Basler BE1-CDS220, Instruction Manual

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13-38 Testing And Maintenance BE1-CDS220
Sidebar 13-6. Average Restraint When Increasing One Input from Balance - Continued
Example (Increasing One Input from Balance):
Tap1 = 2.00 Minpu = 0.30
Tap2 = 3.80 Slope = 15%
Input 1 current at balance = 3 per unit (6 amperes)
Input 2 current at balance = 3 per unit (11.40 amperes)
Input 1 is being increased relative to a fixed input 2 current.
I
restraint at balance
= 3 > 0.3






−
5 . 0
15 . 0
1
= 1.85 per unit
Then,
I
1trip
= I
2balance
* (1+((2*
100
slope
)/(2-
100
slope
))) = 3(1+0.30/1.85) = 3.486 per unit
I
restraint
=
2
2 I 1 I
+
= (3.0 + 3.486)/2 = 6.486/2 = 3.243 per unit (see the following figure)
1 2 3 4 5
AVERAGE RESTRAINT CURRENT (IN MULTIPLES OF TAP)
OP
E
RA
T
ING CU
RRE
NT
(I
N
M
ULT
IP
L
E
S
O
F
T
A
P)
12
3
Slope =
I
OP
*100/I
RESTR
= 15%
minimum pickup
= 0.30 x tap
Differential current
3.243
Average Restraint Characteristic Example
You may also use the average restraint operating characteristic and test the relay by decreasing one
current from a balanced condition. For additional information on testing in this manner, see Sidebar 13-7.
Sidebar 13-7. Average Restraint When Decreasing One Input from Balance
A second way to test the restrained pickup of the BE1-CDS relay is to decrease one of two currents,
initially applied in balance, to create an imbalance. In this narrative, input 1 current will be the input to be
changed. A similar analysis can be made for changing input 2 current.
By decreasing the input current I
1
from balance, the value of I
1trip
is defined as:
I
1trip
= I
2balance
(1- ((2*
100
slope
)/(2+
100
slope
))) in per unit