Robert J. Harrington

New approach to determine the critical capacitance for self-excited induction generators

This paper presents a new simple approach for computing the minimum value of capacitance necessary to initiate the self-excitation process in three-phase isolated induction generators. The method proposed in this paper is based on the analysis of the complex impedance matrix of the induction generator when loaded with a general inductive load. The advantage of this method is its simplicity since it involves simple algebraic equations and only one equation is solved iteratively to get the value of minimum capacitance. A simple computer algorithm has been developed to predict the minimum value of capacitance necessary for the onset of self-excitation. Using the same approach, the algorithm is modified to predict the minimum value of capacitance necessary to maintain the generator terminal voltage at a preset value under specific load and speed conditions. Computer simulations obtained using the proposed method are compared with those obtained experimentally to confirm the validity and accuracy of the proposed method.

Implementation of a Computer Model to Include the Effects of Corona in Transient Overvoltage Calculations

By means of a previously developed model, the effects of corona on transient overvoltage calculations are presented. The development of a suitable current source model for insertion at critical points along the line and the effects of corona as predicted by the model on 3 phase lines are also demonstrated. Comparison is made with energization studies on EHV lines.

Proposed Methods to Reduce Transient Sheath Voltage Rise in Gas Insulated Substations

Gas insulated substation systems (GIS) are vulnerable to surges which inevitably cause transient sheath voltage rise (TSVR). This paper discusses a mathematical model to simulate short gas-insulated transmission line subjected to internal breakdown during disconnect switch operations and subsequent, restriking of the gap. A formula for the transmitted coefficient of a containment wave guide (CWG) has been developed. A study to investigate the effects of system materials and CWG on TSVR is here presented. It is shown that a combination of CWG and high permeability and resistivLty system material has a, considerable effect in decreasing and damping TSVR. This has important safety and measurement implications.

Performance analysis of energy storage systems connected to a doubly fed induction generator

Wind Energy is a viable source of renewable energy to solve global problems. However, the disadvantage is that wind power is variable, depending critically on wind speed. The simula- tion tool Power System Computer Aided Design/Electromagnetic Transients Direct Current (PSCAD/EMTDC) is used to simulate the model of the Doubly Fed Induction Generator (DFIG) connected to the Energy Storage Systems (ESS). In terms of technical analysis, DFIG which was equipped with the ESS can partly compensate the unstable active power output from the variable wind output power. In addition, this paper analyzed about the performance of Total Harmonic Distortion (THD) for different ESS options such as Super Capacitor ESS (SCESS), Battery ESS (BESS), Two Layer (TL) ESS in the DFIG as 1.5MW ,60Hz under mean wind speed 12 m/s during the 12 second. From the simulation results, The average THD of Hybrid ESS as SC-B ESS, SC- TLESS is the best options to reduce the THD for power quality improvement compared to other ESS options. In terms of economical analysis, the payback time of Battery ESS and Super Capacitor ESS are 3.47 years and 15.76 years respectively. The pay back time of Hybrid ESS is between these two payback time, therefore the system can still be affordable. This paper will provide a better understanding of the performance of different ESS systems, and will be a help for practical applications of ESS in future wind energy projects.

New insights for capacitance requirements for isolated induction generators

This paper presents a simple and accurate approach to compute the capacitance requirements for the self-excitation process in three-phase isolated induction generators. The method proposed in this paper is based on the nodal analysis of the generalized equivalent circuit commonly used in the analysis of the induction generators. The proposed method involves simple algebraic equations and only one equation is solved iteratively to determine the capacitance requirements for the self-excitation process in induction generators. Simple computer algorithms are developed to predict the minimum value of capacitance for all loading conditions. The computer simulations obtained using the proposed method are compared with those obtained by solving the sixth order polynomial to confirm the validity, accuracy and simplicity of the proposed method.

Power management strategy for residential housing connected to the rooftop solar PV

Solar Photo Voltaic(PV) is one of the hottest trends of residential applications due to the increasing concerns about environmental sustainability and adopted feed-in tariffs in many countries. However, rooftop PV generates unstable output due to load variation and solar irradiation due to clouds and rain. To overcome this problem, this paper investigates operation mode control for residential housing which consists of the rooftop solar PV and Battery Energy Storage System(BESS) which could be regulated by a Charging/Discharging Controller incorporated into a power management strategy. It could operate on the DC-AC Converter which depends on the State of Charge (SOC%), real time of resident load, and real time Solar PV panel generation. The proposed strategy not only supports the grid power stability due to demand of the residential house loads but also compensates impacts of solar variations by passing clouds and other causes. This design and simulation output was verified by PSCAD/EMTDC Software.

Image reconstruction in the presence of non-linear mixtures utilizing wavelet variable-dependency modeling in compressed sensing algorithms

In Compressed Sensing (CS) Theory sparse signals can be reconstructed from far fewer measurements than the Nyquist Sampling Limit. Initial Compressed Sensing algorithms implicitly assume that sparsity domain coefficients are independently distributed. Accounting for and exploiting statistical dependencies in sparse signals can improve recovery performance. Wavelets and their theoretical principles, and the structural statistical modeling of dependencies, are applied to improve feature optimization in the presence of non-linear mixtures. Sparsifying Transforms, such as the Discrete Wavelet Transform (DWT), are used for spatial dependencies such as in natural images. This can exploit hierarchical structure and multiscale subbands of frequencies and orientation, exploiting dependencies across and within scales. Bayes Least Squares-Gaussian-scale Mixtures accurately describe statistical dependencies of wavelet coefficients in images, and, therefore, can be incorporated to address dependencies and improve performance. Sparsifying Transforms and Bayes Least Squares-Gaussian-scale Mixtures are incorporated to model and account for dependency characteristics during the coefficient-weight construction of Compressed Sensing algorithm iterations. The resulting accuracy and performance improvements of incorporating wavelets and their theoretical principles, and incorporating the structural and statistical modeling of dependencies, to account for variable-dependencies in image reconstruction algorithms are shown, both quantitatively and qualitatively.

Transient response of interconnected power systems to single line-to-ground faults

An interconnected power system containing synchronous and induction machines has been simulated. The total fault current and the behavior of each machine have been calculated under single line-to-ground fault conditions for a fault time of 500 ms. The negative-sequence torque has been calculated for faulted and unfaulted machines. The results show the importance of the negative-sequence torque in decreasing the rotor swing amplitudes of synchronous machines during the fault period, while it has a deleterious effect on induction motor speeds which tend to run-down such that they may be unable to recover during the post-fault period.<<ETX>>

A proposed numerical solution for the diffusion equation

Both one and two-dimensional diffusion equations are treated numerically, on a purely mathematical basis with the aid of a digital computer. One and two-dimensional models are considered to represent the n-region of a p-n junction. The impurity profile is assumed to be exponential, resulting in drift fields of constant magnitude. In the two-dimensional analysis the already existing one-dimensional theory of the mechanism for minority carriers is extended to respond to the requirements of the boundary conditions. Furthermore, the lateral dimension, and the position of the metal contact are taken into account. A qualitative description of the variation of reverse switching times with the variation of some physical parameters characterizing the models, as well as a rango of possible solutions, are provided.