Basler Electric BE1-87T - Manual (Page 85)

9171300990 Rev V BE1-87T Installation 4-43
Step 2. Determine the CT secondary current (I
S
):
HIGH LOW
Step 3. Three-Phase Units Only: Adjust the phase compensation jumpers on Analog Board #2, shown
in Figure 2-4 (or use the procedure listed in TESTING THREE-PHASE UNITS WITHOUT
CHANGING JUMPERS, in Section 5). Because of the grounded winding in this example, as
shown in Figure 4-37, the high-side and low-side zero-sequence currents must be canceled.
Because the CTs are connected in wye and the high-side currents lead the low-side currents by
30°, select the ∆2 position. This connection advances the low side phasors by 30° to match the
phasors from the high-side.
HIGH LOW
Jumper Position: WYE ∆ 2
On single-phase units, the zero-sequence currents must be canceled by connecting the low
side CTs in delta.
Step 4. Determine the relay current (I
R
):
I
R
=I
S
x Conversion Factor
Three-Phase Units Only: When using either ∆ 1 or ∆ 2 jumper positions, shown in Figure 2-4,
multiply the secondary current I
S
by the conversion factor (square root of three) just as if the
CTs were connected in delta. If the system CTs are connected in delta (either three-phase or
single-phase units), the same square root-of-three conversion factor must be applied.
HIGH LOW
Step 5. Determine the spread ratio of the relay currents (largest/smallest) which must be less than the
4.45 capability of the BE1-87T:
Spread = 10.02/2.79 = 3.59
If the spread exceeds 4.45, consider changing CT ratios or use auxiliary CTs.
Step 6. Determine the Driving Input (DP) which we define as the input assigned to the smallest current
in Step 4.
DP=I
M
DP=HIGH (INPUT 1)
I
I
S
P
=
CT ratio
I
I
S
S
=
=
167.35
60
2.79
I
I
S
S
=
=
925.98
160
5.79
I
I
R
R =
= (2.
2
79) (1)
79 .
I
I
R
R
=
= 5 3
10
.
.
79
02