Electromagnetic Transient Simulation Program Research Articles

Power Loss Modeling of Individual IGBT and Advanced Voltage Balancing Scheme for MMC in VSC-HVDC System

This paper presents the new power dissipation model of individual switching device in a high-level modular multilevel converter (MMC), which can be mostly used in voltage sourced converter (VSC) based high-voltage direct current (HVDC) system and flexible AC transmission system (FACTS). Also, the voltage balancing method based on sorting algorithm is newly proposed to advance the MMC functionalities by effectively adjusting switching variations of the sub-module (SM). The proposed power dissipation model does not fully calculate the average power dissipation for numerous switching devices in an arm module. Instead, it estimates the power dissipation of every switching element based on the inherent operational principle of SM in MMC. In other words, the power dissipation is computed in every single switching event by using the polynomial curve fitting model with minimum computational efforts and high accuracy, which are required to manage the large number of SMs. After estimating the value of power dissipation, the thermal condition of every switching element is considered in the case of external disturbance. Then, the arm modeling for high- level MMC and its control scheme is implemented with the electromagnetic transient simulation program. Finally, the case study for applying to the MMC based HVDC system is carried out to select the appropriate insulated-gate bipolar transistor (IGBT) module in a steady-state, as well as to estimate the proper thermal condition of every switching element in a transient state.

Fault location on transmission lines little longer than half-wavelength

AC transmission lines little longer than half-wavelength have been widely investigated as an alternative for bulk power transmission in power networks where the generation plants are very distant from the load centers. However, studies regarding the performance of fault location methods applied to this type of line have not been done. In this paper, two contributions are presented. First, it is shown that conventional impedance-based fault location methods may fail to correctly identify the fault point even when the line shunt capacitance effect is taken into account. Then, to overcome this drawback, an innovative two-terminal impedance-based fault location algorithm is proposed. The algorithm considers the distributed parameter line model with line shunt capacitances thereby is able to reliably identify and correct erroneous fault point estimations that arise due to atypical operational features of this particular type of transmission line. The performance evaluation of the proposed algorithm is carried out by means of Electromagnetic Transients Program (EMTP) simulations, from which a wide variety of faults in a 1000kV AC transmission line 2613km long is analyzed. The obtained results indicate high reliability of the proposed algorithm, which is almost insensitive to the fault characteristics, power system load flow, power factor and line transposition schemes.

Analysis of Induced Voltage on Telecommunication Line in Parallel Distribution System

A current flowing through a distribution conductor produces induced voltage, which is harmful to a telecommunication line. Previous research on induced voltage has been focused on single- circuit lines in the distribution system. However, the double-circuit lines, referred to as parallel distribution lines, are widely used in distribution systems because they have significant economic and environmental advantages over single-circuit lines. Therefore, a study on the induced voltage in double-circuit lines is needed. This paper presents a method of calculating the induced voltage in a parallel distribution system using four-terminal parameters and vector analysis. The calculation method is verified by the Electromagnetic Transient Program (EMTP) simulation.

Probabilistic evaluation of failure risk of transmission line surge arresters caused by lightning flash

Transmission line surge arresters (TLAs) are vital elements for protection of power networks against the lightning surges. The proper selection of TLAs leads to a reduction of the lightning-related outages as well as the costs imposed to the power utility, because of the undelivered energy and damage to the equipment. The selection of the optimal arrester depends on how well its stresses can be estimated. Although a ground flash very frequently consists of multiple strokes, it is usual to consider only a single lightning stroke to calculate the lightning-related failures. A probabilistic method is presented for risk calculation that considers multiple strokes of each lightning flash to estimate the annual outage rate of TLAs. In the presented method, once the equivalent wave of the flash is computed, the probability of arrester failure is estimated by means of two indices, including total charge and maximum energy stress by the flash, separately. The energy stress caused by the flash is calculated using a few electromagnetic transient program (EMTP) simulations. Then, the obtained results from EMTP simulation are utilised to estimate the probability of failure. The accurate evaluation of failure probability of arresters permits the power utility to select the optimal arresters, considering a desirable average life.

Detection of Electromechanical Wave Propagation Using Synchronized Phasor Measurements

Abstract Considering electrical network as a continuum has become popular for electromechanical wave analysis. This paper reviews the concept of electromechanical wave propagation. Analysis of large number of generator ring system will be an easy way to illustrate wave propagation. The property of traveling waves is that the maximum and minimum values do not occur at the same time instants and hence the difference between these time delays can be easily calculated. The homogeneous, isotropic 10 generator ring system is modeled using electromagnetic transient simulation programs. The purpose of this study is to investigate the time delays and wave velocities using Power System Computer Aided Design (PSCAD)/Electromagnetic Transient Program (EMTP). The disturbances considered here are generator disconnections and line trips.

Particle-Swarm-Optimization-Based Nonintrusive Demand Monitoring and Load Identification in Smart Meters

Compared with the traditional load monitoring system, a nonintrusive load monitoring (NILM) system is simple to install and does not need an individual sensor for each load. Accordingly, the NILM system can be applied for wide load monitoring and become a powerful energy management and measurement system. Although several NILM algorithms have been developed during the last two decades, recognition accuracy and computational efficiency remain as challenges. To minimize training time and improve recognition accuracy, particle swarm optimization is adopted in this paper to optimize parameters of training algorithms in artificial neural networks. The proposed algorithm is verified through the combination of Electromagnetic Transients Program simulations and field measurements. The results indicate that the proposed method significantly improves recognition accuracy and computational efficiency under multiple operation conditions.

External Network Equivalent of Wind Power Simulation for Fu Jian

In recent years, there was a rapid development of wind power. The impact of large amount of wind power integration into power system on the voltage and power quality could not be ignored. The characteristic of internal dynamics of wind turbine was complicated, as a result, it could not be simulated by electromechanical transient simulation soft (BPA). It was necessary for transformation from BPA to PSCAD which was electromagnetic transient simulation program. However, the modeling work for the external power grid was enormous and meaningless. In this paper, external network was equivalent based on the BPA data of actual grid combined with PSCAD. This method not only could simulate the influence both simple and effective, but also could establish the detailed model of the regional power grid and wind power. At the same time it has been effectively used in the analysis of wind power integration into actual wind projects of Fujian power grid which achieved very good results.

Series-Compensated Double-Circuit Transmission- Line Protection Using Directions of Current Transients

This paper presents the development of a new protection method for series-compensated double-circuit transmission lines using current transients. Using the proposed method, the faulted circuit can be identified locally, by comparing the polarities of wavelet coefficients of the branch currents. Applicability of the proposed method is demonstrated using a 500-kV transmission system simulated in an electromagnetic transient simulation program. Comparisons with the conventional distance and phase comparison protection schemes show that the proposed method can provide faster and more reliable protection for the series-compensated double-circuit transmission systems. The security of the relay can be further enhanced if the fault direction information is exchanged between the relays at two ends.

A Traveling-Wave Detection Method Based on Park's Transformation for Fault Locators

A novel algorithm for transient detection based on Park's transformation is proposed. It is very simple, self-adapts to electrical noise and phase imbalances, and is appropriate to be used in connection with traveling-wave fault location (TWFL) methods. The proposed technique is evaluated through Electromagnetic Transients Program simulations. A 230-kV transmission system case study is carried out, in which power system voltage and current waveforms are picked up one sample at a time. It is shown that the method is very reliable and suitable for multiterminal TWFL algorithms.

Adaptive distance protection of transmission line in presence of SVC

In this paper, the analytical and simulation results of the application of adaptive distance protection scheme for the transmission line incorporating Static Var Compensator (SVC) connected at the mid-point is presented. The mal-operation of the distance protection for the transmission line with SVC at various locations are studied. The simulation results show the under-reaching and over-reaching is more severe with SVC at mid-point of the transmission line. To mitigate the mal-operation of the distance protection, the adaptive scheme is presented based on recursive simulation study. The simulation result with adaptive scheme is outperformed as compared with the conventional scheme. Electro-magnetic Transient Program (EMTP) simulations on two machine system is used to substantiate the claim.

Switching Capacitor Bank Back-to-Back to Underground Cables

This paper addresses the capacitor bank switching back to back to underground cables. The high currents recorded during the capacitor bank switching occur due to the traveling waves in the underground cables. The detailed analytical study of the capacitive inrush currents is done. The closed-form expressions of the inrush current waveforms due to the initial current surges as well as due to the superposition of the initial and reflected current waves are derived. The formulas for the peak inrush current and its maximum rate of rise are obtained. The case study of the 24-kV capacitor bank switching back to back to the underground cables is described. The results of the field measurements are compared with the results of Electromagnetic Transients Program simulation. The dependence of the inrush current peak on the number of the cables, and the equivalent inductance between the capacitor bank and the substation busbar as well as on the cable length are analyzed. The inrush currents caused failures of the capacitor bank circuit breakers. Since the described capacitor inrush current significantly exceeds the “inrush current of the isolated capacitor bank,” the selection of the capacitor bank switchgear should be taken into account.

Optimal Deployment of Wide-Area Synchronized Measurements for Fault-Location Observability

This paper considers the problem of strategically placing a minimum number of synchronized measurements in a transmission system so that faults can be detected and identified irrespective of their locations. The proposed solution is based on a fault-location method which was developed and documented in an earlier paper by the authors. Hence, it is intended as an extension of the previous work to facilitate its efficient implementation via optimal sensor placement. The paper will first provide a brief review of the fault-location method and will then describe the optimal deployment scheme for placing synchronized voltage sensors in the transmission system. Simulated fault transients by an electromagnetic transients simulation program will be used to illustrate the performance of the developed technique.

Time Domain Transformation Method for Accelerating EMTP Simulation of Power System Dynamics

Electromagnetic Transients Program (EMTP) is widely used in power system dynamics studies. However, in most cases EMTP is found inadequate for dealing with the realistic size power systems due to the small time step resulting in relatively slow simulation speeds. To accelerate the EMTP simulations of power system dynamics, a novel frequency-adaptive methodology is proposed. In this method, a new transformation is presented. The properties of the transformation and the numerical solutions based on the transformation are discussed. The component models obtained by discretizing the differential equations at the branch level are also given which are convenient for EMTP implementation. The proposed method allows using large time steps without sacrificing accuracy, which greatly improves the simulation speed. To validate the proposed methodology, a general program has been developed. Furthermore, various case studies substantiate the claims and demonstrate the application of the method.

Power System Subsynchronous Oscillations Electromagnetic and Electromechanical Transient Hybrid Real-Time Simulation Based on RTDS

In this paper, power system electromagnetic and electromechanical transient hybrid real-time simulation technology is expounded in details, which has advantages of the electromagnetic transient simulation program and electromechanical ones. The more details needed to analyze the dynamic characteristics of power systems are provided by this hybrid simulation technology, and the scale of power system simulated is not limited in the hybrid simulation program. The hybrid simulation program is applied to analyze the power system subsynchronous oscillation problem occurred in a power plant with 4 turbine generators located in the northwestern China. According to the simulation results, it is clear that the stability of generators is threatened by the subsynchronous oscillations caused by capacitor series compensation in the transmission line connecting the power plant and the load center system. In meantime, the effectiveness of the countermeasure is validated simultaneously by the hybrid simulation results.

Development and Hardware Implementation of a Fault Transients Recognition System

This paper presents the development and hardware implementation of a classification scheme to distinguish the transients originated by faults from other types of transients. In the proposed scheme, a set of Hidden Markov Model-based classifiers is employed to recognize the fault transients. Input features for the classifiers are the energy contained in wavelet coefficients of the measured current waveforms. A laboratory prototype of the fault recognition system was implemented on a floating-point digital-signal-processor (DSP)-based hardware platform. The classification system was tested using the transient signals generated by a real-time waveform playback unit. The test waveforms were generated by simulating an actual extra-high-voltage transmission system on an electromagnetic transient simulation program. The operation of the classification system was further verified using waveforms obtained from an actual fault recorder. The performance of the classifier was investigated under different practical scenarios, such as current transformer saturation, measurement noise, and lightning faults.

Initial Voltage Change on Capacitor Switching

This letter presents field measurements of capacitor switching transients with initial bus voltage changes different from widely used assumptions. Instead of being pulled toward zero in all three phases, initial voltage changes in both directions are seen in grounded capacitor switchings. Electromagnetic Transients Program simulation shows that the reason could be pole spread in breaker closing and mutual coupling between the three phases. The letter suggests that this transient pattern be considered in capacitor switching research.

Integrated D-STATCOM with Supercapacitor Used in IEEE Industrial Distribution System

In this paper, a new control method for DSTATCOM (Distribution STATIC Compensator) applied in IEEE 13-bus industrial distribution system is proposed. The operation of this control method enables D-STATCOM to mitigate every type of voltage distortions caused by Single Line to Ground (SLG), Double Lines to Ground (DLG) and Three Lines to Ground (TLG) faults. This new method is based on two factors; firstly, integrating D-STATCOM and supercapacitor energy storage system and secondly, using of feedback in controller system and determining proportional gain of Proportional-Integral (PI) controller, intelligently. In addition, the 12-pulse DSTATCOM configuration with IGBT is designed and the graphic based models of the D-STATCOM are developed using the PSCAD/EMTDC electromagnetic transient simulation program. As a case study, a 13- bus IEEE industrial distribution system is simulated to verify operation of proposed D-STATCOM.

Design and coordination of a capacitor and on‐load tap changer system for voltage control in a wind power plant of doubly fed induction generator wind turbines

ABSTRACTLarger percentages of wind power penetration into the grid translate to more demanding requirements coming from grid codes; for example, voltage support at the point of connection has been introduced recently by several grid codes from around the world, thus making it important to analyse this control. Voltage control is actuated by reactive power injection, and for a wind power plant of doubly fed generator turbines, reactive power capability can be a challenge, which typically is overcome by installing reactive power compensators. The integration and the interaction between all these reactive power sources and the on‐load tap changer of the main substation transformer need to be analysed and taken into account in the control design.In this paper, a novel coordination and control strategy for capacitor banks and on‐load tap changer for a wind power plant is introduced. The capacitor banks are controlled in such way that the steady‐state usage of the converters for reactive power injection is driven below to a maximum desired value of 0.1 pu. Additionally, the control transients because of the capacitor bank switching are minimized by using a suitable control structure. The tap changer control is coordinated with the plant control to decrease the impact of the capacitors reactive power in the line drop calculation, thus reducing the amount of tap operations and improving the accuracy of the line drop voltage estimation.The coordination of the central controller with the plant components is analysed and tested through electromagnetic transient program simulations. Copyright © 2011 John Wiley & Sons, Ltd.

Location of faults in power distribution laterals using superimposed components and programmable logic controllers

In this study, a digital fault location and monitoring technique using programmable logic controller (PLC) for primary overhead power distribution networks is presented. This technique employs pre- and post-fault current and voltage information along with data from the laterals. By using lateral current data transferred through shielded coaxial cables to the substation, the possibility of multiple fault point locations are eliminated. The effectiveness of this method is verified through Electromagnetic Transients Program (EMTP) simulations.

Fault ride through capability enhancement for self-excited induction generator-based wind parks by installing fault current limiters

This study presents a new technique for improving the fault ride through (FRT) capability of self-excited induction generator (SEIG)-based wind parks by implementing fault current limiters (FCLs) using the electromagnetic transient program simulation program (PSCAD/EMTDC). A non-inductive high-temperature superconducting coil of an FCL is developed comprising its major components, operation control algorithm, sequence of events and fault detection techniques. The test system is adopted with an integrated 80 MW SEIG-based wind park that comprises a static synchronous compensator (STATCOM) at each wind turbine. A novel damping voltage control algorithm for the STATCOM is presented for improving the FRT and damping the power system oscillation. FCLs are installed in series with the high voltage (HV) side of the substation transformers of the wind park. The operation of the FCLs is tested in the proposed system to demonstrate its superior performance for reducing the high fault currents and improving the FRT capability. The system performance is tested in steady-state operation and in response to system contingencies, taking into account the impact of the short circuit ratios on the transient stability margin with and without FCLs. Thereafter, the simulation results are presented to demonstrate the effectiveness of installing the FCLs for improving the FRT and transient stability margin of the wind park.