Showing papers on "Power system simulation published in 1994"

A BCU method for direct analysis of power system transient stability

Abstract: A boundary of stability region based controlling unstable equilibrium point method (BCU method) for direct analysis of power system transient stability is presented. Features distinguishing the BCU method from the existing direct methods are that it consistently finds the exact controlling unstable equilibrium point (UEP) relative to a fault-on trajectory and that it has a sound theoretical basis. Moreover, the BCU method appears to be fast. This method is based on the relationship between the boundary of stability region of a power system and that of a reduced system. The BCU method finds the controlling UEP of the original system via a reduced system whose controlling UEP is easier and cheaper to compute. Effective numerical schemes to speed up the presented method are also proposed. This method has been tested on several power systems with very promising results. Simulation results on a 50 generator, 145 bus system are presented along with a comparison between the results obtained using the BCU method and another existing method. >

Voltage stability analysis using generic dynamic load models

Abstract: This paper investigates the dynamic nature of voltage stability. Using a generic load model representing the dynamic behaviour of aggregate loads, the mechanism of voltage collapse is revealed by examining the interaction of load dynamics with the supply network. The relationship between power flow based static techniques and time simulation based dynamic techniques for voltage stability analysis is established. Guidelines for voltage stability control are developed. >

Ramp-rate limits in unit commitment and economic dispatch incorporating rotor fatigue effect

Abstract: In this study, a rigorous mathematical method is proposed for dealing with the ramp-rate limits in unit commitment and the rotor fatigue effect in economic dispatch An iterative procedure is employed to coordinate the unit commitment and the power dispatch for obtaining an economical solution within a reasonable time The Lagrangian relaxation method is used to generate the unit commitment schedule with relaxed power balance constraints A network model is adopted to represent the dynamic process of operating a unit over the entire study time span, as the required unit commitment schedule can be achieved by searching for the shortest path in the network In order to find the global optimal solution for the economic dispatch problem within personal computer resources, a piecewise linear model is used for thermal units Furthermore, linear programming is used in optimizing the benefits of ramping the units, with low operating cost against the cost of shortening the service life of the turbine rotor In this regard, linear programming is used to dispatch the power generation among committed units by considering a ramping penalty for the fatigue effect in rotor shafts, while preserving the operational constraints of the system as well as the generating units >

Evaluation of reliability worth in composite systems based on pseudo-sequential Monte Carlo simulation

Abstract: This work describes a new methodology for calculating total system interruption costs in composite generation and transmission systems. The proposed approach, called pseudo-sequential simulation, is based on the nonsequential Monte Carlo sampling of system states and on the chronological simulation of only the sub-sequences associated with failed states. Case studies with the IEEE Modified Reliability Test System (MRTS) and a 415-bus system derived from the Brazilian Southeastern region are presented and discussed. >

Synchronized phasor measurements of a power system event

Abstract: The paper describes one of the first field measurements of positive sequence voltage phasors at key system buses during a switching operation at Plant Scherer of the Georgia Power Company. The phasor measurements were synchronized using time transmissions from the Global Positioning System (GPS) satellites. The data show the first ever observation of power swings recorded via synchronized phasors at several points on an integrated power network. Measurements were made on the Georgia Power Company (GPC) system, the Florida Power and Light (FPL) system, and on the Tennessee Valley Authority (TVA) system. The disturbance was also simulated on a stability program. Results of the simulation, and a comparison with the observed field data are also included. >

Real-time EMTP-based transients simulation

Abstract: A computer program has been written for the simulation of power system transients in real time. The program is based on EMTP models and solution techniques optimized for maximum performance in superscalar computer architectures. Timings ranging from 38 to 107 /spl mu/s have been obtained for systems from 18 to 30 nodes using an IBM RISC System/6000 Model 560 workstation. These timings are considered adequate for real-time testing of protective relaying equipment. The program is compatible with existing EMTP data cases. >

Transient stability index from conventional time domain simulation

Abstract: This paper presents a practical and efficient method to incorporate energy analysis into conventional power system time domain transient stability simulation for producing a first swing stability index. The proposed method is a variation of the potential energy boundary source approach, utilizing a numerical transient energy function and a pseudo-fault-on trajectory starting from the dominant potential energy peak point of the postfault system trajectory. The transient stability index not only provides additional insight into the stability studies, but also has the potential of speeding up the stability limit derivation process by reducing the number of program runs. >

Comparison of simulated power system dynamics applying various load models with actual recorded data

Abstract: Time domain stability simulation results using derived load models were compared with corresponding data obtained from transient disturbance recorders to validate the accuracy of the load models. Observations of real and reactive power load responses at primary substations and real and reactive power flows on major trunk lines indicated that using a composite (dynamic and static) load model provides a more accurate representation than other models, and closely matches the actual recorded values from the Taipower System. A severe fault, during which enormous voltage and frequency excursions occurred in the system, was extensively examined considering load rejection due to large voltage drops. >

Price-based ramp-rate model for dynamic dispatch and unit commitment

Abstract: The ramp-rate limits of generators can significantly impact power system operation. As a result, they need to be properly modeled in power system production simulations. This paper presents a price-based ramp-rate model. This model is particularly suited for application to power system scheduling models that are based on dual formulation (i.e. price-based). In this model, the impact of binding ramp-rate limits is reflected via the hourly marginal ramp-rate values ($/MW-Hr) of generators. In the paper, the proposed ramp-rate model is applied to price-based dynamic dispatch and price-based unit commitment. Simple examples are used throughout the paper to illustrate the concept of the proposed model. >

Multi-area unit commitment via sequential method and a DC power flow network model

Abstract: This paper presents a multi-area unit commitment method based on the sequential commitment procedure that resembles "bidding". Instead of the linear flow network representation usually used in multi-area production simulations, the proposed method employs a DC power flow model to represent the inter-area transmission network. In this paper, the proposed method is outlined and illustrated via sample application results. >

Simulation and real-time modelling of space photovoltaic systems

Abstract: A photovoltaic (PV) array simulator consisting of a computer controlled DC power supply producing up to 100 Watts and associated control software was developed to generate real-time current-voltage (I-V) output characteristic curves of space solar power systems (SSPS) under simulated conditions. The control software uses feedback of the output voltage and current to iteratively solve for the correct operating point of any connected load. The main advantage of such a simulator is in its ability to simulate different types and sizes of arrays under any illumination and temperature condition using actual loads, The system will be used to study the short-term and long-term performances of SSPS and to predict end-of-life (EOL) efficiencies. The simulator is a far more cost effective and reliable replacement for flight testing. This research will have future applications in the communication and space industries.

Short term operation and power exchange planning of hydro-thermal power systems

Abstract: This paper considers a unified problem of short-term operation planning and power exchange scheduling of large hydro-thermal power systems including: unit commitment, hydro power plant operation planning, pumped-storage hydro power plant operation planning and scheduling of power exchange with other power utilities. The criterion function is the total variable profit incurred by energy production, sales of energy to the users inside the power system, sales of energy to other power companies and purchase of energy from them, or from other sources. The overall problem is solved using the Lagrangian relaxation method. A decomposition technique is applied to solve the dual (mixed-integer) and primal (continuous programming) problem. Dynamic programming, feasible direction method and linear programming method are used for the solution of subproblems. The results of the application of the method to a numerical example are given. >

Operation of the unified power flow controller as harmonic isolator

Abstract: The unified power flow controller (UPFC) is a tool in the implementation of flexible AC transmission systems (FACTS). It provides for the equivalent of static VAr compensation and series injection using back-to-back force commutated converters. This paper proposes a control strategy to extend UPFC operation to allow for the isolation of harmonics due to nonlinear loads. Simulation results based on the Electromagnetic Transients Program (EMTP) are used to illustrate device performance in a power system environment. Experimental results based on a single phase laboratory implementation verify the proposed control algorithm.

Extensive evaluation of high performance protection relays for the Hydro-Quebec series compensated network

Abstract: This paper reports on an extensive study to compare the performance of 8 preselected high performance power line protection systems on the Hydro-Quebec series compensated network. The paper first presents an evaluation of the commissioning aspects and manufacturing quality of the tested relays. It then describes the simulated network, the relay testing procedure, and the laboratory test results obtained on a modern real time power system simulator. Published results of relay performance on series compensated lines are scarce and this paper provides valuable information for utility protection engineers. A total of 115,000 network disturbances were simulated and recorded on 20 different 735 kV lines; fractional test results for 84,030 cases are presented in the paper. The approach using real time power system simulation proved to be an efficient technique for evaluating protection relay performance. The laboratory test results demonstrated that the two best protection principles to be applied on the Hydro-Quebec series compensated network are those based on current differential and segregated phase comparison. The analysis does not take into account telecommunication requirements or other external constraints. >

A graphical user interface for design, simulation, and analysis of power plant electrical auxiliary systems

Abstract: An interactive graphical user interface (GUI) package for the design, simulation and analysis of a power plant electrical auxiliary system is presented in this paper. The purpose of this package is to assist the engineer in performing nonreal-time, what-if, analysis in an interactive and intuitive environment. The package, AUXSYS, is capable of performing load flow and motor starting simulations. It provides a graphical interface for designing the one-line diagram of the plant and analyzing the output of the simulations. It is currently used for modelling Wisconsin Electric Power Company's (WEPCO) power plant electrical auxiliary systems and is implemented for use on PCs. >

Implementation of the unit commitment problem on supercomputers

Abstract: This paper proposes the application of vectorization and parallelization techniques for solving the unit commitment problem on supercomputers. A modified dynamic programming method which takes full advantage of the vector processors present in a supercomputer is presented. Parallel processing is used to further speedup the computation time. Computer simulation of a 26-unit power system is performed on a CRAY Y-MP2/216 in both scalar and vector codes. The computation time results for the conventional dynamic programming algorithm and modified algorithm are compared to demonstrate the effectiveness of the proposed method. >

Classification of power system disturbances through fuzzy neural network

Abstract: Electric power utilities have launched comprehensive data collection programs to evaluate the power quality problems in their systems. Computerized classification and characterization of the data will help in dealing with voluminous quantities of monitored data. An artificial neural network (ANN) approach with and without a fuzzy system for classifying the disturbances in a power system is developed and tested. The results obtained demonstrate the power of neural networks in classifying the commonly encountered disturbances of sags, swells, waveform distortions, interruptions and impulses and the effect of the fuzzy system on the network. >

Predicting steady-state instability

Abstract: The ability to know how much load can be met and how much power can be sold while maintaining a safe distance from the point of voltage collapse and steady-state instability is of great concern both in the real-time dispatch and during the operations planning and scheduling activities of power systems. This is particularly true in an increasingly deregulated electric utility industry where power systems are, and will be, dispatched within smaller voltage and steady-state stability margins than in the past. The authors describe a new application of REI-Dimo techniques which targets power system operation close to the maximum power transfer capability while maintaining a safe distance from critical states. >

Dynamic simulation studies on electric industrial systems for designing and adjusting load shedding schemes

Abstract: This paper presents the most important results obtained from several dynamic studies performed on industrial power systems, focusing on chemical and petrochemical power systems. The purpose is to determine appropriate load shedding schemes and to establish settings for the related protective schemes, such as the disconnection of transmission links by means of inverse power and underfrequency relays, which divide the system into several isolated subsystems in order to reduce severe load-generation unbalances, while acting together within the load shedding scheme of each subsystem. The simulations required were executed with a transient stability program to determine the dynamic performance of the power system during severe load-generation unbalances. >

The reference active source current for active power filter in an unbalanced three-phase power system via the synchronous detection method

Abstract: This paper describes the method of applying the concept of trigonometrics in the synchronous detection method to measure and calculate the reference active source current in an unbalanced three-phase system for an active power filter. A new approach based on the synchronous detection method is proposed for a three-phase four-wire system to achieve the reference active source current with pure sinusoidal, in-phase to source voltage and no neutral line current. The proposed method is formulated with strong supports of simulation results and test results with circuit hardware implementations. >

A modified benders' decomposition technique for solving large scale unit commitment problems

Abstract: We have presented a modified Benders' decomposition technique suitable for solving multi-period unit commitment problems used for optimizing industrial power plants. The problem is formulated as a large MIP-model, where 0/1-integer variables are used for encoding on/off-states of devices and other non-linearities.

An improved train network simulator

Abstract: This paper presents the capabilities of a new computer program called the Queen's Energy Management Model (QEMM). This new program performs simultaneous calculation of multi-train and network performance characteristics by solving a dynamic power system in which the train loads move as time is incremented. The magnitudes of the loads also vary as the trains traverse the route. Performance characteristics of AC, DC, or combined AC/DC networks can be computed by this program. Results of different simulations performed on the Scarborough ALRT system using different propulsion system models are presented and discussed. >

Power system security with the consideration of economic dispatch

Abstract: Operation of power systems demands a high degree of security to keep the system satisfactorily operating, if it is subjected to a disturbance. On the other hand, systems operation requires attention to economy. In this work, the proposed approach reconciled the possible conflict between dynamic security and economy requirements. Firstly, the pattern recognition technique was used to assess dynamic security. Linear classifiers, that determine the stability of the electric power system were developed and presented. This set of classifiers were added to the other system stability and operational constraints, in the quadratic programming, that has been traditionally used in economic studies. The problem was then formulated to satisfy a secure-economic preventative strategy. This strategy directly presented a solution, that ensured economy and security of the power system. The method has been tested by applying it to two test systems, usually used in the literature. The technique showed ease and applicability to different areas of power system analysis. >

EMTP simulation of an HVDC rectifier operating with a weak AC system

Abstract: The study of the transient performance of an HVDC power converter using EMTP requires detailed modelling of the controls and power system elements. Furthermore, owing to the complexities associated with EMTP, considerable care has to be exercised during simulation. These requirements take on added importance particularly when the HVDC power converter is operated with a weak AC power system. This paper looks at the impact of the gate firing unit, the valve snubber in the power converter model and the initialization technique when operating a rectifier with a weak AC power system. >

Power system simulation equipment

Abstract: PURPOSE:To make it possible to quickly perform a simulation for a power system by efficiently paralleling a portion for solving simultaneous linear equations. CONSTITUTION:With respect to the portion for solving simultaneous linear equations among the simulation calculations for a power system, part of the advance and regression substitution calculations is replaced with the calculations with inverse matrix factors when performing the advance and regression substitution. At first, bus lines are separated to several independent groups in step 51, and advance substitution calculations are made in parallel. Then in step 52, the products of inverse matrix factors and vectors are calculated by parallel processing for each line for the remaining buses. In step 53, buses are separated to groups likewise in step 51 and parallel regression substitution calculations are performed. By paying attention to a resolution passgraph during LU resolution, paralleled by replacing with calculations using inverse matrix factors for the trunk portion of the graph. By doing this, simulation for power system can be performed at a high speed.

Closed-loop identification and tuning for damping of interarea modes

Abstract: An iterative closed-loop identification method is applied to obtain linear models of a power system for use in controller design. Two different probing levels are used for model identification to demonstrate both the underlying nonlinear nature of the power system and the effectiveness of using the closed-loop iterative identification method in the case of large probing inputs. The identified plant models contain non-minimum phase zeros, and controllers are designed using linear quadratic Gaussian theory with partial loop transfer recovery (LQG/LTR). Simulation results are presented to illustrate the robustness of the resulting controller to changes in operating point. >

Short Term Operation of District Heating Systems: An Application of Mathematical Programming

Abstract: This work treats the introduction of rigorous optimisation methods as a decision aid in the short term operation of district heating systems. The conditions for operation of district heating systems are investigated. Arguments for the necessity of a systems model that is capable of handling the discrete nature of the problem are presented. A generic representation of district heating systems, representative for Swedish conditions is established. Subsequently a mixed integer programming modelling framework for the most complex case is developed. The model covers unit commitment and operation of heat storage devices over a time period of one to several days, accounting for minimum load constraints, start-up costs, ramp-rate constraints, common steam headers, and other technical constraints, continuous and logical. The intricate structure of the Swedish system for taxes and emission fees is explicitly included in the model. The non-convexity resulting from the conditions for short term electricity exchange is modelled through the introduction of additional integer variables in order to guarantee global optima. It is also shown how dual information from the solution can be used to asses the economic advantage of storing heat in the network itself. The model is implemented for use in the control room of a major Swedish district heating utility displaying all the possible complexity of the generic system. The main experience from the development and implementation of the model is that the creation of a model is not a limiting factor, but rather the willingness and ability on behalf of the user to exploit the advantages of a systems model.