What's the Latest in Power Quality Monitoring?
The shift from troubleshooting to predictive analysis and performance assessment has improved response times
As with many other aspects of the power delivery industry, deregulation and restructuring are changing how utilities and customers approach power quality monitoring. Traditionalists view PQ monitoring as a reactive process, in which PQ technicians or facility electrical maintenance personnel use instruments on a case-by-case basis to help identify and characterize existing problems. However, a new approach that incorporates continuous PQ monitoring into the normal assessment of system performance at utilities and customer facilities is fast becoming the standard (see Fig. 1).
Permanently installed power quality monitors come with software and communications capabilities for data collection, data processing, and results presentations. The software maintains a database of system performance information you can access for real-time data or long term summaries. The Table offers some options in this category.
The general procedure for implementing an intelligent monitoring system that can process raw measurement data and provide useful information is shown in Fig. 2). Most systems will log an overwhelming amount of data, so it's necessary to sift through it, pull out the important information, and look for patterns before making any decisions upon which to base your report.
While manufacturers have improved the functionality of power quality monitoring equipment, other contributing factors and recent industry trends like deregulation of the electric utility industry have helped increase the value of permanently installed systems for continuous performance assessment.
In today's technologically advanced climate, the need for high reliability is essential. Facility personnel define reliability as any problem that causes equipment or processes to misoperate. This includes a wide variety of power quality problems besides traditional power interruptions. Continuous PQ monitoring systems are critical for understanding events that cause power disruptions and for evaluating system performance.
Base level requirements.
The process of benchmarking expected PQ levels has been an important practice for a number of years. It started with the Electric Power Research Institute's (EPRI) distribution power quality (DPQ) project, which set PQ standards for power distribution in the United States. Many electric utilities followed up with their own projects to define expected power quality performance at the local level. Other countries have also conducted significant benchmarking projects that have become the basis of contracts and premium power services. Needless to say, setting base level requirements is an ongoing process that requires continuous assessment.
Focusing on customers.
Electric utility personnel traditionally determine capital expenditures for system maintenance based on solving problems, handling growth, and maintaining an acceptable level of reliability. A more customer-driven approach, however, considers the costs of system disturbances to end-users. In this period of deregulation, such an approach is particularly important. Understanding how power quality variations affect end-users requires PQ monitoring and communication with customers.
Power quality data interchange format (PQDIF).
Electric utility personnel and customers are now placing new monitoring instruments alongside legacy equipment, generating tremendous interest in data formats that enable different types of instruments to work together. Currently, most software programs for downloading and analyzing data are incompatible with other instruments, making comprehensive analysis difficult or impossible.
In response to this dilemma, EPRI developed the PQDIF, which allows engineers to incorporate a wider range of instruments into their overall systems. Later, the Institute of Electrical and Electronics Engineers (IEEE) established a task force to define a PQDIF standard, which several manufacturers have since adopted.
Establishment of power quality indices.
One of the important advantages of PQ indices, such as those used by electric utilities like System Average Interruption Frequency Index (SAIFI), System Average Interruption Duration Index (SAIDI), Customer Average Interruption Frequency Index (CAIFI), and Customer Average Interruption Duration Index (CAIDI), is the ability to compare the performance of different systems and track a given system over time in a standardized manner. EPRI defined indices for power quality characteristics as an extension of the DPQ project. The IEEE is currently looking at indices for PQ reporting, especially for voltage sag performance.
New standards for equipment performance.
More and more industry groups are recognizing the importance of power quality on equipment operation. As a result, their members have begun to define standards for equipment performance. The Information Technology Industry Council (ITIC) developed a new curve defining the performance of data processing equipment. The semiconductor industry defined a specification for semiconductor manufacturing tools (SEMI F47), and the IEEE defined an overall approach for coordinating equipment performance with supply-system performance (IEEE Standard 1346). Permanently installed monitoring systems can assess system power quality with respect to these standards for convenient evaluation of performance expectations and results.
Facility personnel are interested in monitoring energy use to help identify savings opportunities and assess power-use charges toward different parts of an operation. Engineers can now enhance submetering systems with PQ monitoring capabilities to help identify causes of PQ problems and characterize the performance of individual loads and systems.
Different facilities have different power quality needs. Demand has grown substantially for service contracts tailored to the individual needs of specific customers. PQ monitoring helps establish the necessary benchmarks to facilitate these contracts, and it has become an integral part of the implementation. Detroit Edison is one utility that has demonstrated the viability of including power quality considerations in these contracts.
Internet connectivity and Web interfaces.
PQ monitoring is moving toward integration with the Internet and company intranets. One manufacturer has built a completely Web-based system, which eliminates the need for software to download and control the monitors by relying on a standard Web browser. All manufacturers, in fact, are trying to incorporate Web-interface capabilities into individual instruments or at least central databases, which would make PQ monitoring systems easier to use and access.
Development of preventive maintenance systems.
Systems that measure real-time conditions rather than a maintenance log and identify problems before they occur are the ultimate in PQ monitoring. These systems save time and money and provide improved reliability for the overall system. Unlike earlier PQ monitoring equipment, preventive maintenance systems can detect such anomalies as:
Resonance conditions that may lead to localized harmonic distortion problems.
Breaker problems that cause restrikes during capacitor switching.
Arcing conditions caused by bad connections and cable insulation problems.
Fault-performance problems that result in high numbers of voltage sags and momentary interruptions.
Grounding problems that result in stray voltages and neutral problems.
Industrial PQ monitoring applications
Several applications exist for an intelligent PQ monitoring system, including the following:
Energy and demand profiling with identification for energy savings and demand reduction.
Harmonics evaluations to identify transformer loading concerns, sources of harmonics, problems indicating misoperation of equipment, and resonance concerns associated with power factor correction.
Evaluation of voltage sag effects to identify sensitive equipment and possible opportunities for process ride-through improvement.
Power factor correction evaluation to identify proper operation of capacitor banks, switching concerns, resonance concerns, and optimizing performance to minimize electric bills.
Motor starting evaluation to identify switching problems, inrush current concerns, and protection device operation.
Short-circuit protection evaluation to analyze proper operation of protective devices based on things like short-circuit current characteristics and time-current curves.
Power quality monitoring systems will play an increasingly important role in preventive maintenance systems because they provide diagnostic- and condition-based information. Several companies are organizing efforts to identify and test advanced substation monitoring applications. Many of these applications are already in the prototype stage and are finding a real home in monitoring systems.
McGranaghan is vice president of consulting services for EPRI-PEAC, Knoxville. Tenn. Smith manages marketing and business development for EnerNex Corp., Knoxville, Tenn.