Method for diagnosing faults inside capacitor in distribution network series compensation

The invention discloses a method for diagnosing faults inside a capacitor in distribution network series compensation. The method comprises the following steps: firstly, extracting capacitor voltage, fundamental waves of current and each harmonic wave through a FFT (fast fourier transform algorithm), respectively calculating the fundamental waves and the capacitor value under each harmonic wave, performing weighted average based on fundamental waves and each harmonic current effective value on fundamental waves and capacitance value under each harmonic wave, processing to form an estimation formula of the capacitor capacitance value, and taking the difference value of the estimation value and the normal capacitor capacitance value as diagnosis basis of internal faults. The method is relatively high in judging precision and meets the needs of diagnosing faults inside the capacitor in distribution network series compensation in a project.