Frequency change sine wave signal Fourier calculation method and relay protection device

The invention relates to a frequency change sine wave signal Fourier calculation method and a relay protection device, and the method comprises the steps: adding a decimal part when the number of sampling points of a cyclic wave after frequency change is calculated, and giving a certain sampling value to the decimal part; and finally, fusing the sampling point value of one cycle obtained by calculation with the sampling value of the decimal part, and jointly calculating to obtain a calculated value. According to the method, the sampling point value of one cycle after frequency change is compensated through the sampling value of the decimal part so that the error is greatly reduced. According to the method, the real and imaginary parts of the voltage and current vectors of the system can beaccurately calculated when the frequency of the system fluctuates slowly so that the problem that the calculation error of the real and imaginary parts of the voltage and current vectors in the relayprotection device is too