Basler BE1-CDS240, Instruction Manual, Page: 569 / 580

S = S
i
+ Slope Margin S = 29% + 10% = 39%
Calculate Offset Current I Step 3.
ugh current loading so it tends to offset the operating slope S
i
upward from the origin. Thus, it decreases the safety arg ial tripping
characteristic knee point (intersection of the minimum pickup tripping characteristic and the
slope-tripping characteristic).
I
OFFSET
= IE + I
unmon
I
OFFSET
= 0.24 + 0 = 0.24
where:
IE
is assumed less than 4% of the self-cooled rating.
OFFSET
. The margin at the knee point of the tripping characteristic is
illustrated in Figure D-2. The additional mismatch caused by excitation current and unmonitored
loads does not vary with thro
m in at the different
9365200990 Rev F BE1-CDS240 Settings Calculations D-19
cooled forced MVA
cooled self MVA
024 0
20
12
IE IE

X cooled self * *
1 04 0 IE
. * * .
 
where:
-34.
I
unmon
is the unmonitored load calculated in Calculate Minpu, Step 2, Equation D-35.
Step 4. Calculate Operating Margin M
o
. The Operating Margin M
o
is given by this equation:
X is the tap conversion factor defined in Calculate Minpu, Step 1, Equation D
OFFSET
i
o
I
S
Minpu M





 
1
S
 
The conservative calculation of margin at the knee point uses
S
i
as calculated in Calculate Slope , Step 1.
For this example,
M
o
in times tap is the following equation:
tap times 040 . 0 024 . 0
39
1 * 25 . 0 M
o
 




 
29
 
The above calculation of margin is conservative. For the low current level where the margin at the tripping
characteristic knee point is of interest, the CT error will typically be less than 1%. Thus, calculating the
margin using
S
I
= 20 (replace 10% CT error with 1% CT error) yields the following result in this equation:
tap times 098 0 024 0
39
o
 
20
1 25 0 M . . * .
 



 

Step 5. Convert the margin to primary amperes. As a reality check, convert the margin to high side and
low side primary amperes.
If the conservative calculation yielded a margin less than or equal to 0, the minpu and/or the slope
settings should be increased.
The equation to do so is similar to the equation in the middle of page
D-16.
4 16
60
1
79 2 098 0
Ipri
.
* . * .
 
amps @ 69 kV 8 90
1
160 79 5 098 0 * . * .
Ipri .
 
amps @ 12.47 kV
The recommended harmonic restraint settings have been in effect successfully for many years. Most
applications should use these settings. When second harmonic sharing is enabled, restraint for the A
phase differential element is determined by:
Harmonic Restraint Settings