Abstract: The electric power system protection device according to the present invention includes a transformer including a primary winding and a secondary winding which are electrically isolated from each other. The primary winding is to be connected to a first electric path which is to be connected to an external power supply configured to supply AC power by use of a secondary battery, so as to receive the AC power from the external power supply. The secondary winding is to be connected to a second electric path to be connected to a power supply path from a commercial electric power system to an electric load.

Abstract: A first coil is wound around a first core, and have one end that is connected to ground and the other end that is connected to one end of a second coil. The second coil is wound around a second core, and has the one end that is connected to the first coil, and the other end that is connected to an excitation unit via a current-limiting resistor. A magnetic flux is generated in the first core by an excitation signal outputted from the excitation unit. Induced electromotive force is generated in the conductor due to the magnetic flux generated in the first core. The direction of the magnetic flux generated in the second core is opposite to the direction of the magnetic flux generated in the first core, and the induced electromotive forces of them generated in the conductor are cancelled each other out.

Abstract: A first threshold Vf1 that is compared with a measurement value of a charging current and a second threshold Vf2 that is compared with a measurement value of a discharging current are set to mutually different values by a determination unit 12. Also the first threshold Vf1 relating to the charging current is set to a value higher (greater) than the second threshold Vf2 relating to the discharging current.

Abstract: The electric power system protection device according to the present invention includes a transformer including a primary winding and a secondary winding which are electrically isolated from each other. The primary winding is to be connected to a first electric path which is to be connected to an external power supply configured to supply AC power by use of a secondary battery, so as to receive the AC power from the external power supply. The secondary winding is to be connected to a second electric path to be connected to a power supply path from a commercial electric power system to an electric load.

Abstract: A first coil is wound around a first core, and have one end that is connected to ground and the other end that is connected to one end of a second coil. The second coil is wound around a second core, and has the one end that is connected to the first coil, and the other end that is connected to an excitation unit via a current-limiting resistor. A magnetic flux is generated in the first core by an excitation signal outputted from the excitation unit. Induced electromotive force is generated in the conductor due to the magnetic flux generated in the first core. The direction of the magnetic flux generated in the second core is opposite to the direction of the magnetic flux generated in the first core, and the induced electromotive forces of them generated in the conductor are cancelled each other out.

Abstract: A current detection device includes: a core to be disposed in the vicinity of a conductor as a detection target; a winding wound around the core; an excitation unit configured to apply an excitation signal, having a magnitude and a direction that change at a constant period, to the winding; a magnetic flux detection unit (comparator and averaging circuit) configured to detect a magnetic flux generated in the core due to current flowing through the conductor; and an adder unit configured to add a feedback signal to the excitation signal such that the magnetic flux detected by the magnetic flux detection unit is cancelled.

Abstract: The electric-vehicular charge and discharge device of the present invention includes a power converter, a grounding unit, a ground fault detector, and a switcher. The power converter is interposed between an external circuit and a pair of power terminals of a secondary battery unit of an electric vehicle, and is configured to convert power between the external circuit and the secondary battery unit. The grounding unit connects at least one of the pair of power terminals of the secondary battery unit to a grounding point to be connected to the power converter. The ground fault detector determines whether a ground fault has occurred in a power supply path between the power converter and the secondary battery unit. The switcher separates the secondary battery unit from the power supply path when the ground fault detector determines that a ground fault has occurred in the power supply path.