Section 3 Analog inputs
3.1 Introduction
Analog input channels are already configured inside the IED. However the IED has to
be set properly to get correct measurement results and correct protection operations.
For power measuring and all directional and differential functions the directions of the
input currents must be defined properly. Measuring and protection algorithms in the
IED use primary system quantities. Setting values are in primary quantities as well and
it is important to set the transformation ratio of the connected current and voltage
transformers properly.
The availability of CT and VT inputs, as well as setting parameters depends on the
ordered IED.
A reference PhaseAngleRef must be defined to facilitate service values reading. This
analog channels phase angle will always be fixed to zero degrees and all other angle
information will be shown in relation to this analog input. During testing and
commissioning of the IED the reference channel can be changed to facilitate testing
and service values reading.
3.2 Operation principle
The direction of a current depends on the connection of the CT. The main CTs are
typically star (WYE) connected and can be connected with the Star (WYE) point to the
object or from the object. This information must be set in the IED.
The convention of the directionality is defined as follows:
• Positive value of current or power means that the quantity has the direction into
the object.
• Negative value of current or power means that the quantity has the direction out
from the object.
For directional functions the directional conventions are defined as follows (see figure
2)
1MRK 505 277-UUS C Section 3
Analog inputs
35
Technical Manual
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