Mark McGranaghan

Voltage sags in industrial systems

A description is given of the causes of voltage sags in industrial plants, their impact on equipment operation, and possible solutions. The definition proposed focuses on system faults as the major cause of voltage sags. The sensitivity of different types of industrial equipment, including adjustable speed drive controls, programmable logic controllers, and motor contactors, is analyzed. Available methods of power conditioning for sensitive equipment are also described.<<ETX>>

Economic Evaluation of Power Quality

Electric power quality disturbances can have significant economic consequences for many different types of facilities. A wide variety of solution technologies exist for mitigating the consequences of such disturbances, and a methodology for performing a comparative economic analysis is featured in this article. Different technologies are evaluated by estimating the improved performance that can be expected after the technology has been applied. The power quality cost savings are calculated for each technology along with the costs of applying the technology. The net benefits, expressed in terms of annual costs, are shown as a means of comparing the various technologies.

Bridging the gap between signal and power

This article focuses on problems and issues related to PQ and power system diagnostics, in particular those where signal processing techniques are extremely important. PQ is a general term that describes the quality of voltage and current waveforms. PQ problems include all electric power problems or disturbances in the supply system that prevent end-user equipment from operating properly.

Designing harmonic filters for adjustable speed drives to comply with IEEE-519 harmonic limits

This paper discusses the application of the revised IEEE-519 Harmonics standards to typical industrial facilities employing adjustable speed drives (ASDs). The harmonic generation characteristics of ASDs are described, Requirements for control of the harmonic currents are developed as a function of the ASD characteristics, overall plant loading level, power system characteristics, and power factor correction requirements. Filter design procedures are presented for controlling the harmonic currents injected onto the power system.

Interpretation and analysis of power quality measurements

This paper describes advances in power quality monitoring equipment and software tools for analyzing power quality measurement results. Power quality monitoring has advanced from strictly problem solving to ongoing monitoring of system performance. The increased amount of data being collected requires more advanced analysis tools. Types of power quality variations are described and the methods of characterizing each type with measurements are presented. Finally, methods for summarizing the information and presenting it in useful report formats are described.<<ETX>>

Voltage flicker prediction for two simultaneously operated AC arc furnaces

An EMTP-based arc furnace model was developed for evaluation of flicker concerns associated with supplying a large integrated steel mill as they go from one to two furnace operation and as system changes are implemented that will affect the short circuit capacity at the 230 kV power supply substation. The model includes a dynamic arc representation which is designed to be characteristic of the initial portions of the melt cycle when the arc characteristics are the most variable (worst flicker conditions). The flicker calculations are verified using previous measurements with one furnace operation. Flicker simulations were then performed to evaluate a variety of different possible system strengths with both one and two furnaces in operation. The primary flicker measure used for this study is the unweighted RMS value of the fluctuation envelope, expressed as a percentage of the RMS line-to-ground voltage magnitude.

Shortfalls of existing methods for classification and presentation of voltage reduction events

This paper discusses the theoretical and practical aspects of various methodologies currently used for definition and characterization of voltage sags and short interruptions. Existing power-quality standards and procedures that are recommended for classification and presentation of sags and interruptions are critically reviewed and their shortfalls are highlighted.

Signature analysis to track capacitor switching performance

Although capacitor switching transient events are one of the most common disturbance events on distribution systems, information on whether the capacitor bank is energized properly or as desired is often not available. The capacitor switching performance tracker is designed to examine capacitor switching transient events and determine the condition relative to the events. The module identifies if the root cause of the event is due to energizing a capacitor bank. It then determines the relative location of the bank, i.e., upstream or downstream from the monitoring location, and examines if the kVAr generated from the capacitor bank is added properly to the system and if the kVAr is distributed evenly among all phases. By determining the kvar changes, it is possible to identify unsuccessful energization, blown fuses, or even failed capacitor cans on one of the phases.

A new method for classification and presentation of voltage reduction events

This paper describes a new method for classification and presentation of voltage sag and short interruption performance information for individual sites and entire systems. The method expands on traditional methods by including information about the individual phase voltages during the disturbance, rather than just a single magnitude and duration. This improved method provides better information for correlation with equipment impacts associated with the voltage sags and short interruptions. The method is validated with sag and interruption data measured/recorded in actual power systems and with results of simulations on an example system.

Overview of the guide for applying harmonic limits on power systems-IEEE P519A

IEEE 519-1992 provides the basis for applying harmonic limits on both the power system and for injection of harmonics from individual customers. This standard, along with IEC 1000-3-6, has been used as the basis for other harmonic standards being implemented around the world. As the standard has been applied, many applications concerns have been identified: (i) where to select the point of common coupling; (ii) how to select the base current for evaluating harmonics from individual customers; (iii) evaluating the direction of harmonic flow when a customer has power factor correction capacitors and/or harmonic filters; (iv) how to evaluate harmonics that occur only for short durations or infrequently (statistical nature of harmonic levels); and (v) how to evaluate compliance through measurements. A new task force was developed in IEEE to address these concerns. A draft of a new application guide-Guide for Applying Harmonic Limits on Power Systems, has been completed by Task Force P519A. This paper describes some of these important application concerns associated with applying and evaluating harmonic limits. Recommended methods for addressing these concerns are summarized and illustrated with an industrial customer example.