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 operating an electric power converter and an electric power converter configured to convert DC power into AC power supplied to a three-phase AC network, conclude, during the converting, that a single-phase tripping has started in the three-phase AC network connected to the three-phase output of the converter, and after the concluding that the single-phase tripping has started in the three-phase AC network, control an active current in the three-phase output of the converter such that a negative sequence voltage in the three-phase output of the converter remains at or below a predetermined level, wherein the converter is configured to perform the controlling until concluding that the single-phase tripping has ended in the three-phase AC network.

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.

An uninterruptible power supply (UPS) for a three-phase alternating current network, in particular a medium-voltage network, includes an energy storage system, a switch, an LC resonant circuit, which is a series circuit of an inductance and a capacitance, and a control unit for controlling the switch. The switch and the LC resonant circuit are connected in series, and the series circuit of the switch and the LC resonant is arranged between a network feed and the energy storage system which is connected to a load. There is also described a method for operating such a UPS and a corresponding computer program.

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.

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.

An electric circuit device and method is for recognizing a closed switch contact as well as a protective ground conductor interruption in a one- or multiphase electric supply line. A control of a residual current monitoring device (RCMB control) includes one fault current control unit for generating a control signal pattern including a series of switching-on impulses forwarded to a first electronic switch unit to activate a possible artificial passive fault current on one or more active conductors and the protective ground conductor (as a return conductor), this fault current actually flowing, being recognized, and evaluated in a closed circuit in a closed switch contact to be tested and an intact protective conductor. Owing to control signal patterns varying during monitoring, a reliable detection of the artificial passive fault current is ensured even in large dynamic disturbance levels while the electric installation (supply line) to be monitored is in operation.

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 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.