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Automated Fast Fourier Transform Analysis

FFTSES is a Fast Fourier Transform engineering module designed to help SES software users automate the time domain (lightning and switching surges) analysis based on frequency domain results obtained from CDEGS engineering modules such as SPLITS, MALZ, and HIFREQ. The forward and inverse Fast Fourier transformations, the sample selection of the frequency spectrum, and related reporting and plotting functions have been automated in FFTSES.

FFTSES automates all transformation steps from time-domain to frequency domain

Technical Highlights

When a transient current, such as a lightning surge, strikes a man-made facility (eg., a building, a substation, a tower, etc.), the following safety concerns often need to be addressed:

  • Excessive values of touch and step voltages which may be dangerous to personnel in the vicinity of a grounding system.
  • Excessive strengths of electromagnetic fields within the substation which can result in equipment damage.

The FFTSES module, together with frequency domain computation software such as HIFREQ, can provide accurate solutions to both spatial and temporal distributions of the scalar potential and electromagnetic fields in the vicinity of grounded structures subjected to a transient surge excitation. These solutions allow one to design grounding systems so that the touch and step voltages nearby do not exceed acceptable limits; they also help to minimize equipment damage by simply relocating equipment within the substation to places where electromagnetic field strength is relatively low, avoiding unnecessary overdesign due to otherwise necessary conservative approaches involving lowering the overall level of electromagnetic fields throughout the whole substation.

Technical Features

In the forward FFT, the built-in time domain transient analysis and error diagnosis algorithms will warn the user of any inappropriate input data and the "Sample Selection of Frequency Spectrum" algorithm will automatically select a subset of frequency components out of the full spectrum, reducing the computation time of a transient analysis by a few orders of magnitude compared to the conventional "full spectrum frequency analysis". In addition, many of the time-consuming tasks, such as the modulation of the frequency spectrum of input surge by the system response in the inverse FFT operation are done automatically by the module, further facilitating the user’’s work.

In the inverse FFT, the frequency domain data computed by HIFREQ and MALZ can be quickly collected, analyzed and displayed. Data from other sources can also be studied. The program analyzes the frequency domain response, searching, in particular, for possible resonances in the signal, and suggests appropriate frequencies at which further data should be collected (if necessary) to improve the accuracy of the results.

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