Abstract: An apparatus for detecting an islanding state of a power generation device is disclosed. The apparatus includes a first acquisition unit for acquiring a first current amount at a substation; a second acquisition unit for acquiring a second voltage phasor at the power generation device; a processing unit connected with the first acquisition unit and the second acquisition unit, for determining the interconnection impedance between the power generation device and the substation according to the ratio of the variation of the second voltage phasor and the variation of the first current within the same time period, and determining that the power generation device is in an islanding state under the condition that the interconnection impedance meets a predetermined condition. Furthermore, a method for detecting an islanding state of a power generation device and a system for detecting the islanding state of the power generation device is disclosed.

Abstract: The present disclosure relates to a method for motor thermal overload protection, including: obtaining a motor thermal limit curve; selecting a first and a second overload factor calculation point on the curve, and calculating the first and second overload factors based on a preset heating time constant; calculating a modified overload factor based on the first and second overload factors; selecting at least two time constant calculation points on the motor thermal limit curve, and calculating a modified heating time constant for each time constant calculation point based on the modified overload factor; obtaining a modified heating time function for each motor operating point based on the modified heating time constant for each time constant calculation point; calculating a stator heat level at each motor operating point based on the modified overload factor and heating time function; comparing the stator heat level with the first and second predetermined thresholds.

Abstract: A frequency measurement method is provided, which comprising: sampling a voltage to be measured with a fixed sampling frequency; obtaining a positive-sequence voltage angle change amount for a predetermined operation interval time by using a sampling sample obtained by the sampling and based on a discrete Fourier transform (DFT) calculation; obtaining a frequency offset amount by using the positive-sequence voltage angle change amount; and obtaining a frequency-related measurement value by using the frequency offset amount. A frequency measurement apparatus is also provided. measurement value. This frequency measurement method does not require iterative calculations, and directly obtains frequency-dependent measurement values, thereby responding quickly to frequency changes. In addition, a frequency measurement apparatus is also provided.

Abstract: The present invention provides method, apparatus, and computer readable storage medium for an electrical islanding detection. The method for electrical islanding detection method includes: receiving a three-phase voltage in an electrical power system; for the three-voltage voltage, calculating a voltage angle sudden-change of each phase, respectively; determining whether an absolute value of the voltage angle sudden-change of each phase is greater than a first angle sudden-change setting value; determining whether directions of the voltage angle sudden-changes of three phase are the same if the absolute value of the voltage angle sudden-change of each phase is greater than the first angle sudden-change setting value; and determining that the electrical islanding appears if the directions of the voltage angle sudden-changes of the three phases are the same.

Abstract: A frequency measurement method is provided, which comprising: sampling a voltage to be measured with a fixed sampling frequency; obtaining a positive-sequence voltage angle change amount for a predetermined operation interval time by using a sampling sample obtained by the sampling and based on a discrete Fourier transform (DFT) calculation; obtaining a frequency offset amount by using the positive-sequence voltage angle change amount; and obtaining a frequency-related measurement value by using the frequency offset amount. A frequency measurement apparatus is also provided. measurement value. This frequency measurement method does not require iterative calculations, and directly obtains frequency-dependent measurement values, thereby responding quickly to frequency changes. In addition, a frequency measurement apparatus is also provided.

Abstract: A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same to the sampling module unit as a new sampling frequency; and a frequency measurement value computation and outputting unit that computes and outputs a frequency measurement value in accordance with the selected angle offset.

Abstract: The present invention provides method, apparatus, and computer readable storage medium for an electrical islanding detection. The method for electrical islanding detection method includes: receiving a three-phase voltage in an electrical power system; for the three-voltage voltage, calculating a voltage angle sudden-change of each phase, respectively; determining whether an absolute value of the voltage angle sudden-change of each phase is greater than a first angle sudden-change setting value; determining whether directions of the voltage angle sudden-changes of three phase are the same if the absolute value of the voltage angle sudden-change of each phase is greater than the first angle sudden-change setting value; and determining that the electrical islanding appears if the directions of the voltage angle sudden-changes of the three phases are the same.

Abstract: A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same to the sampling module unit as a new sampling frequency; and a frequency measurement value computation and outputting unit that computes and outputs a frequency measurement value in accordance with the selected angle offset.