FUNCTION CHARACTERISTICS
118
NA30 - Manual - 04 - 2022
Frequency tracking
Within the frequency range 45...55 Hz (
f
n
= 50 Hz). or 54...63 Hz (
f
n
= 60 Hz), a frequency tracking al-
gorithm 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 1.08 kHz with f = 45 Hz to 1.512 kHz with
f= 63 Hz
For a frequency step change the tracking response time is 0.1 Hz/s.
The frequency measure is based on the largest phase current.
• If the larger phase input current is lower than 25%
I
n
the sampling frequency is fixed to
f
n
(50 or 60 Hz).
• If the measured frequency is outside the locking range
,
the sampling frequency is fixed to the lower
or upper value (45 or 55 Hz with
f
n
= 50 Hz, 54 or 63 Hz with
f
n
= 63 Hz).
All protective elements are always operative; accuracy is guaranteed inside locked frequency
band.
Displayed value
Locked frequency
Locked frequency (Displayed value)
Displayed value
Locked frequency
Locked frequency (Displayed value)
Frequency tracking
IF.ai
Frequency tracking
0.25
I
n
0.25
I
n
40 45
60
55
f
(Hz)
50 Hz (0 Hz)
Nominal frequency
f
n
= 50 Hz
Max I
L1...L3
40 Hz
45 Hz
60 Hz
55 Hz
40
54
70
63
f
(Hz)
60 Hz (0 Hz)
Nominal frequency
f
n
= 60 Hz
Max I
L1...L3
40 Hz
54 Hz
70 Hz
63Hz
I
L1
I
L2
I
L3
Max I
L1...L3
> 0.25
I
n
