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 x Un at Fn.
• 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 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.
11.5 Measurement modes
In many current or voltage dependent function blocks, there are four 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:
1YHT530004D05 D Section 11
General function block features
615 series 839
Technical Manual
To Next Page
Loading...
