Section 9 General Function Block Features; Frequency Measurement; Measurement Modes - ABB Relion SMU615 Technical Manual

1MRS758407 B
Section 9
9.1
9.2
SMU615
Technical Manual
General function block features

Frequency measurement

All the function blocks that use frequency quantity as their input signal share the
common features related to the frequency measurement algorithm. The frequency
estimation is done from one phase (phase-to-phase or phase voltage) or from the
positive phase sequence (PPS). The voltage groups with three-phase inputs use PPS as
the source. The frequency measurement range is 0.6...1.5 × F
range always starts from 0.6 × F
regarded as out of range and a minimum or maximum value is held as the measured
value respectively with appropriate quality information. The frequency estimation
requires 160 ms to stabilize after a bad quality signal. Therefore, a delay of 160 ms is
added to the transition from the bad quality. The bad quality of the signal can be due
to restrictions like:
• The source voltage is below 0.02 × U
• The source voltage waveform is discontinuous.
• The source voltage frequency rate of change exceeds 15 Hz/s (including stepwise
frequency changes).
When the bad signal quality is obtained, the nominal or zero (depending on the Def
frequency Sel setting) frequency value is shown with appropriate quality information
in the measurement view. The frequency protection functions are blocked when the
quality is bad, thus the timers and the function outputs are reset. When the frequency
is out of the function block's setting range but within the measurement range, the
protection blocks are running. However, the OPERATE outputs are blocked until the
frequency restores to a valid range.

Measurement modes

RMS
The RMS measurement principle is selected with the Measurement mode setting
using the value "RMS". RMS consists of both AC and DC components. The AC
component is the effective mean value of the positive and negative peak values. RMS
is used in applications where the effect of the DC component must be taken into
account.
RMS is calculated according to the formula:
General function block features
. When the frequency exceeds these limits, it is
n
at F .
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Section 9
. The df/dt measurement
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