Arcteq AQ-F210, Инструкция по эксплуатации

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Instruction manual –AQ F210 Feeder Protection IED 51 (292
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4.1.2 F
REQUENCY TRACKING AND SAMPLING
In AQ-2xx series the measurement sampling can be set to frequency tracking mode or fixed
user given frequency sampling mode. Benefit of the frequency tracking is that the
measurements are in given accuracy range even when the fundamental frequency of the
power system changes.
Measurement error with fixed 50Hz sampling
frequency when frequency changes. Constant
current of 5A, frequency sweep from 6 Hz to 75 Hz
Measurement error with frequency tracking when
frequency changes. Constant current of 5A, frequency
sweep from 6 Hz to 75 Hz
Figure 4.1.2-9 Frequency tracking effect when the fundamental frequency is changing from
6 Hz to 75 Hz
As can be seen in the figure above the sampling frequency has major effect to the
measurement accuracy of the IED. If the sampling is not tracked to the system frequency it
can be seen that even a change from set 50Hz to measured system frequency 60Hz (most
common system frequencies) already gives measurement error of roughly over 5% in the
measured phase currents. From the figure can also be seen that when the frequency is
tracked the measurement accuracy is about -0.2% - 0.1% error in the whole frequency
range when the sampling is adjusted according to the detected system frequency.
The system frequency independent measurement accuracy has been achieved in AQ-2xx
series devices by adjusting the samplerate of the measurement channels according to the
measured system frequency so that the FFT calculation has always whole power cycle in
the buffer. Further improvement for the achieved measurement accuracy is the Arcteq
patented method of calibrating of the analog channels against 8 system frequency points
for both, magnitude and angle. This frequency dependent correction compensates the used
measurement hardware frequency dependencies. These two mentioned methods
combined shall give the result of accurate system frequency independent measurement.