Application of Fast Fourier Transform (FFT) in Partial Discharge (PD) measurement

PD is a phenomenon that occurs in high-voltage equipment, such as transformers, cables, and switchgear, due to insulation breakdown or imperfections. PD generates small electrical discharges that produce high-frequency signals. These signals can be detected using sensors and analyzed using FFT to identify the source of the discharge.

In order to analyze the PD signals, they are first acquired by sensors placed on or near the equipment being tested. These signals are then digitized and stored in a computer for analysis. The digitized signal is a time-domain signal, meaning that it represents the amplitude of the signal over time.

FFT is used to convert the PD signal from the time domain to the frequency domain. The frequency domain representation of the signal shows how much of each frequency component is present in the signal. The amplitude of each frequency component is plotted against its frequency, resulting in a graph called a power spectral density (PSD) plot.

The PSD plot provides valuable information about the frequency content of the PD signal. Different types of PD produce different characteristic frequencies, and FFT analysis can help distinguish between them. For example, corona discharge produces a characteristic high-frequency signal, while partial discharges in insulation produce a broad range of frequencies.

By analyzing the PSD plot, it is possible to determine the type of PD occurring, as well as the amplitude, phase, and frequency of the signal. This information can be used to assess the condition of the equipment being tested and to identify potential problems before they become more serious.

In addition to analyzing the frequency content of the PD signal, FFT can also be used for PD localization. PD localization systems use multiple sensors to measure the PD signal, and the phase difference between the signals is used to determine the location of the PD source. The phase difference is calculated using FFT analysis of the signals.

In summary, FFT is an essential tool in PD measurement, allowing for the identification of PD signal characteristics and localization of the PD source. It provides valuable information for assessing the condition of high-voltage equipment and identifying potential problems.