Voltage sag analysis peaks customer service

For short-circuit analysis in industrial and commercial power systems, a new approach of the ohmic method in such a form as to facilitate, as far as possible, its use and the realization of its evaluation is suggested. The 'characteristic' current method, by replacing the impedance of each equipment with the corresponding value of the 'characteristic' current, permits the application of the impedance properties to the inverse of the current values, either in meshed or nonmeshed networks. In order to achieve the correct design, rating and protection coordination of the whole power system, it is necessary to know and calculate step by step the values of short circuit current for each system component, from the utility or local generating connection point until the branch-circuits and the utilization equipments. The proposed approach assumes the above mentioned short-circuit current directly as calculation and comparison parameters. With the 'characteristic' currents as parameters the short-circuit analysis of substantial radial systems is made easier and a better matching of power system design requirements is permitted. >

In light of the rapid growth of dc loads, ICPS created a small team to outline design considerations for dc distribution and controls. Broad interest in the subject brought in a large group who provided substantial support for the Team. The report begins with a brief background followed by discussion of design considerations that affect ICPS and IAS. The key part of the report is Part IV, which outlines in detail a path forward for ICPS and for IAS. Appendix A outlines an approach toward developing dc standards or recommended practices for design of industrial and commercial power systems. Appendix B lists some of the organizations and individuals that are working on related dc issues at present.

In industrial and commercial sectors, loads are becoming increasingly sensitive to brief supply voltage disturbances. As a consequence, today voltage dips have more impact than just a few years ago. Fast voltage conditioners, improving the load immunity characteristics and accordingly reducing the expected number of load interruptions or malfunctions due to supply voltage dips, can allow large cost savings. Different categories of voltage conditioners are existing today, ranging from energy‐stored devices (like uninterruptible power supply) to no energy‐stored devices (like static voltage booster). To reduce the effects of supply voltage dips on a given plant, usually several different possible arrangements must be investigated, depending on the conditioners type, size and bus location. To determine the optimal arrangement is not always immediate. A methodology based on the minimum revenue requirement (MRR) is proposed in the paper, and a numerical example is given as well.

Voltage sag (including short supply interruption) has been recognized as the most important problem nowadays. Voltage sags are normally characterized by their magnitude and duration, so some methods such as statistical assessment, stochastic prediction and electromagnetic transient analysis are put forward, in order to determine voltage sag by analyzing the voltage sag characteristics in recent time. Countermeasures against sags have been studied meanwhile to mitigate the impact to load. In this paper, it is proposed the comparison among different methods on voltage sag analysis, and the countermeasures are also compared on the basis of fault types leading to voltage sag. The conclusion has been given after comparison in the end. (5 pages)

Voltage sag distributions were calculated for six different 20 kV electricity distribution systems. Results are highly dependent on the distribution system. The percentage of deep severe sags is much higher in urban systems while the annual number of sags is bigger in rural areas. AM/FM-GIS has proved to be an efficient tool in distribution system planning. Often costs are included in these studies. As a new development step, sag analysis was introduced to be integrated to these tools. A pilot software has already been developed in this project.

IEEE Std. 902-1998, Guide for Maintenance, Operation, and Safety of Industrial and Commercial Power Systems, also known as the IEEE Yellow Book, has been an excellent resource for management, safety professionals, and maintenance personnel since it was published in 1998.

This paper presents a method for the assessment of voltage sags caused by short-circuit faults in a large chemical industry. The supply arrangement for the industry is discussed. The connected equipment of the industry is fed from the 6.6-kV bus. The voltage sag analysis is performed for faults at different voltage levels in the power supply network. For every voltage level, the critical distance and expected number of voltage sags have been calculated. Since the industry has its own generator, thus the influence of local generation in voltage sag analysis is also investigated.

This paper presents a method for assessment of voltage sags caused by short circuit faults in a large chemical industry. The supply arrangement for the industry is discussed. The connected equipment of the industry is fed from the 6.6 kV bus. The voltage sag analysis is performed for faults at different voltage levels in the power supply network. For every voltage level, the critical distance and expected number of voltage sags have been calculated. Since the industry has its own generator, thus the influence of local generation in voltage sag analysis is also investigated.

In This work a power quality (PQ) problem in an industrial plant is analyzed and its possible solutions explored, specifically regarding voltage sags. It is analyzed a plant's electrical system sensitivity regarding voltage sags, how does the magnitude depression and its duration affect the performance of the electrical loads (mainly induction motors). Several proposals are discussed and explored for voltage sag mitigation and their feasibility for the plant's PQ problem. Finally, settings of the voltage sag mitigation equipment (timer or latching relay) are made analyzing voltage recovery times after voltage sag has occurred.

This paper summarizes a software algorithm used to automatically classify voltage sags using an expert systems and machine learning algorithms. In particular, the paper focuses on algorithms used to classify voltage sag events that were caused by downstream events (faults, inrush, or load start events) and voltage sags cause by upstream events.

Sensitive electrical equipment in industrial facilities can be shut down suddenly by voltage sags. The tolerance of these devices to deviations in the magnitude of the supply voltage varies, but the most sensitive equipment often is critical to operations. This paper describes the results of a study that assessed methods for reducing the impact of voltage sags on an industrial plant power system. The study investigated several methods for reducing the depth of sags by modifying the electric utility and industrial power distribution systems. The study emphasized conventional methods of improving this aspect of power quality through system modifications, and especially on finding the most cost-effective methods. A sliding-fault method was used to determine the effectiveness of specific mitigation solutions. (5 pages)

This paper discusses bus and breaker fail protection in modern industrial and commercial power systems. Fault current levels are increasing due to increases in power transmission system capacities and in-plant power generation. Such high fault currents as well as in-plant generator dynamics and system arc flash incident energy limiting requirements necessitate fast bus fault clearing. Meanwhile advancements of numerical relays proved more appealing economically and technically for MV and LV bus protection applications. On the other hand, when bus and breaker fail protection operate, the interrupted segment of the system is larger than a single feeder protection's operation. Consequently, mal-operations of either bus or breaker fail protection are less tolerable than mal-operations of single feeder schemes. This paper is intended to aid protection engineers in making decisions; first if dedicated fast bus and breaker fail protection schemes are required and second what concerns need to be addressed during the selection and the design of such systems. The topics are presented in two separate parts. Part 1 covers scope, introduction and bus protection topics. Part 2 covers breaker fail protection concepts, conclusions and bibliography of additional reference material.

Power quality problems such as momentary interruptions and voltage sags do not great influence on loads at past. However, the interests in power quality problems increase as the use of sensitive loads with microprocessor like computers increases recently. Accordingly, power system reliability research focusing to sustained interruption and momentary interruption partially needs more accurate evaluation methods including momentary and instantaneous problems. That is, many sensitive loads being tripped by voltage sags result in interruption costs. In this paper, new reliability worth evaluation method is presented considering voltage sags. We calculated the magnitude of voltage sags using fault studies and the duration of voltage sags using the trip time of protective relays for each fault. Moreover, we includes the customer interruption cost resulted from sensitive load trip by voltage sags. Through case studies, we evaluate the effects of voltage sags for permanent faults.

Distributed Generation (DG) generally refers to small scale generation located near the source of the load which it serves. Distributed generation have impacts on the performance system to which it is connected. DG can also provide power supply to the customers during the scheduled interruption. Application of distributed generation in distribution system is expected to increase in near future due to its positive impacts such as voltage support, improved reliability, small size and loss reduction. However DGs may have negative impacts on power quality, such as voltage regulation, harmonic distortion, islanding and confliction with relaying and reclosing. This paper deals with the effect of voltage sag which is considered as most important power quality problem. This paper presents a comparative analysis of the impact of synchronous generator and Induction Generator on voltage profile and voltage sag in distribution system. From the analysis it is observed that voltage profile is improved with synchronous generator and its negative impact is less than that of Induction Generator.

Many system reliability prediction methods are based solely on equipment failures, neglecting the human component of man-machine systems (MMS). These methods do not consider the identification of the root causes of human errors. The reliability and safety of industrial and commercial power systems and processes (i.e., MMS) are dependent upon human characteristics and many dependent and dynamic interactive factors. The consequences of human errors are very diverse and can range from damage to equipment and property, injury to personnel or fatalities, to disruption of scheduled system operation, all of which represent a significant cost to society. This paper focuses on accidents-injuries and the disruption of scheduled system operation caused by human element factors and shows that the human element is a very significant factor affecting the reliability and safety of electrical systems. The paper initially presents several case studies to reveal the frequency of human errors which disrupted scheduled computer and utility system operation. This paper also presents statistics on the injury accident rate in electric utilities and the number of days lost to injury accidents. It presents some of the factors that direct human behavior and discusses how these factors help identify the possible root causes of electrical accidents, using an accident-injury sequence model to determine the cause of human errors. Knowledge of human factors can be used to mitigate their impact on power system interruptions and injury accidents (e.g., increased productivity, increased reliability, decreased errors, increased safety, etc.).