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Technical description
4 Measurement functions
4.1 Measurement accuracy
VM55.EN005
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99
4.
Measurement functions
All the direct measurements are based on fundamental
frequency values. The exception is frequency. Most protection
functions are also based on the fundamental frequency values.
The figure shows a current waveform and the corresponding
fundamental frequency component f1, second harmonic f2 and
rms value in a special case, when the current deviates
significantly from a pure sine wave.
Figure 4-1 Example of various current values of a transformer inrush
current.
4.1.
Measurement accuracy
Voltage inputs U
A
, U
B
, U
C,
U
D
The usage of voltage inputs depends on the configuration
parameter “voltage measurement mode”. For example, Ud is
the zero sequence voltage input U
0
if the mode “3LL + U
0
” is
selected.
Measuring range L- N
0 – 300 V
(LL measurement 0 – 520 V)
Inaccuracy
0.5 % or 0.3 V
The specified frequency range is 45 Hz – 65 Hz.
Frequency
Measuring range
16 Hz – 75 Hz
Inaccuracy
10 mHz
The frequency is measured from current signals.
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