A method for locating a ground fault in an IT network which has a converter with a rectifier connected to a power transmission network, a DC link and an inverter connected to an electrical machine includes measuring a common-mode voltage property of the converter or of the power transmission network and comparing the common-mode voltage property with an output voltage property of an output voltage of the inverter. When the IT network experiences a ground fault, the comparison of the common-mode voltage property with the output voltage property is used to determine whether a machine area of the IT network connected downstream of the converter, which includes the electrical machine and a connecting line between the electrical machine and the converter, causes the ground fault.

A circuit interrupting device including a line terminal, a wideband current sensor configured to measure a current flowing through the line terminal, a zero cross detection circuit configured to measure a voltage and frequency of the line terminal, and a microcontroller including an electronic processor. The microcontroller is configured to apply a digital filter to a line current measurement signal received from the wideband current sensor and estimate spectral density of the filtered line current measurement signal. The microcontroller is further configured to calculate an arcing characteristic based on the spectral density, determine whether an arc fault is present within the circuit interrupting device based on a comparison of the arcing characteristic to one or more thresholds, and activate an interrupting device when an arc fault is present.

A transmission and distribution system with electric shock protection function includes a transmitting terminal and a receiving terminal. The transmitting terminal includes a switch, a current measurer, a signal generator, and a controller. The receiving terminal includes a filter. The switch is coupled to a first DC power and a transmission line. The current measurer is coupled to the transmission line, and measures a current of the transmission line and provides a current signal. The signal generator provides a disturbance signal to the transmission line. The controller receives the current signal and controls the switch. If the controller determines that the current signal contains the disturbance signal, the controller turns off the switch.

The discharge detector of the present invention includes a filter circuit configured to pass a noise superimposed on the current or voltage in a predetermined frequency range; an amplifier configured to amplify a level of the noise passed through the filter circuit; and a processor configured to detect occurrence of discharge based on the noise level amplified by the amplifier. The processor is set to have a threshold related to the noise level and a determination time to determine whether discharge has occurred. The processor is capable of selectively executing either one of a discharge detection mode or a learning mode. The processor in the learning mode executes process of sampling the noise at the level of the threshold or more and resetting the value of the setting of the determination time based on a result of the sampling.

A circuit includes a detector and controller circuit configured to detect a high field RF (radio frequency) electromagnetic fields indicating a potential of an electromagnetic pulse event capable of damaging electrical equipment connected to a power grid. The circuit also includes controller receiving an input from the detector circuit, the controller being included within a shielded enclosure and configured to initiate an event in response to detection of the high field electromagnetic pulse field to remove the electrical equipment from the power grid.

A detection scheme for temporary overvoltages and/or ground fault overvoltages in electric power systems is described. Current passing through a surge arrestor component of the power system is monitored. An algorithm for identifying one or more frequency components of the measured current signal is performed to screen out unwanted harmonics. In some embodiments, this is a frequency domain analysis. The frequency component(s) of the current signal is then compared to a calculated pickup current or pickup voltage of the system to determine if system protection steps should be undertaken.

A system includes a transformer rectifier unit (TRU) having three inputs, a first AC bus configured to supply power to a first of the three inputs, a second AC bus configured to supply power to a second of the three inputs, and a third AC bus configured to supply power to a third of the three inputs. The system includes a power quality sense device electrically connected to each of the first, second and third AC busses. The system includes an electrically held contactor electrically connected between the TRU and the power quality sense device. The electrically held contactor is configured and adapted to be switched ON or OFF depending on whether the power quality sense device is energized or de-energized.

A heating device includes a heater, an AC-voltage input section between which an AC voltage is applied, a fuse, a switcher, an AC-voltage-abnormality detector configured to detect an abnormality of the AC voltage, a controller. The controller is configured to execute a current-flowing operation in a state in which connection of a first connection terminal to a second connection terminal is a non-connecting state. The current-flowing operation is an operation in which an electrical current flows through the heater. The controller is configured to execute a connecting process in response to detection of the abnormality of the AC voltage by the AC-voltage-abnormality detector detected in the middle of the current-flowing operation. The connecting process is a process of switching a connection of a first connecting point to a second connecting point from a non-connecting state to a connecting state.

An arcing fault recognition unit is for an electric low-voltage circuit. In an embodiment, the arcing fault recognition unit includes at least one current sensor for periodically ascertaining electric current values in the electric circuit, the current sensor being connected to an analysis unit which is designed in such a way that an arcing fault recognition signal is output when a variation in the rate of current rise exceeds a first threshold value or drops below a second threshold value.

An arcing fault recognition unit is for an electric low-voltage circuit. In an embodiment, the arcing fault recognition unit includes at least one current sensor for periodically ascertaining electric current values in the electric circuit, the current sensor being connected to an analysis unit which is designed in such a way that an arcing fault recognition signal is output when a variation in the rate of current rise exceeds a first threshold value or drops below a second threshold value.