# Why the frequency variation is negative in the curve of instantaneous frequency vs time curve of faulted phase current ?

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Siddharth Kamila on 14 Jan 2023
Edited: Muskan on 24 Mar 2023
I am working on the analytic signal concept for observing the frequency variation in the faulted phase current waveform in MATLAB/Simulink model. In MATLAB/Simulink model, I have used analytic signal block and hilbert's transform method to calculate the real and imaginary components of the faulted phase current. After that I have used the data of real and imaginary components of the faulted phase current to calculate the magnitude, phase, and instantaneous frequency. When I plotted the curve between the instantaneous frequency variation vs time for the faulted phase current, I observed that the frequency variation is negative in the curve of instantaneous frequency vs time for the faulted phase current. Why it is so ?
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### Answers (1)

Muskan on 24 Mar 2023
Edited: Muskan on 24 Mar 2023
Hi Siddharth,
As per my understanding of the question, the rate of change of the analytic signal's phase is effectively calculated when you use the real and imaginary components of the analytic signal to compute the instantaneous frequency of the faulty phase current. The phase of the analytical signal will change by -90 degrees for every positive change in the imaginary component because the imaginary component is 90 degrees out of phase with the real component. As a result of this negative phase change, Tthe curve of instantaneous frequency vs. time for the faulty phase current exhibits a negative frequency fluctuation. as a result of this negative phase change.
I hope this resolves your query.
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