Schweitzer Engineering SEL-387-0, Instruction Manual, Page: 60 / 556

3.10
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Differential Element
CT Ratio (CTR1—CTR4)
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—W4CTC)
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—VWDG4)
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—TAP4)
When a value is entered in the MVA setting (i.e., MVA is not set to “OFF”),
the relay uses the MVA, winding voltage, CT ratio, and CT connection
settings you have entered and automatically calculates the “TAP
n ” values.
You can also directly enter tap values. Set MVA = OFF, and enter the TAP1
through TAP4 values directly, along with the other pertinent settings.
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
NOTE:
TAP
MAX
/TAP
MIN
must be less
than or equal to 7.5.