The automatic measuring system for transient overvoltages was developed and applied to the actual power stations and substations in service. The surge voltage sensor has the frequency bandwidth from 5Hz to 10MHz, and can measure all types of transient overvoltages such as the temporary overvoltage, switching surge, lightning surge and disconnector switching surge. This system was installed and now operating at three 550kV power stations and substations. Up to the present, 176 records were obtained for the first time with high accuracy. They include induced lightning surges, lightning back flashover surges, circuit breaker closing surges and a disconnector restriking surge.

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In a contemporary bulk power system, the voltage instability phenomenon caused by insufficient power supply capability to load of constant power type is becoming an important problem. On the other hand, the increase of the short circuit capacity of power system is also becoming a serious problem, which may deteriorate the voltage stability.
In this paper, the static and dynamic characteristics of power supply to each load in hybrid AC-DC power system are analyzed by using static and transient P-V curves respectively. In this analysis three kinds of DC transmission system control schemes are compared.
It is made clear that the DC transmission system has an advantage of increasing power supply capability at an inverter node. Also made clear is that constant firing angle-constant current control makes it possible to provide the inverter node with a larger power than the two conventional control methods, such as constant current-constant voltage control and constant power -constant extinction angle control methods. Transient digital simulations show that the DC interconnection improves the voltage stability under opening of DC inerconnected line or one-line opening of AC double-circuit interconnected lines.

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Thermal puffer type gas interrupter, which is a kind of self extinguishing type interrupters, blows out an arc with the high pressure gas expanded by the arc heat, and seems to have a potential on a small operating force gas circuit breaker. However, the thermal puffer type interrupter has a critical current in a small current interruption, which can not be interrupted.
The authors investigated the interrupting ability of the thermal puffer type interrupter equipped with an auxiliary interrupting method to eliminate the critical current. Two types of the thermal puffer equipped with an auxiliary method were investigated. One consisted with small puffer and the other consisted with suction chamber. The breaker terminal fault was chosen as the test condition. The interrupter with the small puffer was tested with the Weil-Dobke's synthetic test circuit for a circuit breaker having ratings of 84kV 31.5kA. The interrupter with the suction chamber was tested directly with a short circuit generator, where the test voltage was 7.2kV and the test current was varied from 10% to 100% of 12.5kA. The former could interrupt all the region from small current to large current keeping interruptible arcing time width of 0.5cycles. Furthermore, it was confirmed that a high gas pressure rise was obtained with the arc heat and acted effectively for large current interruption in the interrupter with a small puffer in the same manner as a genuine thermal puffer interrupter. On the other hand, the interrupter with suction chamber could also interrupt the critical current, and succeeded to interrupt all the region of the required current to interrupt. The reaction force at the beginning of opening motion was decreased by the improvement of suction chamber shape. This means that the operating force can be decreased.

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A novel three-phase superconducting fault current limiting reactor (SCFCLR) is fabricated. The SCFCLR has three superconducting windings with the same number of turns wound on an iron core. The rating of SCFCLR is 200V, 10A. Two SCFCLRs are inserted in the sending and the receiving ends of the model power-transmission line. And the line fault test of a model power system with two SCFCLRs is carried out. The fundamental behavior of this reactor is confirmed. In the case of single-line-to-ground fault, the fault current is limited to very small value by the large zero-phase-sequence reactance of the SCFCLR without quench. In the case of three-phase short circuit, the SCFCLR quenches, and the short circuit current is limited by the normal conducting resistance of the winding. It is confirmed that the transient stability of the system during the line faults is greatly improved by the insertion of SCFCLRs.

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Present study examines the possibility of application of a superconducting coil (SC) to the energy storage for photovoltaic power generation systems (PV systems). A solar cell should be operated at the maximum output point on the I-V characteristic curve with constant current and constant voltage in order that the solar energy be fully utilized. On the other hand, the suerconducting coil carries a variable current according to the stored energy. Therefore, a current transforming circuit is to be put between the solar cell and the SC.
In this paper, we propose a circuit which interconnects a PV system to a power system via an SC. A step-down chopper is put between the solar cell and the SC, and a DC-AC converter is installed between the SC and the AC power system. The SC can be used as an energy storage system for the PV system, and also, as an ordinary SMES (Superconducting Magnetic Energy Storage) when the PV system is not in operation. The control strategy of the chopper is presented, which keeps the operating point of the solar cell at its maximum output point. Expericental results are shown with the analysis of the storage efficiency. Furthermore, an example of real-scale system is designed with the proposed circuit, and its operation is simulated.

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The Application of superconductivity technology to electric power apparatuses is very important from the viewpoint of energy saving. Especially the superconducting generators using superconductors as the field windings have many merits compared with conventional generators. Super-GM has been researching and developing 70MW class model machines since FY 1988 for a scheduled period of eight years, aiming at a 200MW class superconducting generator. This paper describes the basic specifications and designs of 70MW class superconducting generators by Super-GM and also describes the propriety of these basic specifications and designs.

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In order to find out the most appropriate impregnating epoxy resin for superconducting coils, three types of epoxy resin were examined from various points of view. Those epoxy resins were amine curing type A, anhydride curing type B with tertiary amine accelerator and anhydride curing type C without accelerator.
From the examinations, resin A was found to be more superior in thermal shock resistance against cryogenic temperature than resins B and C because of its high tensile strength at cryogenic temperature and its small cure shrinkage. However, the test coil impregnated with resin A experienced more repeated premature quenches than the coil impregnated with resin C. This result might be explained by the crackings which started from microscopic defects, and which occured gradually in resin A compared with resins B and C. Moreover, the viscosity of resin A increased more rapidly during the impregnating process than that of resins B and C, so that resins B and C appear to be more appropriate for large superconducting coils than resin A.

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Diameter of the superconducting AC composite strand is small, typically 0.1 mm, because the strand must be twisted in a very short pitch, to reduce coupling losses, therefore, current capacity of the single strand is small and in the range of_??_10A. In large scale electric power apparatuses, the conductors must be able to carry large currents and hundreds of these composite strands should be bundled. The composite strand is highly unstable and susceptible to a very small disturbance due to a frictional wire motion, because the main matrix of the wire is highly resistive CuNi.
For stable operation of an AC superconducting winding, every strands in the bundle cable should be fixed firmly. An effective technique to fix strands is to impregnate the winding by epoxy. In this case, the AC losses in the winding are to be cooled by heat conduction through the epoxy. Therefore, it is important to estimate temperature rise of the winding to discuss that the epoxy impregnation technique is applicable to the AC superconducting electric power apparatuses. In this paper, mechanism of thermal conduction of the epoxy impregnated winding at 4.2 K region is discussed based on experimented data and the temperature rise of a large scale cable bundled by 7 × 7 × 7 strands calculated considering thermal resistivity at the interface between the epoxy and the strand. The calculated value well agree with the measured value.

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Recently, Optical current and voltage measuring systems based on measuring principles different from those of traditional apparatus have been developed actively. This paper deals with the development of an optical current transformer (CT), whose optical signal transmission system has some portions of free space light propagation, for its application to gas insulated switchgear (GIS).
The analyses of free space light propagation through plano-convex lenses or micro-lenses were carried out firstly and compared with the measured values. Then, the piano-convex lens system was confirmed to be preferable to long distance light transmission in free space. Using an optical CT with the piano-convex lens system, optical loss distribution in the light transmission system was investigated, and total optical loss of less than 20 dB was obtained. Finally, an optical CT system with light transmission in SF₆ gas space was developed and incorporated into a full-scale 77 kV GIS model. Test results for the optical CT system showed that it has excellent measuring characteristics conformed with JEC 1201. No variation of current measuring characteristics was observed during long-term field tests.

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The objective of the present paper is to simulate the electrical nonuniformities caused by coal slag polarization in coal-fired MHD power generator channels. The basic equations are the Maxwell equation and the generalized Ohm's law. In numerical analyses a 2-D equivalent circuit method is applied for MHD channels. Simulation results of the electrical non-uniformities agree well with experimental data, showing effectiveness of the present modeling of the electrical nonuniformities. The present engineering model can be used for examination of control circuits.

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This paper presents experimental studies on cell voltage-current density characteristics and the CO₂ evolution phenomena of phosphoric acid fuel cells for various supplied air/hydrogen, hydrogen/hydrogen, nitrogen/nitrogen, air/air, nitrogen/hydrogen, air/nitrogen and hydrogen/air conditions to the air electrode/fuel electrode, respectively.
No CO₂ gas is detected from a hydrogen-supplied electrode at positive and negaive current conditions. From a nitrogen-supplied electrode operating as an anode, current dependent CO₂ evolution is observed, although no CO₂ is detected from the same electrode operating as a cathode.
There is also CO₂ evolution from an air-supplied electrode near the zero current. The CO₂ evolution can be suppressed slightly by hydrogen diffusion from the opposing electrode.
Cell voltage-current density characteristics are represented as equivalent circuits in which corrosive or non-corrosive current can be evaluated separately. For a hydrogen/hydrogen condition, the cell can be expressed as a resistor having low resistivity. For an air/hydrogen or an air/air condition, the cell can be expressed as a series circuit of ideal cells and resistors, whereas for nitrogen/nitrogen, nitrogen/hydrogen or air/nitrogen conditions diodes should be added to the circuit in order to express the potential barrier. Currents on this potential barrier are zero except for the nitrogen/hydrogen condition where hydrogen is diffused from the opposing electrode.
These characteristics are useful for analyzing performance distribution in cells at transient conditions such as start-up, shut-down or abnormal conditions such as a local circuit in a cell, gas cross over nr over enrrent.

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