ABB Relion 611 Series, Technical Manual

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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
n
at F
n
.
• 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.
9.5 Measurement modes
In many current or voltage dependent function blocks, there are various alternative
measuring principles.
• RMS
• DFT which is a numerically calculated fundamental component of the signal
• Peak-to-peak
• Peak-to-peak with peak backup
Consequently, the measurement mode can be selected according to the application.
In extreme cases, for example with high overcurrent or harmonic content, the
measurement modes function in a slightly different way. The operation accuracy is
defined with the frequency range of f/fn=0.95...1.05. In peak-to-peak and RMS
measurement modes, the harmonics of the phase currents are not suppressed, whereas
in the fundamental frequency measurement the suppression of harmonics is at least
-50 dB at the frequency range of f= n x fn, where n = 2, 3, 4, 5,...
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:
1MRS757454 D
Section 9
General function block features
611 series 487
Technical Manual