Time-varying phasorIn communication theory, time-varying phasors are used for analyzing narrow-band signals, whose signal bandwidths in the frequency domain are considerably smaller than the carrier frequency.[1][2] Time-varying phasors are mostly used for analysis of frequency domain of band-pass systems.[2][1] The method uses classical impulse response.[1] In electrical power system, phasors are used for transient analysis of the power system keeping the quasi-stationary conditions.[1][3][4] They were introduced to facilitate the computation and analysis of power systems in stationary operation.[3] Time-varying phasors are used in dynamic analysis of a large power system.[1][5] The phasor representation of sinusoidal voltages and currents is generalized to arbitrary waveforms.[2] This mathematical transformation eliminates the 60 Hertz (Hz) carrier which is the only time-varying element in the stationary case.[3] The longer usage of time-varying phasors in large power systems since 1920s have created many misconceptions. One of the misuses suggest that quasi-stationary models are always accurate, but only when the system dynamics are slow as compared to nominal system frequency which is usually 60 Hz.[4] The concern to study time-varying phasors is raised to understand in-depth the fast amplitude and phase variations of emerging electrical power generator technologies.[4] This is because current and voltage signals of latest machines may have harmonic components and they can damage the entire transmission system which is coupled with the machine.[3][4] However, if we employ quasi-static model, we can accurately model AC signals by using time-varying phasors as opposed to traditional quasi-static model which supports constant voltage and current signals throughout the network.[5] References
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