Schweitzer Engineering Laboratories SEL-387E - Connection Compensation (W1 CTC through W3 CTC); CT Ratio (CTR1 through CTR3); Current TAP (TAP1 through TAP3); Internal Winding;Ct Connection Compensation (ICOM)

Date Code 20080110 Protection Functions 3-9
SEL-387E Instruction Manual
For delta-connected CTs, the secondary currents into the SEL-387E Relay current inputs are
phase-phase difference currents (e.g., phase-phase difference current I
A
– I
B
flows into current
input IAWn). To create a pseudo phase-neutral value for display or use in algorithms, these
phase-phase difference currents are divided by √3 (divided by 1.732).
CT Ratio (CTR1 through CTR3)
Range: 1–50000
Determine the CT ratio by dividing the nominal primary CT current by the nominal secondary CT
current. If, for example, the nominal primary CT current is 2000 A and the nominal secondary
CT current is 5 A, the ratio is 2000/5 or 400. For this example, enter a value of 400.
Maximum Transformer Capacity, Three-Phase MVA (MVA)
Range: OFF, 0.2–5000 MVA, in 0.1 MVA steps
Use the highest expected transformer rating, such as the FOA (Forced Oil and Air cooled) rating
or a higher emergency rating, when setting the maximum transformer capacity.
Internal Winding/CT Connection Compensation (ICOM)
Range: Y, N
This Yes/No variable defines whether the input currents need any correction, either to
accommodate phase shifts in the transformer or CTs or to remove zero-sequence components
from the secondary currents. If this setting is Yes, the relay permits the user, in the next group of
settings, to define the amount of shift needed to properly align the secondary currents for the
differential calculation.
Connection Compensation (W1CTC through W3CTC)
Range: 0, 1, …, 12
These settings define the amount of compensation the relay applies to each set of winding
currents to properly account for phase shifts in transformer winding connections and CT
connections. For example, this correction is needed if both wye and delta power transformer
windings are present, but all of the CTs are connected in wye. The effect of the compensation is
to create phase shift and removal of zero-sequence current components.
Line-to-Line Voltage, kV (VWDG1 through VWDG3)
Range: 1–1000 kV, in 0.01 kV steps
Enter the nominal line-to-line transformer terminal voltages. If the transformer differential zone
includes a load tap-changer, assume that it is in the neutral position. The setting units are
kilovolts.
Current TAP (TAP1 through TAP3)
Range: 1 A: 0.1–31 A, secondary, in 0.01 A steps
5 A: 0.5–155 A, secondary, in 0.01 A steps