ABB RELION RET670, Applications Manual

Page: 89 / 1016

Where:
1) shows how to connect three individual phase currents from a delta connected three-phase CT
set to three CT inputs of the IED.
2) is the TRM where these current inputs are located. It shall be noted that for all these current
inputs the following setting values shall be entered.
CT
prim
=600A
CT
sec
=5A
• CTWyePoint=ToObject
•
ConnectionType=Ph-Ph
3) are three connections made in Signal Matrix Tool (SMT), Application configuration tool (ACT),
which connect these three current inputs to first three input channels of the preprocessing
function block 4). Depending on the type of functions which need this current information, more
then one preprocessing block might be connected in parallel to these three CT inputs.
4) is a Preprocessing block that has the task to digitally filter the connected analog inputs and
calculate:
• fundamental frequency phasors for all three input channels
• harmonic content for all three input channels
• positive, negative and zero sequence quantities by using the fundamental frequency
phasors for the first three input channels (channel one taken as reference for sequence
quantities)
These calculated values are then available for all built-in protection and control functions within
the IED, which are connected to this preprocessing function block. For this application most of
the preprocessing settings can be left to the default values.
If frequency tracking and compensation is required (this feature is typically required only for
IEDs installed in the generating stations) then the setting parameters
DFTReference shall be
set accordingly.
Another alternative is to have the delta connected CT set as shown in figure 18 :
1MRK 504 163-UUS A
Section 4
Analog inputs
Transformer protection RET670 2.2 ANSI 83
Application manual