Sequence Analyzer

Block Sequence Analyzer outputs the amplitude and phase of the forward, reverse, and zero sequence components of a set of three balanced or unbalanced signals. The index 1 stands for the forward sequence, the index 2 stands for the reverse sequence, and the index 0 stands for the zero sequence. The signals may additionally contain harmonics. Three components of a three-phase signal sequence (voltage , , or currents , , ) are calculated as follows:

where

First, Fourier analysis is applied to the three input signals in a sliding window of one cycle of a given signal frequency. It evaluates the values of the vectors , and at a given fundamental frequency or harmonic frequency. The transformation is then applied to obtain the forward, backward, and null sequences.

Since the unit uses a moving average window to perform Fourier analysis, one simulation cycle must be completed before the output values match the correct amplitude and phase values. For example, the block’s reaction to an abrupt change in the vector It is a single-cycle linearly varying signal. During the first simulation cycle, the output values are kept constant and correspond to the values set by the initial input parameters.