Electromagnetic Transient Characteristics Research Articles

A novel multi‐slice electromagnetic field‐circuit coupling method for transient computation of long‐distance gas‐insulated transmission lines

AbstractAccurate calculation of short‐circuit electromagnetic force is crucial for both mechanical strength check and the optimal design of gas‐insulated transmission lines (GIL). Since the full 3D numerical simulation method is highly time‐consuming, a novel lightweight 2D multi‐slice electromagnetic field‐circuit coupled method for computing transient electromagnetic force is proposed, where appropriate port voltage degrees of freedom (DoFs) are introduced for the solid GIL conductor terminals. When the transient magnetic field equations are combined with the constraint equations of circuit part, including nodal voltage and loop current DoFs, a direct field‐circuit coupling scheme is thus derived. The proposed method can simultaneously consider the effect of interphase‐shunts and ground wires, as well as the skin effect and proximity effect. It can accurately capture the transient electromagnetic characteristics of GIL spanning from several to tens of kilometers under different short‐circuit conditions. The transient electromagnetic forces, as well as the induced voltages and currents of the enclosure, are analysed by the proposed method for both single‐phase and three‐phase enclosed GIL under various short‐circuit conditions. The proposed method has the advantages of high accuracy and lightweight computational cost, and thus it is also suitable for conducting important simulation tasks such as mechanical strength checks during the design optimisation phase of long‐distance GIL.

Transient power equalization control strategy of virtual synchronous generator in isolated island microgrid with heterogeneous power supply

In the parallel supply system of synchronous generator and virtual synchronous generator, the physical structure and control structure of the two kinds of power supply are quite different, and it is difficult to distribute the transient power of the two kinds of power supply evenly when the load changes abruptly. Especially in the case of sudden load increase, virtual synchronous generator bears too much load in the transient process because of its fast adjustment speed, and even causes short-term overload, which makes the capacity of virtual synchronous generator can not be fully utilized. In view of this problem, firstly, the mechanism of transient power uneven distribution of two heterogeneous power sources is explained from the differences of frequency modulation, voltage regulation and output impedance. Secondly, virtual speed regulation, virtual excitation and dynamic virtual impedance are added to the traditional virtual synchronous generator control to simulate the speed regulation characteristics and electromagnetic transient characteristics of the synchronous generator, so as to realize the transient and steady-state power equalization between heterogeneous power supplies when the virtual synchronous generator and the synchronous generator run in parallel. Thirdly, in order to ensure the fast dynamic response characteristics of the virtual synchronous generator in independent operation mode, the traditional virtual synchronous generator control algorithm is still maintained in independent operation mode, and the mode switching control link based on state tracking is designed to realize smooth switching between the two working modes. Finally, the hardware in loop experiment results based on RT-LAB show that the proposed control method can realize the transient and steady-state power equalization when the virtual synchronous generator and the synchronous generator operate in parallel, it can keep the fast voltage regulation and frequency modulation ability when the virtual synchronous generator operates independently, and can realize smooth switching between independent and parallel operation modes.

An investigation of electromagnetic transient characteristics on a practical 500 kV submarine cable system

This paper performs an investigation on electromagnetic transients for a practical 500 kV cable system. The system consists of 500 kV overhead lines, submarine and underground cables. In order to study the insulation coordination of the cable system, the transient simulations are performed using EMTP. The modal propagation constants of submarine cable are also investigated. Moreover, the cable series and shunt parameters are calculated using the newly developed Line/Cable Data Module in EMTP. The voltage and current characteristics of the cable system in steady-state, and for switching, fault and lightning transients, are studied. The transient overvoltage levels are also compared with requirements of insulation coordination in local standards. The work shown in this paper could provide a reference for the insulation design of 500 kV cable system.

Electromagnetic transient characteristics and overvoltage suppression strategy of renewable energy-oriented power system connected by gas-insulated transmission lines

New energy systems, such as wind power and photovoltaic and distributed power supply, in the power generation and grid-connected transmission system basically will use stronger insulation design, higher operational safety, and smaller footprint GIL equipment, while the new energy transmission system of the smart grid development trend requires accompanying the electronic transformer equipment to promote a large area. However, the current GIL equipment used in new energy transmission systems has caused great electromagnetic interference to the electronic equipment due to the compact layout of the equipment and the transient signals generated by normal operation, which has seriously restricted the development of smart grids and became a major obstacle to the grid connection of new energy systems. In order to study the characteristics and developmental law of transient electromagnetic interference signal of GIL equipment in new energy transmission and transformation system, this study proposes a dynamic arc model based on an optimized arc extinguishing criterion, verifies the correctness of the improved dynamic arc model through theoretical analysis, simulates calculation combined with the test measurement data, and compares and analyzes the simulation results with test measurement data to study the transient electromagnetic interference source signal during arc burning duration. The simulation results and test data are compared and analyzed to study the pulse steepness, size of the wave head, and overall waveform development law of the transient electromagnetic interference source signal during the arc burning process. It is concluded that the dynamic arc model based on the optimized arc extinguishing criterion can be better used to study the transient electromagnetic interference signal in the GIL equipment. Meanwhile, the transient electromagnetic interference signal has the characteristics of large amplitude and high frequency, the maximum overvoltage can reach 1.9 p.u., the UHF can reach 30 MHz, and the wave head rise time is about 12 ns. This study provides theoretical support for subsequent research on suppressing transient electromagnetic interference source signals, improving the anti-electromagnetic interference performance of electronic devices, and is dedicated to solving the obstruction problem in the process of grid connection of new energy transmission and substation systems.

Analysis of Electromagnetic Transient Characteristics on the Winding of UHVDC Converter Transformers Based on an Improved Broadband Model

This work proposes an improved broadband equivalent circuit model of the winding system of an ultrahigh-voltage direct current (UHVDC) converter transformer and the validation experiment of the model conducted on a tapped transformer. The matrices of the inductance, capacitance, and resistance parameters in the improved model were all obtained by the finite element method according to the winding system structure of a UHVDC transformer. Then, the potential distributions along the windings under impulse voltages with different waveforms were studied in detail. Finally, the relationship between the potential gradient and waveforms was obtained. This work provides a convenient method to acquire the broadband electromagnetic transient characteristics of the winding systems within UHVDC converter transformers.

Prescribed Performance-Based Adaptive Terminal Sliding Mode Control for Virtual Synchronous Generators

Due to the lack of inertia and damping in the distributed power system with power electronic devices as interface, the stability of the power system will be adversely affected when the distributed power system is connected to the grid. In order to solve the problem of low inertia and improve stability, an adaptive terminal sliding mode control method based on the electromagnetic transient characteristics of virtual synchronous generators is proposed. During the design process, projection operators and parameter adaptive law control methods are introduced to compensate for parameter errors caused by environmental interference. Furthermore, by utilizing a prescribed performance function, the terminal sliding surface of the system will have the desired dynamic response, and variations of the system tracking error can be restricted. Simulation results show that the proposed controller has improved control accuracy and response speed, frequency stability, and power response.

A simplified model of Type‐4 wind turbine for short‐circuit currents simulation analysis

The electromagnetic transient (EMT) model of Type 4 wind turbine generator (WTG) requires a small simulation step, and cannot be simplified based on Thevenin-Norton theorem, which results in the low simulation efficiency of large-scale Type 4 WTG-based wind power plants (WPPs) widely connected to the power grid, bringing challenges to the short-circuit currents analysis in the research of protection. Therefore, in order to solve the problem of low simulation efficiency, a simplified model of Type 4 WTG is proposed based on the principle of internal active power balance of Type 4 WTG. The simplified model is represented by controlled voltage source, which eliminates the power electronic switch and DC-link, greatly simplifies the typical EMT model of Type 4 WTG, and does not require small simulation step. The simplified model has simple modelling process and high universality of modelling method. The simulation results show that the proposed model can accurately reflect the EMT characteristics of Type 4 WTG under fault. Compared with the typical EMT model, the simulation time of this simplified model is significantly reduced, and the EMT simulation efficiency of the power grid connecting with large-scale Type 4 WTG-based WPPs has been effectively improved.

Accurate Modeling Simulation and Experimental Study of Hybrid Multi-Terminal UHVDC Transmission System

This study researches on the Wudongde hybrid multi-terminal Ultra High-Voltage Direct Current Transmission (UHVDC) project (referred to as Wudongde transmission project in short) from the electromagnetic transient model and simulation and establishes an accurate simulation model of the hybrid multi-terminal UHVDC transmission system with the Power Systems Computer-Aided Design (PSCAD). The hybrid multi-terminal UHVDC transmission system consists of the primary system and the control system. The simulation model of the primary system adopts the parameters of the Wudongde transmission project, and the simulation model of the control system refers to the control system benchmark model of HVDC transmission and 9-terminal DC grid in the International Council on Large Electric Systems (CIGRE). According to the characteristics of the hybrid multi-terminal UHVDC control system, the benchmark model of HVDC transmission and 9-terminal DC grid control system in the CIGRE is modified accordingly, and a simulation model of the control system applicable to the hybrid multi-terminal UHVDC transmission system is established. The accuracy and credibility of the model are verified through the comparison of the recording waveform and the simulating waveform of the steady-state and transient operation. The simulating and field recording waveforms show that the model can accurately simulate the Wudongde transmission project and be used as an effective tool for further studying the electromagnetic transient characteristics of the hybrid multi-terminal UHVDC transmission system.

Transient electromagnetic characteristics of coal seams intruded by magmatic rocks.

The intrusion of magmatic rocks into coal seams affects the coal quality and leads to unforeseen hazards in safety of the coal mines’ production. This paper summarizes the mechanism of magmatic rocks intruding into coal seams, depicts the electromagnetic characteristics of the coal seams intruded by magmatic rocks, briefly describes the characteristics of transient electromagnetic method (TEM), and introduces the method of detection by TEM and the data processing steps. Then, the effectiveness of TEM in detecting the ranges of the coal seams intruded by magmatic rocks is theoretically analysed. It is observed that after the intrusion of magmatic rocks in the coal seams, the electromagnetic characteristics (secondary field potential and resistivity) will be dramatically affected, namely high secondary field potential and low resistivity. For experimental verification purposes, this study selects the test project of the Tongxin Minefield in the Datong Coalfield in Shanxi, China as an example, and the accuracy for the detection of the ranges of the coal seams intruded by magmatic rock using TEM is successfully verified.

Research on Losses and Heat Dissipation of Saturable Reactor Used in Converter Valve

Based on the analysis of the principle and structure of a saturable reactor used in a converter valve of HVDC transmission, this paper analyzes its power loss composition and summarizes and derives the power loss equations. According to finite element analysis, the saturable reactor is modeled, its transient electromagnetic characteristics are simulated, and the core loss density distribution is studied. The influence of the cooling circuit and air on the heat dissipation of the saturable reactor is studied. The power loss density obtained by the electromagnetic field finite element analysis is mapped as the heat source to the finite fluid element for thermal simulation in order to obtain the spatial temperature distribution of the saturable reactor. The maximum temperature of the case is about 68.5°C, while the maximum temperature of the iron core is about 87.9°C. The converter valve operation test validates the accuracy of the heat dissipation analysis and temperature field simulation. The research results can serve as a reference for the design of saturable reactors used in converter valves.

Analysis of Transient Operating Characteristics of the 10 Kv Tri-Axial HTS Cable Under Fault Current

The Tri-axial high temperature superconducting (HTS) cable usually subjects to the impact of the fault currents in the power system. During the fault, a large amount of the Joule heat is generated, which may be damage cable. In this paper, an analysis model of electromagnetic thermal transient characteristics of the 10 kV/1 kA cable is built. The transient characteristics of the HTS cable are analyzed under a fault current of 15 kA rms lasting 0.14 s, and the current, resistance and temperature of the HTS cable are obtained. The maximum temperature of the HTS cable is 153.1 K under fault current. Meanwhile, the safe operating range of the HTS cable under the fault current of 15 kA to 25 kA is obtained. the analysis results will provide the theoretical basis for the quench protection and relay protection strategy of the tri-axial HTS cable in the Grid.

Study on electromagnetic transient characteristics of multi-terminal LCC-HVDC with DC circuit breaker

Study on electromagnetic transient characteristics of multi-terminal LCC-HVDC with DC circuit breaker

Simulation Research on Lightning Protection Effect of Distribution Line Lightning Protection Measures

Due to the low insulation level of distribution lines, the electromagnetic transient characteristics of lightning strikes are quite different from those of high-voltage transmission lines; the lightning protection measures used in high-voltage lines cannot be well applied to distribution lines. In order to further understand the various lightning protection measures and the effect of lightning protection measures on the improvement of the lightning resistance level of distribution lines, this paper evaluates the working principles, characteristics, lightning protection effects and existing deficiencies of various lightning protection measures used in distribution lines And using ATP-EMTP software to analyze several kinds of lightning protection measures commonly used in 10kV distribution lines, it has certain reference value for the selection of lightning protection measures of 10kV distribution lines.

Application and Design of Resistive SFCL in ±160 kV MMC-HVdc System

The modular multilevel converter (MMC) high voltage direct current transmission (HVdc) technology plays a great role on multilevel dc systems and large capacity transmission systems gradually. Therefore, the protection for the MMC-HVdc system becomes particularly important, for the impact acreage of dc short faults is wider, and damage is more serious. In this paper, the MMC-HVdc system electromagnetic transient characteristics of fault are analyzed and the superconducting fault current limiter (SFCL) resistance model is established for a resistive SFCL (R-SFCL) during the short fault. The thermal-electrical process of R-SFCL limiting short current is calculated by iteration method. Then, an R-SFCL based on noninductive bifilar pancake is designed for a ±160 kV bipolar MMC-HVdc system. The validity of the theoretical calculation method and design scheme is justified by the simulation in software PSCAD. The results show that the response time of the R-SFCL based on noninductive bifilar pancake is 0.1 ms and the short circuit current suppression rate is 35%-50% in 3-8 ms after the dc short fault.

Adaptive Command-Filtered Backstepping Control for Virtual Synchronous Generators

Distributed energy sources are usually interfaced to the grid using power electronic converters, and lack of inertia in inverter dominated microgrids can affect the system stability. This paper presents a new method for virtual synchronous generator (VSG) control in order to solve the low system inertia and support the grid frequency problem. In this paper, the VSG based on electromagnetic transient characteristics is improved and an adaptive command filter back-stepping controller is designed. Firstly, the rotor swing equation and power part are modeled to complete the controller design for achieving system stability in the islanded, grid-connected and transition modes. In addition, a limited-amplitude command filter is used to deal with computational complexity and nonlinear saturation problems in the design process. Secondly, projection operator, and adaptive inertia and damping control are introduced to reduce the modeling error and disturbance caused by changing parameters. This ensures the boundedness of the estimated value and further improves the frequency response, especially in the transition mode. Finally, simulation results show that the proposed controller is more effective than the traditional control method for achieving power stability and frequency improvement.

A Non-Uniform Transmission Line Model of the ±1100 kV UHV Tower

The modeling of the Ultra-High Voltage (UHV) tower plays an important role in lightning protection analysis of transmission lines because the model used will directly affect the reliability of the results. Moreover, the higher the voltage level is, the more prominent the impact becomes. This paper first analyzes the inapplicability of the Hara multi-segment multi-surge impedance model for the ±1100 kV UHV towers, and then builds a non-uniform transmission line model of the tower. Secondly, the multi-segment multi-surge impedance model is used to study the influence of the tower’s spatial structure changes on its electromagnetic transient characteristics. It is concluded that the more accurately the nominal height of the tower is modeled, the more accurately its electromagnetic transient response is reflected. Finally, the lightning electromagnetic transient responses of the tower with the non-uniform transmission line model and with the multi-segment multi-surge impedance model are compared and analyzed, which shows that the non-uniform transmission line model is more in line with the actual situation under the lightning strikes.

Fault Ride through Strategy for Virtual Synchronous Control based Doubly-Fed Induction Generators

Virtual Synchronous Control (VSynC) strategy for Doubly-Fed Induction Generator (DFIG) has attracted much attention because of its advantages in providing dynamic supports of frequency and voltage. In this way, most researches of VSynC strategy concentrate on analysis of its electromechanical behaviours, but pay little attention to its electromagnetic transient responses and fault characteristics, which may hinder its promotion in engineering application. This paper pays special attention to the electromagnetic transient behaviours of VSynC-based DFIG and proposes a voltage compensation VSynC strategy to implement fault ride through during symmetrical grid faults. The proposed strategy improves the transient response of existing VSynC strategy, capable of limiting the overcurrent in DFIG rotor circuits and suppressing the oscillations of electromagnetic torque. Simulation results validate the effectiveness of the proposed strategy.

A new topology of the distributed power flow controller and its electromagnetic transient characteristics

In this paper, the modular multilevel converter (MMC) is introduced into the shunt side of the distributed power flow controller (DPFC), and a new topology of distributed power flow controller is constructed. The mathematical models are developed, in these models the internal energy relationship between the MMC module and the single-phase converter in the shunt side, as well as between the shunt-side single-phase converter and series-side single-phase converter are considered, and the corresponding control strategies are proposed based on the mathematical models. The internal electromagnetic transient characteristics of the MMC based DPFC are studied in PSCAD/EMTDC. The simulation results show that the MMC based DPFC is able to adjust the control variables such as voltage amplitude, phase angle and line reactance of the power system individually or simultaneously, and also the DPFC is able to respond to the power flow regulation demand effectively.

Research on Electromechanical-electromagnetic Hybrid Modeling and Simulation of UHVDC in Jilin Power Grid by ADPSS

In order to accurately analyze Jilin power grid with UHVDC, this paper builds the electromagnetic transient model of Jilin HVDC system and the electromechanical model of the rest of Jilin power grid based on the winter heavy load of Jilin power grid in 2018 with full digital real-time simulation platform power system. Based on the electromechanical- electromagnetic hybrid model built up, the steady state simulation of Jilin HVDC is carried out. The transient simulation results of electromechanical transient model and electromechanical-electromagnetic hybrid model are compared in the case of bipolar blocking. The simulation results show that the electromechanical electromagnetic hybrid model can effectively reflect the electromagnetic transient characteristics of the UHVDC transmission system in Jilin, and is suitable for studying the very complex and fast transient process in the DC system. The hybrid simulation model lays a foundation for the study of the impact of Jilin UHVDC.

Virtual Transient Flux Linkage Control of Doubly Fed Induction Generator Under Symmetrical Grid Fault

The overcurrent and overvoltage of the rotor side converter are mainly caused by the transient component of the stator flux under the grid symmetrical fault. A virtual transient flux linkage control method is proposed in this paper, which is based on the analysis of the electromagnetic transient characteristics of doubly fed induction generator (DFIG). Compared with the traditional demagnetization control method, the proposed method does not require the flux linkage observation, extraction and fault switch module. Simulation results show that the rotor voltage could be effectively limited and the transient process can be shortened, and the capability of low voltage ride through (LVRT) of the DFIG is enhanced with the proposed method.