Showing papers on "Voltage sag published in 1997"

Characterisation of voltage sags experienced by three-phase adjustable-speed drives

Abstract: It is shown in this paper that voltage sags experienced by three-phase loads, such as adjustable-speed drives, can be classified into four types. Each sag can further be characterized by a magnitude and a phase-angle jump. Relations between fault type, sag type and load connection are presented. The transfer of sags through transformers is discussed. The magnitude and phase-angle jump of sags are directly related to the voltage in the faulted phase, or between the faulted phases, at the point-of-common coupling between the load and the fault.

Characterization of voltage sags in industrial distribution systems

Abstract: This paper describes the various characteristics of voltage sags experienced by customers within industrial distribution systems Special emphasis is paid to the influence of the induction motor load on the characterization of voltage sags During a fault, an induction motor operates as a generator for a short period of time and causes an increase in sag magnitude Its reacceleration after the fault clearance results in an extended post-fault voltage sag The influence of the induction motor on the imbalanced sags caused by single line-to-ground faults (SLGFs) and line-to-line faults (LLFs) has been analyzed in detail For an imbalanced fault, the induction motor current contains only positive- and negative-sequence components Induction motors create a low impedance path for the negative-sequence voltage due to an imbalanced fault This causes a small sustained nonzero voltage with large phase-angle jump in the faulted phase and a voltage drop in the nonfaulted phases with a small phase-angle jump The symmetrical components of the induction motor during the imbalanced sags have been studied The results show that induction motor behavior is determined by positive- and negative-sequence voltages during the imbalanced sag

Voltage sag ride-through for adjustable speed drives with active rectifiers

Abstract: Adjustable-speed drives (ASDs) trip due to voltage sags, interfering with production and resulting in financial losses. In this paper, a methodology for incorporating voltage sag ride-through in the design of ASDs with active rectifiers is presented. The magnitude of the voltage sag for which ride-through can be provided is determined by the current rating of the active rectifier and load condition of the ASD, but a sag of any duration can be compensated for.

Effects of voltage sags on AC motor drives

Abstract: Voltage sags are normally described by magnitude variation and duration. In addition to these quantities, sags are also characterized by unbalance (asymmetry), nonsinusoidal waveshapes, and phase angle shift (phase jump). These factors are important for determining the behavior of AC motor drives during sags. Voltage unbalance and phase angle shifts cause large unbalanced source currents to excessive voltage ripple in the DC-link, and reduced DC-link average voltage. The response of the motor and drive to these varies considerably. Experimental results clearly show the load dependent behavior of a typical drive. The ability of the drive to ride-through a voltage sag is dependent upon the energy storage capacity of the DC-link capacitor, the speed and inertia of the load, the power consumed by the load, and the trip point settings of the drive. The control system of the drive has a great impact on the behavior of the drive during the sag and after recovery. The trip point settings of many drives can by field-adjusted and greatly improve many nuisance trips resulting from minor voltage sags.

Voltage sag/swell testing station

Abstract: A computer controllable testing and monitoring station forms short-term intervals of simulated alternating current power level disturbance, either undervoltage (sag) or overvoltage (swell). The station forms the short term voltage sags or swells so that their effects on sensitive equipment can be measured. The starting point of the sag or swell disturbance, as well as the time duration of the disturbance, can be accurately controlled.

An experimental assessment of AC contactor behavior during voltage sags

Abstract: This paper presents experimental results that demonstrate the impact of voltage sags on AC contactors. Duration and amplitude are the parameters that have been normally used to classify voltage sags. This paper proves the necessity to include the point-in-wave of voltage sag initiation to explain the impact of sags on the behavior of AC contactors. The experimental setup used to obtain the results is described in detail. Several experiments are presented that describe the effects of point-in-wave on the performance of AC contactors. The outcome of the experiments show that the magnitude and duration alone do not adequately explain the behavior of AC contactors during voltage sags.

Non-rotating portable voltage sag generator

Abstract: A non-rotating portable voltage sag generator includes for each phase a pair of cascaded standard industrial auto-transformers each having, for example, six taps and when they are cascaded the final output voltage of each phase is a product of the per unit value of each individual auto-transformer. Closed transition switching is provided to switch the auto-transformer into and out of the circuit effectively only during the time a voltage sag is desired. All of the switches and auto-transformers are conveniently carried in a single portable enclosure. There are no moving parts or diesel engines; thus, the non-rotating sag generator is useable in any part of an industrial plant.

Regulator with asymmetrical voltage increase/decrease capability for utility system

Abstract: A regulator is provided for establishing asymmetrical voltage increase/decrease capability between an input node and an output node for enhanced regulation of either a voltage sag or a voltage swell within a utility system The regulator includes an autotransformer having an input tap coupled to the input node of the regulator and an output tap coupled to the output node The regulator further includes an electronic tap changer system coupled to the winding of the autotransformer Together, the autotransformer and the electronic tap changer system provide the regulator with its asymmetrical voltage increase/decrease capability between the input node and the output node thereof The regulator can be configured for voltage increase only, voltage decrease only, or both, provided an asymmetrical voltage increase/decrease capability is defined

An integrated application for voltage sag analysis

Abstract: Voltage sags affect many more customers than momentary interruptions do. The sags on a distribution feeder are likely to result in damage to a customer's sensitive equipment on all of the adjacent feeders. It is essential to understand the characteristics of sags in order to determine the most suitable distribution feeder configuration and equipment specifications. In this paper, the development and implementation of an integrated software tool for voltage sag analysis is presented. It integrates the available historical outage data, analytical calculation algorithm and advanced computer graphic capabilities together to provide valuable voltage sag information. State-of-the-art software technologies are used to ensure the effectiveness, openness and flexibility of the integration approaches. Initial field experiences at PG&E (USA) have indicated a great demand of such an informational tool.

Analysis and mitigation of voltage disturbances at an industrial customer's corporate campus

Abstract: This paper presents the analysis of voltage sag data collected over several years at an industrial customer's corporate campus. Facilities on the campus include office buildings, pilot plants, R&D laboratories, chiller plants and boiler plants. The paper examines the "cause and effect" of voltage dips to the processes at the campus. It also details what the electric utility and the industrial customer did, or is doing, to mitigate additional dips to the campus. The determination of the final configuration of the power distribution system and its effect on the customers power quality is also discussed.

Tracking power quality disturbance waveforms via adaptive linear combiners and fuzzy decision support systems

Abstract: The paper presents the classification of power quality disturbances in power supply networks using a hybrid notch filter-linear combiner. The adaptive notch filter is used to provide the frequency estimate of the power supply network voltage signal, while the linear combiner computes the peak amplitude of the fundamental voltage with the total harmonic distortion factor, THD. The various power line disturbances like voltage sag, swell, outage, and surge, etc. are then classified using a fuzzy decision system using the fuzzified values of amplitude ad its rate of change of the peak fundamental voltage component. The distorted waveform is classified using the THD factor. Detailed digital simulation results for an AC system supplying nonlinear converter load via a transmission network and subjected to a variety of transient disturbances are presented to identify these disturbances.

Frequency and duration of voltage sags and surges at industrial sites-Canadian National Power Quality Survey

Abstract: The occurrence of voltage sags and surges originating on the primary and secondary sides of industrial facilities can disrupt continuous and noncontinuous industrial computer processes, a costly issue for society. This paper attempts to answer several questions concerning the frequency and duration of voltage sags and surges posed by industrial customers. The answers to these questions are based on Canadian national survey results of the frequency and duration of voltage sags and surges at industrial sites monitored at their utilization voltage levels (e.g., 120, 347 V) and on the utility primary side of their facilities. The survey results provide a knowledge base for monitoring, designing and utilizing voltage sag and surge mitigating technologies.

A fast series compensator for voltage sag correction

Abstract: This paper shows a fast active and reactive power series compensator applied to voltage sag correction. This disturbance is common in longer distribution lines, such as rural electrical systems, or in transmission ones. To analyse the voltage sag, this study is centralized in a low voltage effect during an induction motor start-up fed through a weak line. The control methodology is based on active and reactive power compensation in the line. A PWM voltage converter is used for the voltage sag correction. The simulated results confirm the excellent performance for the studied case.

Control and characteristics of a static VAr generator under single-line-to-ground faults

Abstract: In recent years, static VAr generators (SVGs) have been developed for improving power factor and stabilizing transmission systems. The active/reactive power control based on the p-q theory or the d-axis/q-axis current control based on d-q transformation is applied to an SVG. This paper deals with a comparative study of the two control schemes under single-line-to-ground faults. With the focus on three-phase supply currents and the DC capacitor voltage of the SVG, the two schemes are compared by computer simulation under an unbalanced condition that a supply voltage sag is caused by a single-line-to-ground fault.