A conventional technique makes a configuration complicated. Provided is an apparatus including: a voltage measuring unit configured to measure each of instantaneous voltages of three-phase AC voltage; and a determination unit configured to determine a state of a power supply source of the three-phase AC voltage based on a result of comparison between a comparison target value corresponding to a sum of n-th powers (n is a positive even number) of the instantaneous voltages of the three-phase AC voltage and a reference value.

The present disclosure relates to a 3-phase undervoltage trip device capable of automatically tripping a circuit breaker based on an under-voltage of a 3-phase line voltage, including lines to which a 3-phase power is applied. The undervoltage trip device is connected to lines to which a 3-phase power is applied and configured to operate to automatically trip a circuit breaker when an open phase condition occurs on any one of three phases of the power. As the undervoltage trip device automatically trips the circuit breaker when the open phase condition occurs on any one of three phase, occurrence of the open phase condition due to disconnection or an accident on the line may be easily detected.

The present disclosure relates to a 3-phase undervoltage trip device capable of automatically tripping a circuit breaker based on an under-voltage of a 3-phase line voltage, including lines to which a 3-phase power is applied. The undervoltage trip device is connected to lines to which a 3-phase power is applied and configured to operate to automatically trip a circuit breaker when an open phase condition occurs on any one of three phases of the power. As the undervoltage trip device automatically trips the circuit breaker when the open phase condition occurs on any one of three phase, occurrence of the open phase condition due to disconnection or an accident on the line may be easily detected.

A monitor circuit that monitors power delivered by an electrical utility or other source to a consumer. The device may be located at or near an entry point, such as near an electrical meter. The device senses a material change in voltage, and terminates power to the consumer until normal voltage is restored. The device automatically resets when normal voltage is restored, without need for a service call.

A safety electronic switch, having a first terminal, a second terminal, a third terminal, a surge voltage suppression unit, a comparator, and a relay. The surge voltage suppression unit is connected to a safety circuit through the first terminal. The first terminal is provided with a live wire end and a neutral wire end. The surge voltage suppression unit is connected to the comparator. The comparator is connected to the relay. The relay is connected to the second terminal and the third terminal. The third terminal is connected to a low-voltage power supply. The third terminal is provided with a positive electrode and a negative electrode that are connected to the low-voltage power supply.

A system and method for controlling electrical power in a multi-phase electrical service to a load is provided. The system includes an electric meter that determines when an electrical characteristic of a phase of a multi-phase electrical service is below a threshold. A first switch and second switch are coupled to the first phase and second phase respectively and disconnect the phases from a power source. A bridging switch is coupled between the phases, the bridging switch being arranged between the load and the first and second switches. A controller is coupled between the electric meter, the first switch, the second switch, and the bridging switch. The controller causes the first switch to open in response to the electrical characteristic of the first phase being below the threshold and causing the bridging switch to close when the first switch is opened.

A system and method for controlling electrical power in a multi-phase electrical service to a load is provided. The system includes an electric meter that determines when an electrical characteristic of a phase of a multi-phase electrical service is below a threshold. A first switch and second switch are coupled to the first phase and second phase respectively and disconnect the phases from a power source. A bridging switch is coupled between the phases, the bridging switch being arranged between the load and the first and second switches. A controller is coupled between the electric meter, the first switch, the second switch, and the bridging switch. The controller causes the first switch to open in response to the electrical characteristic of the first phase being below the threshold and causing the bridging switch to close when the first switch is opened.

A method for detecting an open-phase condition of a transformer having a grounded-wye high voltage side connection including monitoring current flowing in a neutral connection on the high voltage side of the transformer in real time by voltage relaying and current relaying to identify an open phase condition signature in a signal capable of characterizing change of current magnitude. A current signal may be injected onto the neutral terminal and the zero-sequence mode of the transformer monitored to detect an open-phase condition indicated by an increase in network impedance and decrease or elimination of the injection current.

A method for detecting an open-phase condition of a transformer having a grounded-wye high voltage side connection including monitoring current flowing in a neutral connection on the high voltage side of the transformer in real time by voltage relaying and current relaying to identify an open phase condition signature in a signal capable of characterizing change of current magnitude. A current signal may be injected onto the neutral terminal and the zero-sequence mode of the transformer monitored to detect an open-phase condition indicated by an increase in network impedance and decrease or elimination of the injection current.

A protection circuit provides a control voltage to a 3-phase contactor, where the three phases of the 3-phase power supply are inputs to the 3-phase contactor. The protection circuit includes: four input terminals, configured to be connected respectively to the three phases and to the neutral line of the 3-phase power supply; an output terminal, providing the control voltage to a control line of the 3-phase contactor; and control circuitry configured to provide the control voltage when any one or more of the three phases are live and when the neutral line is connected, and to provide no control voltage when all three phases are disconnected or when the neutral line is disconnected.