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.
