ABB RET670 Commissioning Manual page 291

1MRK 504 165-UEN A
Transformer protection RET670 2.2 IEC
Commissioning manual
If the directional function shows "No direction" for only some of the three
phases, this probably means a wrong CTs/VTs connection.
4. The measured impedance information is available under the same menu. These
values are not affected by the minimum operating current setting of ZDRDIR
or ZDMRDIR and the measured values are shown any time the load current is
higher than 3% of the base current:
• L1R
• L1X
• L2R
• L2X
• L3R
• L3X
The measured impedance information can still be used to determine the
direction of the load. A positive resistance measured in all phases indicates a
forward (exporting) resistive load (active power), while a negative sign
indicates a reverse (importing) resistive load (active power). Usually it is
enough to look at the resistive values to get information of the load direction,
that must anyway be compared with the indication given by external
equipment measuring the same power flow.
Section 13
Checking the directionality
285