Long-duration Voltage Research Articles

Fully Automated MV Cable Monitoring and Measurement System for Multi-Sample Acquisition of Artificial Aging Parameters

The Power quality of our networks is influenced by transients, short- and long-duration variations, voltage unbalance, waveform distortions, voltage fluctuations and power frequency variations. These impacts affect the aging rapidity of the electrical equipment and finally the entire electrical network. By partial discharge (PD) and tan(δ) analyses, it is possible to determine the electrical equipment’s condition. The significance of the results depends on the quality of the measurement system and of the data interpretation. Based on these results, a reliable maintenance and investment strategy could be made, and the reliability of the network could be improved. A specially designed aging system for the accelerated aging of MV cables has been developed to point out the most relevant aging parameters and their limits, and, in this way, to upgrade the accuracy of the MV cable diagnostics. In this paper, the system’s “intelligence”, which controls the aging process and acquires, evaluates and stores all necessary data is presented.

Calculation of inlet capacitance for long-duration induction voltage test of single-phase three-winding converter transformers

The converter transformer is one of the core equipment in the high-voltage DC (HVDC) transmission project. The capacity of the converter transformer is much larger than that of an ordinary AC transformer, and its main function is to convert the AC system voltage to the phase change voltage required by the converter. The long-duration induction voltage test is an important technical means to assess the insulation strength of electrical equipment, and the calculation of the inlet capacitance of the converter transformer in the test design is extremely critical. This paper conducts circuit and mathematical modeling based on the structure of a single-phase three-winding converter transformer, calculates the equivalent capacitance between each winding of the converter transformer and each winding to ground by the model, and uses each equivalent capacitance to calculate the voltage added inlet capacitance, then obtains the appropriate compensation inductance. Moreover, the calculated inlet capacitance is verified by using the field test data, and the verification results show the reasonableness of the model. Finally, the calculation results are analyzed for errors and possible sources of errors are pointed out. This inlet capacitance calculation method has some universality and is expected to be promoted and applied in this field.

Voltage profile assessment in smart distribution grids considering BESS and communication network failures

• Sequential monte carlo simulation for assessing voltage profile of smart grids. • modeling failures in the BESS systems and the communication network (CN). • BESS optimization models for day ahead scheduling and voltage profile correction. • The results shows that communication failures have impact on the voltage profile. Battery energy storage systems (BESSs) are expected to play a major role in voltage control of smart distribution grids (SDGs) due to the high penetration of intermittent renewable energy. However, neither these devices nor the communication infrastructure needed for their control, are fully reliable. Due to this, BESS unavailability might occur, degrading voltage profile. This paper presents a new fixed-time sequential Monte Carlo simulation for assessing indices of SDGs’ long-duration voltage variations (LDVVs) considering both failures in BESS systems and in the communication network (CN). Results show that these failures have significant impact on the LDVV indices of the SDG.

Generalized Formulation of Steady-State Equivalent Circuit Models of Grid-Forming Inverters

Abstract: This work proposes positive- and negative-sequence equivalent circuits of grid-forming inverters for steady-state analysis. The proposed models are especially attractive for performing long-duration voltage regulation analysis and short-circuit studies involving grid-forming inverters. Our proposed equivalent circuit models are based on the inverter’s voltage and current control loops in the αβ and dq frames. For this reason, they operate according to prescribed control functions and specified impedances (i.e., filter impedance, current limiter block, virtual admittance block, and PI/PR controller block). The equivalent circuit model accuracy is validated by comparing system steady-state voltage and current responses obtained by detailed time-domain models in PSCAD/EMTDC to those by the equivalent circuit models implemented in steady-state load flow program (e.g., OpenDSS). Two distinct control structures implemented in the αβ and dq frames are used for the validation. Single line-to-ground and line-to-lineto-ground faults are simulated in a small islanded microgrid as well as the IEEE 34-node test feeder. Fault impedances varying from 0 to 5 ohms are simulated. We show that the equivalent models precisely replicate the steady-state response of the detailed time-domain models.

Comparative analysis of line-start permanent magnet synchronous motor and squirrel cage induction motor under customary power quality indices

Super premium efficiency (IE4) line-start permanent magnet synchronous motor (LSPMSM) is one of the good alternatives to the squirrel cage induction motor (SCIM), especially for a line-start application. Motor performance parameters like efficiency, input power consumption, power factor, starting behavior and torque ripple are affected primarily because of the customary power quality indices. The problems originate due to furnaces, power electronic converters, nonlinear loads, digital controllers, modern electrical equipments and lively load variations. Hence, the performance analysis of LSPMSM and SCIM is essential to understand the motor behavior. Voltage harmonic distortion, voltage unbalance factor and long-duration voltage variation are considered in this study. Customary power quality indices (CPQI) are collected using power and energy analyzer in a sugar industry at various measured points. In the present study, 2.2 kW LSPMSM is designed and prototyped for constant load operation. The designed motor and SCIM are used for analyzing the performance using finite element analysis under the influence of measured CPQI and the effects on its individual performance parameters.

A Novel Method to Enhance of Power Quality in Distribution System using IDVR

The dynamic voltage trained worker (DVR) offers series compensation and better management resolution to voltage-sag drawback; as a results of the voltage restoration technique provides Active Power injection into the distribution system, to spice up active power at intervals the system ids done correct alternative of DVR in given network, considerably for mitigating long-duration voltage dips i.e. sag, and sag mitigation amount depends on the energy storage capability of the DVR. This paper prove higher answer in modeling the simulation of voltage sag compensation through Interline Dynamic Voltage trained worker (IDVR) and it provides some way to top off dc-link energy storage dynamically. The IDVR consists of the various} DVRs connected to numerous distribution feeders within the power System. The DVRs within the IDVR system share common energy storage. one all told the DVR compensates for voltage sag showing throughout this feeder, the opposite DVRs top off the energy within the common dc-link dynamically. Thus, one DVR within the IDVR system works in voltage-sag compensation mode whereas the opposite DVRs within the IDVR system operate in constant power management mode. this system involves SPWM technologies to spice up the Doctor of Theology. The simulation results unit of measuring enclosed may additionally} the operative principles of a DVR and shows the effectiveness and also the power of the projected IDVR system to spice up power quality

A Novel Constant Active-current Limit Coordinated Control Strategy Improving Voltage Sag Mitigation for Modular Multi-level Inverter-based Unified Power Quality Conditioner

This article presents a novel coordinated control approach for a unified power quality conditioner based on a modular multi-level converter that could apply to higher voltage levels with increasing the number of modular multi-level converter submodules. The conventional approach is based on constant DC voltage regulated by a shunt controller or uncontrolled DC voltage to mitigate system voltage sag utilizing series controller. However, their mitigation capability is circumscribed, compensating deeper and longer duration voltage sags for the limit of device capacity. In this article, the voltage sag compensation mechanism of the modular multi-level converter-unified power quality conditioner is analyzed. A constant active-current limit coordinated control scheme is proposed considering the compensation energy derived from both DC capacitors in the submodules and source side. No additional expended capacity devices are required, and the compensation energy is increased via restricting the active current value of the shunt modular multi-level converter. The coordinated control strategy is flexible and easy to implement. Experimental work and simulation results are provided to validate the effectiveness of the proposed approach in compensation of deep and long-duration voltage sags.

Probabilistic evaluation of long‐duration voltage variations in distribution networks with wind power plants

The main aim of this study is to estimate long-duration voltage variations considering uncertainties associated with stochastic fluctuations in the output power of the wind distributed generation (DG) and system load. In the proposed methodology the uncertainties were represented using the time series models: Fourier analysis and auto-regressive moving average. These models were used in the quasi-sequential Monte Carlo simulation method to generate the system operation scenarios. The Monte Carlo simulation method was also used to model failures in the DG. The proposed methodology to estimate long-duration voltage variations was tested in a test system with 33 buses. The results showed that the insertion of wind DG in the system has a significant impact on the voltage profile. Furthermore, it was demonstrated that failures in DG and fluctuations in the load and wind speed caused large variations on the nodal voltages.

Mitigation of Voltage Sag and Swell Using Direct Converters with Minimum Switch Count

A new simplified topology for a dynamic voltage restorer (DVR) based on direct converter with a reduced number of switches is presented. The direct converter is fabricated using only three bi-directional controlled switches. The direct converter is connected between the grid and center-tapped series transformer. The center-tapped series transformer is used to inject the compensating voltage synthesized by the direct converter. The DVR can properly compensate for long-duration, balanced, and unbalanced voltage sag and swell by taking power from the grid. The switches are driven by ordinary pulse width modulation signals. Simulation and hardware results validate the idea that the proposed topology can mitigate sag of 50% and swell of unlimited quantity.

Phase Angle Analysis for Three-Phase PWM-Switched Autotransformer Voltage-Sag Compensator

Dynamic voltage restorer (DVR) is among the other voltage sag compensators introduced to mitigate voltage sag occurrences. DVR requires energy storage but is inadequate for compensating deep and long-duration voltage sags. AC–AC sag compensators, next introduced, need no storage device, being capable of what DVR was not. Dropped AC voltage needs AC–AC converter to become regulated AC voltage. This paper presents two tasks. First, a new three-phase voltage sag detection controller that is based on phase-angle analysis is developed. This technique is able to detect and compensate three-phase sag the moment it occurs. Beside fast detection response, it is simple to implement and involves less mathematical computation. Second, a three-phase topology of voltage sag compensator is introduced. The advantage of this detection technique is the detection time. It is capable of detecting and compensating voltage sag the moment sag occurs, without delay. Its effectiveness and capability were verified via MATLAB/Simulink simulation while the proposed detection technique was further investigated through a controller developed using TMS320F2812 DSP.

Measurement and Analysis of Electric Power Quality for Commercial Vessels

Owing to more and more sensitive loads installed in modern ships, ship owners and builders have been faced with rising numbers of complaints about the quality of power. However, the existing power monitoring facilities installed onboard for recording deviations of power parameters is only over steady-state conditions due to limited capacity of measurement equipment and ignores short-duration phenomena. To understand the true supply quality in ships, a power quality (PQ) monitoring technique is employed in this paper. The PQ parameters including short-duration and long-duration voltage and frequency variations in a practical commercial vessel power system under different operating conditions are analyzed and their statistic data are reported. Through PQ measurement and analysis, the quality of supply can be quantified and assessed according to classification society standards. Analysis model developed in this paper can assist them in understanding true supply quality in ships for further determining proper PQ mitigation options.

Three-Phase PWM-Switched Autotransformer Voltage-Sag Compensator Based on Phase Angle Analysis

Many voltage sag compensators have been introduced, including the traditional dynamic voltage restorer (DVR), which requires an energy storage device but is inadequate for compensating deep and long-duration voltage sags. The AC-AC sag compensators introduced next do not require a storage device and they are capable of compensating voltage sags. This type of compensator needs an AC-AC converter to regulate the output voltage. Presented in this paper is a three-phase PWM-switched autotransformer voltage sag compensator based on an AC-AC converter that uses a proposed detection technique and PWM voltage control as a controller. Its effectiveness and capability in instantly detecting and compensating voltage sags were verified via MATLAB/Simulink simulations and further investigated through a laboratory prototype developed with a TMS320F2812 DSP as the main controller.

Interphase AC–AC Topology for Voltage Sag Supporter

A new topology is proposed in this paper to compensate voltage sags in power distribution systems. Voltage sag is one of the major power quality problems encountered by industries. The traditional voltage sag compensator, which is a dynamic voltage restorer based on energy storage device with a series-connected voltage-source inverter, is not adequate for compensating deep and long-duration voltage sags. As per the sensitive load concern, deep and long-duration sags are more vulnerable than shallow and short-duration sags. To compensate the voltage sag, a new interphase ac-ac topology is proposed that needs no storage device. The compensator of each phase is connected on the other two phases and the power is tapped from them. A single-phase compensator is realized with two ac chopper circuits and two transformers. By controlling the duty cycle of each ac chopper, the required voltage is realized to compensate the voltage sag. Analysis, simulation, and experimental results are presented to demonstrate the proposed concept.

Slow Spike Frequency Adaptation in Neurons of the Rat Subthalamic Nucleus

Neurons of the subthalamic nucleus (STN) are very sensitive to applied currents, firing at 10-20/s during spontaneous activity, but increasing to peak firing rates of 200/s with applied currents <0.5 nA. They receive a powerful tonic excitatory input from neurons in the cerebral cortex, yet in vivo maintain an irregular firing rate only slightly higher than the autonomous firing rate seen in slices. Spike frequency adaptation acts to normalize background firing rate by removing slow trends in firing due to changes in average input. Subthalamic neurons have been previously described as showing little spike frequency adaptation, but this was based on tests using brief stimuli. We applied long-duration depolarizing current steps to STN neurons in slices and observed a very strong spike frequency adaptation with a time constant of 20 s and that recovered at a similar rate. This adaptation could return firing to near-baseline levels during prolonged current pulses that transiently drove the cells at high rates. The current responsible for adaptation was studied in voltage clamp during and after high-frequency driving of the cell and was determined to be a slowly accumulating K(+) current. This current was independent of calcium or sodium entry and could be induced with long-duration voltage steps after blockade of action potentials. In addition to the adaptation current, driven firing produced slow inactivation of the persistent Na(+) current, which also contributed to the reduced excitability of STN cells during and after driven firing.

A Novel Technique to Compensate Voltage Sags in Multiline Distribution System—The Interline Dynamic Voltage Restorer

The dynamic voltage restorer (DVR) provides a technically advanced and economical solution to voltage-sag problem. As the voltage-restoration process involves real-power injection into the distribution system, the capability of a particular DVR topology, especially for compensating long-duration voltage sags, depends on the energy storage capacity of the DVR. The interline DVR (IDVR) proposed in this paper provides a way to replenish dc-link energy storage dynamically. The IDVR consists of several DVRs connected to different distribution feeders in the power system. The DVRs in the IDVR system share a common energy storage. When one of the DVR compensates for voltage sag appearing in that feeder, the other DVRs replenish the energy in the common dc-link dynamically. Thus, one DVR in the IDVR system works in voltage-sag compensation mode while the other DVRs in the IDVR system operate in power-flow control mode. In principle, IDVR can operate effectively when constituent DVRs are electrically (not necessarily physically) far apart. Closed-loop load voltage and current-mode-control techniques are used as the control strategy in the two modes of operation. Experimental results obtained for a laboratory prototype of the IDVR are presented to show the effectiveness and the efficacy of the proposed IDVR system to improve power quality

Interline Dynamic Voltage Restorer: A Novel and Economical Approach for Multiline Power Quality Compensation

Voltage deviations, often in the form of voltage sags, can cause severe process disruptions and result in substantial economic loss. The dynamic voltage restorer (DVR), a custom power device, has been proposed to protect sensitive loads from the effects of voltage sags on the distribution feeder. One of the main factors which limits capabilities of a particular DVR in compensating long-duration voltage sags is the amount of stored energy within the restorer. This paper proposes a new concept of interline dynamic voltage restoration (IDVR) where two or more DVRs in different feeders are connected to a common dc link. While one of the DVRs compensates for a voltage sag, the other DVRs connected to a common dc Link replenish the dc-link energy storage. A current-mode control strategy is incorporated into the IDVR system in both working modes, voltage sag compensation and power flow control. The reference voltage for power flow control mode is derived from instantaneous active current calculated using the dc-link voltage error signal. Simulation results are presented for a simple system in order to demonstrate the efficacy of the proposed IDVR system.

A novel dynamic series compensator with closed-loop voltage and current mode control for voltage sag mitigation

The increased use of voltage-sensitive equipment in the industrial sector has made industrial processes more susceptible to supply voltage quality problems in the form of voltage sags. Series-connected voltage source converter (VSC)-based devices have been gaining popularity in protecting sensitive loads against voltage sags. This paper presents a novel transformerless dynamic series compensator (DSC) to mitigate long-duration voltage sags effectively. A line-side controllable rectifier connected to the proposed DSC maintains the dc-link voltage at a specific value while the DSC compensates voltage sags. The DSC is controlled by a closed-loop voltage and current mode controller which provides better damping and dynamic performance than that of in open-loop controller. The closed-loop controller consists of an outer voltage loop and an inner current loop derived from filter capacitor current. Performance of the proposed DSC is tested under varied voltage sag conditions, and simulated and experimental results are presented to show the effectiveness of the proposed DSC in mitigating long-duration voltage sags.

Small-scale embedded generation effect on voltage profile: an analytical method

Nowadays, deep concern is focused on the introduction of small-scale embedded generation (SSEG) in LV networks, since some technologies have a natural inclination to be easily integrated into urban LV distribution networks. As a consequence, studies on the effects produced on LV distribution systems by SSEG are gaining more and more relevance. Some aspects regarding the quality of the power supplied to customers are dealt with, taking into consideration long-duration voltage variations in the presence of SSEG. In particular, the effect on the voltage profile in a LV distribution feeder is examined with reference to both distributed loads and lumped loads. Some analytical expressions are derived to determine the limit value of the power that can be injected into a single node of a distribution feeder without causing overvoltages. The expressions derived for distributed loads are compared to those for lumped loads in order to assess if the analytical evaluation of the current threshold can be performed by means of an equivalent model based on continuous quantities with a negligible error, since actually, the analysis of real cases implies dealing with lumped loads.

Impulse Electrical Breakdown Fields of Short Vacuum Gaps

Prebreakdown currents for a long-duration impulse voltage were measured as a function of a wide range of gap spacing using a . air of plane-parallel copper electrodes in a vacuum of 3xlO Pa. The field-emitted component of the prebreakdown current was found to follow the Fowler-Nordheim field emission theory and the field enhancement factor at the cathode was determined from the Fowler-Nordheim plot. The B was found to increase from 15 to 230 with increasing electrode separation in the range from 0.003 to 2.5 mm. The breakdown voltage and the average field strength were also measured in the same gap range. It was found that the average field strength decreased from 700 kV/mm to 33 kV/mm with increasing electrode separation, however, the critical microscopic electric field at breakdown is determined to be (10.2±1.5) X107 V/cm in the range investigated.

Behaviour of delayed current under long-duration voltage clamp in snail neurones

1. 1. When the depolarization of the somatic membrane of Helix pomatia giant neurones under a long-duration voltage clamp exceeds —25 mV, the outward current after reaching the maximum value declines. The time course of this decline is approximately exponential with a time constant of 500 msec. 2. 2. Double-step voltage clamp experiments show that the outward current decline is caused both by a decrease in the membrane conductance and by a shift in the equilibrium potential in the positive direction. 3. 3. The maximum value of the outward current for a given level of depolarization can be considerably altered by preceding shifts in the membrane potential. The preceding depolarization decreases and the hyperpolarization increases the maximum value of the outward current, probably causing changes in the degree of the potassium inactivation. 4. 4. The time course of the potassium inactivation removal by hyperpolarization is approximately exponential. The time constant of this process varies from 0·5 sec to several seconds. 5. 5. In some cases, beginning with a certain level of the preceding hyperpolarization so large an increase in the outward current during depolarization is observed that a transient breakdown of the membrane can be supposed. 6. 6. The mechanisms of the effects produced by preceding shifts in the membrane potential upon the action potential generation are discussed.