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Power Quality Case Studies

General Power Quality Reference:

General Reference - Power Quality Glossary
This case provides a glossary of terms related to power quality analysis and measurements.

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General Reference - Common Power Quality Problems and Solutions
This case provides a brief summary of common power quality problems and solutions.

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General Reference - Performing Power Quality Audits
This case provides a guide for performing a power quality audit.

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General Reference - Power Quality Assessment Procedure
This case describes a general procedure for performing on-site case studies of power quality concerns.

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Harmonics:

General Reference - Modeling for Harmonic Analysis
Harmonic problems can generally be solved using a comprehensive approach including site surveys, harmonic measurements, and computer simulations. This case provides an overview of harmonic modeling for system studies.

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General Reference - Effects of Harmonics at Industrial Facilities
Potential harmonic-related problems include overheating of transformers, equipment misoperation and capacitor failures. The major sources of harmonics are saturable devices, arcing devices, and electronic power converters. The characteristics of different types of ASDs is discussed and the effect of power factor correction capacitors on harmonics is presented in this case study.

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Low Voltage Harmonic Filter Design
When mitigation of harmonic distortion is required, one of the options is to apply a filter at the source of harmonics, or at a location where the harmonic currents can be effectively removed from the system. The most cost effective filter is generally a single-tuned passive filter and this will be applicable for the majority of cases. This case presents the design of a low voltage shunt passive harmonic filter that is applied to improve poor power factor and reduce excessive voltage distortion levels.

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IEEE Std. 519 Compliance
IEEE Std. 519-1992 is a standard that addresses the need for limiting the harmonic current a customer injects onto the utility system. It also protects the customer by specifying maximum harmonic voltage distortion levels that utilities can supply. The installation of a 3% choke on each drive and a 150kVAr harmonic filter on the bus reduced the harmonic currents to acceptable values. This case presents the evaluation of IEEE Std. 519 compliance for an industrial facility supplying adjustable-speed drives.

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Impact of Compact Fluorescent Lights on Distribution Systems
This case study presents the results of a research investigation into the impact of compact fluorescent lights (CFLs) on an existing distribution system. The analysis uses a combination of EMTP simulations and conventional harmonic analysis simulations to predict the distribution system distortion levels as a function of system characteristics and CFL penetration levels. Compact fluorescent light characteristics from measurements and distribution system data collected are utilized to develop simulation models.

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PQ Investigation for SW County School District
The County School District has a concern for increasing computer loads at the local High School. There are approximately 300 computers currently in use at the school and plans are to increase the number of computers significantly over the next 3-4 years. The existing computer loads are on the same circuits with lighting loads, other office loads, and building HVAC loads. This case study describes the findings from the site survey and outlines recommended procedures for dealing with the new computer loads.

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Transformer Derating
Power transformers are affected by harmonic current distortion. Distortion of transformer load current is the most significant impact, leading to higher than normal temperatures at "hot spots" within the windings. This case study presents an evaluation of transformer derating due to harmonic current.

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Medium Voltage Filter Design
A utility was experiencing voltage distortion levels throughout their distribution network that were exceeding IEEE Std. 519 limits. One customer, a plastic extrusion plant, was experiencing blown fuses in their switched capacitor banks along with capacitor failure. The scope of the case study was to investigate the impact of surrounding capacitor banks on voltage distortion levels and to make recommendations with regards to mitigating the harmonic problem.

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A Single-Phase 25 Hz Frequency Converter
This case study describes a static frequency converter (60Hz three-phase to 25Hz single-phase). This IGBT based converter supplies a signaling network used in the New York transit system and must be capable of withstanding various operational restraints such as, 25Hz signaling network short-circuits, non-linear loads and parallel operation with other sources.

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Transmission System Harmonics Study
A utility operates two 16.8 MVAr capacitor banks in a 161/69kV substation that supplies various loads including a steel manufacturing facility. The utility is investigating the installation of three additional 16.8 MVAr, 69kV capacitor banks to be installed within the substation. This case study presents some of the findings associated with a resonance study that included power quality monitoring and harmonic distortion simulations.

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Harmonic Evaluation at an Industrial Facility
This case study summarizes a harmonic evaluation that was performed at the plastic film manufacturer's facility. The goals of the evaluation were to develop a solution to mitigate the harmonic voltage distortion caused by the ac and dc adjustable speed drives; the solution must allow the utility to install power factor correction equipment on the 13.8 kV distribution system that supplies the facility.

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Concrete Facility Harmonic Evaluation
A Kiln ID fan drive (12 pulse rectifier) powers a 3000 HP medium voltage (4kV) motor. The associated harmonic filter periodically becomes overloaded and trips the corresponding 4kV breaker. The associated isolation transformer caught on fire within the first three months of operation. There have also been problems with the power factor correction capacitor banks. The case study presents a summary of a harmonic evaluation that was performed before the plant substation was upgraded.

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Industrial Harmonic Filter Design
The industrial harmonic problem can be solved using a comprehensive approach including site surveys, harmonic measurements, and computer simulations. This case study presents the configuration of low voltage power factor correction capacitors as harmonic filters to improve poor power factor and reduce excessive voltage distortion levels.

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Substation Resonance and Harmonic Filter Application
A utility operates a 16.2 MVAr capacitor bank on a 24kV substation bus that supplies various customers that have significant amounts of nonlinear loads. The utility is investigating the possible conversion of the capacitor bank into a harmonic filter bank to control the frequency response characteristic and reduce the overall harmonic distortion levels. This case study presents some of the findings associated with a harmonic resonance study that included frequency scan simulations.

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Harmonic Resonance Evaluation for Feeder and Substation Capacitor Banks
A utility operates 25.56kV feeder and substation capacitor banks. The utility uses frequency scan simulations to determine the effect of distribution feeder and substation capacitor banks on harmonic resonance and frequency response characteristics. It is assumed that the simulations will show that the frequency response characteristics of the feeder are very dependent on the status of the feeder and substation capacitor banks. This case study evaluates the effect of substation and feeder capacitor banks on the frequency response characteristic of a 25.56kV distribution feeder.

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Effect of Distribution Feeder Loading on Harmonic Resonance
A utility operates 1200 kVAr and 600 kVAr capacitor banks on a 25.56kV distribution feeder. The utility uses frequency scan simulations to determine the effect of the capacitor banks and seasonal load levels on the impedance vs. frequency response characteristics for the feeder. It is assumed that the results will be more severe for the low load condition because there are lower levels of damping. This case study evaluates the effect of seasonal load variation on the frequency response characteristic of a 25.56kV distribution feeder.

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Harmonic Measurement Data Evaluation
This case study presents a harmonic data analysis for a utility12.47kV substation monitoring location for a two-week period. The analysis included trends of the rms voltage and current and statistical summaries of the voltage and current distortion values. The results of the analysis showed that the harmonic distortion levels were below the IEEE Std. 519 voltage limits.

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Harmonic Current Cancellation Evaluation
This case study presents the results for a customer step-down transformer harmonic current cancellation evaluation. The analysis was completed using the SuperHarm program. The simulation results show the reduction of the customer primary harmonic current distortion level due to the phase shifting caused by the different step-down transformer connections.

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Industrial Customer IEEE Std. 519 Compliance Evaluation
This case study presents the results for an industrial customer IEEE Std. 519 compliance evaluation. The simulations were completed using the SuperHarm program. The results showed a harmonic resonance when the customer power factor correction capacitor banks were in service. The voltage distortion levels were mostly within the specified limits.

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Arc Furnace Harmonic Evaluation
This case study presents the results for an arc furnace harmonic evaluation. The case study was completed using the SuperHarm program. The simulation results show harmonic resonances that increase voltage distortion levels when the utility substation capacitor bank was in service.

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Commercial Facility Harmonic Evaluation
This case study presents the results for a commercial facility harmonic evaluation. The simulations were completed using the PSCAD program. The analysis evaluates the effects of transformer connections to determine the harmonic current distortion levels on both the primary and secondary sides of the customer transformers. The simulation results show the third harmonic neutral current and a K-Factor transformer derating analysis.

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Distribution Feeder Resonance and Harmonic Filter Evaluation
This case study presents the results for a utility distribution feeder resonance and harmonic filter evaluation. The analysis was completed using the PSCAD program. The study evaluated the effects of distribution capacitor banks on the frequency response characteristic and the resulting harmonic distortion levels.

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Distribution Substation Harmonic Measurement Data Evaluation
This case study presents a harmonic data analysis for a substation monitoring location for a three-month period. The utility substation included a step-down transformer and a number of distribution feeders that supplied a mix of residential and commercial customers. One of the feeders had a switched 600 kVAr capacitor bank that was being used for power factor correction and voltage control. The analysis included trends of the rms voltage and statistical summaries of the voltage and current distortion values.

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Distribution Substation Capacitor Bank Evaluation
This case study presents a utility distribution substation capacitor bank harmonic analysis. The simulations were completed using the SuperHarm program. The investigation included frequency response and harmonic distortion simulations for a utility substation that included a step-down transformer and a number of distribution feeders with a significant number of small capacitor banks and several industrial customers.

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Industrial Facility IEEE Std. 519 Compliance Evaluation
This case study presents an industrial facility IEEE Std. 519 harmonic compliance evaluation. The analysis included frequency response and harmonic distortion simulations for a substation and a single industrial customer with a number of lower voltage power factor correction capacitor banks. The analysis included IEEE Std. 519 compliance calculations for various system contingencies. The mitigation alterative applied included a shunt passive harmonic filter which reduced voltage distortion levels below the specified limitations.

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Distribution System Harmonic Evaluation
This case study presents a utility distribution system harmonic analysis evaluation. The simulations were completed using the SuperHarm program. The analysis included frequency response and harmonic distortion simulations for a 13.2kV substation and several industrial customers with power factor correction capacitor banks. The mitigation alterative included a shunt passive harmonic filter which reduced voltage distortion levels below the specified limitations.

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Wind Plant IEEE Std. 519 Compliance Evaluation
This case study presents the results for a wind plant substation IEEE Std. 519 harmonic measurement compliance evaluation. The wind plant substation supplied 65 wind turbine generators and the power quality monitor was connected to the 34.5 kV transformer secondary winding, which was considered the point of common coupling (PCC) for the harmonic analysis.

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Transients:

General Reference - Modeling for Transient Analysis
This general reference case provides an overview of transient modeling for system studies.

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General Reference - Utility Capacitor Switching
Capacitor switching is generally considered a normal operation for a utility system and the transients associated with these operations are generally not a problem for utility equipment. These low frequency transients, however, can be magnified in a customer facility or cause nuisance tripping of power electronic based devices (e.g., drives). This general reference case provides information regarding utility capacitor switching.

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General Reference - Utility Capacitor Switching – Common Waveforms
This case study includes a number of representative transient power quality waveforms that deal with utility capacitor bank applications. Relevant information and waveform characteristics are also provided.

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Utility Capacitor Switching Trips Electronic Voltage Regulator
This case presents the results of measurements associated with capacitor switching on the utility system and the resulting problems for an industrial process facility. An electronic tap switching voltage regulator was affected by the transient voltages caused by capacitor switching on the utility system.

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Utility Capacitor Switching Causes Nuisance Tripping of ASD
Adjustable-speed drives are susceptible to dc link overvoltage trips caused by utility capacitor switching. In general, an increase in input inductance will reduce the possibility of nuisance tripping. However, if the customer has power factor correction capacitors on the same bus, it may be necessary to take additional remedial actions. This case investigates the interaction between utility capacitor switching and ASD operation.

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PWM Drive Motor Failures due to Transient Voltages
In an effort to improve the efficiency of many industrial processes, equipment has been retrofitted with adjustable speed drives (ASDs). The ASDs allow for better speed control, soft starting of motors, and increased efficiency of the overall process operation. Unfortunately, there can be some drawbacks when using ASDs. While the effects of ASDs on the power system are well known, many engineers and system integrators are unaware of the effects that an ASD can have on the motor that it drives. This case study addresses one of the adverse affects; motor winding failure due to over voltages.

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Utility Capacitor Switching Fails VAX Disk Drive
This case study illustrates a situation where a power conditioning device was the weak link in an overall equipment protection scheme. The power conditioner, which was located near the sensitive equipment, was magnifying utility capacitor switching transients that were not very severe in magnitude.

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Transient Voltages at an Industrial Facility
This case study describes concerns for capacitor switching transients within customer facilities. Magnification of transients initiated at higher voltage capacitors and tripping of sensitive variable frequency drive (VFD) loads are evaluated in particular. The results of measurements and simulations associated with capacitor switching on the utility system and the resulting impacts at an industrial process plant are presented.

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Phase-to-Phase Transients at Transformer Terminations
There are a number of important transient related concerns when transmission capacitor banks are applied. These concerns include insulation withstand level, switchgear capabilities, energy duties of protective devices, and system harmonic considerations. The considerations should also be extended to include distribution systems and sensitive customer equipment. This case study presents a summary of the model development and simulations results for a phase-to-phase transients at transformer terminations evaluation.

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Study of 345 kV Transient Recovery Voltages
Transient recovery voltage (TRV) is the voltage across the terminals of a pole of circuit breaker following current zero when interrupting faults. An engineering study found that for a number of cases, the TRV waveshapes exceeded their related TRV capability limits. The study evaluated the application of an additional capacitance on the line side of the circuit breakers. This case study presents a summary of the model development and simulations completed during the 345kV TRV study.

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Evaluation of Capacitor Bank Switch Restrikes
There are a number of important transient related concerns when utility capacitor banks are applied, including insulation withstand level, switchgear capabilities, energy duties of protective devices, and system harmonic considerations. The considerations should also be extended to include distribution systems and sensitive customer equipment. This case study presents methods for determining transient overvoltage and arrester duties and during capacitor switch restrike events and sample simulation and field measurements of restrike waveforms.

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Voltage Magnification and Nuisance Tripping during Capacitor Bank Switching
The application of utility capacitor banks has long been accepted as a necessary step in the efficient design of utility power systems. In addition, capacitor switching is generally considered a normal operation for a utility system and the transients associated with these operations are generally not a problem for utility equipment. However, if the customer has power factor correction capacitors on the same bus, it may be necessary to take additional remedial actions. This case study investigates the potential for voltage magnification and nuisance tripping during utility capacitor bank switching on a 24kV distribution system.

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Effect of Synchronous Closing Control on Capacitor Bank Energizing Transients
Adjustable-speed drives are susceptible to dc link overvoltage trips caused by utility capacitor switching. In general, an increase in input inductance (choke or isolation transformer) will reduce the possibility of nuisance tripping. However, if the customer has power factor correction capacitors on the same bus, it may be necessary to take additional remedial actions. This case study investigates the potential for voltage magnification and nuisance tripping during utility capacitor bank switching on a 24kV distribution system.

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Impact of Capacitor Outrush Reactors on Breaker Transient Recovery Voltages
Excessive TRVs may cause the capacitor bank circuit breaker to fail to clear during certain fault conditions. A study was completed to evaluate the TRVs for various capacitor bank circuit breaker operations, system contingencies, and mitigation alternatives. This case study presents a summary of the model development and simulations completed during the outrush reactor TRV study.

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Customer Adjustable-Speed Drive Motor Failure Evaluation
This case study presents a customer adjustable-speed drive motor winding failure analysis. The study investigated the potential for severe high frequency transient overvoltages at induction motor terminals for an adjustable-speed drive that utilized a pulse-width modulation inverter, along with a significant length of cable between the inverter and motor. Several power conditioning mitigation alternatives including series reactors and motor terminal filters were evaluated using computer simulations.

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Nuisance Tripping of Sensitive Customer Power Electronic Equipment
This case study presents an investigation of nuisance tripping of sensitive customer power-electronic equipment during utility capacitor bank switching. The simulations for the analysis were completed using the PSCAD program. The power conditioning solutions included utility switches with pre-insertion resistors and customer series chokes. Both mitigation alternatives prevented the customer sensitive power-electronic equipment from tripping during the power quality events.

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Distribution System Transient Measurement Data Evaluation
This case study presents a distribution system transient measurement data analysis. The distribution system included a number of feeders that supplied a mix of residential, commercial, and industrial customers. The causes of the transients measured during the monitoring period included capacitor bank switching, transformer energizing, single-phase faults, recloser operations, switch failures, and current-limiting fuse operations.

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Feeder Lightning Transient Analysis
This case study presents a distribution feeder lightning transient overvoltage evaluation. The case study investigated the potential for severe high frequency transient overvoltages on distribution feeder primary and customer secondary buses during a lightning strike on the feeder primary. The power conditioning mitigation alternative of MOV surge arresters was also evaluated.

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Temporary Overvoltage and Grounding Transformer Analysis
This case study presents the results for a wind plant temporary overvoltage (TOV) and grounding transformer transient analysis. The case study investigated the potential for excessive temporary overvoltages during single-phase faults on a 34.5 kV wind plant collector circuit. The results show that the application of properly rated grounding transformers can reduce the resulting temporary overvoltage levels on the collector circuit below the surge arresters capability.

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Substation Transformer Switching and Dynamic Overvoltages
This case study presents the results for a wind plant substation transformer energizing and dynamic overvoltage evaluation. Transformer inrush currents contain harmonic components that may create dynamic overvoltages if a substation transformer is energized with a collector circuit or capacitor bank on the secondary bus. Mitigation alternatives for this problem include energizing a capacitor bank separately from the transformer and energizing the transformer/capacitor bank combination with enough secondary loads to sufficiently damp the transient overvoltages.

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Wind Plant Lightning Transient Overvoltage Evaluation
This case study presents a wind plant substation lightning transient overvoltage evaluation. A high-frequency transient model was created to simulate the lightning transients and resulting overvoltages and arrester energy duties. A high-frequency model was required to accurately represent the lightning phenomena. MOV surge arresters were evaluated as the power conditioning alternative.

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Distribution Feeder Wind Turbine Generator Analysis
This case study presents a distribution feeder wind turbine generator analysis. The investigation included several potential causes of turbine and feeder overcurrents and overvoltages, including wind speed variations, cut-out and cut-in switching operations, ground faults, and islanding during feeder isolation. Mitigation alternatives for high temporary overvoltages (TOV) on distribution feeders include application restrictions, grounding transformers, direct transfer trip schemes, and crowbar switches.

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VCB Current Chopping Evaluation
This case study presents a customer vacuum circuit breaker (VCB) current chopping transient overvoltage evaluation. A high-frequency transient model was created to simulate vacuum circuit breaker opening and closing and the resulting transient overvoltages and arrester energy duties. The simulation results show that properly-designed R-C snubbers will reduce the initial rate-of-rise of the transient voltages, which may be beneficial because severe dv/dt transient voltages can damage the first few turns of insulation of dry-type transformers and motors or excite internal transformer resonances producing severe overvoltages.

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Measurement:

General Reference - Using Simulations and Measurements in PQ Analysis
Simulations provide a convenient means to characterize power quality problems, predict disturbance characteristics, and evaluate possible solutions to problems. They should be performed in conjunction with monitoring efforts and measurements for verification of models and identification of important power quality concerns. This general reference case provides background information regarding the usage of simulations and measurements in power quality analysis.

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General Reference - Approach to Systems Monitoring
Power quality monitoring is an essential service many utilities perform for their industrial and other key commercial customers. Because of the technology and software now available, this monitoring is highly effective. This general reference case provides background information regarding systems monitoring.

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Monitoring Objectives - Distribution Feeder Capacitor Bank Application
Power quality monitoring is used to characterize harmonics and transients at various locations on utility and customer power systems. This case study introduces the subject of monitoring objectives and screening procedures and provides a distribution feeder capacitor bank application monitoring example.

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Common Power Quality Waveform Signatures
Power quality problems encompass a wide range of disturbances and conditions on utility and customer power systems. They include everything from very fast transients (microseconds) to long duration (hours) outages. This case study presents a collection of representative waveforms for various power system fault and power quality events, including voltage sags, momentary interruptions, voltage swells, harmonics, capacitor switching transients, transformer energizing transients, and ferroresonance.

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Customer Data Analysis Case Study
This case study summarizes a commercial customer power quality measurement data evaluation. Monitoring is often used to characterize power quality levels at various locations on utility and customer power systems. Field measurements provide a convenient means to characterize power quality problems. The monitoring period was for twelve months.

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Overvoltage/Ferroresonance:

General Reference - Ferroresonance
The term ferroresonance refers to a special kind of resonance that involves capacitor and iron-core inductance. The most common condition in which it causes disturbances is when the magnetizing impedance of a transformer is placed in series with a system capacitor. There are several modes of ferroresonance with varying physical and electrical characteristics. This case presents an overview of ferroresonance and a number of example measured and simulated waveforms.

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Modeling Ferroresonance in an Underground Distribution System
The objective of this case study is to provide an overview of ferroresonance phenomena, its modeling aspects, and practical experience in recognizing, avoiding, and solving the problem. In particular, it will present symptoms of ferroresonance. An actual example simulation analysis involving an underground cable circuit with blown fuses is presented along with solutions to avoid ferroresonance.

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Ferroresonance Analysis - 25kV Single 5-Legged Core Transformer
Ferroresonance is a concern for medium voltage underground systems. As part of an evaluation of the design of a new 25kV underground system, the potential for ferroresonance was analyzed. The results of the analysis are summarized in this case study.

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Transformer Energizing and Dynamic Overvoltages
Energizing power transformers results in inrush currents that are rich in harmonic components. Dynamic overvoltages are long-term resonant overvoltages lasting many cycles that can cause damage to capacitor units and other adjacent equipment, such as transformers and surge arresters. This case study presents a transformer energizing and dynamic overvoltage evaluation for a 34.5kV distribution system.

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Distribution Feeder Energizing
The energization transients for distribution feeders are generally a combination of line energizing, transformer inrush, and load inrush. Line energizing transients typically decay to negligible values in about one-half cycle and they generally do not pose significant problems for customer equipment. Energizing a distribution circuit can create a transient overvoltage similar to that generated by a capacitor bank energizing. This case study presents a feeder energizing evaluation for a 34.5kV distribution system.

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Ferroresonance in an Underground Distribution System
The term ferroresonance refers to a special kind of resonance that involves capacitor and iron-core inductance. The most common condition in which it causes disturbances is when the magnetizing impedance of a transformer is placed in series with a system capacitor. In many cases it may be may be difficult to tell if ferroresonance has occurred, unless there are witnesses or power quality monitoring instruments installed. This case study presents a ferroresonance evaluation for a 34.5kV underground distribution system.

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Power Factor Correction:

General Reference - Power Factor Correction
Power factor is a measurement of how efficiently a facility uses electrical energy. A high power factor means that electrical power is being utilized effectively, while a low power factor indicates poor utilization of electric power. This general reference case provides an overview of the concept of power factor, including impacts on the electrical distribution system, effects on power quality, benefits of improvements, and estimating financial savings.

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Harmonic Issues Related to Power Factor Correction
Power factor correction is an important facet of power quality. Capacitors may be installed on customer systems to minimize charges for poor power factor on their electric bill. These installations may create problems by altering the harmonic frequency response of the network or introducing transient disturbances during their energization. This case study presents an overview of the impact of power factor correction on harmonics issues, such as resonance.

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Transient Issues Related to Power Factor Correction
This case study presents an overview of the impact of power factor correction on transient issues, such as voltage magnification and nuisance tripping of customer equipment (e.g., adjustable-speed drives).

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Industrial Power Factor Correction
This case study presents the application of low voltage power factor correction capacitors to improve poor power factor in an industrial environment.

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Power Factor Correction and Harmonic Control for dc Drive Loads
This case study describes the design of power factor correction and harmonic control equipment for loads at a plastic film manufacturing plant. Measurements were performed to characterize the harmonic generation and power factor requirements of the load. The electric utility supplying the new facility is requiring that the plant meet the harmonic current limits specified in IEEE Std. 519-1992.

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Power Factor Correction - Estimating Financial Savings
Low power factor means that you are using a facility's electrical system inefficiently. It can also cause equipment overloads, low voltage conditions, and greater line losses. Most importantly, low power factor can increase total demand charges and cost per kWh, resulting in higher monthly electric bills. This case study provides a summary of interrupting electric utility rates and billing, and estimating financial savings when applying low voltage power factor correction capacitors.

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Voltage Sags and Momentary Interruptions:

General Reference - Modeling for Voltage Variation Analysis
Voltage variations, such as voltage sags and momentary interruptions are two of the most important power quality concerns for customers. The most important of these variations occur during faults on the power system. Since it is impossible to completely eliminate the occurrence of faults, there will always by voltage variations to contend with. This case provides an overview of system modeling for voltage variation studies.

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Voltage Sag Study for a Distribution System Customer
Customers understand that interruptions cannot be completely prevented on the power system. However, they are less tolerant when their equipment mis-operates due to momentary disturbances which can be much more frequent than complete outages. This case presents the results of analysis of voltage sags caused by utility faults and their impact on a distribution system customer.

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Voltage Sag Study - Application of a Static Transfer Switch
The purpose of this case study is to determine the feasibility of reducing process equipment disruptions due to utility voltage sags at a large industrial facility. The facility consists of many injection molding machines, resulting in an industrial process that is extremely sensitive to distribution voltage variations. The case study investigates various distribution system modifications to determine the most effective and efficient means for providing the level of power quality necessary for proper plant operation.

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Voltage Sag Evaluation - Improving Equipment Ride Through
Voltage variations, such as voltage sags and momentary interruptions are two of the most important power quality concerns for customers. Customers understand that interruptions cannot be completely prevented on the power system. However, they are less tolerant when their equipment mis-operates due to momentary disturbances which can be much more frequent than complete outages. This case presents the results of measurements and analysis of the impact of voltage sags on a process controller.

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MG Set Provides Voltage Sag Ride-Through Support
This case study shows an example of high-tech computer and multi-media equipment requiring "clean" electric power protected against normal split-second voltage variations. A technology that has recently received much attention for providing this ride-through is the written-pole motor-generator set.

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Municipal Elevator Study - Improving Elevator System Performance
Elevator shutdown due to system design and operation of elevator and drive system controls is the key problem experienced by the customers. It was believed that sustained voltage reduction for system load relief, rms variations because of feeder faults, and utility capacitor switching were among the voltage anomalies that have an effect on reliable elevator operation.

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Voltage Sag Protection Using a Micro-SMES Device
This case study describes the use of a micro-SMES device to improve power quality at a large semiconductor manufacturing facility by providing short term back-up power during utility system voltage sags and interruptions. This facility has critical electronic chip testing loads that are very sensitive to voltage variations. An explanation of why the micro-SMES was chosen instead of other technologies will be presented along with a brief overview of the technology as well as performance.

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Voltage Sags and Their Impact on Industrial Customers
This case study describes the impact of voltage sags on a utility and one industrial customer. Several utility measures are presented to minimize the customer's exposure to voltage sags. However, these measures cannot completely eliminate the impact of voltage sags on sensitive equipment.

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Customer Induction Motor Starting Evaluation
This case study shows the results for simulations completed to determine the severity of an undervoltage condition during starting of a customer induction motor starting. The simulations for the case were completed using the PSCAD program. The effectiveness of a primary resistor starter is also summarized.

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Distribution Feeder Voltage Sag Evaluation
This case study shows the results for simulations completed to evaluate the impact of a distribution feeder fault on the operation of a customer adjustable-speed drive during the resulting voltage sag and momentary interruption. The simulations for the case were completed using the PSCAD program. A voltage swell on the feeder primary is also illustrated. The potential solution of increasing the dc link capacitance for the adjustable-speed drive was shown to be effective for the simulated conditions.

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Distribution Substation Voltage Variation Measurement Data Evaluation
This case study presents a voltage variation data analysis for a 12.47kV substation monitoring location for a three-month period. The analysis included trends of the rms voltage and unbalance and statistical analysis of the rms variation events. The results of the analysis showed that most of the events were short duration voltage sags.

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Voltage Fluctuation/Flicker:

Electric Arc Furnace Modeling for Voltage Flicker Evaluation
A steel manufacturer is planning to add a second arc furnace to their existing facility. Concerns are raised as to whether the additional furnace will cause levels of voltage flicker that might possibly affect neighboring loads. This case summarizes the time-domain model (EMTP) of the existing and proposed arc furnace and a flicker meter. The results gathered are used to evaluate system changes that will be needed prior to installation of the second furnace.

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Electric Arc Furnace Flicker and Harmonic Control
A steel manufacturer plans to construct an electric arc furnace-based steel facility using a thin slab casting machine directly coupled to a hot strip rolling mill. The planned melt shop contains two dc electric arc furnaces and will supply two ladle metallurgy furnaces which will feed two thin slab casting machines. This case evaluates the need for an SVC to control voltage fluctuations and to develop a harmonic filter design that will provide required reactive compensation and control harmonic levels to meet IEEE Std. 519 limits.

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Wind Plant Voltage Flicker Data Analysis
This case study presents the results of a wind plant voltage flicker data analysis. The characteristics of voltage flicker are mainly determined by load characteristics and the short-circuit capacity. The wind plant substation supplied 65 wind turbine generators and the power quality monitor was connected to the 34.5 kV transformer secondary winding, which was considered the point of common coupling (PCC) for the voltage flicker harmonic analysis.

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Substation Voltage Flicker Data Analysis
This case study presents a substation arc furnace flicker measurement data evaluation. The analysis included a helpful index for comparing voltage flicker measured at a source and at a remote substation. The measurement results showed that the three-phase voltage flicker Pst measured at the 138kV Steel Mill Substation and the three other substations exceeded the CP99 compatibility limit. Mitigation alternatives for excessive voltage flicker may include a synchronous compensator (STATCOM).

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Voltage Notching:

Voltage Notching and Distribution Systems I - Large Induction Motor Drive
This case study describes voltage notching associated with large adjustable speed drives. The notching is a normal characteristic of a phase-controlled rectifier but this case illustrates problems that can occur on systems with low short circuit levels where the voltage notching can excite the natural frequency of the distribution system. The notching characteristics and the interaction with the distribution system frequency response characteristics are described, along with possible solutions.

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Voltage Notching and Distribution Systems II - Large DC Drive
This case study describes voltage notching associated with large DC drives. The notching is a normal characteristic of a phase-controlled rectifier but this case study illustrates problems that can occur on systems with low short circuit levels where the voltage notching can excite the natural frequency of the distribution system and cause significant distortion in the supply voltage. An example problem and the corresponding solution associated with a large DC drive is presented.

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Wiring & Grounding:

General Reference - Wiring and Grounding
Wiring and grounding problems are responsible for many power quality variations within customer facilities. Some electric utility engineers have estimated that 80% of all the power quality problems reported by customers are found to be due to their own wiring and grounding problems. This case provides general information on proper grounding practices and outlines common problems that are encountered.

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High Neutral-to-Ground Voltages
An office complex was experiencing continual operational problems with some of their electronic equipment not protected by power conditioning equipment. The equipment would periodically exhibit strange behavior. An infrared heat detector was used to locate loose wiring connections, and once these connections were fixed, the neutral-to-ground voltages disappeared as well as the equipment problems. This case presents the results of measurements and analysis of electronic equipment problems.

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PQ Investigation at a Battery Facility
This case study presents the results of a power quality investigation at a battery manufacturing facility. The facility had been experiencing a high rate of motor failures and was experiencing problems with its computer control system. Ground noise caused by the ungrounded 480 V system and ground loops was part of the problems identified with the computer control system.

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Flickering Lights
This case study presents a residential electrical system problem. The homeowners were experiencing light flicker when loads were energized and de-energized in their home.

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