Frequency Measure Element

Properties: Determines the fundamental frequency of a bus voltage symbol

Features: Can be used with any bus in the network using a basic frequency

General Parameters

Basic Frequency: Normal fundamental frequency of the network used as the main frequency of the bandpass filter (Hz)

Bandpass Filter Parameters
Bandwidth: Width of bandpass filter (Hz)

List of Available Signals
At acquisition, the following signals are made available by the sensors:

Freq_label	Fundamental frequency (Hz)
Periode_label	Fundamental period (s)
Vaf label	Filtered bus voltage for phase A (V)
Vbf label	Filtered bus voltage for phase B (V)
Vcf_label	Filtered bus voltage for phase C (V)

Frequency Measure Control Panel

The following figure shows an example of the parameters used for a 60 Hertz test.
Frequency measure control panel

Frequency Measure Model

The block diagram of the frequency measure element is shown in the next figure. The bus voltages are read and filtered, then the time between two zero crossings of these voltages is calculated.
When a voltage rise is detected, a counter is reset and increments until the next rise. The mean of three calculated periods is then determined and inverted to obtain the frequency. The variables
used in the block diagram are defined as follows:

Va, Vb, Vc	Bus voltages
Vaf, Vbf, Vcf	Filtered voltages
FB	Basic frequency
LB	Filter bandwidth
Num	Parameters for the numerator polynomial of the filter
Den	Parameters for the denominator polynomial of the filter
Ra, Rb, Rc	Signals to reset the counters used to calculate the period
Pa, Pb, Pc	Calculated periods for three phases
f	Fundamental frequency

Block Diagram of Frequency Measure 1