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CHARACTERISTICS
73
NV021 - Manual - 08 - 2012
Frequency tracking
Within the frequency range 20...63 Hz a frequency tracking algorithm adjusts the currents sampling
frequency, so as to keep the number of samples in any given period constant.
With 24 samples for periods the sampling rate is adjusted from 480 Hz with f = 20 Hz to 1.512 kHz with
f= 63 Hz.
For a frequency step change the tracking response time is 5 Hz/s for NV10P.
The frequency measure is based on the largest voltage input.
[1]
If the larger input voltage is lower than 1.5 %
E
n
the sampling frequency is fi xed to
f
n
(50 or 60 Hz).
If the measured frequency is outside the locking range
,
the sampling frequency is fi xed to the lower
or upper value (20 or 63 Hz).
All protective elements are always operative; accuracy is guaranteed inside locked frequency
band.
Note 1 For inputs from sensors versions the frequency is measured on the phase voltages
(
U
L1
,
U
L2
,
U
L3
)
, while for versions with inputs from inductive
VTs the frequency is measured on line-to-line voltages
(
U
12
,
U
23
,
U
31
)
.
Inside the diagrams
U
L1
,
U
L2
,
U
L3
are the input phase-to neutral or phase-to-phase voltages according to the corresponding versions
—
•
•
Displayed value
Locked frequency
Locked frequency (Displayed value)
Frequency tracking
U
L1
U
L2
U
L3
Max U
L1...L3
> 0.015
E
n
IF.ai
Frequency tracking
1.5%
E
n
16 20
90
63
f
(Hz)
50 Hz (0 Hz)
Max U
L1...L3
16 Hz
20 Hz
90 Hz
63 Hz
Displayed value
Locked frequency
Locked frequency (Displayed value)
Frequency tracking
U
L1
U
L2
U
L3
Max U
L1...L3
> 0.015
E
n
IF.ai
Frequency tracking
1.5%
E
n
16 20
90
63
f
(Hz)
50 Hz (0 Hz)
Max U
L1...L3
16 Hz
20 Hz
90 Hz
63 Hz