Abstract: Respective contact terminals in respective arc-suppressing spaces of respective breakers are opened at a voltage zero point of any phase of three phases, simultaneously among the three phases. If current breaking is carried out for the three phases at the same time, when the breakers of the three phases are opened, the residual magnetic levels of the respective phases of a transformer can be controlled so that the residual magnetic flux level of the phase opened at the voltage zero point is maximum (for example, ?2 K or +2 K) and the residual magnetic flux level of the other two phases are opposite in polarity to the residual magnetic flux level of the phase concerned and equal to substantially the same residual magnetic flux (for example, +K and +K or ?K and ?K) which is equal to about one half of the residual magnetic flux level of the phase concerned.

Abstract: A frequency measuring device can measure the frequency of a noisy power system at high speed. The system voltage is measured at timings obtained by equally dividing one reference-wave period. Voltage vectors are calculated which have tip ends, each voltage vector consisting of a real part of a first measured voltage and an imaginary part of another voltage measured at timing 90 degrees before the first measured voltage. The length of a chord connecting tip ends of adjacent voltage vectors is calculated. A voltage root-mean-square value is calculated from voltages measured between two timings spaced from each other by the one reference-wave period. Chord lengths obtained between two timings spaced from each other by the one reference-wave period are summed. Based on the total of the chord lengths and the voltage root-mean-square value, there is calculated a phase angle between two adjacent voltage vectors, from which the system frequency is calculated.

Abstract: A distribution network monitoring and control system for monitoring and controlling a distribution network system including monitoring and control means for taking in an information and for outputting a control information for the switches thereof, status grasping means for judging charging and outage state of the distribution network system, switch status take-in means for taking in status of the switches in a range to which power was transmitted when the fault was generated, fault section judging means for judging a fault section according to a fault information, and fault section expanding means for expanding a fault section to a load side when status of the switches at the load side of the fault section cannot be taken out and for notifying an expanded fault section to the fault section judging means. The fault section judging means decides the expanded fault section as the fault section.

Abstract: A compact and economical gas-insulated switchgear is provided. The gas-insulated switchgear includes: a grounding metal housing 1 filled with insulating gas, and in which the disconnector part 2 having a moving side electrode part 2a and a stationary side electrode part 2b is accommodated; and composite insulating shields 17a, 17b integrally formed into one metal-dielectric member in which surface of a high electric field part located in the vicinity of ends of openings is coated with a dielectric so as to cover the moving side and stationary side electrode parts 2a and 2b with the dielectric. To form the composite insulating shields 17a, 17b, a metal shield of less than 0.6 in non-uniform constant before coating with the dielectric is coated with dielectrics 18a, 18b having a thickness of not more than approximately 30% of an inter-electrode distance from a facing electric-field relaxation shield.

Abstract: A frequency measuring device can measure the frequency of a noisy power system at high speed. The system voltage is measured at timings obtained by equally dividing one reference-wave period. Voltage vectors are calculated which have tip ends, each voltage vector consisting of a real part of a first measured voltage and an imaginary part of another voltage measured at timing 90 degrees before the first measured voltage. The length of a chord connecting tip ends of adjacent voltage vectors is calculated. A voltage root-mean-square value is calculated from voltages measured between two timings spaced from each other by the one reference-wave period. Chord lengths obtained between two timings spaced from each other by the one reference-wave period are summed. Based on the total of the chord lengths and the voltage root-mean-square value, there is calculated a phase angle between two adjacent voltage vectors, from which the system frequency is calculated.

Abstract: A distribution network monitoring and control system for monitoring and controlling a distribution network system including monitoring and control means for taking in an information and for outputting a control information for the switches thereof, status grasping means for judging charging and outage state of the distribution network system, switch status take-in means for taking in status of the switches in a range to which power was transmitted when the fault was generated, fault section judging means for judging a fault section according to a fault information, and fault section expanding means for expanding a fault section to a load side when status of the switches at the load side of the fault section cannot be taken out and for notifying an expanded fault section to the fault section judging means. The fault section judging means decides the expanded fault section as the fault section.

Abstract: A control system for canceling load unbalance of a three-phase circuit includes phase current detectors for detecting phase currents caused to flow through a secondary circuit of a current transformer provided in high voltage distribution lines, respectively, phase change-over switches through which phases of the high voltage distribution lines, and primary sides of distribution transformers provided across high and low voltage distribution lines are connected to each other, a control center for, when a magnitude of a zero-phase current detected by the zero-phase current detector is larger than a predetermined value, on the basis of the phase currents, respectively, out putting a control signal so that the load of the phase having a maximum current appearing therein is changed over to the phase having a minimum current recognized therein, and a phase change-over slave station for controlling the phase change-over for the phase change-over switches in accordance with the control signal.

Abstract: The system of the present invention includes transformers 12-1, 12-2 and 12-3 for detecting voltages received at a power receiving point in the power system, a negative-phase-sequence component voltage detector 18 for arithmetically operating the voltage of a negative-phase sequence component from the received voltages and amplifying the voltage of a negative-phase-sequence component to output the amplified voltage of a negative-phase-sequence component, and a negative-phase-sequence voltage compensation input unit 14 for injecting the outputted voltage of a negative-phase-sequence component into a system as an object of compensation to compensate for the received voltages at the power receiving point. The voltage of a negative-phase-sequence component is cancelled for a load 17 as an object.

Abstract: A compact and economical gas-insulated switchgear is provided. The gas-insulated switchgear includes: a grounding metal housing 1 filled with insulating gas, and in which the disconnector part 2 having a moving side electrode part 2a and a stationary side electrode part 2b is accommodated; and composite insulating shields 17a, 17b integrally formed into one metal-dielectric member in which surface of a high electric field part located in the vicinity of ends of openings is coated with a dielectric so as to cover the moving side and stationary side electrode parts 2a and 2b with the dielectric. To form the composite insulating shields 17a, 17b, a metal shield of less than 0.6 in non-uniform constant before coating with the dielectric is coated with dielectrics 18a, 18b having a thickness of not more than approximately 30% of an interelectrode distance from a facing electric-field relaxation shield.