Basler BE1-CDS220, Instruction Manual

Page: 348 / 476

13-34 Testing And Maintenance BE1-CDS220
Sidebar 13-3. Maximum Restraint Operating Characteristic – Continued
Under test and in-service conditions, the following equations determine whether the relay operates
along the flat minimum pickup or slope of the operating characteristic. If:
I
restraint at balance
> minpu x






−
1
100 / slope
1
in per unit, use Equation 1, or if
I
restraint at balance
< minpu x






−
1
100 / slope
1
in per unit, use Equation 2.
Example (Increasing One Input from Balance):
TAP 1 = 2.00 Minpu = 0.30
TAP 2 = 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. Thus, the maximum restraint used by the
relay is input 1, the larger of the two currents in per unit.
I
restraint at balance
= 3 > 0.3






−
1
15 . 0
1
= 1.70 per unit
Then,
I
1trip
= I
1balance
/(1-(
100
slope
)) = 3/(1-0.85) = 3.53 per unit (see the following figure)
1 2 3 4 5
MAXIMUM RESTRAINT CURRENT (IN MULTIPLES OF TAP)
OP
ERAT
IN
G
C
U
R
R
E
N
T (I
N
MU
LT
IPLE
S
O
F
T
AP)
12
3
Slope =
I
OP
*100/I
RESTR
= 15%
minimum pickup
= 0.30 x tap
Differential current
3.53
Maximum Restraint Characteristic Example
You may also use the maximum 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 13-4.