摘要:

AbstractBi‐doped garnet is a rare metal iron garnet made up of a ferrimagnetic substance, of which some portion of the rare metal element is replaced with bismuth. It illustrates a strong Faraday effect and has been applied to optical isolators. In magnetic field sensing applications, however, a shortcoming is apparent: Faraday rotation of Bi‐doped garnet reveals temperature dependencies when the garnet is not magnetically saturated. Close attention has been paid to the magnetization of each rare earth element's different temperature characteristics; garnet compositions have been investigated by calculations and experiments in order to find a garnet that shows flat temperature characteristics between −10 and 80°C. The liquid phase epitaxy (LPE) method was established to obtain a single crystal of the garnet [Bi13(Y, La)0.9Ho0.8Fe4.5Ga0.5O12]. A magnetic field sensor of fiber optic based on the Faraday effect of this single crystal is highly accurate in detecting conductor currents of power cables. The developed sensor is small and lightweight compared to conventional current transformers; additionally, optical fiber transmission of detected current signals is free from both electric and magnetic

ISSN:0424-7760    

DOI:10.1002/eej.4391170101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractPower flow calculation is a basic tool for power system planning and control which includes power flow analysis, voltage control, service restoration, network reconfiguration, and other operation functions for control centers. In these applications, it is very important to solve the power flow problem as efficiently as possible.This paper presents a fast power flow using parallel processing for radial power systems. This method can be applied to secondary systems and distribution systems. Since it uses as state variables only active and reactive power injection to main lines and laterals, reduction of the number of state variables can be realized. Radical networks are mapped to the tree structure of parallel processor systems in the proposed method. The forward/backward sweep approach is realized by communication from a root processor to leaf processors and vice versa. Using the mapping scheme of the proposed method, each processor has to communicate with only neighboring processors. The proposed method is evaluated on various radial systems with promising results.

ISSN:0424-7760    

DOI:10.1002/eej.4391170102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper proposes a new electric power network that makes it possible for many types of dispersed generation plants owned by nonutility organizations to participate in an electric power market without the disadvantages of existing power utility and customers. This power network is called an open electric energy network (OEEN) because the network is open to the many types of plants for the participation. For achieving such openness, electric power storage devices, load controller at each customer and data communication network are installed in OEEN; the flow of excess electric power generated by each plant is controlled autonomously and in a distributed way. That is, the control is done by transmitting the data on excess electric power such as generation and demand point, power quality, price, etc., from each dispersed generation plant to the power storage devices and the load controllers through the communication network. Since this data‐driven power flow control is similar to the mail system for a packet with the addresses of sender and receiver, it is called packet electric power transportation.In OEEN the storage device plays a different role from load leveling. Therefore, the way to determine the storage capacity differs from the conventional approach. In this paper, the applicability of queuing theory for determining the capacity is also discusse

ISSN:0424-7760    

DOI:10.1002/eej.4391170103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents a new approach to identify a fault point in a power system on real time. Based on the topology theory, the characteristics of a fault in the power system are treated as a pattern of the fault. Therefore, the calculation complexity of traditional approaches can be avoided. The aim of the proposed method is to identify fault points through directly analyzing the type of fault. Since each type of fault has each characteristic pattern of power flow, fault points can be identified by abstracting characteristics of power flow at each node of the power system. In order to abstract fault characteristics, neocognitron in which symmetrical three phase decomposition and data normalization are calculated using power flow at each node is introduced. Thus, the impacts of voltage grade and unbalanced load can be removed. Since each neocognitron corresponds to one node of the power system, hierarchical autonomous decentralization can be realized. Therefore, the proposed approach can be applied to a large power system. Fault point location is done by BP network. Since the neuro of BP network only corresponds to the nodes of the topologized power system, the training of the neural network can be performed independently. From this point of view, the applicability and flexibility of proposed approach are high. The effectiveness and applicability of the proposed approach are demonstrated on a simple power system model.

ISSN:0424-7760    

DOI:10.1002/eej.4391170104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractSuperconducting technology is regarded as a breakthrough to future electric power transmission because of its highly densified and large transmission capability. This paper proposes a concept of the future power system composed of various superconducting apparatuses. A prototype model system called “PROMISE (PROspective power transmission Model system Integrated under Superconducting Environment)” is constructed to prove the realization of the above concept. PROMISE is composed of a superconducting transformer (60 Hz, 6/3 kV, 1000 kVA class), superconducting fault current limiter (6 kV, 200 A class), and superconducting power cable (5 m, 6 kV, 650 A class). This paper also shows that PROMISE realized the transmission of the electric power of 3.8 kV–460 kVA (50 Hz). This is the first achievement in the world. The voltage‐current synthetic test verified that PROMISE can withstand ac voltage of 6 kV while carrying ac current of 170 A (60 Hz). The ac loss of superconducting cables, the heat leak of cryostat and the core loss of the superconducting transformer are measured to estimate the transmission loss of PROMISE. These fundamental performances of PROMISE may indicate the feasibility of the future introduction of superconducting technology for electric power

ISSN:0424-7760    

DOI:10.1002/eej.4391170105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractVoltage distortion of 6.6‐kV distribution systems has been increasing recently especially in commercial areas. Harmonic currents of certain orders are amplified and voltage distortions are generated by the resonance between system impedance and static capacitor under the leading power factor condition.This paper describes the results of a test on suppression effects on model systems and an actual system. The effect of the use of an active power filter on the resonant harmonics of the system including capacitor was verifie

ISSN:0424-7760    

DOI:10.1002/eej.4391170106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractA static Var compensator (SVC) can improve the steady‐state stability (or the small signal stability), if it is located appropriately. The present paper proposes a method for selecting the best siting of SVC in large‐scale power systems for damping effectively.Conventionally, it is thought that SVC improves steady‐state stability by its voltage regulating ability. From this point of view, the stability can be improved significantly if SVC is located at the bus which has a large voltage fluctuation due to the lightly damped power swing mode. In contrast to the conventional viewpoint, the present paper makes it clear that the steady‐state stability deteriorates by the conventional voltage regulating control of SVC in some cases. Therefore, the voltage fluctuation is not an appropriate index for effective damping.This paper explains the mechanism of improvement of steady‐state stability by SVC in terms of modal analysis. On the basis of modal analysis, an index for determining the location of SVC is derived. The index is called LIED (Location Index for Effective Damping) by the authors. Digital simulations are conducted for an 8‐machine longitudinal system and a 29‐machine looped system to demonstrate the validity of the p

ISSN:0424-7760    

DOI:10.1002/eej.4391170107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractAn improved method of degradation diagnosis for medium‐size distribution transformers is described. The proposed method uses refined criteria of degradation for specific application for 200‐ to 1000‐kVA range transformer diagnostics. The new criteria were established with a 95 percent confidence limit of data after extensive case studies focusing on the relationship between the amounts of CO and CO2generated in transformer oil and the length of operating time of the transformer. Another feature of this diagnostic technique is the provision of a capability to estimate the thermal history of the insulation material by examining the amounts of certain trace products of decomposition present in the transformer oil. For this purpose, a thermal history discriminant chart was devised by application of a canonical discriminant analysis m

ISSN:0424-7760    

DOI:10.1002/eej.4391170108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractIt is important to consider the stabilization problem for a large‐scale power system. This paper uses a dynamic compensator based on observer theory such that desired poles are placed for a closed‐loop multimachine power system. Since the system dimension is large, it is difficult to apply a conventional dynamic compensator method to an excitation control problem for a multimachine power system.The homotopy method is introduced to solve fundamental nonlinear equations which are required for observer synthesis. To show the effectiveness of the proposed method an excitation control of generators for a multimachine power system is considered. From the simulation result, it is shown that the present method is useful in stabilizing a multimachine power sys

ISSN:0424-7760    

DOI:10.1002/eej.4391170109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY

摘要:

AbstractIn industrial motor drive systems such as those used in industrial plants and robots, a torsional vibration is often generated as a result of the elastic elements present in the torque transmission systems. This vibration makes it difficult to achieve quick speed responses and may result in plant damage. Such systems are simply modeled as two‐mass mechanical systems.The H∞control theory is applied herein to design a speed controller for the two‐mass system. This controller determines closed‐loop characteristics, including suppression of torsional vibration, rejection of torque disturbance and robust stability. Moreover, two types of two‐degrees‐of‐freedom control systems, which includes the H∞controller, are proposed to improve command response. One is based on the TDOF PI control, in which the PI controller included in the H∞controller is rearranged for the TDOF system. Another is based on the model matching feedforward control, in which the prefilter and the feedforward compensator are added to the H∞controller. The proposed control system is applied to two types of resonant mechanical systems having different inertia ratio. Several examinations demonstrate that the proposed speed control system is useful for a resonan

ISSN:0424-7760    

DOI:10.1002/eej.4391170110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1996

数据来源: WILEY