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.
As can be noted generally that the frequency dependent sampling improves the measurement
accuracy signi cantly also there can be seen that the measurement hardware is not linear considering
the measured analog signal frequency. For this reason the magnitude and angle measurements need
to be calibrated against frequency. For this purpose measured channels FFT result fundamental
frequency component is corrected for magnitude and angle errors by Arcteq AQ-2xx series patented
calibration algorithms.
Troubleshooting
It is possible that for some reason the measured currents may not be as expected. For these cases
following checks may be helpful.
Problem
Check / Resolution
Measured current or voltage amplitude is too
low compared to what it should be. Values
are “jumping” and are not stable.
Set system frequency may be wrong. Check the set frequency and that it
matches to your local system frequency or change the measurement mode to
“Tracking” and the IED will adjust the frequency by itself.
Frequency readings are wrong.
In tracking mode frequency interpreted by the relay may be wrong if there is
no current/voltage injected to the CT or VT. Check the frequency
measurement settings.
Settings
Table. 5.2.4. - 50. Settings of the frequency tracking
Name
Range
Step
Default
Description
Sampling
mode
0:Fixed
1:Tracking
-
0:Fixed
Selection of the IED measurement sampling mode either xed user
settable frequency or tracked system frequency
System
nominal
frequency
5…75Hz
1Hz
50Hz
User settable system nominal frequency when Sampling mode has
been set to Fixed.
Tracked
system
frequency
5…75.0Hz
0.1Hz
-
Display of rough measured system frequency
Sampl.freq.
used
5…75.0Hz
0.1Hz
-
Display of used tracking frequency at the moment
Freq.Reference
1
0:None
1:CT1IL1
2:CT2IL1
3:VT1U1
4:VT2U1
-
CT1IL1
Frequency tracking reference source 1
Freq.Reference
2
0:None
1:CT1IL2
2:CT2IL2
3:VT1U2
4:VT2U2
-
CT1IL2
Frequency tracking reference source 2
AQ-F255
Instruction manual
Version: 2.00
43
© Arcteq Relays Ltd
