Basler Electric BE1-87T - Manual (Page 82)

4-40 BE1-87T Installation 9171300990 Rev V
HIGH TERTIARY LOW
) 50 )( 0 . 6 (
) 40 )( 8 . 16 (
=
T
I
=2.24
) 250 )( 5 . 2 (
) 200 )( 55 . 7 (
=
T
I
=2.42
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.
Figure 4-37. Slope Needed to Accommodate Total Mismatch with Adequate Margin
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:
S
M
I
T
T
= +
+
−
3
35 3
23 4
( )
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
For a three-winding transformer application, such as this example, the maximum of the three
values of M
T
and of I
T
is used.
M
T
is 10.6 (from Step 11) and I
T
is 2.42 (Step 20):
I
T
=
=
6 04 200
2 0 250
2
.
.
.42
( )
( )
( )
( )
60%
15%
MARGIN
MARGIN
XMFR EXCITING CURRENT
D610-010
3-2-91
BE1-87T
MAXIMUM I IN MULTIPLES OF TAP
R
TOTAL MISMATCH
M
U
L
T
I
P
L
E
S
O
F
T
A
P
I op
I
N