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Measure positive-, negative-, and zero-sequence components of three-phase signal

Extras/Measurements

A discrete version of this block is available in the Extras/Discrete Measurements library

The Three-Phase Sequence Analyzer block outputs the magnitude and phase of the positive- (denoted by the index 1), negative- (index 2), and zero-sequence (index 0) components of a set of three balanced or unbalanced signals. The signals can contain harmonics or not. The three sequence components of a three-phase signal (voltages V1 V2 V0 or currents I1 I2 I0) are computed as follows:

*V*_{1} = (*V _{a}* +

where

*V _{a}*,

A Fourier analysis over a sliding window of one cycle of the
specified frequency is first applied to the three input signals. It
evaluates the phasor values *V _{a}*,

The Three-Phase Sequence Analyzer block is not sensitive to
harmonics or imbalances. However, as this block uses a running average
window to perform the Fourier analysis, one cycle of simulation has
to be completed before the outputs give the correct magnitude and
angle. For example, its response to a step change of *V*_{1} is
a one-cycle ramp.

The discrete version of this block allows you to specify the initial magnitude and phase of the output signal. For the first cycle of simulation the outputs are held to the values specified by the initial input parameter.

You can modify any parameter during the simulation in order to obtain the different sequence and harmonic components of the input signals.

**Fundamental frequency f1**The fundamental frequency, in hertz, of the three-phase input signal.

**Harmonic n**Specify the harmonic component from which you want to evaluate the sequences. For DC, enter

`0`. For fundamental, enter`1`.**Sequence**Specify which sequence component the block outputs. Select

`Positive`to calculate the positive sequence, select`Negative`to calculate the negative sequence, select`0`to compute the zero sequence of the fundamental or specified harmonic of the three-phase input signal. Select`Positive Negative Zero`to get all the sequences.

The `power_3phsignalseq``power_3phsignalseq` example
illustrates the use of the Discrete Sequence Analyzer block to measure
the fundamental and harmonic components of a three-phase voltage.
A 25kV, 100 MVA short-circuit level, equivalent network feeds a 5
MW, 2 Mvar capacitive load. The internal voltage of the source is
controlled by the Discrete 3-phase Programmable Voltage Source block.

A positive sequence of 1.0 pu, 0 degrees is specified for the fundamental signal. At t = 0.05 s a step of 0.5 pu is applied on the positive-sequence voltage magnitude, then at t = 0.1 s, 0.08 pu of fifth harmonic in negative sequence is added to the 1.5 pu voltage.

Two Discrete Three-Phase Sequence Analyzer blocks are used to measure the positive-sequence fundamental component and the negative-sequence fifth harmonic of the three-phase voltage.

As the Three-Phase Sequence Analyzer blocks use Fourier analysis, their response time is delayed by one cycle of the fundamental frequency.

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