Section 3 Analog inputs
3.1 Introduction
Analog input channels in the IED must be set properly in order 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 in order to reflect the way the current transformers are installed/connected in
the field ( primary and secondary connections ). Measuring and protection algorithms
in the IED use primary system quantities. Consequently the setting values are
expressed in primary quantities as well and therefore 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 connected and can be connected with the star point towards the object or
away 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)
• Forward means the direction is into the object.
• Reverse means the direction is out from the object.
1MRK 502 048-UEN A Section 3
Analog inputs
45
Technical manual
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