Schweitzer Engineering SEL-387-0, Instruction Manual

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3.21
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Differential Element
Figure 3.10 Primary Currents and Secondary Currents as Measured by the
Relay
Further, select the delta winding as the reference. The delta
current is connected to Terminal W3 of the SEL-387 Relay.
Therefore, set W3CTC = 0. The wye currents are connected to
Terminal W1 and W2 of the SEL-387 Relay, so W1CTC and
W2CTC must be determined. IAW1 and IAW2 must be rotated
330 degrees (11 multiples of 30 degrees) in the
counterclockwise direction for a system with an ABC phase
rotation to be 180 degrees out-of-phase with IAW3. Therefore,
set W1CTC = 11 and W2CTC = 11. The resulting
compensation settings are:
ICOM =
Y
(choose to define the CT compensation)
W1CTC = 11
W2CTC = 11
W3CTC =
0
The relay multiplies the wye CT currents from the wye
transformer windings by the CTC(11) matrix to give the same
results as the physical DAC CT connection.
Step 5. Enter winding line-to-line voltages. The relay needs these
voltages for the tap calculation. Voltages are in units of kV. For
this example we enter the following values:
VWDG1 = 230
VWDG2 =
138
VWDG3 =
13.8
The relay now calculates each tap current, using the formula
stated previously:
Equation 3.7
Thus, we have the following:
Equation 3.8
30°
IA
Ia
Primary
330
°
IAW1
Secondary
IAW1 (Compensated)
IAW3
150
°
TAPn
MVA 1000
•
3 VWDGn CTRn
• •
-----------------------------------------------------------
C
• =
C 1 for wye CTs
=
 
TAP1
100 MVA 1000
•
3 230 kV 120
• •
-----------------------------------------------
1
• =
TAP1 2.09 A
=