Search

This paper describes a procedure for calculating generator circuit breaker duty. Currently, commercially available software products help in determining the duty for a general-purpose circuit breaker. However, further calculations are needed to determine the duty for a special-purpose generator circuit breaker. IEEE Std C37.010-1999 provides the calculation procedure for general-purpose circuit breakers. In order to evaluate a special-purpose generator circuit breaker, this paper will expand the steps and methodology used in IEEE C37.010-1999 by presenting a procedure and detailed calculations for finding a duty multiplication factor based on the test $X/R$ ratio of generator circuit breakers given in IEEE C37.013-1997 (Standard for AC High-Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis). This way, engineers can still make a generator circuit breaker assessment although generator circuit breaker evaluation module is not included in many commercial short-circuit programs. [ABSTRACT FROM AUTHOR]

This paper discusses the conceptual design and operation of an isolated power system, recognizing the reality that generator or turbine trips will occur. The level of reserve generating capacity must be set with proper balancing of capital expenditures and operating costs against revenue lost in a production shutdown. The way that reserve capacity is provided is as important as the amount of reserve; seemingly adequate reserve can turn out to be badly insufficient if it is not well distributed across the available reserve sources. The dynamic behavior of reserve capacity, as much as the amount of capacity that is ultimately available, is critical in determining how an isolated facility will behave in the wake of a unit trip or the loss of a grid connection. In this paper, experiences with detailed dynamic simulations of a range of isolated systems are described. These are related to test work and operational incidents that have provided practical calibrations. Based on simulation and experience, some guidelines are offered for configuring generation and selecting strategies for maintaining stability in large, isolated continuous-process facilities. [ABSTRACT FROM PUBLISHER]

Neutral of large unit-connected generators is normally grounded through a large impedance; therefore, a small current passes from a stator phase to ground (PG) fault location. Consequently, locating the fault position cannot usually be performed based on a visual inspection. There are different methods for detecting the stator slot with a PG fault, which have practically been used for many years. These methods have some drawbacks such as further damages to the faulty generator, low accuracy, requiring expensive equipment, and taking long time for detection. This paper introduces a novel strategy for realizing a stator slot with the PG fault which can be used in large generators. This strategy can be easily implemented, and it is able to detect the fault location precisely. Based on this strategy, three different methods are proposed and their performances are investigated using a simulation based on the finite elements method. The simulation results are also verified using comprehensive experimental tests. [ABSTRACT FROM PUBLISHER]

In order to simplify and increase the reliability of wind generators, a new type of a direct-drive directly grid-connected wind generator known as a slip–synchronous permanent-magnet generator (SS-PMG) is proposed. It consists of two integrated generating units, i.e., a directly turbine-connected slip PMG unit and a directly grid-connected PM synchronous generator unit. The main aim of this paper is to determine if this generator is stable under transient wind turbine and grid conditions. A transfer function model is developed to evaluate the dynamic performance of the wind generator system. The transient response of a single 15-kW grid-connected system is evaluated. It is shown that the generator is very stable under transient turbine torque conditions. Furthermore, it acts as a filter to prevent voltage flickering due to oscillatory turbine pulsations. A very important design aspect to take into account is the torque ripple characteristics of the slip PM generator as torque ripple can be transferred to the grid current under certain conditions. Simulated and dynamically measured results are shown for a series of 15-kW SS-PMG prototypes. [ABSTRACT FROM PUBLISHER]

With the advent of power electronics, the size, weight, and cost of power converters have been drastically reduced while efficiency is improved. The use of variable-speed wind power generators has seen considerable growth. The use of gearboxes in the wind turbines allows for smaller size, lower weight, and higher speed generators. However, gearboxes have shown to be one of the least reliable components of the wind turbines. In this paper, we propose a method that can extend the life and reliability of wind turbine gearboxes by reducing the mechanical stress on gearbox components. Reduction of mechanical stress is achieved by the generator torque control that minimizes resonant torsional vibrations within a drivetrain caused by variations in wind velocity. A detailed model for the drivetrain of a 750-kW wind turbine, including a gearbox is presented. Experimental results are used to calculate the parameters of the gearbox. A controller is designed to adjust the generator torque at the end of the drivetrain to remove the unwanted and damaging torque variations from the drivetrain. Simulation results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present an improved model-based controller for power turbine generators (PTGs) on a shipboard grid system. Propulsion can be accomplished by means of main diesel engines. One arrangement for the onboard power requirements of merchant ships is the PTG extract part of the exhaust gas from the main diesel engines. The speed control, however, is difficult to keep in place because of fouling conditions and variations across time. The proposed controller is evaluated by comparing it with the conventional controller in a simulation. Furthermore, the proposed controller is evaluated in a prototype. In the simulation result using the proposed controller, the limit speed overshooting as a transient response is improved by more than 25 \%. In the prototype test, the limit frequency overshooting is 0.60\%, and the settling time is 3.8 s. Hence, the proposed controller is confirmed to have an excellent property. [ABSTRACT FROM AUTHOR]

In this article, a sliding mode control (SMC) is applied to regulate the delivered power of a symmetrical six-phase induction generator. For this, the SMC strategy associated to the field-oriented control strategy is used in order to adjust the inner current loops of a squirrel cage six-phase induction generator (SC6PIG). In this way, the control algorithm switches between positive and negative feedback according to the position of the operating point in the phase plane. This technique guarantees the robustness of the SC6PIG in case of the loss of one to three stator phases or machine converter legs. The switching line slope and the initial operating point have been set so that the system starts with a negative feedback, then it continuously switches back and forth to positive feedback in order to maintain the desired trajectory of the system. The simulation and experimental results demonstrate the effectiveness and the robustness of this technique since the delivered power of the SC6PIG presents the same dynamics in healthy or faulty modes with one to two phase losses. [ABSTRACT FROM AUTHOR]

This work aims to improve the combined flow and thermal network (CFTN) accuracy for radially air-cooled generators by investigating the possible error stemming from the flow part. The nonlinear resistance characteristics of the T-junction dividing flow are first time considered for such cooling arrangement, which is achieved by employing the Gardel equations and the blend equation as the governing equations. Compared with the CFD model results as the benchmark, the nonlinear CFTN predicts an accurate flow rate in the radially extended airducts, making only 9% root mean square (rms) error for all the airducts. On the contrary, the linear CFTN fails to obtain a reliable flow distribution, as the rms error is as large as 34%. As a result, the nonlinear CFTN improves the accuracy of the maximum winding temperature by 6.4% over the linear CFTN and gives a more reasonable temperature gradient in the axial direction. Furthermore, the relative difference between the linear and nonlinear CFTNs is found to be even larger in the following conditions: large cooling air flow rate, wide airgap, low slot fill factor, and large airduct number. The proposed nonlinear CFTN modeling approach is also validated against experimental measurements for a prototype. The modeled temperatures match well with the measurements at different axial positions. According to the aforementioned findings, the nonlinear CFTN modeling approach is considered to be a reliable thermal analysis tool for the radial air-cooling arrangement. [ABSTRACT FROM AUTHOR]

In this study, a characteristic simulation method of a megawatt three-blade horizontal axis wind turbine (MW-THAWT) is proposed based on a laboratory kilowatt low-power motor system, which can realize the parameter correspondence and the rotational inertia compensation between the simulation platform and the wind turbine. First, the virtual proportional THAWT model of MW-THAWT is established to make the parameters of the motor and the wind turbine correspond. The control strategies of speed output and torque output are then designed to solve the problem that the conventional method cannot simulate the unstable region. The dynamic simulation strategy combining the shaft torque feedback rotational inertia compensation method and load characteristic simulation is proposed, which can ensure the consistency of the change time and mode between the simulation platform and the wind power system in the dynamic process. Finally, the MW-THAWT simulation experiment platform based on 1.4-KW motor is developed for theoretical verification. The experimental results verify that the proposed method can realize the characteristic simulation of static and dynamic of MW-THAWT in full speed range and is suitable for industrial production and laboratory research of wind turbine. [ABSTRACT FROM AUTHOR]

This article proposes a mathematical model for a switched reluctance (SR) generator feeding a dc link through a power electronic converter. SR machines are operated in single-pulse mode at close to and above base speed. The SR generator is modeled as a current source, controllable with dc-link voltage $V_{\text{dc}}$ , prime mover speed $\omega _m$ , and switching angles ($\alpha _{\text{on}}$ and $\alpha _{\text{off}}$) of the converter. This current source model is used to predict the dc-link dynamics for constant resistance, constant current, and constant power loads. This is further utilized to derive the voltage build-up condition for an SR generator. The generator model, dc-link dynamics and voltage build-up conditions are validated through simulations and experiments. [ABSTRACT FROM AUTHOR]