ABB REB670 - Breaker Failure Protection; Non-Directional Instantaneous and Definitive Time, Phase and Residual Overcurrent Protection

sn
R
al alreq f max CT L
2
pn n
I
S
E E 0.2 I R R
I I
³ = × × × + +
æ ö
ç ÷
è ø
EQUATION1668 V1 EN-US (Equation 92)
21.1.6.2 Breaker failure protection
M11621-3 v5
The CTs must have a rated equivalent limiting secondary e.m.f. E
al
that is larger than
or equal to the required rated equivalent limiting secondary e.m.f. E
alreq
below:
sn
R
al a lreq CT L
2
pn n
op
I
S
E E 5 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1677 V1 EN-US (Equation 93)
where:
I
op
The primary operate value (A)
I
pr
The rated primary CT current (A)
I
sr
The rated secondary CT current (A)
I
n
The nominal current of the protection IED (A)
R
ct
The secondary resistance of the CT (W)
R
L
The resistance of the secondary cable and additional load (W). The loop resistance containing the
phase and neutral wires, must be used for faults in solidly
grounded
systems. The resistance of a
single secondary wire should be used for faults in high impedance grounded systems.
S
R
The burden of an IED current input channel (VA). S
R
=0.020
VA/channel for I
r
=1 A and S
R
=0.150
VA/channel for I
r
=5 A
21.1.6.3 Non-directional instantaneous and definitive time, phase and residual
overcurrent protection
M11622-3 v5
The CTs must have a rated equivalent limiting secondary e.m.f. E
al
that is lar
ger than
or equal to the required rated equivalent limiting secondary e.m.f. E
alreq
below:
1MRK 505 370-UUS A Section 21
Requirements
Busbar protection REB670 2.2 ANSI 529
Application manual