A study of transfer switching for the purpose of fault detection in FRIENDS

The authors have proposed a new concept of a distribution system “Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS)” with intent to solve imminent operating problems faced by utilities in providing their customers with reliable supply of power at several levels of quality. The main idea of FRIENDS is to introduce new facilities, so‐called Quality Control Centers (QCCs), which are installed very close to the customers for the purpose of implementing multiple functions, such as Customized Power Quality Service. In addition, these QCCs form a network for energy and information transmission at a level below distribution substations. QCCs make it possible to frequently change configuration of the network depending on the system and load conditions. These frequent reconfigurations of the network require fast and reliable Transfer Switching in the QCCs to ease an effect on customers. The reconfiguration for the purpose of fault area isolation also requires a fast Fault Detection feature. This paper presents a new method for controlling Transfer Switching and a method of Fault Detection in order to realize a fast and reliable reconfiguration of QCC network in a normal state, as well as under fault conditions. This paper also analyzes the methods in terms of instantaneous values calculated by PSCAD/EMTDC. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 25–35, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10298     

Approximate Expressions for Maximum Values of Transient Magnetic Fields and Electromagnetic Forces Imposed on Windings in Superconducting Generators

As superconducting generators have a number of advantages, the investigations for such machines have actively been carried out throughout the world. In the superconducting generator, it is very important to support the field winding and to protect it from quenching. On the other hand, since the armature winding is of air core, the evaluation of eddy current loss in the winding and the way it is supported arc inevitable. Thus, the magnetic fields and the electromagnetic forces acing on both the field and the armature windings at the early stages of the machine design should be known. In previous papers the transient behavior of magnetic fields and electromagnetic forces acting on the windings of a superconducting generator based on a computer simulation for a sudden 3-phase fault have been discussed in part. However, the behavior of magnetic fields and electromagnetic forces during transient period is very complicated and many calculations are required to determine their maximum values. In this paper, for practical use at the early stages of the machine design, approximate expressions are derived to calculate the maximum values of the magnetic fields and electromagnetic forces on the windings in the case of a 3-phase fault. To check these expressions numerically, a 1000-MVA superconducting generator was conceptually designed. The numerical results obtained by using these expressions agree well with the computer simulation results.     

Preventive control based on complex-valued load-flow technique to avoid voltage instability in power systems

This paper presents a method for obtaining preventive control strategies based on nonlinear optimization for power systems which will incur voltage instability when load demand increases. An algorithm is proposed to determine an appropriate and effective control action taking into account the operating constraints to widen the margin between the present operating point and a voltage collapse point, thereby improving the system state. The method proposed here is based on a complex-valued load-flow technique using the Newton-Raphson method which has been developed already by the authors. Consequently, the preventive control algorithm also can evaluate the voltage instability in the event the present operating point becomes closer to the critical point and the system state becomes unfeasible at increased loading point. Further, in optimization, two-types of objective functions are introduced so that voltage stabilization and dissolution of constraint violation can be attained simultaneously. In addition, this paper discusses the extension of the proposed preventive control to the successive control method which carries out the control action to avoid voltage collapse while the load demand is increasing. Numerical examples for various model systems demonstrate the effectiveness of the proposed method.     

Effect of bound water on piezoelectric,dielectric, and elastic properties of wood

The interaction of water with wood, such as bamboo and cedar, is investigated by measuring their complex piezoelectric, dielectric, and elastic constants between -150 and 150°C at 10 Hz. Bamboo and cedar are found to have two hydration-dependent elastic loss peaks; one is observed at about -100°C and the other at about -40°C. The former loss peak is due to the adsorbed water in the hydration range between 0 and 4% moisture content (MC) and the latter to the adsorbed water above 4% MC. These two types of water are considered bound on different sites in the regions around crystalline cellulose, where molecules of one type associate with each other and molecules of the other are unassociated. We consider that the piezoelectric polarization of wood is attributed to the rotation of hydroxyl groups in the crystal lattice of cellulose. The piezoelectric constants are observed to decrease but the elastic and dielectric constants to increase with increasing hydration. The effect of adsorbed water on elastic losses in bamboo and cedar are found to be similar to that in collagenous substances.     

Carbonization of aromatic hydrocarbons—V: Microscopic features of carbons obtained by the aid of catalysts

Microscopic observation of carbons obtained from pure aromatic hydrocarbons by the aid of carbonization catalysts was carried out to clarify the microstructure of these carbons of different features. Reflected polarized-light microscopy distinguished needle, mosaic and isotropic cokes, former two of which were produced with aluminum chloride and the last with potassium. High resolution microscopy revealed that these carbons calcined at 1250° had different degree of layered structure, corresponding to the crystallographic parameters of these samples graphitized at 2500°C. The reasons for the carbons produced with potassium to be non-graphitizable are discussed from the macro- and micro-features of the carbons.