and suburban areas.

The project required monitoring both harmonics and decibel levels, because the problem resided at the intersection of sound and power behavior. Practitioners should be aware that power behavior does not exist in a vacuum, and measurement of non-electrical parameters may be required to obtain a complete account of the causes and solutions to power problems.

Variable-frequency drives (VFDs) were included in the pump stations. As with so many similar facilities, the nonlinear loads produced by the pump station drives created harmonics and associated problems—audible noise due to the magnetizing effect of extremely fast current changes and lower power factor.

In VFD applications for deep-well pumps, motors can be as far as 1,600 feet from the VFD. Over this distance, excessive voltage drop often becomes a problem. While deep-well pump stations are equipped with step-up transformers to avert voltage drop, the transformers themselves can add to the audible noise problem. Figure 1 illustrates conditions similar to those found at the pump stations in this project.

Along with the neighbors' noise complaints, the pump station owner faced looming utility fines for low power factor. A series of visits were set to monitor the impact of potential measures to mitigate harmonics at the sites, assessing the effects of each in terms of power behavior and decibel levels. Solutions considered included:

Line and load reactors and filters.

"Clean" VFDs, which are manufactured with 12, 18, 24 and even 30 pulses per cycle instead of the more popular and much less expensive six-pulse drives.

Transformers designed with noise mitigation in mind.

Monitoring throughout the project was performed with a handheld meter with capability for harmonic analysis. Baseline measurements were established during the first visits. Subsequent visits entailed monitoring VFDs with the addition of line reactors and the addition of line reactors plus an active filter.

Results indicated that while properly sized line reactors and active filters would likely reduce the noise associated with the utility transformer, they would not address the noise from the step-up transformers. Moreover, line reactors and active filters do very little to correct power factor.

An ensuing visit went beyond adding corrective equipment. The effects of changing out VFDs with 12-pulse units and replacing step-up transformers with noise-attenuated units were assessed. Measurements were made with five different setups, with VFD output changed to document performance under different speeds and to extrapolate a much better comparison between the different pieces of equipment used by the facility.

Using the meter, it was found that the 12-pulse drive lowered the total harmonic current distortion from 35% to 10%. One particular step-up transformer, specially designed as a quiet, noise-dampened transformer, reduced noise by 10 decibels; another, though not so specially manufactured, yielded nearly the same results.

The result was that the step-up transformer was replaced with the unit specifically designed with noise-dampening attributes. Additionally, a filter and line reactors were added to the drives.

Taking Measure

Engineers are often called upon to perform fieldwork. Most commonly, this involves observing a contractor to verify compliance with contract drawings and specifications. Sometimes, however, owners ask for assistance with troubleshooting power distribution problems that may require hands-on interaction with power measuring instrumentation. The consultant should be aware of the full range of power measurement and analysis methods and of the potential hazards of working with live equipment.

Three items essential in obtaining field data are proper tools, checklists and instrumentation. Provisions for tools are typically coordinated with the owner, who in many cases has electricians on hand for opening panelboards, transformer covers and termination cabinets.

Checklists and forms helpful for tracking field data are available through publications including the Institute of Electrical and Electronics Engineers (IEEE) Standard 1100, known as the emerald book. Custom forms, of course, can be developed by the engineer.

Obviously, the most important item in gathering field data is the power-measurement device. Hand-held portable devices, or larger transportable instruments, serve a wide range of uses, and a consultant may want to have several available—such as a harmonic analyzer, digital storage oscilloscope and demand recorder.

Field engineering requires a significant level of observation, dedication and caution. Power-quality problems point to potential distribution-system safety hazards: The possibilities of National Electrical Code violations, poor workmanship or simple equipment failure require the engineer to exercise extreme caution. In addition, depending on the nature of the facility being monitored, power-measurement data may have to be obtained late at night or during weekends. In some cases, insurance companies may not cover claims involving engineers in these or other fieldwork roles.

Taking Measure

Engineers are often called upon to perform fieldwork. Most commonly, this involves observing a contractor to verify compliance with contract drawings and specifications. Sometimes, however, owners ask for assistance with troubleshooting power distribution problems that may require hands-on interaction with power measuring instrumentation. The consultant should be aware of the full range of power measurement and analysis methods and of the potential hazards of working with live equipment.

Three items essential in obtaining field data are proper tools, checklists and instrumentation. Provisions for tools are typically coordinated with the owner, who in many cases has electricians on hand for opening panelboards, transformer covers and termination cabinets.

Checklists and forms helpful for tracking field data are available through publications including the Institute of Electrical and Electronics Engineers (IEEE) Standard 1100, known as the emerald book. Custom forms, of course, can be developed by the engineer.

Obviously, the most important item in gathering field data is the power-measurement device. Hand-held portable devices, or larger transportable instruments, serve a wide range of uses, and a consultant may want to have several available—such as a harmonic analyzer, digital storage oscilloscope and demand recorder.

Field engineering requires a significant level of observation, dedication and caution. Power-quality problems point to potential distribution-system safety hazards: The possibilities of National Electrical Code violations, poor workmanship or simple equipment failure require the engineer to exercise extreme caution. In addition, depending on the nature of the facility being monitored, power-measurement data may have to be obtained late at night or during weekends. In some cases, insurance companies may not cover claims involving engineers in these or other fieldwork roles.

Taking Measure

Engineers are often called upon to perform fieldwork. Most commonly, this involves observing a contractor to verify compliance with contract drawings and specifications. Sometimes, however, owners ask for assistance with troubleshooting power distribution problems that may require hands-on interaction with power measuring instrumentation. The consultant should be aware of the full range of power measurement and analysis methods and of the potential hazards of working with live equipment.

Three items essential in obtaining field data are proper tools, checklists and instrumentation. Provisions for tools are typically coordinated with the owner, who in many cases has electricians on hand for opening panelboards, transformer covers and termination cabinets.

Checklists and forms helpful for tracking field data are available through publications including the Institute of Electrical and Electronics Engineers (IEEE) Standard 1100, known as the emerald book. Custom forms, of course, can be developed by the engineer.

Obviously, the most important item in gathering field data is the power-measurement device. Hand-held portable devices, or larger transportable instruments, serve a wide range of uses, and a consultant may want to have several available—such as a harmonic analyzer, digital storage oscilloscope and demand recorder.

Field engineering requires a significant level of observation, dedication and caution. Power-quality problems point to potential distribution-system safety hazards: The possibilities of National Electrical Code violations, poor workmanship or simple equipment failure require the engineer to exercise extreme caution. In addition, depending on the nature of the facility being monitored, power-measurement data may have to be obtained late at night or during weekends. In some cases, insurance companies may not cover claims involving engineers in these or other fieldwork roles.

Taking Measure

Engineers are often called upon to perform fieldwork. Most commonly, this involves observing a contractor to verify compliance with contract drawings and specifications. Sometimes, however, owners ask for assistance with troubleshooting power distribution problems that may require hands-on interaction with power measuring instrumentation. The consultant should be aware of the full range of power measurement and analysis methods and of the potential hazards of working with live equipment.

Three items essential in obtaining field data are proper tools, checklists and instrumentation. Provisions for tools are typically coordinated with the owner, who in many cases has electricians on hand for opening panelboards, transformer covers and termination cabinets.

Checklists and forms helpful for tracking field data are available through publications including the Institute of Electrical and Electronics Engineers (IEEE) Standard 1100, known as the emerald book. Custom forms, of course, can be developed by the engineer.

Obviously, the most important item in gathering field data is the power-measurement device. Hand-held portable devices, or larger transportable instruments, serve a wide range of uses, and a consultant may want to have several available—such as a harmonic analyzer, digital storage oscilloscope and demand recorder.

Field engineering requires a significant level of observation, dedication and caution. Power-quality problems point to potential distribution-system safety hazards: The possibilities of National Electrical Code violations, poor workmanship or simple equipment failure require the engineer to exercise extreme caution. In addition, depending on the nature of the facility being monitored, power-measurement data may have to be obtained late at night or during weekends. In some cases, insurance companies may not cover claims involving engineers in these or other fieldwork roles.

Taking Measure

Engineers are often called upon to perform fieldwork. Most commonly, this involves observing a contractor to verify compliance with contract drawings and specifications. Sometimes, however, owners ask for assistance with troubleshooting power distribution problems that may require hands-on interaction with power measuring instrumentation. The consultant should be aware of the full range of power measurement and analysis methods and of the potential hazards of working with live equipment.

Three items essential in obtaining field data are proper tools, checklists and instrumentation. Provisions for tools are typically coordinated with the owner, who in many cases has electricians on hand for opening panelboards, transformer covers and termination cabinets.

Checklists and forms helpful for tracking field data are available through publications including the Institute of Electrical and Electronics Engineers (IEEE) Standard 1100, known as the emerald book. Custom forms, of course, can be developed by the engineer.

Obviously, the most important item in gathering field data is the power-measurement device. Hand-held portable devices, or larger transportable instruments, serve a wide range of uses, and a consultant may want to have several available—such as a harmonic analyzer, digital storage oscilloscope and demand recorder.

Field engineering requires a significant level of observation, dedication and caution. Power-quality problems point to potential distribution-system safety hazards: The possibilities of National Electrical Code violations, poor workmanship or simple equipment failure require the engineer to exercise extreme caution. In addition, depending on the nature of the facility being monitored, power-measurement data may have to be obtained late at night or during weekends. In some cases, insurance companies may not cover claims involving engineers in these or other fieldwork roles.



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