Section 3 Analog Inputs; Introduction; Operation Principle - ABB Relion Technical Manual

1MRK 502 048-UUS A
Section 3
3.1
3.2
Technical manual
Analog inputs

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.

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 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)
Section 3
Analog inputs
47