Cooper Lighting Low Impedance Bus Differential Relay M-LIB3 - Manual (Page 10)

M-LIB3 Low Impedance Bus Differential Relay
10
2.6 Technical Data
q Standards: IEC 255, 1000, CE
q Rated Frequency: 50/60 Hz
q Rated input current: 1 A
q Current overload: 2 In
q Transient overload: 100 In
q Setting ranges:
•
F
n
= 50/60 Hz
•
I
ds
= zone differential current = (0,2-2) In
•
R = Bias per Unit = (0,4 - 1) p.u.
•
I
SV
= Circuit supervision current = (0,1 – 1) In
•
Operating time:
≤
20 ms
•
Stability level:
≥
40 I
n
max.
2.7 CURRENT TRANSFORMER REQUIREMENTS
Current transformer requirements
Minimum knee point voltage: V
K
≥
F . In . R
T
where
F = Accuracy limit factor (20 recommended)
In = Main CT’s rated secondary current
R
T
= Total CT’s secondary loop resistance (see equivalent diagram)
Minimum power:
2
In R
In F
V
S
CT
K 





−
⋅
≥
RCT = Secondary resistance of main CT
RW = Resistance of connection lead
RP = Primary resistance of auxiliary ratio matching CT
n = IP/IS = Current ratio of auxiliary CT
RS = Secondary resistance of auxiliary ratio matching CT
Rd = Ohmic burden of M-LIB3 : 0.52
Ω
(In=1A)