A ground monitoring tester for an AC power network, the tester comprising: a processor configured to repeatedly conduct impedance measurements of the ground of said AC power network at a point between a neutral reference point and the ground, wherein the processor is configured to conduct the impedance measurements repeatedly at intervals such as between 2 milliseconds and 2 minutes, indefinitely (i.e. without a time limit ending the measurements), whether or not the appliance or system is operational and whether or not there is an indication of a problem in the ground of said AC power network, wherein each of the impedance measurements is based on a voltage differential between a sequence of voltages including a first voltage without an internally generated reference current and a second voltage with an internally generated reference current, and at least one indication output based on the impedance measurements of the ground.

A system for preventing ground fault in a three-phase electric transmission line system caused by a line break, includes: the transmission lines, a programmable relay protection system, including a plurality of existing low sensitivity (LS) relays and a corresponding set of high sensitivity (HS) relays in parallel with the is relays. The HS relays on each line are programmed to include: preset acceptable operating parameter ranges of at least two electric operating conditions, at least one high sensitivity instantaneous undercurrent and at least one high sensitivity condition selected from line differential overcurrent and negative sequence overcurrent (and combinations thereof); monitoring; permitting closed circuit operation when all of the lines show that the two operating conditions are within the preset acceptable operating parameter ranges; tripping a circuit breaker on a broken line when that line shows that the two operating conditions are outside the preset parameter ranges; and shutting down power to the broken line before it otherwise causes a ground fault or other short circuit.

A wiring device including an interrupting device and a controller. The interrupting device electrically connects one or more line terminals to one or more load terminals when the interrupting device is in a reset condition and disconnects the line terminals from the load terminals when the interrupting device is in a tripped condition. The controller is configured to, determine a frequency of an input voltage at the one or more line terminals, determine whether the frequency is within a predetermined range, and when the frequency is within the predetermined range, perform a test of the wiring device.

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 one or more line terminals for connecting to an external power supply, one or more load terminals for connecting to an external load, one or more contacts electrically connecting one or more line terminals to one or more load terminals, and an auto-monitoring circuit. The auto-monitoring circuit configured to monitor one or more signals to determine an operating state of said circuit interrupting device, output a first signal having a first voltage level based on the operating state, wherein the first voltage level is greater than zero volts, and output a second signal having a second voltage level based on the operating state, wherein the second voltage level is greater than the first voltage level.

A leakage current detection interrupter (LCDI) device for an electrical appliance includes a shell and a trip assembly inside the shell. The shell includes an upper cover and a base cover joined together, and either the upper cover or the base cover includes a first cover and a removable second cover. The second cover spatially corresponds to a tail portion of the trip assembly; when it is removed, the tail portion is expose to allow a power cord to be connected to the LCDI device. By using a removable second cover, the cord can be conveniently assembled with the LCDI device when the LCDI device is installed on the electrical appliance, allowing the LCDI to be shipped without the cord. This can reduce the packed size of the LCDI device for easier shipping and storage, as well as lowering cost. It also makes the LCDI device more versatile.

According to an example, an uninterruptible power supply is provided comprising a first input, a backup input, an output to provide output power, an inverter coupled to the first input, the backup input, and the output, a first sensor to detect a voltage at an inverter output, a second sensor to detect a voltage at the first input, a switch coupled between the first input and the output, and a controller coupled to the switch and the first and second sensors, and configured to determine a first voltage difference across the bypass switch using at least one of the first sensor or the second sensor, filter the first voltage difference, determine whether a value derived from the first filtered voltage difference exceeds a threshold, and output an indication of a failure of the bypass switch based on the value derived from the first filtered voltage difference exceeding the threshold.

A circuit interrupting device includes an input conductor for electrically connecting to an external power supply, a load conductor for electrically connecting to a downstream load, a face conductor for electrically connecting to an external load, and a brush conductor in electrical communication with the input conductor and movable between a closed position and an open position. The brush conductor includes a second portion offset from a first portion such that a first terminal and a second terminal are positioned on separate planes. When the brush conductor is in the closed position, the first terminal contacts the load terminal and the second terminal contacts the face terminal to provide electrical communication between the input conductor, the load conductor, and the face conductor. When the brush conductor is in the open position, the first terminal is spaced apart from the load terminal and the second terminal is spaced apart from the face terminal.

Methods and systems for controlling a circuit designed to protect electrical equipment, in particular sensitive power grid equipment such as transformers, are disclosed. In particular, methods of local and remote control of operation of protection circuits are provided that allow for remote access to change an operational mode of such protection circuits, while ensuring that power grid equipment is protected locally regardless of any configuration instructions received from a remote or centralized facility. Override levels may be set to ensure power grid transformer protection, regardless of operational mode or remote instruction.

Systems and methods for mitigating ground induced currents are provided. In one or more examples, the systems and methods can utilize one or more device(s) that can be configured to detect DC currents being induced in and propagated along a power line that is transmitting an AC power signal. In one or more examples the device can be separate the desirable AC power waveform from the undesirable induced DC voltage and determine if the level of induced DC propagating on the power line requires mitigation. In one or more examples, if it is determined that mitigation is required, then the device can be configured to trigger a switch that can be shunt the DC power at the AC waveform zero crossing to a circuit element that is configured to dissipate the undesirable DC current. Filtering can be employed to remove any inadvertent low voltage harmonic distortion. The switch can be triggered during a zero-crossing of the signal to minimize disruption to an end user of the power signal.