Identifying linear models from time domain simulations

Arcing horns interrupting fault current is a new type of arcing horns installed on transmission-line towers, which act to interrupt fault current independently within one cycle of commercial frequency. In this paper, we have developed an Electromagnetic Transients Program (EMTP) simulation model of the arcing horns interrupting fault current to ascertain the application effects and devise an installation strategy. The EMTP simulation model can consecutively simulate the entire process, from fault occurrence to fault clearing, by integrating two different kinds of macroscopic arc models, and is capable of dealing with the entire short-circuit current range by taking into account the characteristics of the arc parameters. Finally, we have verified the validity of the EMTP simulation model by comparing simulation and experimental waveforms, and have shown the simulation of current and voltage waveforms in the event of a system fault by using the Japanese Power System Model as an application example of the EMTP simulation model.

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.

Faster calculation methods are desired for electromagnetic transient (EMT) simulation programs, since circuits simulated are becoming increasingly larger and more complex. If there are time-varying and non-linear elements in the circuit to be solved, the solution process requires repeated factorization of the coefficient matrix of the circuit equations. The repeated factorization, which is often called refactorization, significantly increases the computation time. Up to now, the bottom right arranging (BRA) method has been applied for refactorization in EMT simulation programs in order to reduce the computation load. In this paper, the author proposes the use of the varying elements tracing (VET) method, which is one of the refactorization methods proposed for power flow calculations, for an offline EMT simulation program. Using some test circuits, the computation time by the BRA method and that by the VET method are examined, and the following facts are found. In most test circuits, both methods greatly improve refactorization speed, but in some test circuits, the BRA method shows degraded refactorization speed due to increased fill-ins. As for the entire EMT simulation time, the VET method improves the refactorization speed by a factor of 1.6 times at most. On the other hand, the BRA method improves the refactorization speed by a factor of 1.5 times in the best case but degrades it in some test circuits.

The interior overvoltage in the extra-high voltage (EHV) power system determines the equipment insulation and safe operation of the system. At first, the paper expounds the problems brought from the application of traditional fixed high voltage shunt reactor to limit the overvoltage in our national EHV power system. Therefore this paper brings forward a proposition to solve these problems by adopting magnetically controlled shunt reactor. This paper mainly introduces a novel type of controlled shunt reactor: Magnetically controlled shunt reactor (MCR). Then its structure and principle of magnetically controlled shunt reactor is presented. The harmonic distribution characteristics, the voltage-current characteristics, control characteristics and response time of MCR are analyzed successively. Afterwards, this paper takes a 500 kV EHV transmission line from Sanyou to Jingzhou for an example, the line model and MCR model are built up. Based on Electromagnetic Transient Program (EMTP), analysis and numerical simulation has been performed to calculate frequency overvoltage and switching overvoltage in the EHV power system with magnetically controlled reactor. (7 pages)

This study presents a stochastic-based approach to evaluate the probabilistic transient stability indices of a power system incorporating wind farms (WFs). In this context, investigations have been conducted on a hypothetical test system representing a typical power system taking into consideration the uncertainties of the factors associated with the practical operation of a power system, namely fault type, fault location, fault impedance, fault clearing process, system parameters and operating conditions and high-speed reclosing process. The effects of the WF sizes and locations on the overall system stability have been investigated. Moreover, this study presents stochastic models for the wind turbine as well as the spring constant of the reduced two-mass shaft model of the wind generator. The time-domain simulations are obtained using the electro-magnetic transient programme.

Summary form only given. Small signal stability analysis in a power system is typically concerned with electromechanical oscillations. For this purpose, it is adequate to model the transmission system using a constant admittance matrix. For torsional oscillations and HVDC interactions, the frequency of interest is much higher and the constant admittance representation is not sufficient. This paper proposes a hybrid model, which allows the parts of the transmission network in the vicinity of HVDC converters or any other dynamic devices to be modeled with their dynamics and the remaining parts to be modeled as constant admittances. The proposed hybrid methodology for small signal stability assessment is the main contribution of this paper. The proposed methodology is validated against an electromagnetic transient simulation program (PSCAD/EMTDC) using time responses. The proposed model and two other small signal models are compared against each other in the frequency domain using modal analysis.

This paper presents further investigations into using an energy recovery (ER) filter for mitigating harmonic instabilities in integrated AC/DC power systems. For certain system conditions, a low quality factor (Q) filter is desirable and for other conditions a high Q is better. This inspired the concept of a "controllable Q filter" in which the power absorbed in the filter is controllable by electronic means. The controllable Q filter uses an ER link so that this power is recovered. The investigations are conducted through computer simulation using an electromagnetic transient simulation program. The CIGRE benchmark model is selected as the base system. The results show that the controllable Q filter helps the system recover from faults.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Time domain transient stability simulation of large interconnected power systems is becoming increasingly computationally intensive. With the addition of high levels of variable generation that can aggregately ramp over many hours, both the complexity and time horizon for which power system simulations will need to be conducted are increasing. Additionally, extended-term time domain simulation is required to analyze power system security when cascading events across the system span minutes or even hours. Analysis of these occurrences requires modeling power system dynamics over tens of minutes to many hours rather than tens of seconds. Because of the required high computational intensity, there are presently no stability modeling/simulation platforms that combine the needed computational capabilities with the required power system models relevant for representing and analyzing the potential reliability implications of phenomena that occurs over both short- and extended-term dynamic timeframes.

The power system economy and safety demand is likely to force more and more power systems to interconnect. But the power transfer capability in the tie-lines is largely limited by small signal instability. A technique for low frequency oscillation analysis of bulk interconnected power system by combining sparse eigenvalue analysis with Prony method is presented in this paper, which uses Prony analysis to provide approximation of the oscillation modes for initial shift points of the sparse eigenvalue analysis. Based on the result of the sparse eigenvalue analysis, the PSSs that are installed on selected generators to damping the inter-area low frequency oscillation modes; time-domain simulations and sensitivity analysis of the power flow in the tie-line verify their performances. The simulation results of a practical power system demonstrate its effectiveness

95/00500 On the maximum efficiency of transmission lines: Part II

Simulators of the electromagnetic transients program (EMTP) are widely used for the accurate simulation of transients in electric power networks. EMTP simulations are inefficient in representing low-frequency transients whose Fourier spectrum is concentrated on a narrow bandwidth around the carrier frequency of either 50 Hz or 60 Hz as typically found in AC electric power networks. This is because the carrier frequency component is always tracked even if the main interest is concerned with envelope information. Recently it was proposed to modify the EMTP formulation through the introduction of analytic signals and the shift frequency as a novel simulation parameter such that efficient simulation of both high-frequency and low-frequency transients is made possible. The shift frequency allows one to specify by how much the Fourier spectrum associated with the analytic signal is shifted. In the case study presented in this paper, the added value of this technique is illustrated through the simulation of network energization, transitional steady state, and deenergization

Future power systems in terms of Cyber - Physical Energy Systems (CPES) apply the integration of IT and physical processes using local and wide area communication networks. The smart grid is a typical example of the application of CPES and poses additional challenges to the engineering as these networks consist of two components: the power system itself and an underlying communication network applied for transmitting monitoring and control information. Therefore, performance evaluations of CPES need to take into account both networks in detail in order to provide meaningful results. In this paper, we introduce our simulation environment INtegrated co-Simulation of Power and ICT systems for Real-time Evaluation (INSPIRE), which is based on the Hybrid Simulator Architecture [1] and capable of evaluating both power system and communication network within a co-simulation framework. Besides the simulator architecture, we detail our time synchronization approach, which is applied for interconnecting communication and power system simulation. Secondly, we present reference scenarios and configuration settings for the combined simulation system. Finally, we introduce the first performance evaluation carried out using INSPIRE, covering characteristics of the communication network and highlighting the retroactive effects on the power system using an exemplary control algorithm.

This paper presents a study on the state-of-charge (SOC) reference based active cell balancing in real-time. The optimal references of SOC are determined by using the proposed active cell balancing system with the bidirectional DC/DC converters via the dual active bridge (DAB) type. Then, the energies between cells can be balanced by the power flow control of DAB based bidirectional DC/DC converters. That is, it provides the effective management of battery by transferring energy from the strong cell to the weak one until the cell voltages are equalized to the same level and therefore improving the additional charging capacity of battery. In particular, the cell aging of battery and power loss caused from energy transfer are considered. The performances of proposed active cell balancing system are evaluated by an electromagnetic transient program (EMTP) simulation. Then, the experimental prototype is implemented in hardware to verify the usefulness of proposed system.

This paper describes the theory and the modeling technique of a flexible alternating current transmission systems (FACTS) device, namely, unified power flow controller (UPFC) using an Electromagnetic Transients Program (EMTP) simulation package. The UPFC, in this paper, consists of two solid-state voltage source inverters which are connected through a common DC link capacitor. Each inverter is coupled with a transformer at its output. The first voltage source inverter, known as a static synchronous compensator (STATCOM), injects an almost sinusoidal current, of variable magnitude, at the point of connection. The second voltage source inverter, known as a static synchronous series compensator (SSSC) injects an almost sinusoidal voltage, of variable magnitude, in series with the transmission line. This injected voltage can be at any angle with respect to the line current. The exchanged real power at the terminals of one inverter with the line flows to the terminals of the other inverter through the common DC link capacitor. In addition, each inverter can exchange reactive power at its terminals independently. The functionalities of the models have been verified.

Current-limiting reactors are often used in applications where high fault currents encroach or exceed rated fault duties of downstream switchgear. Transient Recovery Voltages (TRV) that develop across the vacuum or SF6 interrupter contacts of the circuit breaker directly in series with the reactor during the interruption of reactor terminal faults can exceed TRV limits published for specific circuit breakers. This situation occurred in an Oil Sands application, where distribution system enhancements and expanded generation to meet process power and steam requirements resulted in overdutied medium voltage switchgear and required installation of a current limiting reactor. Using this case study from the Oil Sand application, this paper will examine transient program modeling techniques associated with reactor-limited fault current interruption and the subsequent TRV response that develops using electromagnetic transients program (EMTP) simulations. These TRV responses, subsequently, are compared to TRV envelopes established by harmonized IEC and IEEE Standards and, where available, manufacturer's breaker lab testing results. In limited cases where the standards or published limits are exceeded, as did occur in this Oil Sands case study, TRV-reduction techniques and the associated practical solutions will be examined. Such practical solutions discussed in the paper include the application of surge capacitors, RC snubber circuits or uprating the breaker to a higher voltage rating.