A method for detection of a sub-synchronous oscillation in a power system includes measuring a three-phase measurement signal of an electric system value, analyzing the measurement signal to detect an oscillation component of the measurement signal having an oscillation frequency lower than a system frequency of the power system, deciding whether the detected oscillation component at the oscillation frequency qualifies as a sub-synchronous oscillation, and disconnecting a generator from the power system that might be affected by the sub-synchronous oscillation. To detect sub-synchronous oscillations with low computational effort and good accuracy, an amplitude of each phase of the oscillation component is calculated and compared against a threshold, a sub-synchronous oscillation is detected upon exceeding the threshold during a given time delay, and a fault signal is generated upon detecting a sub-synchronous oscillation. A device having a processing unit is also provided.

A method for detecting low-frequency oscillations, in particular subsynchronous resonances, in a grid is provided. The method includes recording a series of measurements, having measurement points, of a grid variable over a measurement time period, for performing a frequency analysis and multiplying the series a time-dependent sinusoidal test function for the same measurement time period. The test function is characterized by a test frequency and a test angle as phase angle. The series for each measurement point is multiplied by the test function in order to obtain a test product for each measurement point. The method includes adding the test products taking into consideration the mathematical sign thereof to give a product sum, and evaluating, depending on the product sum, whether the series of measurements has a low-frequency oscillation having a frequency in the region of the test frequency and a phase angle in the region of the test angle.

A method for detecting low-frequency oscillations, in particular subsynchronous resonances, in a grid is provided. The method includes recording a series of measurements, having measurement points, of a grid variable over a measurement time period, for performing a frequency analysis and multiplying the series a time-dependent sinusoidal test function for the same measurement time period. The test function is characterized by a test frequency and a test angle as phase angle. The series for each measurement point is multiplied by the test function in order to obtain a test product for each measurement point. The method includes adding the test products taking into consideration the mathematical sign thereof to give a product sum, and evaluating, depending on the product sum, whether the series of measurements has a low-frequency oscillation having a frequency in the region of the test frequency and a phase angle in the region of the test angle.

Provided is a method for identifying low-frequency oscillations, in particular subsynchronous resonances, in an electrical supply network, wherein the electrical supply network has a line voltage with a nominal line frequency, comprising the steps: detecting at least one electrical signal of the electrical supply network as at least one test signal and filtering and/or transforming the at least one detected test signal into at least one check signal, temporal derivation of the at least one check signal or difference formation of temporally separated values of the check signal, in order to obtain a gradient signal in each case, identifying the presence of a low-frequency oscillation if the gradient signal or at least one of the gradient signals meets a predetermined check criterion, in particular at least one predetermined check limit is exceeded.

Provided is a method for detecting low-frequency oscillations, in particular subsynchronous resonance, in an electrical supply grid, wherein the electrical supply grid has a grid voltage at a grid nominal frequency, comprising the steps of capturing at least one electrical signal from the electrical supply grid, and evaluating the electrical signal by means of wavelet analysis, during which a time-dependent frequency pattern is created by analyzing a correlation of the captured signal with a predetermined wavelet mother function, wherein the presence of a low-frequency oscillation is assumed if at least one further low-frequency frequency component is present in the time-dependent frequency pattern in addition to a fundamental component.

A signal processing method and a material testing machine are provided. A reference function processing part includes a data interval generation part for cutting out input signal from a load cell into time-domain data interval by cutting out the input signal of a predetermined time length, a reference function determining part for determining a reference function to be used in a transform process, and a transform part for transforming the interval data using the reference function. Considering the approximately straight lines near the two ends of the data interval, the reference function is a third degree polynomial function with tangents overlapping with the approximately straight line at both ends of the data interval.

A signal processing method and a material testing machine are provided. A reference function processing part includes a data interval generation part for cutting out input signal from a load cell into time-domain data interval by cutting out the input signal of a predetermined time length, a reference function determining part for determining a reference function to be used in a transform process, and a transform part for transforming the interval data using the reference function. Considering the approximately straight lines near the two ends of the data interval, the reference function is a third degree polynomial function with tangents overlapping with the approximately straight line at both ends of the data interval.

A method for detection of a sub-synchronous oscillation in a power system includes measuring a three-phase measurement signal of an electric system value, analyzing the measurement signal to detect an oscillation component of the measurement signal having an oscillation frequency lower than a system frequency of the power system, deciding whether the detected oscillation component at the oscillation frequency qualifies as a sub-synchronous oscillation, and disconnecting a generator from the power system that might be affected by the sub-synchronous oscillation. To detect sub-synchronous oscillations with low computational effort and good accuracy, an amplitude of each phase of the oscillation component is calculated and compared against a threshold, a sub-synchronous oscillation is detected upon exceeding the threshold during a given time delay, and a fault signal is generated upon detecting a sub-synchronous oscillation. A device having a processing unit is also provided.

Provided is a method for identifying low-frequency oscillations, in particular subsynchronous resonances, in an electrical supply network, wherein the electrical supply network has a line voltage with a nominal line frequency, comprising the steps: detecting at least one electrical signal of the electrical supply network as at least one test signal and filtering and/or transforming the at least one detected test signal into at least one check signal, temporal derivation of the at least one check signal or difference formation of temporally separated values of the check signal, in order to obtain a gradient signal in each case, identifying the presence of a low-frequency oscillation if the gradient signal or at least one of the gradient signals meets a predetermined check criterion, in particular at least one predetermined check limit is exceeded.

A harmonic detection system (1) comprises a measurement component (71), a harmonic abnormality determination unit (561), and a smartphone (9). The measurement component (71) is installed at a specific position on a distribution line constituting a distribution network (100), and measures data related to the current of the distribution line. The harmonic abnormality determination unit (561) uses some or all of the data related to current as detection data to detect abnormality related to harmonics. The smartphone (9) is owned by a user (G), and notifies the user that an abnormality has occurred in the distribution line when a harmonic is detected.