ABB RET670 Commissioning Manual page 301

1MRK 504 165-UUS -
Transformer protection RET670 2.2 ANSI
Commissioning manual
impedance has an angle which is outside the above given valid angles for determining
forward or reverse direction.
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
295