Instruction manual –AQ F210 Feeder Protection IED
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4.1
M
EASUREMENTS
4.1.1
C
URRENT MEASUREMENT AND SCALING
In AQ-2xx series current measurement module (CT-module) is used for measuring the
currents from current transformers and processing the measured currents to measurement
database and for use of measurement- and protection functions. For the measurements to
be correct it is essential to understand the concept of the AQ-2xx series IEDs current
measurements.
-
PRI
o
Primary current, the current
which flows in the primary circuit
and through primary side of the
current transformer.
-
SEC
o
Secondary current, the current
which the current transformer
transforms according to its ratios.
This current is measured by the
protection IED.
-
NOM
o
Nominal primary current of the
load. Load in this means can be
any electrical apparatus which
produces or consumes electricity
and has rated value for when it is
producing or consuming
electricity in its rated conditions.
Figure 4.1.1-1 Current measurement terminology in AQ-2xx platform
For the measurements to be correct it needs to be made sure that the measurement signals
are connected to correct inputs, current direction is connected correctly and the scaling is
set correctly.
For the scaling relay calculates scaling factors based onto the set CT primary, secondary
and nominal current values. Relay measures secondary current which in this case mean
the current output from the current transformer which is installed into the primary circuit of
the application. In order the relay to “know” primary and per unit values it needs to be told
