Ct Earthing Direction; Setting Guidelines; Setting And Configuration - ABB RET650 Applications Manual

Section 6
Differential protection
6.2.2.6
6.2.3
6.2.3.1
98
REFPDIF
I3PW1CT1
I3P
IdN/I
I3PW1CT2
IEC09000113-3 V2 EN-US
Figure 38: Connection of Restricted earth fault, low impedance function
REFPDIF in multi-breaker arrangements

CT earthing direction

To make the restricted earth fault protection REFPDIF operate correctly, the main
CTs are always supposed to be star -connected. The main CT's neutral (star)
formation can be positioned in either way, ToObject or FromObject. However,
internally REFPDIF always uses reference directions towards the protected
transformers, as shown in Figure 38. Thus the IED always measures the primary
currents on all sides and in the neutral of the power transformer with the same
reference direction towards the power transformer windings.
The earthing can be freely selected for each of the involved current transformers.

Setting guidelines

Setting and configuration

Recommendation for analog inputs
I3P: Neutral point current ( All analog inputs connected as 3Ph groups in ACT).
I3PW1CT1: Phase currents for winding 1 first current transformer set.
I3PW1CT2: Phase currents for winding1 second current transformer set for multi-
breaker arrangements. When not required configure input to "GRP-OFF".
I3PW2CT1: Phase currents for winding 2 first current transformer set. Used for
autotransformers.
1MRK 504 169-UEN A
Protected
winding
IEC09000113-3.vsd
Transformer protection RET650 2.2 IEC
Application manual
M13048-29 v13
IP14942-1 v1
M13052-3 v3
M13052-8 v10