Shunt Reactor Research Articles

Placement of shunt reactors in high-voltage network using fuzzy constraints

In recent years, controlled shunt reactors (CSR) relevant to the class of FACTS facilities have been widely used to control voltage modes and reactive power flows in the high-voltage electrical network. The selection of location, as well as the definition of the law of CSR control in the conditions of stochastic variability of the operation mode of high-voltage power transmission, are associated with numerous technical and economic factors. At the same time, such constraint conditions as ease of use, performance efficiency, purpose and location in the system, as well as the period of commissioning should be taken into account. In the proposed procedure these factors are considered as fuzzy constraints. The procedure of CSR placement in the 330 kV electrical network of Azerenergy system for control of reactive power flows taking into account the mentioned fuzzy constraints is proposed. The obtained simulation results confirm the advantage of the proposed procedure.

An adaptive single-phase reclosing of line in the scheme with intermediate system

Providing the reliability of adaptive single-phase reclosing (ASPR) in line equipped with any number of shunt reactors (SR), including the case of their absence, are considered and analyzed in this paper. The essence of the proposed work is that in order to provide high reliability of ASPR, is carry out short-term (for 0.1 seconds) one-sided switching on of the emergency phase from the side of the intermediate system, is measuring the current value of the current of this phase at the switched end and comparing it with the specified setpoint. If the current is higher than the specified setpoint, then a short or arc fault is detected in the phase and then it gives a command to disconnecting the line, otherwise it is not a short circuit in the phase and it is successfully will turned on to work on the other side of the line.

Multi-variable dependent forecast algorithm for predicting secondary arc characteristics in UHV systems with HRPC

Hybrid reactive power compensation (HRPC) combines step-controlled shunt reactors and series compensation, and will be employed in ultra-high-voltage (UHV) power systems. The single-phase auto-reclosure characteristics of secondary arcs in systems with HRPC require further investigation. In this paper, both the arc-recalling voltage and subsidiary variations in arc current are investigated with and without HRPC. The frequency components of the secondary arc current and variations in arcing time are analyzed for various influential factors, such as the neutral reactor, arc resistance, fault location, degrees of compensation of HRPC, and the length of the transmission line. The non-dominated sorting genetic algorithm II (NSGA-II) and support vector machine regression are combined to create a multi-variable dependent forecasting algorithm to predict the characteristics of the secondary arc in UHV systems with HRPC. This paper provides a theoretical reference for optimizing the parameters of HRPC, and for developing adaptive auto-reclosure schemes and protection equipment.

Breaking Overvoltage of Dry-Type Air-Core Shunt Reactors and its Cumulative Effect on the Interturn Insulation

The mechanism of overvoltage formation in the breaking process of a dry-type air-core shunt reactor (DTACSR) is studied in this paper. In addition, the effect of the overvoltage on the interturn insulation characteristics of the DTACSR is also discussed. Based on the actual working condition of a 66 kV DTACSR used in the Chinese power system, a three-phase simulation model and an equivalent circuit are proposed. The maximum chopping overvoltage and reignition overvoltage are obtained through the combination of theoretical analysis, simulation, and data fitting. An overvoltage accumulation test of the interturn insulation specimens is carried out with our established test platform, and the characteristic parameters of the interturn insulation specimens of the DTACSR in different stages of aging are measured. The results show that the combined method is very effective in evaluating the switching overvoltage of the DTACSR. Compared with the traditional single-phase circuit model, the proposed three-phase circuit model obtains a more accurate overvoltage equation. During the breaking process of a DTACSR, a chopping overvoltage with an amplitude greater than 5 p.u. and a reignition overvoltage with an amplitude greater than 8 p.u. may form. The cumulative effect of the overvoltage causes aging of the interturn insulation, and the degree of aging becomes more serious as the amplitude of the overvoltage increases.

Optimisation of electric arc model parameters based on simplex annealing and genetic algorithms

This paper presents the method for obtaining the coefficients of the dynamic Cassie-Mayr electric arc model by means of annealing and genetic optimisation algorithms. The extraction of the coefficients can be obtained by means of the iterative fitting process based on e.g. multiple measurements results. However, this requires a significant effort and can generate significant costs. The approach presented in this paper relies solely on simulations. The methodology used herein consists in finding the match to the maximum produced TRV generated during high-voltage shunt reactor current breaking, for ideal switch and conductance based Cassie-Mayr circuit breaker models. This is done for a given chopping current value assigned to the ideal switch which is used as a target. The arc model coefficients are obtained by means of the optimisation process for various values of the desired chopping current level to be reflected by the Cassie-Mayr conductance-based electric arc model. As a result, an advanced conductance based model can be used for assessment of switching overvoltage. Genetic and simplex annealing algorithms have been selected for optimisation. The models as well as the optimisation process were conducted in EMTP-ATP software using its built-in functionalities. The article presents the error assessment and sample traces.

Influences of secondary arc-based grading capacitor of multi-break circuit breaker on the transient stability of power system

The grading capacitor (GC) of circuit breaker (CB) is one of the most cost-effective methods to suppress secondary arc. Taking the double-break CB as an example, its topology is briefly introduced. The electric circuit for power system with GC is then established. From the perspective of minimizing secondary arc current, the formula for the capacitance of GC is deduced according to the Kirchhoff's voltage law. Based on the equal-area criterion, the transient process of power angle and speed of generator in the event of fault is investigated, and the role of GC in the transient stability is quantitatively investigated. Meanwhile, the expressions for the accelerating and decelerating areas are computed through the numerical calculus, and the impact of GC capacitance on the critical clearing time (CCT) is discussed. Furthermore, to verify the aforementioned analysis, a model is established in the environment of MATLAB/Simulink, and two cases are considered, i.e., a single machine infinite bus (SMIB) power system and a multi-machine power system. Both the theoretical analysis and the simulation results demonstrate that the use of GC can strength the electrical connection between two remote power sources, undermines the oscillating amplitude of power angle, and shorten the attenuation duration. As a result, the CCT and transient margin would be increased. In other words, we can prong the dead time and guarantee the successfulness for autoreclosure scheme. The GC of CB is much superior to the existing four-legged shunt reactor and high speed grounding switch in addressing the secondary arc issue.

Simulation and research on over‐voltage suppression for high voltage transmission line

For different types of fault in transmission line, the generation mechanism of tripping and closing over-voltage is analysed. To built the double power supply system of high-voltage transmission line simulation model by PSCAD/EMTDC, finally, for the operation of over-voltage, when the line occurs of different types faults, simulation to study tripping and closing over-voltage's size and the extent of influence, derived its tripping and closing over-voltage suppression measures and control strategies. The results showed that: for the circuit breaker tripping and closing over-voltage, the circuit breaker shunt reactor has better effect on the over-voltage suppression and improves the reliability of operation and the safety of protection of the system.

Evaluation of Capacitive Current Compensation Strategies to Current Differential Protection for Long Distance Transmission Lines

In UHV and EHV, distributive capacitive current to current differential protection has serious problem. Nowadays, to deal with the problem of distributed capacitive current a stimulating modern technology is being used in current differential protection with high operating threshold. Many schemes have been used into current differential protection for capacitive current compensation, which was based on shunt reactor, phasor compensation algorithm, Bergeron method. Those techniques were also reducing operating speed and sensitivity of current differential protection. To solve the problem of distributed capacitive current of the line, novel principle of current differential protection is described in this article. Current calculated from set point to both the ends give rise to a differential criterion. Differential protection is launched under the phenomenon of low sampling frequency to improve the expediency of the criterion. The calculation of set point distributed current is achieved at low sampling frequency by adding an interpolation point at each sampling interval. The point is set in the middle of the line and the calculation for magnitude of the current is done with half data window absolute value integrals, for improved the operating speed of the current differential protection.

THE MEASURES FOR SUPPRESSION APERIODIC CURRENT COMPONENT IN EXTRA-HIGH VOLTAGE LINES 750 kV

At present, the networks of extra-voltage received the SF6 switches with the auto-compression principle of extinguishing the arc. The experience of operation showed the inability of these switches to perform commutation-type quick "on/off" for lines with a high degree of compensation of charging power due to the existence of a long durable aperiodic component in the current flowing in the switch. The results of investigation of the causes of accidents of SF6 circuit breakers during commutation of compensated transmission lines of 750 kV are presented. In the article have been reported, that the presence of a large aperiodical component of current prevent the current from crossing zero for several milliseconds, resulting in serious damage to one pole of circuit breaker.In the work the analysis of abnormal modes of extra high voltage transmission lines with different measures is performed. The article deals with the cycle of three-phase automatic re-inclusion on the 750 kV line with two groups of shunt reactors installed. Electromagnetic processes in compensated transmission lines depending on parameters of the line are investigated. The moments of a sharp change in parameters of transient processes during switching in extra-high voltage lines are revealed. Measures to limit the duration of the existence of the aperiodic component of the current are considered.In the main power Ukrainian grids have replaced air switches for SF6 gas switches. This upgrade was caused by the fact that modern electrical industry does not produce air switches and in the event of damage to repair and restore power would be impossible. Compared to SF6 gas air circuit breakers have certain advantages, the main ones are speed and high breaking capacity, and the possibility of an extra device controlled switching. This upgrade was carried out from 2010 year to 2014.Nevertheless new SF6 breakers have a lot advantages, but some nuances were discovered in the process of using 750 kV on long overhead power lines with shunt reactors installed on them, due to which there were several accidents at the substations. Damage 750 kV circuit breakers, which in recent years have occurred on several foreign substations and also in Ukraine, served as an excuse for starting the necessary development of normative documents, establishing regulations and norms of operation.

Three‐phase adaptive reclosure for transmission lines with shunt reactors using mode current oscillation frequencies

Three‐phase adaptive reclosure for transmission lines with shunt reactors using mode current oscillation frequencies

Lessons Learned From a Regional System Blackout and Restoration in BC Hydro

A BC Hydro regional system experienced a blackout after multiple 500 kV lines, sharing the same transmission corridor, were subjected to lightning strikes in the time span of about three minutes. These lines connect two large generating stations, regional loads, and five nonutility generators to the rest of the BC Hydro system. The protection scheme on the first line tripped three-phase and initiated autoreclose as designed. However immediately after three-phase opening, high magnitudes of low-frequency (about 9 Hz) currents appeared in the line shunt reactor, causing a protection trip, and aborting the autoreclose. Subsequent lightning strikes coupled with a pre-existing line outage disconnected both generating stations from each other as well as from the integrated system. The larger of two generating stations and almost all regional load formed an islanded subsystem, which eventually collapsed and blacked out. During the restoration of the subsystem, the system operator inadvertently picked up the entire regional system without load, causing steady-state resonant overvoltages higher than 145% and damaging a transmission customer. This paper shares lessons learned from forensic analysis of disturbances leading to regional blackout and describes the risk of unsafe overvoltages from near power frequency resonant condition during the restoration process.

Magnetically Controlled Shunt Reactors as Sources of Current and Voltage Harmonics

The focus of this paper is the operation of magnetically controlled shunt reactors in high-voltage electrical grids and their role as sources of current and voltage harmonics. Power quality measurements on real-life magnetically controlled reactors show that these machines can produce harmonics with voltage total harmonic distortion overshooting permissible limits in the points of coupling to the electrical grid. A simulation model of a magnetically controlled shunt reactor has been developed and verified using field test results. The main factors determining the impact of controlled reactors on voltage waveform distortion are examined, and possible limits of such an impact are estimated.

Characteristics of very fast transient currents in ultra high-voltage power system with Hybrid reactive power compensation

Hybrid reactive power compensation (HRPC) consists of a stepped controlled shunt reactor (SCSR) and a series compensation (SC), which will find applications in future ultra high-voltage (UHV) power grids to resolve the problems due to the frequent change of reactive power and bulk power transmission. However, very fast transient currents (VFTCs) are inevitably generated during switching, which would lead to insulation breakdown. In the present work, we first develop the equivalent model for HRPC, following which we deduce the expression of VFTCs in the time domain by using an inverse Laplace transform. The analysis indicates that the amplitude and frequency of VFTCs are both affected by the capacitance of the SCSR and of the SC, as well as the line length, stray capacitance, etc. The oscillating frequency, peak, and amplitude of the main frequency of the VFTCs in the substation can be modified by adjusting the silicon-controlled rectifiers in the SCSR when the disconnecting switch in gas-insulated switchgear is switched on. When the disconnecting switch in the SC is switched on, the VFTC oscillation frequency in SCSR decreases with increasing stray capacitance of SC, but the frequency and peak of the VFTC remains quite large. Increasing the line length between the SC and the SCSR suppresses the VFTC in UHV power systems. These results lay the foundation for developing HRPC methods to suppress VFTCs in UHV substations.

Controlled switching technique for minimization of switching surge during energization of uncompensated and shunt compensated transmission lines for circuit breakers having pre-insertion resistors

Controlled Switching Device (CSD) is considered to be the replacement of Pre-Insertion Resistor (PIR). Moreover, tie Circuit Breaker (CB) used in One-and-a-Half-Breaker (OHB) scheme as well as in line connected with non-switchable reactor scheme are employed with PIR and CSD. In this paper, a new methodology has been proposed using CSD with PIR-CB for further mitigation of the switching surge during energization/re-energization of Un-compensated Transmission Line (UCTL) and Shunt reactor compensated Transmission Line (SCTL). Unlike the existing methodology (both for UCTL/SCTL) which requires line side voltage signatures, the proposed methodology does not necessitate the same for SCTL and requires only the polarity of line side voltages for UCTL. The performance of the proposed methodology has been evaluated by generating diversified cases on 400 kV UCTL and SCTL using PSCAD/EMTDC software package. The proposed switching strategy is able to mitigate the switching surge of the order of 33% for UCTL and 20% for SCTL. Comparative evaluation of the proposed methodology with usual PIR methodology clearly shows its effectiveness with reference to statistical variations of CB. The proposed methodology has been validated during effects of various parameters such as weather conditions, insulation resistance, change in closing phase sequence, and Surge Arrestor (SA).

Investigation on Overvoltage caused by Connecting Shunt Reactors with Vacuum Circuit Breakers in Offshore Wind Farms

Nowadays, the transient overvoltage occurs in offshore wind farms has aroused widespread concern. To improve the existing offshore wind farm model’s accuracy in high frequency conditions, this paper proposes a high frequency model of the vacuum circuit breaker as well as a shunt reactor model considering the influence of stray capacitance. After that, a model of a typical offshore wind farm is constructed for the purpose to analyze the overvoltage occurring at bus bars and wind turbine transformers in the process of connecting a shunt reactor. Simulations show that connecting a shunt reactor in offshore wind farms cause overvoltage of high peak and high steepness compared than with those in onshore wind farms.

Non-unit transient based boundary protection for UHV transmission lines

Different from EHV transmission lines, the boundary of UHV transmission lines naturally consists of busbar stray capacitance, shunt reactor and/or series capacitor. The frequency characteristics of the UHV line boundaries with different structures are analyzed deeply, which have significant attenuation on both high frequency signal and low frequency signal. The attenuation is the inherent characteristic of UHV line boundary. Based on the UHV boundary characteristic, a novel boundary protection principle utilizing backward traveling wave is proposed. The fault direction is identified by means of the time-domain energy of the backward traveling wave. The high frequency energy and the low frequency energy of the backward traveling wave are extracted by wavelet transform, and then the forward internal and external faults are discriminated by the product of high frequency energy and low frequency energy. An adaptive setting calculation method in terms of fault type is presented, which is able to improve effectively the right discriminating rate for internal faults. The simulation model of Jindongnan-Nanyang-Jingmen UHV transmission project is established in ATP/EMTP. The simulation results show that the boundary protection possesses stable performance under various fault situations, and the operation time is less than 2 ms, which is appropriate as the non-unit ultra-high-speed protection element for UHV transmission lines.

Comparative research into transients by switching of high voltage shunt reactor

This article deals with results of performed studies of transient phenomena in application of controlled switching technique by switching high voltage 123kV, 100MVAr shunt reactor. First, for switching a single-pole hydraulically operated SF6 circuit breaker has been selected and after that, one with electric motor-drive. In preparing of experimental part of studies the EMTP-ATP software has been used in computer simulations, further for analyses the cases of optimal controlled switching and switching within time deviation limits. For simulation of uncontrolled switching with current chopping and arc-reignition dynamic model of arc behavior has been implemented. The field tests with both circuit breakers have been repeated in similar network conditions for further statistical analyses. During some tests, the transient phenomena of uncontrolled switching have been observed. The achieved experimental results were compared with the computer simulations.

Suppression of Weakly-Damped Torsional Oscillations in Autonomous Power Systems

Variants are considered for suppression of weakly-damped vibration effects caused by the first critical frequency of torsional oscillations of a gas-turbine unit in the autonomous electric power system of an oil and gas field. It is shown that torsional oscillations can be suppressed with the aid both of a reactive power source installed at the field power system, consisting of a controlled shunt reactor (CSR) and a static capacitor battery, and of an auxiliary active RLC filter, when using in both cases auxiliary control loops of torsional deviation as well as its first and second derivatives. A methodology has been developed for simultaneous coordination of the settings of any regulation system based on a numerical optimization, which permits selecting the characteristics of control loops of the source of reactive power and active RLC filter that are optimal from the point of view of suppressing torsional oscillations.

Application of universal neutral reactor in shunt compensated transmission lines: feasibility study

Single-phase neutral reactors are used in shunt compensated transmission lines (TLs) to accelerate the extinction of the secondary arc through suppression of the arc current. Application of similar shunt reactors with the same capacities is prevalent in the transmission systems. Using the traditional method, however, for each TL, a specially designed neutral reactor is needed that could be in some cases extremely large and practically infeasible. This study investigates the feasibility of application of a properly designed neutral reactor, which is independent of the line length. This solution only depends on the ratio of positive- and zero-sequence capacitances of the line as well as the shunt reactor inductance. Accordingly, for all TLs at the same voltage level equipped with shunt reactors of the same capacities, the proposed neutral reactance would be almost identical which helps to minimise the cost and design complexity. Meanwhile, the required insulation level would be kept sufficiently small for any compensation degree. Based on the steady-state analysis and time-domain simulations conducted using the electromagnetic transient program, it is shown that for the majority of TLs, it is possible to extinguish the secondary arc within an acceptable short period of time by applying the proposed neutral reactor.

Occupational exposure to extremely low-frequency magnetic fields near 20 kV, 3-phase shunt reactors at substations

Directive 2013/35/EU of the European Parliament and Council, among other things, sets values for the occupational exposure of workers regarding the health and safety risks arising from electromagnetic fields. In order to ensure worker safety, the Finnish national grid operator, Fingrid Oyj, conducted several measurements of electromagnetic fields at its substations. One of the goals of the measurements was to ensure that a magnetic flux density of 1000 µT (rms), set as the lower action value by the EU directive, was not reached in any location accessible to substation workers. The highest magnetic flux densities at substations can be found near shunt reactors and their cables, which is why the measurements were focused on those areas. The lower action value of 1000 µT (rms) was surpassed at two locations. This discovery led to immediate actions to prevent workers from accessing these locations.