An electrical apparatus configured to electrically connect to a multi-phase alternating current (AC) electrical power distribution network includes: an input electrical network including: a plurality of input nodes, each configured to electrically connect to one phase of the multi-phase AC electrical power distribution network; at least one non-linear electronic component electrically connected to the input electrical network; an impedance network electrically connected between the input electrical network and ground; and a control system configured to: access a voltage signal that represents a voltage over time at the input electrical network; determine a frequency content of the voltage signal; determine a property of the frequency content; and determine whether an input current performance condition exists in the electrical apparatus based the property of the frequency content.

An electrical apparatus configured to electrically connect to a multi-phase alternating current (AC) electrical power distribution network includes: an input electrical network including: a plurality of input nodes, each configured to electrically connect to one phase of the multi-phase AC electrical power distribution network; at least one non-linear electronic component electrically connected to the input electrical network; an impedance network electrically connected between the input electrical network and ground; and a control system configured to: access a voltage signal that represents a voltage over time at the input electrical network; determine a frequency content of the voltage signal; determine a property of the frequency content; and determine whether an input current performance condition exists in the electrical apparatus based the property of the frequency content.

In order to ensure safe operation of a multi-phase system, even a system including a plurality of phases, a number of phase groups is provided, which comprises some of the phases, wherein phase currents of the number of phase groups are merged in a group node to form a group sum current and a group sum current measurement value of the group sum current is captured. The current measurement values belonging to the number of phase groups are summed up to form a group sum and the group sum is compared with the group sum current measurement value to validate the phase currents of the phases in order to ensure safe operation.

A fault protection system is configured to detect a fault in an electric power system. The fault protection system obtains a differential measurement signal. The differential measurement signal may, for example, indicate, as a function of time, the difference between currents or voltages measured at two or more terminals or boundaries of a fault protection zone of the electric power system. Regardless, the fault protection system generates a fault detection signal by cross-correlating the differential measurement signal with a reference signal. The reference signal may for instance be the differential measurement signal that is expected upon occurrence of a fault. The fault protection system performs fault detection, for detecting a fault internal to the fault protection zone, as a function of the fault detection signal.

Distance protection for electric power systems disclosed herein uses an operating signal and a sequence polarizing signal made up of a supervised sequence current and a supervised sequence voltage. The polarizing signal may be determined based on the fault type and may be weighted toward sequence currents or sequence voltages depending on the power system conditions. For phase-to-ground faults, the sequence currents may include negative-sequence and zero-sequence currents. For phase-to-phase faults, the sequence currents may include negative-sequence currents. The current portion of the sequence polarizing signal may be weighted based on detection of insufficient negative-sequence current magnitude, standing unbalance, current transformer saturation, open pole, three-phase fault, and the like. The distance elements described herein provides improved protection during real-world power system conditions and changes.

Distance protection for electric power systems disclosed herein uses an operating signal and a sequence polarizing signal made up of a supervised sequence current and a supervised sequence voltage. The polarizing signal may be determined based on the fault type and may be weighted toward sequence currents or sequence voltages depending on the power system conditions. For phase-to-ground faults, the sequence currents may include negative-sequence and zero-sequence currents. For phase-to-phase faults, the sequence currents may include negative-sequence currents. The current portion of the sequence polarizing signal may be weighted based on detection of insufficient negative-sequence current magnitude, standing unbalance, current transformer saturation, open pole, three-phase fault, and the like. The distance elements described herein provides improved protection during real-world power system conditions and changes.

Systems and methods to disconnect a faulted region of a power grid are described. For example, a control system may obtain a set of regions of a power grid. The control system may obtain a current magnitude and a voltage magnitude of the power grid. The control system may detect a fault in the power grid based at least in part on the current magnitude. The control system may, from the set of regions, determine a faulted region that the fault is located within based on a voltage magnitude of one or more buses in the power grid, a net change in power with respect to time of one or more regions in the set of regions, or both. The control system may send one or more signals to electrically disconnect the faulted region from the power grid.

Systems and methods to isolate faults and restore power are described herein. For example, an intelligent electronic device (IED) may receive a blocking signal indicating a fault is detected on a power line. The IED may obtain one or more current measurements of the power line. The IED may determine that a fault is not present on the power line at the IED based on the one or more current measurements. The IED may trip a first current interruption device of the IED The IED may send a close permissive signal to another IED indicating that the other IED is permitted to permitted to close an open current interruption device of the other IED to restore power to one or more loads.

The invention provides a method and device for fault section identification in a multi-terminal mixed line. The method comprises obtaining positive sequence voltage and current phasors from measurements of voltages and currents at each terminal of the mixed line. The method further comprises calculating a voltage phasor for each terminal, wherein the calculation of the voltage phasor for a first terminal is performed using at least the voltage and current phasors obtained for one of a second terminal and a third terminal, and the current phasor obtained for the first terminal. Thereafter, the method comprises determining a section of the mixed line having the fault, based on comparison of the calculated and obtained voltage phasors for each terminal. In addition, the method comprises controlling a switching device with a re-trip signal generated based on the determination of the section with the fault.

A differential protection method for monitoring a line of a power grid. Current phasor measured values are captured at the ends of the line and transmitted to an evaluation device which is used to form a differential current value with current phasor measured values temporally allocated to one another. Time delay information indicating the time delay between local timers of the measuring devices is used for the temporal allocation of the current phasor measured values captured at different ends, and a fault signal indicating a fault affecting the line is generated if the differential current value exceeds a predefined threshold value. The reliability of the time synchronization is further increased by forming a quotient of the current phasor measured values to form an asymmetry variable, that is used to check a transit time difference of messages transmitted via the communication connection in different directions.