Methods and devices for insulation monitoring of an ungrounded IT power supply system having at least two phase conductors includes determining an insulation resistance separately for each phase conductor using a separate response value. In one embodiment of the invention, relevant current and voltage distributions are calculated. In another embodiment, a change time window is set within which a second response value is activated. In yet another embodiment, an option of shutting down/continuing operation of the IT power supply system is offered.

Embodiments of the present invention provide for impedance shift analysis for failure prediction in an electrical power distribution network. In an embodiment of the invention, the method includes receiving a sequence of electrical measurements indicative of an impedance measured for a segment of an electrical power distribution network over a period of time. Then, a set of impedance measurements is computed for the period of time and the set of impedance measurements is organized into a distribution correlating each one of the impedance measurement with a corresponding computed current measurement. A trend line for the distribution is identified and a slope computed of the trend line. Finally, on condition that the slope exceeds a threshold steepness, an impending failure in the segment is determined and a notification transmitted over a computer communications network to an end user requesting physical inspection of the segment.

A method and device for timing in time-varying distance protection based on multiple lines of a tower. The method includes: collecting an instantaneous current value at a time-varying distance protection installation location in the multiple lines of the tower, and acquiring preset parameters; calculating, according to the preset parameters and a multi-line ranging model, a multi-line ranging result; calculating, according to the preset parameters, the multi-line ranging result, and an adaptive calculation model, time of a section-II distance protection action and final time of a section-III distance protection action; and determining, according to the instantaneous current value, the preset parameters, and a cross-line failure auxiliary criterion model, final time of the section-II distance protection action.

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.

A power converter includes first and second arms, each having switching elements, and performs power conversion between a DC system and an AC system. An AC circuit breaker and a current control circuit are connected in series between the AC system and the power converter. The current control circuit includes a current-limiting resistor and a disconnector connected in parallel. A controller instructs a disconnector to close after an initial charge of the power converter and opens the AC circuit breaker when an impedance of a line between a first node located on a first end side of the current control circuit and a second node located on a second end side of the current control circuit is not less than a first threshold and an accumulated value of a current flowing through the current control circuit within a certain period of time is not less than a second threshold.

A protection relay comprises a digital processing unit including: a first filter to eliminate a DC component in the time-series data, the first filter having a first window length; a second filter to eliminate a DC component in the time-series data, the second filter having a second window length shorter than the first window length; and a coefficient calculation unit to multiply an amplitude value of an output signal of the first filter and an amplitude value of an output signal of the second filter by first and second coefficients respectively, and integrate multiplication results. An operation determination is performed based on an output of the coefficient calculation unit. The first coefficient is decreased and the second coefficient is increased when a failure of the power system is detected, and thereafter, the first coefficient and the second coefficient are changed with a lapse of time.

A protection relay comprises a digital processing unit including: a first filter to eliminate a DC component in the time-series data, the first filter having a first window length; a second filter to eliminate a DC component in the time-series data, the second filter having a second window length shorter than the first window length; and a coefficient calculation unit to multiply an amplitude value of an output signal of the first filter and an amplitude value of an output signal of the second filter by first and second coefficients respectively, and integrate multiplication results. An operation determination is performed based on an output of the coefficient calculation unit. The first coefficient is decreased and the second coefficient is increased when a failure of the power system is detected, and thereafter, the first coefficient and the second coefficient are changed with a lapse of time.

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.

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.

A protection and monitoring system, device, and method for an electric power system, including a capacitor bank having multiple strings in each phase, voltage and current measuring devices, and relays to protect this capacitor bank. Each string can have multiple capacitor units and each unit can consist of multiple capacitor elements. The method may include: determining steady state operating condition using the obtained current and voltages, calculating and storing present time impedance value of each string into memory, calculating the string per unit impedance incremental quantity, detecting capacitor element failure based at least in part on this incremental quantity and calculating number of failed capacitor elements for each event, accumulating the number of failed capacitor elements, and performing a protection action when healthy capacitor elements are subject to an overvoltage limit. The method may be inherently immune or otherwise insensitive to capacitor variations due to aging, temperature change, instrument transformers errors, inaccuracy in data acquisition, and inherent manufacturing unbalance.