Basler Electric BE1-87T - Manual (Page 86)

4-44 BE1-87T Installation 9171300990 Rev V
Step 7. Determine the Driving Input Tap (T
I
).
If both relay currents are between 2.0 and 8.9 amperes, the tap settings can be set equal to the
relay currents (to the nearest 0.1 ampere). However, choosing the 2.0 tap setting for the
minimum input will yield maximum sensitivity.
T
1
= 2.00
Step 8. Determine the desired Tap (T
D
) for Input 2:
Step 9. Select taps by rounding T
D
to the nearest tenth:
T
1
= 2.0
T
2
= 7.2
Step 10. Determine the CT mismatch (M
N
):
M
N
= 100
Current Ratio - Tap Ratio
the smaller of the above
I
I
T
T
Smaller
R2
=
-
R1 1
2
100
= 0 216 0 22 %
=
-
2.79 2.0
Smaller
100
or . .
=
- 0.2784 0.2778
0.2778
100
10.02 7.2
Step 11. Determine the total mismatch (M
T
):
M
T
= M
N
+ LTC
Add the maximum CT mismatch M
N
(based on the power transformer in the neutral tap
position) to the total permissible tap excursion from neutral. In this example, a ± 10 % load-tap
change (LTC) must be accommodated. Therefore:
M
T
=0.22 + 10 = 10.22%
T T I
I
D
R
R
2 1
2
1
2.0 10.02
2.79
7
=
( )
=
= .18
( )