Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.22
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
currents. The phase shift produced by each physical type of delta depends on
the system phase sequence.
NOTE:
The terms “lead” and “lag”
refer to the assumed
counterclockwise (CCW) rotation of
the phasors for both ABC and ACB
phase rotation. “Lead” implies
movement in the CCW direction; “lag”
is movement in the clockwise (CW)
direction.
In the ABC phase sequence B lags A by 120 degrees and C leads A by 120
degrees. The DAB connection line current at terminal A is A-B, which in this
case is a phasor that leads A winding current by 30 degrees. For this reason,
DAB is often referred to as the “leading connection.” However, DAB is the
leading connection only for ABC phase sequence. In the ACB phase sequence
C lags A by 120 degrees, and B leads A by 120 degrees. Terminal A line
current is still A-B, but current now lags A winding current by 30 degrees.
The DAC connection produces opposite shifts to DAB. In the ABC phase
sequence line current from terminal A is A-C, which lags A winding current
by 30 degrees. In the ACB phase sequence line current A is still A-C, but this
result leads A winding current by 30 degrees.
Five-Step Compensation Process.
The process of determining CTCn for
each winding involves the following five basic steps. Two examples illustrate
important points about the five steps. For an additional resource, see the
“Winding Compensation Settings Worksheet” (SEL_WCTC_R1_0.xls,
available on the SEL-700G Product Literature CD).
Step 1. Establish the phase direction for the terminal-A line voltage for
each three-phase winding of the transformer. (This step
requires transformer nameplate drawings and/or internal
connection diagrams.)
Step 2. Adjust the terminal-A line voltage direction for each set of
input currents by the phase shift (if any) of the current
transformer connection. (Reference Figure 4.13 for this step.)
Step 3. Select any one of the adjusted terminal-A directions from
Step 2, to serve as the reference direction. (The relay
compensates all other windings to line up with this reference.)
Step 4. Choose a setting for CTCn for each set of winding input
currents. This setting is the number of 30-degree increments
needed to adjust each nonreference winding to line it up with
the reference. This number will range from 0 to 12 increments.
For ABC phase sequence, begin at the winding direction and
proceed in a CCW direction until reaching the reference. For
ACB phase sequence, begin at the winding direction and
proceed in a CW direction until reaching the reference.
Figure 4.13 shows these compensation directions.
Step 5. If any winding needs no phase correction (zero degrees), but is
a grounded-wye winding having wye-connected CTs, choose
CTCn = 12 for that winding, rather than CTCn = 0. This setting
will remove zero-sequence current components from the relay
currents to prevent false differential tripping on external ground
faults. (All non-zero values of CTCn remove zero-sequence
current.)
Example for CTCn Selection.
Figure 4.14 illustrates the first example. This
is a two-winding transformer with a DAB delta primary and secondary
connected in grounded wye. The secondary winding has DAB delta-connected
CTs. We assume ABC phase rotation. Using the “hour of the clock”
convention for specifying transformer connections, the transformer is a “Dy1”
connection. This means the transformer has a high-voltage delta whose