GE 845 Instruction Manual page 207

CHAPTER 4: SETPOINTS
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
ANGLE WITH RESPECT TO W1 (only in Winding 2 and Winding 3 menu)
° ° °
Range: 0 , 30 Lag, 60 Lag, 90
° °
Lag, 300 Lag, 330 Lag
°
Default: 0
Enter the angle by which the currents from Winding 2 (Winding 3) are lagging the
currents from Winding 1.
GROUNDING
Range: Not within zone, Within zone
Default: Not within zone
Select "Within Zone", if there is a grounding path at the winding 1(2, 3) side of the
transformer such as grounded neutral, grounding transformer, or grounded corner of a
delta winding. Select "Not Within Zone", if there is no grounding path for the winding in
the zone.
The Delta CT connection has the effect of removing the zero sequence components of
the phase currents. If there were a grounding bank on the Delta winding of the power
transformer within the zone of protection, a ground fault would result in differential (zero
sequence) current and false trips. In such case, it would be necessary to insert a zero
sequence current trap with the wye connected CTs on the Delta winding of the
transformer.
In general, zero sequence removal is necessary if zero sequence can flow into and out of
one transformer winding but not the other winding. Transformer windings that are
grounded inside zone protection allow zero sequence current flow in that winding, and
therefore it is from these windings that zero sequence removal is necessary.
WNDG RESISTANCE (3-Ph)
Range: 0.0001 to 100.0000 ohms in steps of 0.0001
Default: 10.0000 ohms
Enter the three-phase winding resistance from the transformer nameplate.
PHASE RELATIONSHIPS OF THREE-PHASE TRANSFORMERS
Power transformers that are built in accordance with ANSI and IEC standards are required
to identify winding terminals and phase relationships among the windings of the
transformer.
ANSI standard C.37.12.70 requires that the terminal labels include the characters 1, 2, 3 to
represent the names of the individual phases. The phase relationship among the windings
must be shown as a phasor diagram on the nameplate, with the winding terminals clearly
labeled. This standard specifically states that the phase relationships are established for a
condition where the source phase sequence of 1-2-3 is connected to transformer windings
labeled 1, 2, and 3 respectively.
IEC standard 60076-1 (1993) states that the terminal markings of the three phases follow
national practice. The phase relationship among the windings is shown as a specified
notation on the nameplate, and there may be a phasor diagram. In this standard the
arbitrary labeling of the windings is shown as I, II and III. This standard specifically states
that the phase relationships are established for a condition where a source phase
sequence of I-II-III is connected to transformer windings labeled I, II and III respectively.
Magnitude Compensation
The percent differential protection from the 845 relay uses the phase-phase voltage and
the CT primary setting for Winding 1 as a reference, to perform magnitude compensation
for (bring to common base) the currents measured from the other windings: Winding 2 and
Winding 3.
° ° °
Lag, 120 Lag, 150 Lag, 180
SYSTEM
° ° °
Lag, 210 Lag, 240 Lag, 270
4–79
°