CHARACTERISTICS
25
NV021 - Manual - 08 - 2012
4.3 I/O
DESCRIPTION
Metering inputs
The following inputs are provided:
Three phase voltage inputs with programmable nominal voltages within range 5 200...520 V (
U
R
=400 V)
are available. The nominal voltages is user adjustable inside a wide setting range, so the relays can
be employed on plants with different voltages without interposing VTs for low voltage applications.
Signal processing
Various processing levels are involved:
Acquisition (base level).
Direct measures of physical channels (fi rst level).
Calculated measures (second level).
The measures concerning a level are based on data worked out in the previous level.
For each level the required resources concerning the priority for tasks (conditioning circuits, DSP
and CPU) are on hand.
-
u
L1
...
u
L3
Input voltage instantaneous values
From the sampled quantities, several measures are computed for protection, monitoring and meter-
ing purposes.
Direct
Calculated
Average
Direct
Frequency. The measure of period is taken from voltage inputs.
Samples are processed by means DFT (Discrete Fourier Transform) algorithm and the phase and
amplitude of fundamental are computed:
Input voltages
U
L1
,
U
L2
,
U
L3
—
—
•
•
•
•
•
•
•
•
NV021
3 line-to-line voltage inputs
NV021
3 line-to-line voltage inputs
acquisizione-en.ai
ACQUISITION
INSTANTANEOUS MEASURES
≈
acquisizione-en.ai
ACQUISITION
INSTANTANEOUS MEASURES
≈
F. a i
(Hz)
u
L1
u
L2
U
L1
U
L2
ACQUISITION
VT
≈
≈
u
L3
U
L3
≈
f
T
F. a i
(Hz)
u
L1
u
L2
U
L1
U
L2
ACQUISITION
VT
≈
≈
u
L3
U
L3
≈
f
T
U L 1 - e n . a i
ACQUISITION
u
L1
,
u
L2
,
u
L3
DFT
TV
≈
U
L1
,
U
L2
,
U
L3
(
E
n
)
U L 1 - e n . a i
ACQUISITION
u
L1
,
u
L2
,
u
L3
DFT
TV
≈
U
L1
,
U
L2
,
U
L3
(
E
n
)