Wen-Shiow Kao

Modeling and Dynamic Simulations of Doubly Fed Adjustable-Speed Pumped Storage Units

This paper derives the mathematical models of doubly fed adjustable-speed pumped storage units (DFASPSUs) to be utilized in the power system analysis. It adopts the improved induction machine model with ac excitation on the wire-wound rotor as well as the field-oriented control theory for the study and analysis of DFASPSU models. First, the rotor excitation voltage is separated into two components, i.e., the q-axis voltage and the d-axis voltage, so as to control the output active and reactive powers, respectively. Next, a dynamic model of DFASPSU is derived using the swing equation of rotary electric machine and the equation of motion of rotor rotating mass. Finally, computer simulation is carried out to compare its results with practical examples in terms of dynamic characteristics for verifying the correctness of the proposed models.

Load model effects on distance relay settings

The purpose of this paper is to study load model effects on distance protective relay settings in Taipowers transmission system. Five load models have been used in order to explore the effects of load characteristics on relay settings: (1) static ZIP model, (2) dynamic motor model, (3) composite model, (4) PTI IEEE model, and (5) exponential model. The major points of this study include (1) setting of impedance values for the three distance protective relay zones and the protection against loss of synchronicity in the outermost periphery, (2) exploring the effects of load models on impedance angles at the time of distance relay tripping, (3) study whether the load model will cause a malfunction in the distance relay when the system swings due to a sudden change in the power system, (4) analyze the coordination of the blocking time of the out-of-step blocking relay during system power swings, and (5) propose how to select a better load model for accuracy in relay settings.

Study of Solving the Coordination Curve Intersection of Inverse-Time Overcurrent Relays in Subtransmission Systems

This paper presents a practical and effective novel approach to solve the coordination problem caused by the curve intersection of overcurrent relays in subtransmission systems. Based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays, as well as the simulation curve equation for electromagnetic overcurrent relays, lever setting adjustment equations for a selected point on the characteristic curve is derived. Then, centered on the derived equations, a dedicated software program is developed to compute the corresponding relay lever setting with different tap value in order that, passing through the selected point, another curve with the new lever setting is chosen. Finally, assisting with the graphical capability of the commercial ASPEN OneLiner, the proposed fixed-point coordination curve adjustment procedure can completely eliminate the coordination curve intersections. In addition, an actual case of a subtransmission network in Taiwan Power Company is simulated to validate the feasibility of the technique proposed.

Diagnosing Medium Voltage GIS Circuit Breaker by Observing Trip Coil Current with Simulation and Actual Tests

Abstract A few metal clad switchgear (MCSG) trip failures were found in the past two decades and the main causes were found related to the characteristics of operation mechanism. Meanwhile, the characteristics of circuit breaker operation mechanism are related to its trip coil current. Mechanical model and electrical model for trip mechanism of circuit breaker of 23-kV GIS are proposed in this article. Trip coil current with different resist force and shaft gap are simulated with MATLAB. One medium voltage GIS trip coil current under different conditions are measured to make a comparison with computer simulation results. Finally, current patterns are proposed as quick reference data for diagnosing operation mechanism failure.

A Novel Approach to Fast Eliminating the Characteristic Curves Crossing Problem of Relay Coordination in Radial Subtransmission Networks

Abstract A novel approach is presented to solve the coordination problem of overcurrent relays in radial subtransmission networks resulting from the intersection of characteristic curves. Based on the ANSI/IEEE standard characteristic curve equation of digital overcurrent relays, a slope adjustment equation for a selected point on the characteristic curve is derived and then used as the core of a dedicated software program developed to compute the corresponding relay setting with different tap value in order that, passed through the selected point, another curve with steeper slope is chosen and thus able to escape from the crossed position. Finally, with the assistance of the graphical capability of commercial package OneLiner in drawing the upstream and downstream relay coordination curves after adjustment, the curves intersection problem in protection coordination can be readily eliminated. In addition, an actual case of a radial subtransmission network with six buses in Taiwan Power Company is simulated to validate the feasibility of the approach.

Structural planning and implementation of a microprocessor-based human-machine interface in a steam-explosion process application

In this paper, small-scale microprocessor-based human-machine interface (HMI) and programmable logic controller (PLC) standard software libraries are applied to plan, design, implement, and construct models for creating the modular application software. The graphical user interface (GUI) functions used in a specific biomass steam-explosion process, intended to be integrated with the PLC device for HMI, thereby providing excellent GUI-based supervision and control functions. Reviewing these specific case study results, we find that the major advantage is maximum system operating performance at minimum cost. Also, the GUI/HMI operation effectively provides user-friendly and reliable interactions. This GUI/HMI approach is a very cost-effective technique.

Analytical Solution to Harmonic Characteristics of Three-Phase PWM Inverter Using 3-D Modulation Model

The purpose of this article is to analyze the harmonic spectrum of the three-phase PWM inverter drives used in a power system. The analytical methods are based on a 3-D modulation model and double Fourier series (DFS). In this article, with Matlab, we analyzed the harmonic model created by DFS, and used time-domain simulation tools, Pspice and Simulink, to construct the model and simulation of the three-phase DC to AC PWM inverter found in the system. Results show that the harmonics generated by the simulator tools and that generated by DFS method are almost identical, and that the harmonic model constructed by means of the 3-D modulation model proposed is highly accurate.

A novel structural modeling and analysis of VLSI interconnect with an RLC tree network system using a BG/SEBD approach

A practical and effective novel graphical structural modeling and analysis approach is presented. This approach is used for solving the state interactions modeling problem caused by the model approximations in VLSI interconnect for RLC tree network systems. The bond graph (BG) energy model with a simulink energybased block diagram (SEBD) algorithm is developed. The dynamic behaviors of an example of VLSI interconnect with a 20th-order RLC tree are presented. Methods of sequent structuring and the delineation of dynamic interactions can be provided for users applying the BG/SEBD algorithms in the development of structural models. It is shown that the new BG/SEBD structural modeling approach requires neither mathematical higher-order reduction nor physically based model reduction. Therefore, useful information can be extracted from the BG/SEBD representation of physical RLC tree network systems. Both time-domain and frequency-domain simulation results are applied to analyze the dynamic response of energy-storing elements using BG/SEBD algorithm combined with Matlab/Simulink software. Finally, a causal analysis of the system zeros plot from the shortest causal path method is proposed, to predict the dynamic response of energy-storing elements and the system performance for design and verification purposes. The dynamic response outputs from different node points were revealed, and the obtained physical information is significant which suggests feasible directions for design (re-design) improvement toward better overall system performance.

Effect of Load Models on Unstable Low-Frequency Oscillation Damping in Taipower System Experience with and without Power System Stabilizers

This paper uses the eigenvalue analysis approach to observe the impact of load models on an unstable low-frequency oscillation damping, which recently occurred in the Taiwan power system. In order to enhance oscillation damping, the effect of load models on power system stabilizers is also investigated. Three kinds of the derived load models (a dynamic model, a composite model, and an exponential model) based on the component approach with the measured characteristics of power system loads are used in this paper. Time simulation results are used extensively to verify the eigenvalue analysis results with and without power system stabilizers. One set of field test data obtained from the Taiwan power nuclear plant with power system stabilizers is used to determine which load model provides a more accurate result in enhancement of oscillation damping. Depending on the results, the effect of load models on electromechanical oscillation damping with and without power system stabilizers is verified.

Modeling and Simulation in a Electrical Higher-Order RLC Tree Circuit Using Bond Graph/Simulink Approach

This paper applies Bond Graph (BG)/Simulink approach to establish the graphical model and simulation to observe the dynamic behavior in a higher-order tree circuit system. The physically significant energy elements Bond Graph model which can be converted to Simulink energy-based block diagram (SEBD) structure by our developed algorithm. The advantage of a SEBD model used to obtain accurately to investigate dynamic characteristics in the 21(superscript th)-order RLC tree circuit main system. The SEBD algorithm involved neither requires the somewhat complicated order reduction nor adopts the physically insignificant model reduction. The Matlab/Simulink simulation adopted in this paper uses a step function as input signal that join to the tree circuit main system, and three various kinds of load as subsystems which to link with circuit main system, and analyze the magnitudes of voltage and current state variable for every energy storage element. Results from the simulated analysis can then be used to predict the dynamic performance and time-domain trend analysis of the whole system.