Basler BE1-CDS240, Instruction Manual, Page: 567 / 580

Since the
X
tap values are based upon the forced cooled rating
and adjusted if necessary by the factor
calculated in Calculate Minpu, Step 1, equation at the top of this page. The pickup can be calculated by
the following equation:
9365200990 Rev F BE1-CDS240 Settings Calculations D-17
cooled forced MVA
X URO * * 6

cooled self MVA
20
* 1 * 6 URO
12

6 . 3

URO
This
URO
value (3.6 rounded up to 4
step will determine the value required
.0) is the minimum setting to avoid tripping during inrush. The next
to avoid tripping for the maximum external fault under worst case
tep 1. Calculate the maximum external fault (IE) in multiples of tap. Use these two equations.
For wye connected CT’s For delta connected CT’s (See Setting Note 2)
CT saturation.
Calculate Maximum External Fault
S
Fau Maximum
Tap
lt
IE

phase Fault 3
Tap
Maximum
IE
3 *

Equation D-38 Equation D-39
69 kV Side 12.47 kV Side
5 . 11
79 . 2
60
1916








IE 4 . 11
79 . 5
160
10603








IE
S The transient monitor function provides security from tripping for external through faults by
doubling the unrestrained unit pickup setting when saturation is detected. Calculate the
unrestrained pickup such that 2 times the unrestrained pickup is greater than 70%
tep 2.
of the
maximum external through fault in times tap. This calculation assumes that the CTs carrying
the maximum fault saturate severely, yielding only 30% of the expected ratio current. This leaves
70% of the fault current as false differential current.
02 4
2
URO .
 
5 11 . * 70 0 .
99 3
2
URO
.
 
Step 3. Select the unrestrained pickup setting. Choose the larger
4 11 70 0
. * .
of the unrestrained pickup values
and above two equations. Round the result up to the
Step 4. Convert pickup setting to primary amperes.
kup sensitivity to high side and low side
The equation to do so is similar to the equation in the middle of page D-16.
calculated in the first equations on this page
next integer value. (In the first URO equation above, because 4.02 is very close to 4.0, do not round up
to 5.) This results in a setting of URO = 4 times tap for this example.
As a reality check, convert the unrestrained pic primary amperes.
670 706 , 3
1
160 * 79 . 5 * 4
 
Ipri
60 * 79 . 2 * 4
1
 
Ipri
amps @ 69 KV amps @ 12.47 KV
us the restraint current (
I
restraint
) that will cause a trip. The
percentage differential characteristic can operate on a slope setting that is a percent of the maximum of
the through currents or a percent of the average of the through currents.
Calculate Slope
The percentage restrained tripping characteristic is defined by the slope ratio. The slope setting S is the
ratio of the differential current (
I
op
) vers