Detection and protection against electric power generator stator ground fault conditions in multiple-generator high-impedance grounded installations is provided herein. In one embodiment, a generator protection element may block a determination of a fault using third harmonic voltages when the third harmonic voltage from the generator is less than a factor of the maximum third harmonic voltage from all of the generators on the common bus. A tripping subsystem may issue a trip command based upon detection of a stator ground fault condition.

An earth leakage circuit breaker includes a current sensing unit configured to sense current in a circuit, a converter configured to detect a fundamental wave component and a specific harmonic component from the sensed current, the specific harmonic component being one of a plurality of harmonic components, and a controller. The controller is configured to compare a harmonic component ratio with a threshold component ratio, to determine whether the sensed current is abnormal current, and to control cutoff of the circuit according to the result of determination. The harmonic component ratio is a ratio of the specific harmonic component to the fundamental wave component. The converter is configured to convert the sensed current from an analog signal into digital data and to perform Fourier transform with respect to the converted digital data to detect the fundamental wave component and the specific harmonic component.

Detection of electric power generator stator ground fault conditions and protection of the generator due to such conditions is provided herein. In one embodiment, a generator protection element may calculate generator third harmonic voltage quantities using measurements from the generator terminals, and determine a stator ground fault condition using the calculated generator third harmonic voltage quantity. A tripping subsystem may issue a trip command based upon detection of a stator ground fault condition.

Detection and protection against electric power generator stator ground fault conditions in multiple-generator high-impedance grounded installations is provided herein. In one embodiment, a generator protection element may block a determination of a fault using third harmonic voltages when the third harmonic voltage from the generator is less than a factor of the maximum third harmonic voltage from all of the generators on the common bus. A tripping subsystem may issue a trip command based upon detection of a stator ground fault condition.

An apparatus for mitigating GIC (geomagnetically induced current) effects through a fuzzy logic controlled variable resistor. Under GIC conditions (or any unbalanced fault current condition), the GIC or unbalanced fault current flows through the neutral of a power transformer. It is detected by the fuzzy logic controller, which sends a signal to a switch to open. The resistor is in the circuit and impedes the flow of current through the neutral, thereby protecting the transformer from getting overheated.

An apparatus for mitigating GIC (geomagnetically induced current) effects through a fuzzy logic controlled variable resistor. Under GIC conditions (or any unbalanced fault current condition), the GIC or unbalanced fault current flows through the neutral of a power transformer. It is detected by the fuzzy logic controller, which sends a signal to a switch to open. The resistor is in the circuit and impedes the flow of current through the neutral, thereby protecting the transformer from getting overheated.

The present disclosure relates to systems and methods for calculating noise distributions in an electric power system. In one embodiment, a system to calculate a noise distribution in an electric power system may comprise a measurement subsystem to obtain a plurality of raw measurements of a parameter in the electric power system. A noise distribution determination subsystem may be configured to generate a plurality of scaled raw measurements from the plurality of raw measurements, generate a power spectrum density from the plurality of scaled raw measurements, generate a cumulative distribution from the power spectrum density, and determine a noise distribution from the power spectrum density. A protective action subsystem may monitor the parameter in the electric power system to identify a signal of interest by utilizing, at least in part, the noise distribution and generating a control action in response to the signal.

A relay protection method against LC parallel circuit detuning faults comprises the steps of: a relay protection device samples a current of a parallel LC, that is, a reactor and a capacitor, and samples a total current flowing through the whole LC; convert the current of the reactor into a current of an equivalent capacitor; calculate amplitudes of the current of the equivalent capacitor and a current of a realistic capacitor and calculate an amplitude of the total current flowing through the LC; calculate a current amplitude ratio of the equivalent capacitor to the realistic capacitor; and when the amplitude of the total current flowing through the LC is large enough, send an alarm signal or a trip after a setting time delay if the current ratio exceeds a preset upper and lower limit range. Also provided is a corresponding relay protection device.

A relay protection method against LC parallel circuit detuning faults comprises the steps of: a relay protection device samples a current of a parallel LC, that is, a reactor and a capacitor, and samples a total current flowing through the whole LC; convert the current of the reactor into a current of an equivalent capacitor; calculate amplitudes of the current of the equivalent capacitor and a current of a realistic capacitor and calculate an amplitude of the total current flowing through the LC; calculate a current amplitude ratio of the equivalent capacitor to the realistic capacitor; and when the amplitude of the total current flowing through the LC is large enough, send an alarm signal or a trip after a setting time delay if the current ratio exceeds a preset upper and lower limit range. Also provided is a corresponding relay protection device.

A motor drive device includes: reverse converter that converts DC power from a forward converter into AC power; a DC link capacitor provided in a DC link; a first current detection part that detects current flowing between the forward converter and capacitor; a second current detection part that detects current flowing between the capacitor and reverse converter; a voltage detection part that detects a voltage of the capacitor; and a capacitance decline detection part that obtains a change value in electric charge of the capacitor from a n integrated value by integrated a predetermined time of a difference in current values detected by the current detection parts, obtains a capacitance value of the capacitor based on the obtained change amount in electric charge and change amount in voltage of the capacitor for the predetermined time, and detects a capacitance decline in the capacitor based on the obtained capacitance value.