29
NC20 - Manual - 01 - 2015
FUNCTION CHARACTERISTICS
4.3 I/O
DESCRIPTION
Metering inputs
The following input are provided:
Three phase current inputs.
One unbalance neutral current input.
The nominal currents are independently adjustable at 1 A or 5 A through DIP-switches.
Three phase voltage inputs with programmable nominal voltages within range 50...130 V (
U
R
=100 V).
The nominal voltages is user adjustable inside a wide setting range, so the relays can be employed
on plants with TV different secondary voltages.
The input circuits are appropriately dimensioned in order to withstand currents and voltages which
arise when a fault occurs, both in transient and steady state condition.
Signal processing
Various processing levels are involved:
Acquisition (base level).
Direct measures of physical channels (fi rst level).
Calculated measures (second level).
Derived (third 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.
ACQUISITION (base level)
The input signals are sampled 24 times per period:
-
i
L1
...
i
L3
Phase current instantaneous values
-
i
N
Unbalance neutral current instantaneous value
-
u
L1
...
u
L3
Phase voltage instantaneous values
From the sampled quantities, several measures are computed for protection, monitoring and meter-
ing purposes.
Direct
Calculated
Harmonic
Demand
•
•
•
•
•
•
•
•
•
•
•
•
sensori.ai
Three phase voltage inputs
Three phase current inputs
Neutral unbalance current input
NC20
52
sensori.ai
Three phase voltage inputs
Three phase current inputs
Neutral unbalance current input
NC20
52
acquisizione.ai
ACQUISITION
INSTANTANEOUS MEASURES
≈
acquisizione.ai
ACQUISITION
INSTANTANEOUS MEASURES
≈