摘要:

AbstractTransmission power cables are heated by conductor current. The morphology of the XLPE insulation may be changed by thermal aging. Disk‐shaped insulating materials with semiconductive electrodes were used to understand this thermal effect against the dielectric breakdown strengths. The disk specimens were aged at 80 and 100°C before the breakdown strength measurements.These results showed that the dielectric breakdown strengths were improved with aging time. Analytical investigation of the insulating materials indicated that there were morphological changes such as increases of the lamella thickness and the spherulite diameter and decrease of the averaged lamella angle through heating. Cable specimens aged thermally with the same condition as the risk specimens also were observed with similar morphological changes in the insulation. Therefore it is concluded that the promotion of the crystallization by thermal aging is effective in improving the breakdown strength of the XLPE insulation unless it causes extreme deteriorati

ISSN:0424-7760    

DOI:10.1002/eej.4391130801

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

年代:1993

数据来源: WILEY

摘要:

AbstractInsulation deterioration of power cables can be measured by the method of partial discharge. If a large partial discharge is detected in a cable, the cable is considered to be defective and a partial discharge is located to find the position of the defect. However, partial discharge location methods are generally disadvantageous in that they require much skill for operation and have inferior sensitivity and accuracy.To solve these problems, the authors developed a locating method using two‐phase cable and an automatic partial discharge locator which automatically localizes the generating site of discharge immediately after making partial discharge measurement by simple operations. Field measurements are made on SL (separately lead‐covered) cables and other cables with the locator to test its accuracy and reliability, and it was found that the device is effective and use

ISSN:0424-7760    

DOI:10.1002/eej.4391130802

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

年代:1993

数据来源: WILEY

摘要:

AbstractAccording to the recent analysis results of temporary ac overvoltage in the ac system connected with a frequency converter station, large‐magnitude over‐voltages were confirmed to occur under some special system conditions.Most of the station insulators currently used cannot withstand such overvoltages according to an evaluation based on the data obtained earlier.The necessity of tests to be done to evaluate such performance more accurately was recognized. Both power frequency and switching impulse overvoltage flashover tests were made on contaminated insulators by the method well simulating the natural wetting condition.Switching impulse flashover voltage with the waveshape having a long wavefront time of 2 ms can be well correlated with the flashover voltage characteristics of temporary ac overvoltage. Higher flashover voltage characteristics were obtained by a clean fog test method compared with those obtained by equivalent fog test met

ISSN:0424-7760    

DOI:10.1002/eej.4391130803

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

年代:1993

数据来源: WILEY

摘要:

AbstractToday's power systems are characterized in that more power demand is concentrated in urban areas, increasingly centralized power facilities are becoming larger in size and located in more remote places, and power condensers tend to be upgraded to improve the power factor. These movements each reduce the stability power limit, thereby permitting the effect of a power failure to spread much farther.In such an interconnecting power system, when power is transmitted from a power source (a small system) in a remote place to a large city (a large system) with great power demand, it is expected that a zero‐power flow phenomenon will occur where power transmission is impossible when power flow in the interconnecting power system is zero depending on a combination of the size of branch load and its power factor. In future power systems that will extend farther, have a larger capacity, and be more capacitive, such a phenomenon would be more iable to take place. In this paper, a new formula to analyze a zero‐power flow phenomenon is derived, and using the formula, areas in which a zero‐power flow phenomenon takes place also are discussed. With an experimental system simulating a practical 500‐kV power system, the occurrence of a zero‐power flow phenomenon could be

ISSN:0424-7760    

DOI:10.1002/eej.4391130804

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe optical ZCT (Zero‐phase Current Transformer) which combines an optical magnetic field sensor with a magnetic ring core of silicon steel plates has been developed. Bi‐doped YIG [Yttrium Iron Garnet, (BiYbGd)3Fe5o12] having a large Verdet constant is used as a Faraday element. The optical ZCT detects the conductor current of 0 to 2000 A at high resolution and has been applied to the fault section detection system for 66‐kV underground branch transmission lines which monitors a multiterminal line having Y‐branch joint box in on‐line state. Optical ZCTs and a section detector/indicator are connected with optical fibers which are capable of nonrepeatedly transmitting signals over 6 km, and allow monitoring long‐distance underground power transmission lines. A developed system is now operating on the JR Kasai line (Shinkawa pump line) of Tokyo Electric Po

ISSN:0424-7760    

DOI:10.1002/eej.4391130805

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes a new partial‐discharge detection method for an XLPE‐insulated copper wire‐shielded cable line using a “yoke coil.” Partial discharges are measured with the yoke coil which detects the azimuthal component of the current flowing through the copper wires wound on an outer semiconducting layer with a given angle against the axial direction of the cable.The highest detection sensitivity of 2 pC has been achieved at a frequency range of 5 to 20 MHz using a 77‐kV 100‐mm2model cable line (200 m in length). It was confirmed that the partial discharge caused by an artificial defect has successfully been detected using the proposed method.In the PD measurement for an actual 77‐kV XLPE‐insulated live line, the detection sens

ISSN:0424-7760    

DOI:10.1002/eej.4391130806

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes detection by the AE (acoustic emission) sensor of partial discharge in a prefabricated joint, one of the accessories for XLPE cables which is composed of factory‐formed parts. Since the prefabricated joints can be installed in a short time, an increasing number of such joints has been used on power transmission lines. However, the interface between the parts of prefabricated joints tends to exhibit weak points because of a structure peculiar to this type of joint.The AE sensor is provided for practicability in comparison with conventional electrical defect detection methods. In the course of the present study, a method for locating a defect using multiple signals from the AE sensors was developed and its validity was evaluated by the dielectric breakdown tes

ISSN:0424-7760    

DOI:10.1002/eej.4391130807

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

年代:1993

数据来源: WILEY

摘要:

AbstractWith increased demands for optical fiber cable removal, a system which reduces circuit quality degradation due to optical fiber switching has been strongly required. The optical switching elements and optical fiber switching systems were studied aimed at shortening optical switching time, optical loss and other optical specifications. However, the circuit quality degradation cannot be evaluated by these specifications. For this reason, it is important to study the circuit quality degradation due to optical fiber switching, and the study must comprehend the transmission system performance after optical fiber switching.To analyze the circuit quality degradation during optical fiber switching, the standard analysis model and the optimum analysis parameters were defined. Using them, the frame hunting time after optical fiber switching was studied theoretically and its influence on a working transmission system was estimated. The circuit degradation was evaluated experimentally with regard to an actual transmission system, and experimental results agreed with the estimation. Moreover, by utilizing the results of these studies, it was found that the reduction of circuit quality degradation can be realized firmly and the effect of these studies was verified.

ISSN:0424-7760    

DOI:10.1002/eej.4391130808

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

年代:1993

数据来源: WILEY

摘要:

AbstractA single‐phase diode bridge rectifier with a filter capacitor on the dc side is often employed to convert ac input into a dc voltage. The input current of the rectifier contains harmonic currents which cause undesirable power line effects. Recently, a method using the time domain analysis has been proposed to calculate the harmonic currents of rectifier considering noninfinite capacitance, i.e., non‐zero dc side impedance. This method is very accurate, but it requires a long computing time and a complicated algorithm.This paper proposes a new method that makes it possible to easily calculate the harmonic currents taking into account the effects of the ac and dc side impedances of rectifier. The proposed method, which is based on the frequency domain method, can be executed only with the algebraic computation, and its accuracy is quite high. The validity of the proposed method is also demonstrated by comparison with the results of time simulat

ISSN:0424-7760    

DOI:10.1002/eej.4391130809

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes principles together with analytic and experimental studies of an exciterless, brushless, and self‐excited three‐phase synchronous generator which was devised by authors. Since traditional brushless and dc self‐excited three‐phase synchronous generators without exciter did not have the self‐exciting function by series characteristic component proportional to the load current inside the generator, they need auto‐voltage regulating equipment or a transformer with three windings and condensers to obtain constant voltage characteristics. It also has the following problem in the case of two‐pole traditional generator: oscillatory tension is generated at the shaft of the rotor caused by the magnetic force between magnetic poles of stator and rotor windings, and it causes mechanical vibration and noise.This paper proposes a new brushless and self‐excited three‐phase generator solving the aforementioned problems: the ratio of poles of the windings for providing power to load (armature and field windings) to the windings for supplying exciting power (stator and rotor exciting windings) is 1 to 5. Then oscillatory tension does not generate theoretically. Furthermore, a self‐exciting three‐phase generator using the 5th‐harmonic component of armature reaction which makes series characteristic component proportional to the load current, currently is available.In this paper, the winding construction, the electric circuit, and the principle of the aforementioned generator are described, and the experimental results of the trial‐produced generator show that the three‐phase terminal voltage waveforms are almost sinusoidal and also balanced, and the voltage can be kept almost constant for the change of load. This generator has high reliability because

ISSN:0424-7760    

DOI:10.1002/eej.4391130810

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

年代:1993

数据来源: WILEY