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.

A method and apparatus for detecting a missing phase in a 3-phase twelve-pulse autotransformer rectifier unit (ATRU) which, in use, receives a 3-phase input and delivers a nominal DC output on which a common-mode voltage is impressed. At least one of the frequency and amplitude of the common-mode voltage are monitored thereby to determine whether there is a missing phase in the input. The frequency and/or amplitude of the common-mode voltage may also be monitored thereby to determine whether there is a loss of input voltage.

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.

The present application discloses systems and methods to determine loss of at least one electric power transmission line in an electric power transmission system. In various embodiments, a system consistent with the present disclosure may include an electrical parameter monitoring subsystem configured to receive electrical parameter measurements and to determine a change of the electrical measurements. An analysis subsystem may determine whether a change in the electrical measurements is indicative of loss of at least one transmission line and may calculate a number of transmission lines lost based on the change. In some embodiments, a remedial action subsystem may be configured to implement a remedial action in response to loss of at least one transmission line. The number of transmission lines lost may be determined based on an angle difference ratio and a power ratio between two buses in electrical transmission system.

A method is provided for controlling operation of an air conditioning unit. The method comprises supplying line voltage to activate a motor configured to operate the air conditioning unit, and monitoring a supply of control voltage in order to control operation of the air conditioning unit, the supply of control voltage being derived from line voltage. In response to detecting a control voltage below a predetermined threshold and/or by a predetermined percentage, a time delay is initiated. The method further comprises deactivating the motor if a predetermined increase in control voltage is not detected before the time delay expires.

The present application discloses systems and methods to determine loss of at least one electric power transmission line in an electric power transmission system. In various embodiments, a system consistent with the present disclosure may include an electrical parameter monitoring subsystem configured to receive electrical parameter measurements and to determine a change of the electrical measurements. An analysis subsystem may determine whether a change in the electrical measurements is indicative of loss of at least one transmission line and may calculate a number of transmission lines lost based on the change. In some embodiments, a remedial action subsystem may be configured to implement a remedial action in response to loss of at least one transmission line. The number of transmission lines lost may be determined based on an angle difference ratio and a power ratio between two buses in electrical transmission system.

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.

Exemplary embodiments are disclosed of a relay control or contactor configured to provide adaptive undervoltage protection for a three-phase load using a single current sensor. The current sensor is electrically connected with a corresponding one of a first, second, or third relay for providing information about current from the corresponding relay to a load. The information may be usable to determine a failure condition when: after the relays are energized, the information indicates that: there is no current across the corresponding one of the first, second, and third relays thereby indicating that the corresponding one of the first, second, and third relays is open and the load is running on two phases; or the current across the corresponding one of the first, second, and third relays is at lock rotor current for more than a determined amount of time indicating that the load is running on two phases.

Exemplary embodiments are disclosed of a relay control or contactor configured to provide adaptive undervoltage protection for a three-phase load using a single current sensor. The current sensor is electrically connected with a corresponding one of a first, second, or third relay for providing information about current from the corresponding relay to a load. The information may be usable to determine a failure condition when: after the relays are energized, the information indicates that: there is no current across the corresponding one of the first, second, and third relays thereby indicating that the corresponding one of the first, second, and third relays is open and the load is running on two phases; or the current across the corresponding one of the first, second, and third relays is at lock rotor current for more than a determined amount of time indicating that the load is running on two phases.