Innovative planning approaches for generator interconnection group study

Today, a large number of wind generator interconnection requests have been queued and are being processed. The generator interconnection group study is a way to reduce the generator interconnection cycle time and increase interconnection certainty. However, it is very challenging to identify the “best” transmission upgrades for a large group of generator interconnections. It is also very important to differentiate the constraints caused by each generator interconnection request and identify their responsibilities for transmission upgrades. This paper outlines some innovative study approaches that can be used in a group study with large numbers of generator interconnection requests in a constrained area. Improved study methods are introduced, and a summary and conclusions are derived from the study.

Active and reactive power control of synchronous generator for the realization of a virtual power plant

This paper presents a novel power control strategy that decouples the active and reactive power for a synchronous generator connected to a power network. The proposed control paradigm considers the capacitance of the transmission line along with its resistance and reactance as-well. Moreover the proposed controller takes into account all cases of R-X relationships, thus allowing it to function in Virtual Power Plant (VPP) structures which operate at both medium voltage (MV) and low voltage (LV) levels. The independent control of active and reactive power is achieved through rotational transformations of the terminal voltages and currents at the synchronous generator's output. This paper details the control technique by first presenting the mathematical and electrical network analysis of the methodology and then successfully implementing the control using MATLAB-SIMULINK simulation.

Generator coherency and area detection in large power systems

This paper provides a new general approach for defining coherent generators in power systems based on the coherency in low frequency inter-area modes. The disturbance is considered to be distributed in the network by applying random load changes which is the random walk representation of real loads instead of a single fault and coherent generators are obtained by spectrum analysis of the generators velocity variations. In order to find the coherent areas and their borders in the inter-connected networks, non-generating buses are assigned to each group of coherent generator using similar coherency detection techniques. The method is evaluated on two test systems and coherent generators and areas are obtained for different operating points to provide a more accurate grouping approach which is valid across a range of realistic operating points of the system.

Distribution tap changer adjustment to improve small-scale embedded generator penetration and mitigate voltage rise

This paper addresses the voltage rise constraints that are initiated from increased renewable generation resources in low voltage distribution networks. In this paper, an approach which is able to mitigate these voltage rise constraints and allow for increased distributed generator penetration is presented. The proposed approach involves utilizing the distribution transformers static tap changer to reduce the distribution feeder voltage setpoint. The proposed approach is modeled on a generic low voltage distribution network using the PSS SINCAL© simulation software package and is also implemented in a real low voltage distribution network to verify its practicality. Results indicate that this approach can be implemented to mitigate the voltage rise constraint and increase small-scale embedded generator penetration in a high proportion of low voltage feeders while avoiding any substantial network costs.

Higher uptake of long-acting reversible and permanent methods of contraception by Australian women living in rural and remote areas

Objectives: To examine factors associated with the uptake of i) long-acting reversible, ii) permanent and iii) traditional contraceptive methods among Australian women. Methods: Participants in the Australian Longitudinal Study on Women's Health born in 1973–78 reported on their contraceptive use at three surveys: 2003, 2006 and 2009. The participants were 5,849 women aged 25–30 in 2003 randomly sampled from Medicare. The main outcome measure was current contraceptive method at age 28–33 years categorised as long-acting reversible methods (implant, IUD, injection), permanent (tubal ligation, vasectomy), and traditional methods (oral contraceptive pills, condoms, withdrawal, safe period). Results: Compared to women living in major cities, women in inner regional areas were more likely to use long-acting (OR=1.26, 95%CI 1.03–1.55) or permanent methods (OR=1.43, 95%CI 1.17–1.76). Women living in outer regional/remote areas were more likely than women living in cities to use long-acting (OR=1.65, 95%CI 1.31–2.08) or permanent methods (OR=1.69, 95%CI 1.43–2.14). Conclusions: Location of residence is an important factor in women's choices about long-acting and permanent contraception in addition to the number and age of their children. Implications: Further research is needed to understand the role of geographical location in women's access to contraceptive options in Australia.

A series-connected photovoltaic distributed generator capable of enhancing power quality

Design of a series-connected photovoltaic generator (SPVG) capable of enhancing power quality is investigated. Analysis of the SPVG operations under disturbance conditions shows explicitly how achievable network voltage quality is affected by the SPVG injected power and its apparent power rating, and that voltage quality can be significantly improved even with a modest level of energy storage capacity incorporated in the SPVG. A control system for the SPVG is also proposed. Both simulation and laboratory tests confirm the efficacy of the distributed generator system.

Modeling and analysis of a novel variable-speed cage induction generator

This paper introduces a novel cage induction generator and presents a mathematical model, through which its behavior can be accurately predicted. The proposed generator system employs a three-phase cage induction machine and generates single-phase and constant-frequency electricity at varying rotor speeds without an intermediate inverter stage. The technique uses any one of the three stator phases of the machine as the excitation winding and the remaining two phases, which are connected in series, as the power winding. The two-series-connected-and-one-isolated (TSCAOI) phase winding configuration magnetically decouples the two sets of windings, enabling independent control. Electricity is generated through the power winding at both sub- and super-synchronous speeds with appropriate excitation to the isolated single winding at any frequency of generation. A dynamic mathematical model, which accurately predicts the behavior of the proposed generator, is also presented and implemented in MATLAB/Simulink. Experimental results of a 2-kW prototype generator under various operating conditions are presented, together with theoretical results, to demonstrate the viability of the TSCAOI power generation. The proposed generator is simple and capable of both storage and retrieval of energy through its excitation winding and is expected to be suitable for applications, such as small wind turbines and microhydro systems.

An arteriovenous loop in a protected space generates a permanent, highly vascular, tissue-engineered construct

A major obstacle to 3-dimensional tissue engineering is incorporation of a functional vascular supply to support the expanding new tissue. This is overcome in an in vivo intrinsic vascularization model where an arteriovenous loop (AVL) is placed in a noncollapsible space protected by a polycarbonate chamber. Vascular development and hypoxia were examined from 3 days to 112 days by vascular casting, morphometric, and morphological techniques to understand the model's vascular growth and remodeling parameters for tissue engineering purposes. At 3 days a fibrin exudate surrounded the AVL, providing a scaffold to migrating inflammatory, endothelial, and mesenchymal cells. Capillaries formed between 3 and 7 days. Hypoxia and cell proliferation were maximal at 7 days, followed by a peak in percent vascular volume at 10 days (23.20±3.14% compared with 3.59±2.68% at 3 days, P<0.001). Maximal apoptosis was observed at 112 days. The protected space and spontaneous microcirculatory development in this model suggest it would be applicable for in vivo tissue engineering. A temporal window in a period of intense angiogenesis at 7 to 10 days is optimal for exogenous cell seeding and survival in the chamber, potentially enabling specific tissue outcomes to be achieved.

On the provable security of an efficient RSA-based pseudorandom generator

Pseudorandom Generators (PRGs) based on the RSA inversion (one-wayness) problem have been extensively studied in the literature over the last 25 years. These generators have the attractive feature of provable pseudorandomness security assuming the hardness of the RSA inversion problem. However, despite extensive study, the most efficient provably secure RSA-based generators output asymptotically only at most O(logn) bits per multiply modulo an RSA modulus of bitlength n, and hence are too slow to be used in many practical applications. To bring theory closer to practice, we present a simple modification to the proof of security by Fischlin and Schnorr of an RSA-based PRG, which shows that one can obtain an RSA-based PRG which outputs Ω(n) bits per multiply and has provable pseudorandomness security assuming the hardness of a well-studied variant of the RSA inversion problem, where a constant fraction of the plaintext bits are given. Our result gives a positive answer to an open question posed by Gennaro (J. of Cryptology, 2005) regarding finding a PRG beating the rate O(logn) bits per multiply at the cost of a reasonable assumption on RSA inversion.

Unbalance identification in large steam turbo-generator unit using a model-based method

Fault identification in industrial machine is a topic of major importance under engineering point of view. In fact, the possibility to identify not only the type, but also the severity and the position of a fault occurred along a shaft-line allows quick maintenance and shorten the downtime. This is really important in the power generation industry where the units are often of several tenths of meters long and where the rotors are enclosed by heavy and pressure-sealed casings. In this paper, an industrial experimental case is presented related to the identification of the unbalance on a large size steam turbine of about 1.3 GW, belonging to a nuclear power plant. The case history is analyzed by considering the vibrations measured by the condition monitoring system of the unit. A model-based method in the frequency domain, developed by the authors, is introduced in detail and it is then used to identify the position of the fault and its severity along the shaft-line. The complete model of the unit (rotor – modeled by means of finite elements, bearings – modeled by linearized damping and stiffness coefficients and foundation – modeled by means of pedestals) is analyzed and discussed before being used for the fault identification. The assessment of the actual fault was done by inspection during a scheduled maintenance and excellent correspondence was found with the identified one by means of authors’ proposed method. Finally a complete discussion is presented about the effectiveness of the method, even in presence of a not fine tuned machine model and considering only few measuring planes for the machine vibration.

Doubly Fed Induction Generator for wind energy generation using nine-switch power converter

A Three-Phase Nine-Switch Converter (NSC) topology for Doubly Fed Induction Generator in wind energy generation is proposed in this paper. This converter topology was used in various applications such as Hybrid Electric Vehicles and Uninterruptable Power Supplies. In this paper, Nine-Switch Converter is introduced in Doubly Fed Induction Generator in renewable energy application for the first time. It replaces the conventional Back-to-Back Pulse Width Modulated voltage source converter (VSC) which composed of twelve switches in many DFIG applications. Reduction in number of switches is the most beneficial in terms of cost and power switching losses. The operation principle of Nine-Switch Converter using SPWM method is discussed. The resulting NSC performance of rotor side current control, active power and reactive control are compared with Back-to Back voltage source converter performance. DC link voltage regulation using front end converter is also presented. Finally the simulation results of DFIG performances using NSC and Back-to-Back VSC are analyzed and compared.

Permanent shift: the topology of Didier Vermeiren's Cariatide à la Pierre

Photographic documentation of sculpture produces significant consequences for the way in which sculptural space is conceived. When viewed as discrete mediums the interaction of the photograph and its sculptural subject is always framed by notions of loss. However, when taken as a composite system, the sculpture-photograph proposes a new ontology of space. In place of the fixity of medium, we can observe a topology at play: a theory drawn from mathematics in which space is understood not as a static field but in terms of properties of connectedness, movement and differentiation. Refracted through the photographic medium, sculpture becomes not a field of fixed points in space, but rather as a fluid set of relations - a continuous sequence of multiple ‘surfaces’, a network of shifting views. This paper will develop a topological account of studio practice through an examination of the work of the contemporary Belgian sculptor Didier Vermeiren (b. 1951). Since the 1980s, Vermeiren has made extensive use of photography in his sculptural practice. By analysing a series of iterations of his work Cariatide à la Pierre (1997-1998), this paper proposes that Vermeiren’s use of photography reveals patterns of connection that expand and complicate the language of sculpture, while also emphasising the broader topology of the artist’s practice as a network of ‘backward glances’ to previous works from the artist’s oeuvre and the art-historical canon. In this context, photography is not simply a method of documentation, but rather a means of revealing the intrinsic condition of sculpture as medium shaped by dynamic patterns of connection and change. In Vermeiren’s work the sculpture-photograph, has a composite identity that exceeds straightforward categories of medium. In their place, we can observe a practice based upon the complex interactions of objects whose ontology is always underpinned by a certain contingency. It is in this fundamental mobility, that the topology of Vermeiren’s practice can be said to rest.