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.

A switching power supply (switched-mode power device) includes a rectifier for a mains connection and for rectifying a three-phase AC voltage, a first converter and a second converter, the input voltage of which forms an intermediate circuit voltage, where the first converter regulates the intermediate circuit voltage such that the voltage substantially corresponds to a predefinable output voltage of the second converter multiplied by a load-independent transformation ratio on operation of the second converter with a resonant frequency, where upon forced reduction of the output voltage from the second converter, the first converter can set an, on average, sufficiently low intermediate circuit voltage such that the second converter can be operated substantially with the resonant frequency for a load-independent transformation ratio, where a signal for closed-loop control of the first converter stage can be derived from voltage and/or current information from the second converter.

A circuit for detecting loss of phase in three-phase power systems. The circuit includes a current sensor and a microprocessor. The current sensors are coupled to respective phases of a three-phase power source configured to supply power to a load. The microprocessor is coupled to the current sensors to process current measurements and detect loss of phase in the three-phase power source.

A circuit for detecting loss of phase in three-phase power systems. The circuit includes a current sensor and a microprocessor. The current sensors are coupled to respective phases of a three-phase power source configured to supply power to a load. The microprocessor is coupled to the current sensors to process current measurements and detect loss of phase in the three-phase power source.

A method for detecting a voltage disturbance on an electrical line coupled to a utility that includes calculating a sliding window actual root mean squared (RMS) voltage for each three-phase power signal, calculating a sliding window filtered RMS average voltage for each actual RMS voltage to identify normal changes in the voltage of the power signals from a nominal voltage, and obtaining a difference between the actual RMS voltage and the RMS average voltage for each of the power signals. The method determines whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is greater than a first predetermined percentage, or whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is less than a second predetermined percentage, and if so, disconnects a load from the utility.

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 circuit for detecting loss of phase in three-phase power systems. The circuit includes a current sensor and a microprocessor. The current sensors are coupled to respective phases of a three-phase power source configured to supply power to a load. The microprocessor is coupled to the current sensors to process current measurements and detect loss of phase in the three-phase power source.

A circuit for detecting loss of phase in three-phase power systems. The circuit includes a current sensor and a microprocessor. The current sensors are coupled to respective phases of a three-phase power source configured to supply power to a load. The microprocessor is coupled to the current sensors to process current measurements and detect loss of phase in the three-phase power source.

A motor controller includes a rectifier for converting AC power supplied from an AC power supply into DC power and outputting the DC power; an AC voltage detector for detecting an AC voltage value of the AC power supply and outputting the AC voltage value as a detection value; a power failure detector for determining that a power failure is occurring, when a state in which the outputted detection value is equal to or lower than a regulation voltage has continued for a regulation time or more; and a power failure detection condition determiner for determining or modifying the regulation time.