Showing papers by "Surya Santoso published in 2011"

Dynamic models for wind turbines and wind power plants

Abstract: The primary objective of this report was to develop universal manufacturer-independent wind turbine and wind power plant models that can be shared, used, and improved without any restrictions by project developers, manufacturers, and engineers. Manufacturer-specific models of wind turbines are favored for use in wind power interconnection studies. While they are detailed and accurate, their usages are limited to the terms of the non-disclosure agreement, thus stifling model sharing. The primary objective of the work proposed is to develop universal manufacturer-independent wind power plant models that can be shared, used, and improved without any restrictions by project developers, manufacturers, and engineers. Each of these models includes representations of general turbine aerodynamics, the mechanical drive-train, and the electrical characteristics of the generator and converter, as well as the control systems typically used. To determine how realistic model performance is, the performance of one of the models (doubly-fed induction generator model) has been validated using real-world wind power plant data. This work also documents selected applications of these models.

Time-Domain Modeling of Tower Shadow and Wind Shear in Wind Turbines

Abstract: Tower shadow and wind shear contribute to periodic fluctuations in electrical power output of a wind turbine generator. The frequency of the periodic fluctuations is 𝑛 times the blade rotational frequency 𝑝, where 𝑛 is the number of blades. For three-bladed wind turbines, this inherent characteristic is known as the 3𝑝 effect. In a weak-power system, it results in voltage fluctuation or flicker at the point of common coupling of the wind turbine to the grid. The phenomenon is important to model so as to evaluate the flicker magnitude at the design level. Hence, the paper aims to develop a detailed time-domain upwind fixed speed wind turbine model which includes the turbine's aerodynamic, mechanical, electrical, as well as tower shadow and wind shear components. The model allows users to input factors such as terrain, tower height, and tower diameter to calculate the 3𝑝 oscillations. The model can be expanded to suit studies involving variable speed wind turbines. Six case studies demonstrate how the model can be used for studying wind turbine interconnection and voltage flicker analysis. Results indicate that the model performs as expected.

Distribution fault location using short-circuit fault current profile approach

Abstract: Impedance-based algorithms do not consider load current and non-uniform line impedance per unit, thus introducing errors in fault location estimates. To minimize these errors, this paper proposes a short-circuit fault current profile approach to complement impedance-based algorithms. In this approach, circuit model of the distribution feeder is used to place faults at every bus and the corresponding short-circuit fault current is plotted against reactance or distance to fault. When a fault occurs in the distribution feeder, fault current recorded by the relay is extrapolated on the current profile to get location estimates. Since the circuit model is directly used in building the current profile, this approach takes into account load and non-uniform line impedance. The approach is tested using modified IEEE 34 Node Test Feeder and validated against data provided by utilities. Location estimates are within 0.8 miles of the actual fault location when the circuit model closely represents the distribution feeder.

Effect of load current on fault location estimates of impedance-based methods

Abstract: Impedance-based methods use simple load models to estimate fault location. However loads in a practical system do not conform to the simplified load models leading to an adverse impact on accuracy of estimation. The objective of this paper is to analyze the effect of load current on fault location estimates of the Takagi, positive-sequence reactance and loop reactance methods. The derivations of the three methods are presented paying special attention to load modeling. The methods are then used to conduct fault location analysis on a modified version of the IEEE 34-Node Test Feeder. The analysis is repeated using the long and lightly loaded original test feeder. When these feeders operate under no-load conditions, fault location estimates of all three methods are highly accurate. Increase in level of load current on both feeder conditions does not affect the accuracy of the Takagi and positive-sequencereactance methods severely. They can be used to locate faults under light-load and heavy-load conditions on short as well as long feeders. The loop reactance method gives highly erroneous estimates when load current magnitude is increased.

Quantifying short-term wind power variability

Abstract: Quantifying wind power generation variability is essential to power system operators, since wind variability has a significant effect on the system operating reserve requirements. An underestimation of these requirements can severely affect the reliability of the system. Moreover, quantifying wind power generation variability, regardless of its uncertainty, can provide important characteristics a generator must have so as to accommodate wind fluctuations. The purpose of this paper is to provide a new metric to characterize short-term variability of wind power generation or any other source. The new metric estimates the size of the interval within which the variable source's output values lie over a desired time frame, irrespective of the output's forecasting error levels. A case study exposes the shortcomings of the prevalent variability metric used in power systems, which is based on the spread of the variable source's output step-changes over various time frames. The comparison of the two metrics using real wind generation and demand data reveals that the proposed metric can effectively capture wind variability, and is capable of accommodating demand variability for up to 20.87% more instances.

Fault location using impedance-based algorithms on non-homogeneous feeders

Abstract: Impedance-based algorithms like the positive-sequence reactance and Takagi methods are derived assuming a homogenous line conductor. This assumption is violated in practical distribution feeder circuits. The objective of this paper is to demonstrate that these methods can still be effectively applied to non-homogenous feeders by using the line parameters of the most commonly occurring conductor type in the circuit. This approach is first tested on a modified IEEE Test Feeder by simulating two cases, namely, the reference case and the case with a homogenous feeder. For the positive-sequence reactance method the maximum absolute error in both cases is about 8%, while for the Takagi method it is 6.92% and 9.53% in the homogenous case and reference case, respectively. The proposed approach is then demonstrated using ten fault cases on utility distribution feeders. The average absolute error obtained for the positive-sequence reactance and Takagi estimates is 10.23% and 9.34%, respectively, which corresponds to a median error value of 0.16 miles and 0.15 miles in the location estimates.

Dynamic modeling of short-circuit behavior of a six-pulse rectifier

Abstract: Existing models describing the dynamic behavior of a six-pulse rectifier during a short-circuit fault condition are derived from switch models using average value parametric functions. Unlike these models, new non-parametric dynamic models have been developed using analytical average-value modeling approach. In this modeling approach, depending upon the number of switches conducting during a switching cycle, the operating point of the rectifier is brought into one of three modes of operation of a six-pulse rectifier. The model for each mode is represented by a differential equation and the operating model is selected based on firing angle and overlap angle functions derived in this paper. They completely characterize the dynamic behavior of current flowing through the DC inductor for a wide range of operating conditions with the exception of harmonics and asymmetrical currents which are dominant for faults occuring at the terminals of the rectifier upstream of the smoothing inductor.

Dynamic model for full-converter wind turbines employing permanent magnet alternators

Abstract: Permanent magnet alternators are gaining ground in the wind turbine market due to their low maintenance requirements and suitability for offshore applications. This paper describes the development and testing of a dynamic model for full converter wind turbines employing permanent magnet alternators. The model described here is not proprietary and is a generic, manufacturer-independent model with no restrictions on its use. It can be implemented in any dynamic modeling software. Detailed representations of the wind turbine aerodynamics, mechanical drive-train, permanent magnet alternator, power converters and controllers are employed. This paper also includes details of model testing, as well as a description of the model's response to an event in the dynamic time scale.

Power quality event processing and analysis modules: Capacitors and their circuit switchers

Abstract: Event processing and analysis modules for evaluating the health conditions of transmission capacitor banks, their circuit switchers used to energize and de-energize them, and the power system condition following the energization for any evidence of significant increase in the harmonic distortion level or harmonic resonance are developed and implemented. Algorithms are based on those developed over a decade. The paper demonstrates the applications and efficacy of the modules using both simulated and actual capacitor switching event data.