Basler Electric BE1-87T - Manual (Page 90)

4-48 BE1-87T Installation 9171300990 Rev V
HIGH LOW
Step 21. Select the restrained slope setting.
The recommended restrained slope setting (S) is a function of the total mismatch and the
power transformer exciting current. This provides an ample security margin with respect to the
characteristic kneepoint of the BE1-87T. Refer to Figure 4-36.
Specifically, if the maximum saturation factor S
F
(from Step 16) exceeds 0.5, set the
RESTRAINED PICKUP LEVEL to setting K, which is equal to 60 as shown in the table on the
front panel.
For all other cases, including this example, use the following equation:
Where:
S = restrained slope setting
M
T
= total mismatch in percent
I
T
= rated self-cooled current of the power transformer in multiples of tap
M
T
is 10.2 (from Step 11) and I
T
is 0.84 (Step 20):
S =
= 26.5%
35(10.2 + 3)
23 - 4(0.84)
3 +
Because the maximum saturation factor S
F
for this example is less than 0.5 (from Step 16), use
the next highest slope. Select position D, which = 30%.
For examples of suitable slope settings, see Table 4-2.
I
T =
=
2 79 12
2 0 20
0 84
.
.
.
( )( )
( )( )
I
T =
=
10 02 12
7 2 20
0 84
.
.
.
( )( )
( ) ) (
S
M
I
T
T
= +
+
-
3
35 3
23 4
( )