Provided is a grid-connected inverter safety detection device applied in a photovoltaic inverter system and including voltage detection circuit, a filter circuit, a comparison circuit and a controller. The voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal for any phase of the three-phase power grid and the ground. The filter circuit is configured to filter out an alternating current component of the voltage detected by the voltage detection circuit and to retain an direct current component of the voltage. The comparison circuit is configured to compare the direct current component of the voltage with a preset voltage value and transmit a comparison result to the controller. The controller is configured to determine, according to the comparison result, whether an alternating current side at the output terminal of the inverter has normal insulation.

Provided is a grid-connected inverter safety detection device applied in a photovoltaic inverter system and including voltage detection circuit, a filter circuit, a comparison circuit and a controller. The voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal for any phase of the three-phase power grid and the ground. The filter circuit is configured to filter out an alternating current component of the voltage detected by the voltage detection circuit and to retain an direct current component of the voltage. The comparison circuit is configured to compare the direct current component of the voltage with a preset voltage value and transmit a comparison result to the controller. The controller is configured to determine, according to the comparison result, whether an alternating current side at the output terminal of the inverter has normal insulation.

Disclosed herein are a variety of systems and methods related to detection of a cross-country fault in an electrical power system. In one embodiment, a system consistent with the present disclosure may be configured to monitor electrical parameters in the electrical power system. The system may determine when a voltage magnitude of one phase exceeds a first voltage threshold. The one phase that exceeds the first voltage threshold may be identified as an un-faulted phase. The system may further be configured to determine that the voltage magnitude of the un-faulted phase exceeds a second threshold based on a zero-sequence voltage. The system may further be configured to determine that a phase angle between the un-faulted phase and the zero-sequence voltage is within a range. A protective action to clear the cross-country fault condition may be implemented upon identification of a cross-country fault.

Disclosed herein are a variety of systems and methods related to detection of a cross-country fault in an electrical power system. In one embodiment, a system consistent with the present disclosure may be configured to monitor electrical parameters in the electrical power system. The system may determine when a voltage magnitude of one phase exceeds a first voltage threshold. The one phase that exceeds the first voltage threshold may be identified as an un-faulted phase. The system may further be configured to determine that the voltage magnitude of the un-faulted phase exceeds a second threshold based on a zero-sequence voltage. The system may further be configured to determine that a phase angle between the un-faulted phase and the zero-sequence voltage is within a range. A protective action to clear the cross-country fault condition may be implemented upon identification of a cross-country fault.

A determining method and apparatus for a neutral system working voltage includes a power system having three phase wires and three capacitor banks. Each bank has one terminal connected to one phase wire, and the other terminals form a neutral point. A phase voltage of each phase wire is periodically sampled, obtaining sampling value groups of real-time phase voltages. Each phase voltage group includes a sampling value of a phase voltage of each phase wire by measuring each phase wire. Unbalance rates between the banks are based on the groups of sampling values. The unbalance rate is a ratio between capacitances of every two phase wires. The isolated neutral system working voltage is based on the unbalance rates. The unbalance rates between banks are based on the sampling values measured in real time. The working voltage is based on the unbalance rates, permitting subsequent operations to be accurately performed.

Provided is a method for controlling the opening/closing of a circuit breaker which includes include: a signal inputting step for receiving an input of a signal; a sign change detecting step for detecting a sign change of the signal; a zero crossing reference setting step for setting a zero crossing reference when there is the sign change; a one period integrated value comparing step for checking whether an absolute value of a one period integrated value obtained by integrating the signal for one period from the zero crossing reference exceeds a reference value; a detected phase comparing step for determining whether a detected phase is identical to a set phase; and a circuit breaker opening/closing step for controlling the opening/closing of a circuit breaker when the absolute value of the one period integrated value does not exceed the reference value and the detected phase is identical to the set phase.

Provided is a method for controlling the opening/closing of a circuit breaker which includes include: a signal inputting step for receiving an input of a signal; a sign change detecting step for detecting a sign change of the signal; a zero crossing reference setting step for setting a zero crossing reference when there is the sign change; a one period integrated value comparing step for checking whether an absolute value of a one period integrated value obtained by integrating the signal for one period from the zero crossing reference exceeds a reference value; a detected phase comparing step for determining whether a detected phase is identical to a set phase; and a circuit breaker opening/closing step for controlling the opening/closing of a circuit breaker when the absolute value of the one period integrated value does not exceed the reference value and the detected phase is identical to the set phase.

A safety tripping device for a frame-type ACB drawer seat, which includes a special gear, a first lever, a tension spring, a second lever, and a tripping shaft. The special gear includes the first rotation shaft and the first irregular convex flange feature. The irregular convex flange is lapped with a bending edge of one end of the first lever. The other end of the first lever is connected to the tension spring. An arc-shaped notch is provided at one end of the first lever which corresponds to the connecting spring. An arc-shaped protrusion matching the arc-shaped notch is provided at one end of the second lever. The arc-shaped protrusion engages with or separates from the arc-shaped notch to achieve the tripping operation. The frame-type ACB drawer seat according to the present invention is suitable for large-scale production applications.

A safety tripping device for a frame-type ACB drawer seat, which includes a special gear, a first lever, a tension spring, a second lever, and a tripping shaft. The special gear includes the first rotation shaft and the first irregular convex flange feature. The irregular convex flange is lapped with a bending edge of one end of the first lever. The other end of the first lever is connected to the tension spring. An arc-shaped notch is provided at one end of the first lever which corresponds to the connecting spring. An arc-shaped protrusion matching the arc-shaped notch is provided at one end of the second lever. The arc-shaped protrusion engages with or separates from the arc-shaped notch to achieve the tripping operation. The frame-type ACB drawer seat according to the present invention is suitable for large-scale production applications.

Methods and systems for detecting a falling power line in a power transmission or distribution system are described. Electrical measurements at various points in the power distribution system are used to detect changes in a power line indicating that the conductor has broken or become disconnected. Upon detection, control mechanisms are used to deenergize the conductor while the conductor is falling and/or before it contacts the ground.