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 system for transmitting power and data, particularly including a half-wave control, includes a control unit connected to grid phases, the system having a phase-failure detection device which has bistable multivibrators, especially bistable multivibrators assigned to a respective grid phase. Each bistable multivibrator has an input for setting and an input for resetting, one of the inputs being connected to a digitizing device for digitizing the positive half-waves of a respective grid phase, the other of the inputs being connected to a digitizing device for digitizing the negative half-waves of a respective grid phase. The effective value of the output voltage of the bistable multivibrator is compared by a comparison device to a threshold value to detect a phase failure.

A system for transmitting power and data, particularly including a half-wave control, includes a control unit connected to grid phases, the system having a phase-failure detection device which has bistable multivibrators, especially bistable multivibrators assigned to a respective grid phase. Each bistable multivibrator has an input for setting and an input for resetting, one of the inputs being connected to a digitizing device for digitizing the positive half-waves of a respective grid phase, the other of the inputs being connected to a digitizing device for digitizing the negative half-waves of a respective grid phase. The effective value of the output voltage of the bistable multivibrator is compared by a comparison device to a threshold value to detect a phase failure.

A LCDI power cord circuit is provided. The circuit includes energizing shielded wires and monitoring the energized shields for surges, e.g., arcing, and/or voltage drops, e.g., shield breaks detected by a Power Cord Fault Circuit (PCFC). In addition to shield breaks the PCFC also monitors the energized shields for shield degradation due to, for example, galvanic corrosion.

A LCDI power cord circuit is provided. The circuit includes energizing shielded wires and monitoring the energized shields for surges, e.g., arcing, and/or voltage drops, e.g., shield breaks detected by a Power Cord Fault Circuit (PCFC). In addition to shield breaks the PCFC also monitors the energized shields for shield degradation due to, for example, galvanic corrosion.

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.

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.

An air conditioner includes an outdoor device and an indoor device. The outdoor device includes an outdoor control unit that is operated at the voltage of a smoothing capacitor; a power-supply switching relay to which a signal line is connected; an inrush-current preventing-relay drive unit that is operated when single-phase AC power is supplied between a power-signal common line and the signal line via an outdoor activation relay in the indoor device and the power-supply switching relay; a first inrush-current preventing relay that is connected in parallel with a power supply relay and is controlled by the inrush-current preventing-relay drive unit; and a second inrush-current preventing relay that is connected in parallel with the first inrush-current preventing relay and is controlled by the outdoor control unit. The outdoor control unit closes the second inrush-current preventing relay when the external power supply is interrupted.