This paper proposes a control strategy for a VSC-HVDC for improving the quality of power supply to industrial plants The new idea of this control strategy is to give high priority to keep up the ac voltage and slightly decrease the frequency during disturbances The motivation for choosing this strategy is that the sensitive processing industries are much more sensitive to voltage drops as compared with frequency deviations In order to test this control strategy, the dynamic performance of a VSC-HVDC supplied industrial plant is investigated during sudden load disturbances, balanced and unbalanced faults from the grid Simulation results obtained using PSCAD/EMTDC show that with the use of the proposed control strategy, the system can ride through disturbances such as motor starting and faults by slightly decreasing the frequency The current limit of the VSC-HVDC converters has a significant influence on the dynamics of the system An increase of the current limit significantly improves the power quality of the system The comparison of the behavior between a pure ac supplied industrial plant and a VSC-HVDC supplied industrial plant clearly shows the capability of the VSC-HVDC to mitigate voltage dips during faults

A New Control Strategy of a VSC–HVDC System for High-Quality Supply of Industrial Plants

An experimental study and some calculations on induction motor behavior were carried out. The effects due to short interruptions and voltage sags were investigated. A standard three-phase squirrel-cage motor of 5.5 kW, 1500 r/min, and 380 V was used. The presence of induction motor changes the voltage sag waveform and duration. Protection characteristic curves and contactor ride-through capability together with their improvement are also studied. The interaction between motor load, system hot-load pickup, and voltage sag magnitude determine the motor re-acceleration duration and magnitudes. Besides, on-sag and post-sag currents can reach levels higher than the direct start values. Post-sag overcurrent duration can last more than twice the normal start time period, having specific energies in the same order of magnitude.

Behavior of induction motor due to voltage sags and short interruptions

Latest innovative ideas to make the life easier using the technology depends upon the application of power electronics in turn about power quality. With increasing quantities of non-linear loads being added to electrical systems, it has become necessary to establish criteria for limiting problems from system voltage degradation. This paper presents the power quality problems, issues, related international standard, effect of power quality problem in different apparatuses and methods for its correction, which is actually a technology management. This is important for design engineers and researchers in power quality to know the international standards used for power quality.

http://www.ijaet.org/media/0001/1POWER-QUALITY-ISSUES-PROBLEMS-STANDARDS-THEIR-EFFECTS-IN-INDUSTRY-WITH-CORRECTIVE-MEANS-Copyright-IJAET.docx.pdf?origin=publication_detail

Power quality issues, problems, standards & their effects in industry with corrective means

This paper provides insight into a failure mechanism that impacts a broad range of industrial equipment. Voltage surges have often been blamed for unexplained equipment failure in the field. Extensive voltage monitoring data suggests that voltage sags occur much more frequently than voltage surges, and that current surges that accompany voltage sag recovery may be the actual culprit causing equipment damage. A serious limitation in equipment specification is highlighted, pointing to what is possibly the root-cause for a large percentage of unexplained equipment field failures. This paper also outlines the need for a standard governing the behavior of equipment under voltage sags, and suggests solutions to protect existing equipment in the field.

/pdf/equipment-failures-caused-by-power-quality-disturbances-2r8tc2o8bw.pdf

Equipment failures caused by power quality disturbances

Different methods for voltage sag source detection are discussed. They are based either on disturbance energy, voltage-current characteristic or active (real) current component. It is shown that, in the cases of asymmetrical voltage sags, both current-based methods known from literature do not work well. These two methods are therefore generalised using a vector-space approach. Furthermore, three new methods are introduced using orthogonal Clarke's transformation, which can be used to detect the sources of those voltage sags provoked by earth faults. All the discussed methods for voltage sag source detection have been tested by applying extensive simulations, laboratory tests and field testing. The results obtained show the very high effectiveness of the proposed methods, which are superior to the methods known from literature, especially for detecting sources of asymmetrical voltage sags.

Detection of voltage sag sources based on instantaneous voltage and current vectors and orthogonal Clarke's transformation

This letter proposes a gaming model with coalition among producers in subgroups for the market setting with multiple producers. The possible number of coalitions is obtained for a total number of N(N/spl ges/3) producers. The generic spatial gaming model with coalition has a vector as its objective function, with each vector element representing a coalition profit. Various constraints are formulated, including the spatial constraints (e.g., the DC power flow equations). The Cournot gaming strategy is adopted. A small system is used for testing the model with satisfactory results.

Induction Motor Behavior under Short Interruptions and Voltage Sags

Voltage sag produced by induction motor starting current is one of the main causes of sensitive equipment (SE) dropout. The use of motor starter reduces the voltage sag depth but increases its duration. The subsequent connection to full voltage originates a new sag separated from the first one by a few seconds. An extensive experimental research that aimed at determining the effect of assisted starting characteristics on the generated voltage sag is reported. Results show the existence of critical combinations of commutation time and assisted starting voltage from the SE dropout susceptibility point-of-view. Voltage drop and consequent specific energy of the assisted starting is compared with values corresponding to both direct on-line starting and direct at-reduced-voltage starting.

A Study of Voltage Sags Generated by Induction Motor Starting

An experimental study and some calculations on induction motor behavior were carried out. The effects due to short interruptions and voltage sags were investigated. A standard three-phase squirrel-cage motor of 5.5 kW, 1500 rpm, 380 V was used. The presence of induction motor changes the voltage sag waveform and duration. Protection characteristic curves and contactor ride-through capability together with their improvement are also studied. The interaction between motor load, system hot-load pickup, and voltage sag magnitude determine the motor reacceleration duration and magnitudes. Besides, on-sag and post-sag currents can reach levels higher than the direct start values. Post-sag overcurrent duration can last more than twice the normal start time period, having specific energies in the same order of magnitude.

Behavior of Induction Motor Protection Due to Voltage Sags and Short Interruptions

Of all power quality issues, voltage sags and short interruptions are considered to be the main cause of more than 80% of the problems experienced by sensitive equipment. Customers normally suffer from the effect of the induction-motor and supply-system interaction, and utilities can experience significant loss of load. The motor undervoltage protection could trip the motor contactor if the supply voltage stays too low for a long time. New power quality requirements have an important effect on the motor system interaction, for example, the increasingly popular motor fast reconnection to the same source or to an alternative source. The load characteristics during the reconnection instant are also critical for the motor behavior, since it is possible that the motor would stall and not start when the supply voltage is restored. This article documents an experimental study that is the first part of an extensive project with the goal of developing a simple tool for the study of induction motor behavior and system effects under short interruption and voltage sag conditions.

C. Reineri

Papers

Behavior of induction motor due to voltage sags and short interruptions

Induction Motor Behavior under Short Interruptions and Voltage Sags

A Study of Voltage Sags Generated by Induction Motor Starting

Behavior of Induction Motor Protection Due to Voltage Sags and Short Interruptions

IEEE Power Engineering Society