Teijiro Mori

Application of Microprocessors to the Control and Protection System at Substation

The progress of microprocessors has been so remarkable in recent years that the application of modern digital data processing techniques can solve many problems in power system control and protection field. This paper describes a digital system using thirteen microprocessors which performs all the control and protective functions at a substation. The fundamental concept of this system is Three Data Channel Structure to manage all the signal flows for control and protection. This system has been installed at a substation since December 1977 and the field test has demonstrated its feasibility for commercial application with valuable field experiences.

Usefulness of Permanent Power Fuse in Control Centers with Molded Case Circuit Breakers

The increase in electric power consumption in industry has led to the development of modern distribution systems such as control centers having high kVA ratings and high prospective fault current. In such a situation, the improvement of the system usefulness such as reliability and cost effectiveness is the essential requirement. An index is presented to evaluate the system usefulness using the cost effectiveness for fault protection in a system of given bank kVA. The index is estimated on four different system structures of control centers, including one which utilizes Permanent Power Fuses (PPF). It is presented that the PPF combined with molded case circuit breaker in main circuit effectively improves the cost effectiveness in control centers with high fault current. Operating principles of the PPF and the control center utilizing the PPF are briefly outlined.

Design Considerations on the P. P. F. for a Control Center

Permanent Power Fuse which is called by the abbreviated name P. P. F. is an entirely new reusable fuse with excellent current limiting performance developed by Mitsubishi Electric Corp. of Japan1. Since our previous work on the development of the series of the low voltage P. P. F. up to 800 A1 ., various P. P. Fused devices have been applied to the actual field. Among these applications, the application of the P. P. F. to a control center is an example which makes the very best use of the self-recovering function of the P. P. F. This paper explains the design considerations on the P. P. F. for use in a control center. In the considerations, emphases are put on quantitative discussions on the stable performance for repeated operation and the recovery time.

Superconducting Fault-Current Limiter for 200-Vrms-Class Circuits Using YBa2Cu3Ox Thin Film by Chemical Vapor Deposition

A superconducting fault-current limiter (FCL) for 200-Vrms-class circuits using YBa2Cu3Ox (YBCO) thin film fabricated by chemical vapor deposition (CVD) was investigated. The FCL consisted of a 400-nm-thick YBCO film with meander pattern of 1 mm wide×115 mm long. The film was coated with a protective silver film having a thickness varying between 110 and 130 nm from place to place. Half-cycle alternating voltage (50 Hz) was applied to the FCL device which was immersed in liquid nitrogen (77 K), and a typical current-limiting waveform was measured. When a voltage of 200 Vrms was applied, the fault current with a peak of 400 A was limited to the peak let-through current of 11 A. The beginning time of the current limiting was about 0.1 ms.

Superconducting Current Limiting Element for 200 Vrms-Class Circuit Using YBCO Thin Film by Chemical Vapor Deposition

A superconducting current limiting element (CLE) for 200 Vrms-class circuits using YBa2Cu3Ox (YBCO) thin film by chemical vapor deposition (CVD) was investigated. The CLE consisted of a 400-nm-thick YBCO film with meander pattern of 1 mm wide × 115 mm long. The film was coated with a protective silver film having a thickness varying between 110 and 130 nm from place to place. Half-cycle alternating voltage of 50 Hz was applied to the CLE which was immersed in liquid nitrogen (77 K), and a typical current-limiting waveform was measured. When a voltage of 200 Vrms was applied, the fault current with a peak of 400 A was limited to the peak current of 11 A. The beginning time of the current limiting was about 0.1 ms.

A Study of a High-Tc Superconducting Fault Current Limiter (No. 2): Development of an Element for 100-V Class Power Systems

The application of a high critical temperature (Tc) superconductor with a high critical current density (Jc) to a fault current limiter (FCL) was investigated to obtain a FCL which exhibits superior current limiting performance. When the superconductor changes to normal conduction, it produces a resistance that can limit fault currents. A new current limiting element consisting of a 0.4 μm — thick YBaCuO film coated with a 0.12 μm — thick protective silver film was developed. The element has a current limiting section 1 mm wide and 40 mm long. The critical current density and critical current of the superconducting film were 1.6 × 106 A/cm 2 and 7 A, respectively. For a half cycle, an alternating voltage (50 Hz) was applied to the FCL element immersed in 77K liquid nitrogen, and a typical current limiting waveform was measured. At an applied voltage of 134 Vrms, a fault current with a crest of 320 A was limited to a peak let-through current of 17 A. After the current peaked, it rapidly decreased to less than 7.5 A. By using the protective silver film, a superconducting FCL element for 100-V class power systems was developed.

A new interruption method for low-voltage, high-capacity, air-break contactors suppressing the blowoff of a hot gas

A method was derived to suppress the blowoff of a hot gas from an arc chamber and to shorten arcing time in the interruption of overcurrents. The blowoff of the hot gas is suppressed by cooling with a porous metal plate attached in front of gas-exhausting holes of an arc chamber. From heat analysis, it is estimated that the temperature of the hot gas passing through the porous metal plate is lowered by about 95%. Arcing time is shortened by a unique commutation electrode and arc runner. In the interruption of a current of 6 kA at a 480 V circuit, the maximum arcing time is shortened by about 40%. From observation by a high-speed framing camera, it is concluded that the shortening of arcing time is due to an effective arc-drive by the commutation electrode and arc runner. This method has been applied to contactors of 600 A and 800 A frames having the maximum-rated operational voltage of 660 V.<<ETX>>

A Study on a High-T c Superconducting Fault Current Limiter

The application of a high-Tc superconductor with a high critical current density (Jc) to a fault current limiter has been investigated. When the superconductor changes to the normal conductor, it has a resistance which can limit fault currents. Experiments were made using a current limiting element of a YBaCuO film 0. 2 5 μ m thick. The element has a current limiting portion with 1mm wide and 2mm long to limit fault currents. For a half cycle, an alternating voltage (10 Vp, 5 0 H z) was applied to the element. A typical current limiting waveform was obtained in the experiment. The fault current, with a crest value of 420A, was limited to the crest value of 8A. After that, the current was rapidly decreased and was less than 1.6A.

Limit of Commutation of DC High Current from Main to Parallel Circuit

Commutation of fault current from a main contact to its bypass circuit is usually employed to transfer the current at fault interruption to the bypass circuit which involves arcing contacts, solid state switches, or nonlinear current limiting resistors. Factors which affect the limit of commutation have been studied experimentally. The main contact we tested is rated at 3000 A de and moves at I m/s to a full stroke of 4 mm. The main contact is kicked by a plunger accelerated with a repulsion coil Main currents of up to 8.5 kA have been eommutated to the bypass circuit at various impedance values. Precise measurements of voltage and current transients and time resolved recording of the intensity of the are across the main contact have been made during the commutation by synchroscopes and photomultipliars with light guides. As a result of the study, the limit of commutation has been revealed as a function of arcing time, arc voltage and impedance of the bypass circuit. Rate of erosion on the surface of the contact was observed microscopically and correlations with arc energy and current density of an electrode spot were found. Dielectric recovery characteristics of the main contact was also studied briefly.