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Abstract In recent years, the “asset management” or “managing assets” technique has been expected to support the rationalization of the maintenance and operation of electric power equipment, especially as a countermeasure for aging equipment. For this purpose, the development of diagnostic methods for aging, remaining life, and faults is necessary. Furthermore, it is important to accumulate case studies applying such diagnostic methods to real equipment and the analysing benefits of the applications of the diagnostic methods. In this report, frequency response analysis and a partial discharge measurement are applied to a shunt reactor suspected of occurrence of partial discharge. Results of the diagnostic methods suggest the breakage of the earth bar connecting the iron‐core blocks and the occurrence of the partial discharge at the iron core. From these diagnostic findings, the shunt‐reactor operator decided to postpone the replacement for 2 years, compared with the case where no diagnostic methods were applied. In this report, the benefits of deciding the postponement is also evaluated.

In recent years, the "asset management" or "managing assets" technique has been expected to support the rationalization of the maintenance and operation of electric power equipment, especially as a countermeasure for aging equipment. For this purpose, the development of diagnostic methods for aging, remaining life, and faults is necessary. Furthermore, it is important to accumulate case studies applying such diagnostic methods to real equipment and the analysing benefits of the applications of the diagnostic methods. In this report, frequency response analysis and a partial discharge measurement are applied to a shunt reactor suspected of occurrence of partial discharge. Results of the diagnostic methods suggest the breakage of the earth bar connecting the iron‐core blocks and the occurrence of the partial discharge at the iron core. From these diagnostic findings, the shunt‐reactor operator decided to postpone the replacement for 2 years, compared with the case where no diagnostic methods were applied. In this report, the benefits of deciding the postponement is also evaluated. [ABSTRACT FROM AUTHOR]

Abstract Shunt reactor with auxiliary windings (SRAW) can compensate inductive reactive power for long‐distance transmission lines and supply steady power for low‐voltage devices on offshore platforms. The operation characteristics of SRAW can be commonly described by the air‐core transformer equivalent model. However, this model can only make an approximate simulation of the external characteristics of SRAW, and cannot reflect the actual electrical features inside the SRAW. To solve this problem, the authors propose a three‐segment magnetic circuit equivalent model (TMCEM) of SRAW based on the magnetic circuit decomposition method. This model can accurately describe the coupling relationship inside SRAW and can be used for the analysis of internal fault characteristics. Furthermore, through the fault analysis utilizing TMCEM, a novel protection scheme of SRAW based on virtual magnetizing differential current is proposed for the detection of the inner‐turn fault in SRAW. This protection scheme has high sensitivity and can effectively identify the inner‐turn faults without measuring voltages. By testing the physical model of SRAW, the effectiveness of the TMCEM and the proposed protection scheme against inner‐turn fault has been confirmed.

Abstract Even though shunt compensation of transmission lines (TLs) is a common practice to limit the overvoltages stemming from the Ferranti effect, it may cause transient and steady‐state resonant overvoltages when one phase is left open due to the single‐pole‐open condition following the temporary phase‐to‐ground (Ph‐g) fault. Furthermore, the existing shunt reactors potentially increase the duration of the secondary arc current at the fault point and hence prevent offering fast single‐pole reclosing. To exploit the mentioned issues, in recent studies, a neutral reactor is introduced, which is installed in the neutral point of the shunt reactors; nonetheless, obtaining the appropriate amount of it is remarkably challenging. In this paper, an optimal neutral reactor (ONR) is determined based on an optimization problem, which minimizes the neutral reactor cost subject to limiting both resonant overvoltages and the duration of the secondary arc current. In modelling, the Laplace domain is employed rather than the phasor domain to consider both transient and steady‐state conditions since this technique allows having better control over transient overvoltages as well as transient secondary arc.

Shunt reactor with auxiliary windings (SRAW) can compensate inductive reactive power for long‐distance transmission lines and supply steady power for low‐voltage devices on offshore platforms. The operation characteristics of SRAW can be commonly described by the air‐core transformer equivalent model. However, this model can only make an approximate simulation of the external characteristics of SRAW, and cannot reflect the actual electrical features inside the SRAW. To solve this problem, the authors propose a three‐segment magnetic circuit equivalent model (TMCEM) of SRAW based on the magnetic circuit decomposition method. This model can accurately describe the coupling relationship inside SRAW and can be used for the analysis of internal fault characteristics. Furthermore, through the fault analysis utilizing TMCEM, a novel protection scheme of SRAW based on virtual magnetizing differential current is proposed for the detection of the inner‐turn fault in SRAW. This protection scheme has high sensitivity and can effectively identify the inner‐turn faults without measuring voltages. By testing the physical model of SRAW, the effectiveness of the TMCEM and the proposed protection scheme against inner‐turn fault has been confirmed. [ABSTRACT FROM AUTHOR]

Even though shunt compensation of transmission lines (TLs) is a common practice to limit the overvoltages stemming from the Ferranti effect, it may cause transient and steady‐state resonant overvoltages when one phase is left open due to the single‐pole‐open condition following the temporary phase‐to‐ground (Ph‐g) fault. Furthermore, the existing shunt reactors potentially increase the duration of the secondary arc current at the fault point and hence prevent offering fast single‐pole reclosing. To exploit the mentioned issues, in recent studies, a neutral reactor is introduced, which is installed in the neutral point of the shunt reactors; nonetheless, obtaining the appropriate amount of it is remarkably challenging. In this paper, an optimal neutral reactor (ONR) is determined based on an optimization problem, which minimizes the neutral reactor cost subject to limiting both resonant overvoltages and the duration of the secondary arc current. In modelling, the Laplace domain is employed rather than the phasor domain to consider both transient and steady‐state conditions since this technique allows having better control over transient overvoltages as well as transient secondary arc. [ABSTRACT FROM AUTHOR]

The fault model of the inter-turn short circuit of the dry air-core reactor is first analysed in this study, by which an online monitoring method of the reactor inter-turn insulation fault is proposed by using the change of the power angle. In order to achieve high-precision measurement, the fundamental harmonic separation algorithm improved by Hanning windowed interpolation method can effectively reduce the error of power angle measurement caused by frequency fluctuation and harmonic interference. By comparing it with the power angle measurement errors of fast Fourier transform (FFT) and Hanning window interpolation FFT, the algorithm is verified. The sensitivity and stability of the equipment are verified by the experiment of simulating and eliminating the fault in the initial stage of the inter-turn short circuit. At the same time, an online monitoring system for inter-turn insulation fault of dry-type air-core reactor based on this method is designed, including field monitoring device, the intelligent electronic device of the dry air-core reactor and expert software. The method and monitoring device proposed in this study enables the fault to be accurately monitored in the early stage, which is of great significance for the safe operation of the reactor. [ABSTRACT FROM AUTHOR]

This study describes an actual problem with circulating current at the ground grid of an actual power system that has an air-core reactor. Such reactors generate a large amount of magnetic flux whose path can be closed through its underneath ground grid. This magnetic flux induces a voltage on the ground meshes and thus results in considerable circulating currents that pass through the ground meshes. Indeed, the main novelty of this study is investigating the effect of air-core reactors on the other nearby equipment and considering the air-core reactor's flux underneath ground meshes. This phenomenon occurred in a steel industrial plant and practically leads to severe damages to equipment through which the current has been flowing, including ground grid conductors, cable shields, and foundation armatures. This study addresses the origins of problems raised by the manufactured equipment in a reputable company based on both simulations and experimental studies. Based on the obtained results, several practical approaches are proposed and implemented to overcome the problems mentioned above. [ABSTRACT FROM AUTHOR]

Voltage unbalance is an important power quality issue, which occurs in electrical power systems (EPSs) and causes severe problems for them. In this work, a general mathematical model for EPS including its long transmission line is developed using the generalised circuit parameters method. Then, a hybrid Particle Swarm Optimisation–Artificial Neural Network (PSO–ANN) algorithm is proposed to overcome the voltage unbalance problem by controlling the firing angles of thyristor‐controlled reactor (TCR) which varies the amount of reactive power at the load side. PSO algorithm is responsible for determining the optimal set of TCR firing angles required to retrieve the balance conditions in offline mode for different load changes, employing the developed mathematical model of the EPS. Then, a dataset is taken as training samples for the ANN to be used in online mode. Aqaba Qatranah South‐Amman (AQSA) EPS is considered as a real case study and simulated in MATLAB environment to validate the proposed algorithm. The simulation results are compared with other ANN algorithms available in the literature. Finally, a laboratory prototype is built for AQSA EPS including its long transmission line to test the proposed hybrid PSO–ANN algorithm for real unbalance conditions acquired from the laboratory prototype. [ABSTRACT FROM AUTHOR]

A saturable reactor is one of the important components of converter valves in high-voltage direct current transmission systems. With the ever-increasing capacities of converter valves, the heat losses generated by saturable reactors are also increasing. Thus, a thermal–fluid mechanics coupled heat dissipation model for saturable reactors is proposed. In order to study the factors affecting the thermal dissipation in the saturable reactor, the epoxy resin insulating layers with different thermal conductivity were considered in this work. The simulation results showed that the hot spots in the saturable reactor are on the iron core and close to the pipe inlet that most of the generated heat can be extracted by a cooling pipe and that the effect of heat dissipation can be improved by raising the thermal conductivity of the epoxy resin. The thermal conductivities of the epoxy resin used in the two reactors were 0.8 and 1.2 W/mK, respectively. The time dependence of the iron core temperature was in accordance with the simulation results and the maximum temperatures of the saturable reactor were also consistent with the simulation results. By increasing the thermal conductivity of the epoxy insulation layer, the temperature of the iron core could be significantly reduced.

The large current generated by a direct start of the super-large-capacity high-voltage induction motor would have a huge impact on the power grid as well as the motor itself. Traditional soft starters have the shortcomings of discontinuous adjustment, voltage sags, sudden torque mutation, secondary current impact and high cost. To resolve this issue, the authors propose a novel coupled autotransformer and magnetic-control (CATMC) soft-start method. The structure of the new CATMC soft starter combines the functions of the autotransformer and magnetic control reactor via an innovative electric and magnetic circuit design. In this study, the authors analyse the magnetic circuit structure and working principles of the CATMC soft starter. Then, to validate its principle and performance, the authors conduct a simulation study using ANSYS software and design and test an 18 MW/10 kV CATMC soft starter prototype. The simulation results demonstrate that the CATMC soft starter effectively avoids secondary current impact and constrains the motor starting current to

Due to the influence of the external environment and the performance of measuring equipment, the on-line oil chromatography data contains obvious noise which makes the signal to oscillate. The monitoring data is difficult to be directly applied to the equipment state analysis. A novel wavelet-based de-noising method is proposed for pre-processing the on-line oil chromatography data. By analysing the characteristics of on-line oil chromatography data, the method of determining the decomposition layer number based on the probability distribution of wavelet coefficients and the method of determining the threshold value based on outliers conservation are proposed. The improved wavelet de-noising method is applied to analysing the on-line oil chromatography data of a defective ultra-high voltage (UHV) reactor. The results show that the proposed method is feasible and effective.

Adjustable reactor is an important VAR compensator for AC system, so it has practical significance to do researches on this device. This paper proposed a method of adjusting inductance value based on a controlled magnetic-wedge, which could change the air-gap in the magnetic path by adjusting the depth it inserted. The reactor based on this method was named as magnetic-wedge linear adjustable reactor. Its working principle and inductance's mathematical models were analysed in detail. ANSYS was used to simulate reactor's magnetic field in order to verify the analysis previously. A prototype was made and its inductance's adjustment curve was measured. Results showed that: the inductance's adjustment curve was a piecewise function. When the magnetic-wedge was in positive section, the relationship between inductance and depth of magnetic-wedge inserted was a linear function. If the magnetic-wedge was totally inserted, the air-gap was minimum while inductance was maximum. If the magnetic-wedge was totally pulled out, the air-gap was maximum while inductance was minimum. When the magnetic-wedge was in negative section, the relationship between inductance and magnetic-wedge's position was a double-exponential function, the nearer magnetic-wedge's position was, the more sensitively the inductance changed. Magnetic-wedge could control magnetic flux path and restrain air-gap edge effect.

In this article, the Changji-Guquan ± 1100 kV ultra-high voltage direct current (UHVDC) system has been established by PSCAD software, especially for the arc of the circuit breakers. The AC filter groups and the control strategy have been analysed based on the reactive power demand of this system, AC system voltage amplitude, and harmonic limit. This article mainly studies inrush currents and overvoltage, especially recovery voltage caused by switching circuit breaker of AC filter in the different working conditions. Simulation results show that the currents through circuit breakers are capacitive and contain a variety of harmonics. There will be a high inrush current when a circuit breaker of AC filter is closing, which can be suppressed by phase selection switch device and appropriate closing resistance. A higher DC transmission power and a less short circuit both make the recovery voltage of circuit breakers higher when the AC filters are removed. The maximum transient recovery voltage of circuit breakers of AC filters can be suppressed by adding the parallel opening resistors. In a certain range, higher resistance of opening resistor makes a better suppression effect on recovery voltage.

Phenomena such as current chopping, arc reignition and equivalent current chopping might appear when cutting off shunt reactor. Overvoltage caused by switching will lead to interphase fault in related equipment and inter-turn insulation damage in the shunt reactor, which will threaten the safety of electrical equipment. In recent years, equipment breakdowns caused by 35 kV shunt reactor switching overvoltage in 220 kV substation occur frequently in China, endangering the safe and stable the power grid. In this study, the mechanism, perniciousness and suppression of shunt reactor switching overvoltage are systematically analysed. The strategy of phase controlled breaker is put forward, and the overvoltage measurement and power systems computer aided design (PSCAD) simulation analysis are carried out. The work and conclusion of this study provide the solutions and engineering experience for the switching overvoltage suppression of 35 kV shunt reactor.

The hybrid high-voltage direct current (HVDC) transmission system comprising a line-commutated converter (LCC) on the rectifier side and a voltage source converter (VSC) on the inverter side combines the advantages of both LCC and VSC. It has broad prospects in many application fields. However, at the VSC-based inverter side of the hybrid system, there is no dc filters, and the inductance of the smoothing reactor is much smaller than that of the LCC station. Therefore, it is hard to distinguish line internal and external faults at the VSC side for the conventional protections based on the attenuation characteristic of the line boundary. In order to solve this problem, this study proposes a non-unit protection for hybrid HVDC transmission lines. The protection judges the fault section based on the differences of the backward travelling waveforms under internal and external fault conditions. Simulation results show that the proposed protection is able to distinguish internal faults from external ones, identify the faulty pole exactly, and has enough sensitivity under large resistance faults.

As the only power output channel of wind farms, wind‐powered outgoing lines carry the risk of reclosing to faults as an applied single‐phase reclosing scheme recloses the outgoing line after a fixed time without distinguishing transient and permanent faults. Although various transient‐fault identification (TFI) methods were proposed for conventional power transmission lines with shunt reactors, they can be hardly utilised on wind‐powered outgoing lines with shunt reactors due to the influence of outgoing line complex working conditions and wind farms inconsistent output power. In this study, reactive power was calculated using the instantaneous power algorithm to obtain the equivalent reactance of the outgoing line faulty phase shunt reactor. Then, a TFI method for the outgoing lines with shunt reactors based on online parameter determination was proposed, a relevant adaptive single‐phase auto‐reclosing (ASPAR) scheme was established. Finally, the validity and feasibility of the proposed TFI method and ASPAR scheme were verified by conducting simulation experiments on the software PSCAD/EMTDC. The experiments confirmed that the proposed ASPAR scheme can achieve immunity to changes in fault location and transition resistance, and are therefore suitable for inconsistent output power of wind farms and complex working conditions of outgoing lines. [ABSTRACT FROM AUTHOR]

A three‐dimensional (3D) finite‐element analysis model is established based on the structural characteristics of ±1100 kV oblique‐dry‐type smoothing reactor, to optimisation of the external insulation configuration thereof by the Comsol Multiphysics. The electric field on the grading ring and insulators surface is calculated and analysed. The results show that the electric field is extremely uneven and the electric field strength of the outer layer of the rain cover and the grading ring connected with the lowest layer of the main body is the largest around the whole model. Accordingly, it is proposed to enlarge the diameter of the outer layer of the grading ring, reduce the layer numbers of grading ring on the rain cover, and reduce the smoothing layer numbers of grading ring outside the insulation pillar: this should make the electric field distribution of the reactor surface more uniform. The experimental platform was established in Beijing Changping ultra‐high voltage test base and causal‐comparative tests of setup were undertaken to compare the external insulation characteristics of the smoothing reactor optimised with the original. The experimental results demonstrate that the switching impulse voltage of the smoothing reactor increases and the external insulation performance of the smoothing reactor are thus improved. [ABSTRACT FROM AUTHOR]

The converter is the main component of the converter station and the main noise source of the PLC interference. The accurate modelling of the high-frequency characteristics of the converter is the foundation for the design of the ± 1100 kV UHVDC PLC filter. Based on deep analysis of the high-frequency characteristics of the converter valve, this paper first proposes three high-frequency models of the converter valve. Compared with a real converter valve used in similar HVDC project, model two is chosen to analyse the high-frequency characteristics. Second, the model of Zhundong–Wannan UHVDC transmission project is established in the PSCAD simulation platform to determine the actual high-frequency characteristics of the converter valve. The voltage before the smoothing reactor is calculated, and the high-frequency noise level is obtained by Fourier transform. Considering the practical application of the high-frequency model of the converter valve, this paper finally proposes a formula to express the measured noise level. The noise source expressed by the formula is more practical for research on high-frequency characteristics of the converter station. [ABSTRACT FROM AUTHOR]

Adjustable reactor is an important VAR compensator for AC system, so it has practical significance to do researches on this device. This paper proposed a method of adjusting inductance value based on a controlled magnetic-wedge, which could change the air-gap in the magnetic path by adjusting the depth it inserted. The reactor based on this method was named as magnetic-wedge linear adjustable reactor. Its working principle and inductance's mathematical models were analysed in detail. ANSYS was used to simulate reactor's magnetic field in order to verify the analysis previously. A prototype was made and its inductance's adjustment curve was measured. Results showed that: the inductance's adjustment curve was a piecewise function. When the magnetic-wedge was in positive section, the relationship between inductance and depth of magnetic-wedge inserted was a linear function. If the magnetic-wedge was totally inserted, the air-gap was minimum while inductance was maximum. If the magnetic-wedge was totally pulled out, the air-gap was maximum while inductance was minimum. When the magnetic-wedge was in negative section, the relationship between inductance and magnetic-wedge's position was a double-exponential function, the nearer magnetic-wedge's position was, the more sensitively the inductance changed. Magnetic-wedge could control magnetic flux path and restrain air-gap edge effect. [ABSTRACT FROM AUTHOR]

The hybrid high-voltage direct current (HVDC) transmission system comprising a line-commutated converter (LCC) on the rectifier side and a voltage source converter (VSC) on the inverter side combines the advantages of both LCC and VSC. It has broad prospects in many application fields. However, at the VSC-based inverter side of the hybrid system, there is no dc filters, and the inductance of the smoothing reactor is much smaller than that of the LCC station. Therefore, it is hard to distinguish line internal and external faults at the VSC side for the conventional protections based on the attenuation characteristic of the line boundary. In order to solve this problem, this study proposes a non-unit protection for hybrid HVDC transmission lines. The protection judges the fault section based on the differences of the backward travelling waveforms under internal and external fault conditions. Simulation results show that the proposed protection is able to distinguish internal faults from external ones, identify the faulty pole exactly, and has enough sensitivity under large resistance faults. [ABSTRACT FROM AUTHOR]

In this article, the Changji-Guquan ± 1100 kV ultra-high voltage direct current (UHVDC) system has been established by PSCAD software, especially for the arc of the circuit breakers. The AC filter groups and the control strategy have been analysed based on the reactive power demand of this system, AC system voltage amplitude, and harmonic limit. This article mainly studies inrush currents and overvoltage, especially recovery voltage caused by switching circuit breaker of AC filter in the different working conditions. Simulation results show that the currents through circuit breakers are capacitive and contain a variety of harmonics. There will be a high inrush current when a circuit breaker of AC filter is closing, which can be suppressed by phase selection switch device and appropriate closing resistance. A higher DC transmission power and a less short circuit both make the recovery voltage of circuit breakers higher when the AC filters are removed. The maximum transient recovery voltage of circuit breakers of AC filters can be suppressed by adding the parallel opening resistors. In a certain range, higher resistance of opening resistor makes a better suppression effect on recovery voltage. [ABSTRACT FROM AUTHOR]

Phenomena such as current chopping, arc reignition and equivalent current chopping might appear when cutting off shunt reactor. Overvoltage caused by switching will lead to interphase fault in related equipment and inter-turn insulation damage in the shunt reactor, which will threaten the safety of electrical equipment. In recent years, equipment breakdowns caused by 35 kV shunt reactor switching overvoltage in 220 kV substation occur frequently in China, endangering the safe and stable the power grid. In this study, the mechanism, perniciousness and suppression of shunt reactor switching overvoltage are systematically analysed. The strategy of phase controlled breaker is put forward, and the overvoltage measurement and power systems computer aided design (PSCAD) simulation analysis are carried out. The work and conclusion of this study provide the solutions and engineering experience for the switching overvoltage suppression of 35 kV shunt reactor. [ABSTRACT FROM AUTHOR]

Due to the influence of the external environment and the performance of measuring equipment, the on-line oil chromatography data contains obvious noise which makes the signal to oscillate. The monitoring data is difficult to be directly applied to the equipment state analysis. A novel wavelet-based de-noising method is proposed for pre-processing the on-line oil chromatography data. By analysing the characteristics of on-line oil chromatography data, the method of determining the decomposition layer number based on the probability distribution of wavelet coefficients and the method of determining the threshold value based on outliers conservation are proposed. The improved wavelet de-noising method is applied to analysing the on-line oil chromatography data of a defective ultra-high voltage (UHV) reactor. The results show that the proposed method is feasible and effective. [ABSTRACT FROM AUTHOR]

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm^2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

To research the magnetic field interference on cables nearby three-phase air-core reactors and the shielding effect of different materials, this study analysed the influence on spatial magnetic field by using high-conductivity materials and high permeability materials after the basis of three-dimensional electromagnetic simulation model, and analysed the causes. Furthermore, the induced voltage in different shielding methods is calculated and discussed by using magnetic vector potential resulted from the finite element method. From the result, to achieve a satisfying effect, the shields under three-phase reactors need connect when using high permeability. Moreover, a large number of magnetic leakages on the edge of shield can aggravate the magnetic field interference in surrounding areas. Therefore, the distribution of onsite cables in substation need to be considerate when using high permeability.

The converter is the main component of the converter station and the main noise source of the PLC interference. The accurate modelling of the high-frequency characteristics of the converter is the foundation for the design of the ± 1100 kV UHVDC PLC filter. Based on deep analysis of the high-frequency characteristics of the converter valve, this paper first proposes three high-frequency models of the converter valve. Compared with a real converter valve used in similar HVDC project, model two is chosen to analyse the high-frequency characteristics. Second, the model of Zhundong–Wannan UHVDC transmission project is established in the PSCAD simulation platform to determine the actual high-frequency characteristics of the converter valve. The voltage before the smoothing reactor is calculated, and the high-frequency noise level is obtained by Fourier transform. Considering the practical application of the high-frequency model of the converter valve, this paper finally proposes a formula to express the measured noise level. The noise source expressed by the formula is more practical for research on high-frequency characteristics of the converter station.

Almost all of the fault current limiters (FCLs) have a negligible voltage drop during normal operation mode of the power system and show considerable impedance during the fault period. In addition, the most of the FCLs employ a reactor to limit the fault current, which carrying a DC current and named DC reactor-based FCL (DRFCL) or carrying AC current named AC reactor-based FCL (ARFCL). Here, a novel ARFCL is introduced for radial distribution networks protection. Then, the ARFCL performance on the limitation of the fault current is compared with DRFCL in a simple radial distribution network. The MATLAB software is used to simulate both FCLs performance and their effect on the fault current. The laboratory prototype of the ARFCL is built and tested for the evaluation of the ARFCL performance during normal and fault operation modes. The simulation and experimental results show the superiority of ARFCL to control the fault current, fast, and set the point of common coupling voltage in an acceptable range.

The power demand increases rapidly in China; however, the areas of huge power demands are of long distance from most areas of abundant energy resource in the country. Therefore, China put in great effort to develop ultrahigh voltage (UHV) power transmission systems to optimise its energy allocation. This includes (i) systematically developing key technologies such as overvoltage suppression, external insulation design, and electromagnetic environment control, and (ii) developing key equipment such as UHV alternative current (UHVAC) transformers, circuit breakers, and series compensated equipment, and UHV direct current (UHVDC) converter transformers, smoothing reactors, converter valves, and DC transmission control and protection systems. Eight AC UHV projects and 11 DC UHV projects have been built in China, which play an important role in the optimal allocation of energy. Plus there are one more UHVAC and three more UHVDC transmission projects in construction, while UHVAC gas-insulated lines will be applied in the UHVAC line crossover the Yangtze River and the ±1100 kV UHVDC power transmission technology is in development. Here, the development and application of UHV power transmission technologies in China are described, some main challenges the UHV projects encountered are discussed, and experiences obtained from the operation of UHV systems are introduced. It is concluded that China obtained mature experience in developing, constructing, and operating UHV systems and successfully realised long-distance, large-capacity power transmission, and the UHV power transmission technology has become an important measure for energy allocation in large areas.

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. [ABSTRACT FROM AUTHOR]

Smart grid technologies require advances in various conventional solutions where efficient control of the inductance of reactors is of a significant interest for utilities. Novel solution is presented for inductance control of power reactors which is carried out by developing a virtual air gap (VAG) within the core. The impact of VAG on the magnetisation behaviour of the transformer core has been analysed by using simulation environment of finite‐element method (FEM). Experimental investigation is carried out to observe the performance of VAG for intended inductance variation. Using proposed technique reactor inductance can be tuned in the range of 1 : 20 in less than a millisecond with a significant reduction in harmonics. Implementation of such fast, linear and magnetically controlled inductance along with suitable intelligence can be valuable to enhance smart grid technology for improved integration of renewables and grid optimisation. [ABSTRACT FROM AUTHOR]

This study proposes a zone partitioning protection strategy for DC systems incorporating offshore wind farm. Regarding a DC system which consists of multiple local zones with radial topology, a multi‐port DC hub is introduced to serve as firewall between different zones. By blocking the converter with DC fault blocking capability in the corresponding DC hub port, the fault can be prevented from spreading among zones. On the other hand, an inter‐zone protection centre is designed and built in the DC hub to implement the continuous operation under the situation of any port outage. Furthermore, in every local zone, the hybrid DC circuit breaker is installed in each branch at the side near the star point in order to isolate the faulty branch quickly and selectively via installing the smoothing reactor at the other side to restrict the fault current. Especially, a zone protection centre is designed and built in the star point of each zone to implement the fault detection and fault isolation. A detailed model of the DC system with the proposed protection strategy is built under PSCAD/EMTDCTM environment. Simulation results under different operating conditions demonstrate the feasibility and validity of the proposed strategy. [ABSTRACT FROM AUTHOR]

This study thoroughly studies overvoltages appearing on the isolated phase (s) of shunt reactor compensated transmission‐lines when remaining phases are left energised. The voltage that appears on the isolated phase would settle to a steady‐state component induced from the energised phases. This endures until all other phases are disconnected or the isolated phase is re‐energised. Reactors with different zero‐ and positive‐sequence reactances are less common but not rare. Taking this point into account, a general model is introduced for three‐phase reactors involving those with interphase magnetic coupling. Accordingly, a rigorous analytical formulation is developed to prevent open‐phase damaging overvoltages. As proposed, this is achieved by installing a suitable neutral reactor whose optimal value is obtained using the extracted closed‐form equations. It is shown that in the case of shunt reactors with interphase magnetic coupling, open‐phase overvoltages are more likely to arise even for small degrees of compensation. Based on the defined objectives, a range is determined for the neutral reactance in which no open‐phase overvoltage would appear. This provides a high flexibility in sizing the neutral reactor considering technical and economical limitations. The accuracy of the employed models and effectiveness of the optimised neutral reactance are further illustrated through extensive simulation studies using the electromagnetic transient program EMTP‐RV. [ABSTRACT FROM AUTHOR]

To research the magnetic field interference on cables nearby three-phase air-core reactors and the shielding effect of different materials, this study analysed the influence on spatial magnetic field by using high-conductivity materials and high permeability materials after the basis of three-dimensional electromagnetic simulation model, and analysed the causes. Furthermore, the induced voltage in different shielding methods is calculated and discussed by using magnetic vector potential resulted from the finite element method. From the result, to achieve a satisfying effect, the shields under three-phase reactors need connect when using high permeability. Moreover, a large number of magnetic leakages on the edge of shield can aggravate the magnetic field interference in surrounding areas. Therefore, the distribution of onsite cables in substation need to be considerate when using high permeability. [ABSTRACT FROM AUTHOR]

This study presents an improved algorithm of adaptive single‐phase auto‐reclosing (ASPAR) for extra high voltage transmission lines with shunt reactors. It shows that the odd and even harmonic factors of the faulted phase voltage have different characteristic in different stages after breaker open. During second arc period, the odd harmonics are dominant, while the even harmonics distortion factor calculated by discrete Fourier transform is found in relatively high level after arc extinction. Hence, the calculation of ratio of even harmonic factor to odd harmonic factor (REO) is expected to determine the secondary arc extinction. The algorithm is easy to implement with small computation and no more than 20 ms delay. Moreover, the REO threshold is taken constant at unity and need not be skilfully assigned. Analysis is provided by EMTP emulation as well as filed data, and the high reliability of ASPAR has been verified. [ABSTRACT FROM AUTHOR]

This study presents a novel DC reactor‐based ferroresonance and fault current limiter (DRFFCL) for stabilising ferroresonance oscillations of potential transformer (PT) in 33 kV distribution network and decreasing the amplitude of the fault current to an acceptable level. At first, the ferroresonance overvoltage is introduced and various types of overvoltage in the PT are studied. Then, the effects of the suggested DRFFCL on these oscillations are investigated. It is shown that the proposed DRFFCL not only can control the ferroresonance oscillations, but also can decrease the fault current amplitude in the case of short‐circuit faults occurrence. The DRFFCL performance is simulated using MATLAB software and a scaled‐down laboratory prototype is implemented and tested for the simulation results validation. The measured results are in agreement with the simulation results and clearly show the ability of the DRFFCL for controlling both the ferroresonance overvoltage and fault current. [ABSTRACT FROM AUTHOR]

Thyristor‐based line‐commutated converters (LCCs) are widely used to achieve AC/DC and DC/AC power conversions in UHVDCs (ultrahigh‐voltage direct currents) transmission. Valve saturable reactors are used to protect power thyristors. To improve the efficiency of bulk electricity transmission over long distance, the operating voltage and current of UHVDCs and therefore the thermal stresses applied to the valve saturable reactors have steadily increased over the last decades. Valve saturable reactor iron losses were studied by accounting for the reverse recovery characteristics of the valve thyristors and the non‐linear characteristics of the saturable reactors. The impact of UHVDC current on valve saturable reactor iron losses was quantified and verified. The valve saturable reactor iron losses of an LCC are generated not only at the turn‐on and turn‐off periods of the valve, but also at the off‐state of the valve. The amount of the losses are affected by the AC busbar stray capacitances of the converter, the valve firing and extinction voltages, the rates of change of valve commutation current, and the reverse recovery current of the valve thyristors. The conclusion obtained will help to understand better the forming mechanism of valve saturable reactor iron losses and optimise the valve saturable reactor design. [ABSTRACT FROM AUTHOR]

This study is aimed at calculating the discharge onset voltages and power loss of the AC discharge using the charge simulation technique in a wire‐cylinder reactor with a dielectric barrier at atmospheric pressure and room temperature. The calculation of the discharge onset voltages is based on the criterion of self‐sustained growth of onset streamers and Trichel pulses in positive and negative half cycles, respectively. The emission of ions (space charges) from the wire surface is assumed to take place when the magnitude of the surface charge exceeds the corresponding onset values based on pre‐defined discharge onset voltages for both positive and negative half cycles. The space charges are displaced by the prevailing electric field until accumulated on the glass surface. Discharge power loss corresponds to the energy required for the displacements of emitted space charges. The calculated values of the discharge onset voltage and power loss agreed reasonably with those measured experimentally. [ABSTRACT FROM AUTHOR]

We have developed a loss estimation method that is applicable to three-phase ac reactors using amorphous cores in a 400-kVA UPS. The method is based on measured the B-H curves and iron losses of the cores, modeled with magnetic simulations of a finite-element method considering the directions of the amorphous ribbon planes. The reactors are formed from wound cores. Two types of magnetic legs are proposed: structure A, toroidal-shaped with slits, and structure B, sector prism-shaped cut from a wound core. Their unit volumes are shrunk by 9% and 19%, respectively, compared with that of a conventional silicon-steel core reactor. Both reactors have about half the total losses of the conventional silicon-steel core reactor, resulting in increased UPS efficiencies of up to 0.55%. The calculated iron losses at the pulse width modulation (PWM) carrier frequencies agree with measured losses within 10%. The accuracy of the loss estimation method for PWM-induced reactors is discussed. The method is confirmed to enable accurate design of a reactor for filtering in a high-efficiency inverter system. [ABSTRACT FROM AUTHOR]

We demonstrate a ldquotrading time for signalrdquo approach for the measurement of species-specific optical transmission, in ambients rich in particulates, using the example case of a turbulent fluidized bed reactor. The method is introduced on the basis of Monte Carlo simulations, as well as analysis of experimental data, of beam propagation for a range of path lengths, and particle concentrations. In a particular embodiment for relative propane-concentration measurements, data is acquired only during gated time intervals of partial beam occlusion detected in real time. The digitized data streams from the signal and background beams is processed by algorithms performing gating, digital balanced detection, and dual wavelength ratiometry. This combination, implemented on inexpensive programmable hardware, results in at least an order of magnitude improvement in sensitivity. [ABSTRACT FROM PUBLISHER]

Transients caused by shunt reactor switching have been an important parameter in the design of the relevant equipment (reactor, circuit breaker, insulation) of the Hellenic-Interconnected Power System. Next to the well-known damaging overvoltages produced by shunt reactor de-energization, high dc components of inrush currents with low damping factor have been observed during energization, resulting in excessive electromagnetic stresses to the windings and undesired activation of zero-sequence current relays. In the present study, inrush currents produced by shunt reactor energization are analyzed and the performance of the techniques used for their limitation is investigated. [ABSTRACT FROM PUBLISHER]

A simplified magnetic field model for large air-core reactor coils is proposed. It uses three flexible magnetic dipoles with their numbers of turns and positions flexible. The magnetic flux density was calculated along 5 typical traverses for three different types of coils. At designated field points, close to the coil, the calculation error of the proposed model is less than 5%. The three flexible dipole model proposed is not only simple and easy to be implemented but also gives satisfactory accuracy in the regions of practical interest. It can be applied easily to the calculation of the three dimensional power frequency magnetic field distribution of substations. [ABSTRACT FROM PUBLISHER]