Breaker Failure Protection - ABB REC670 Applications Manual

Section 24
Requirements
24.1.6.1
24.1.6.2
632

Breaker failure protection

The CTs must have a rated equivalent limiting secondary e.m.f. E
or equal to the required rated equivalent limiting secondary e.m.f. E
I
×
³ = × ×
E E 5 I s n
op
a l a lre q
I
pn
EQUATION1677 V1 EN-US
where:
I The primary operate value (A)
op
I The rated primary CT current (A)
pr
I The rated secondary CT current (A)
sr
I The nominal current of the protection IED (A)
n
R The secondary resistance of the CT (W)
ct
R
The resistance of the secondary cable and additional load (W). The loop resistance containing the
L
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 The burden of an IED current input channel (VA). S
R
VA/channel for I =5 A
r
Non-directional instantaneous and definitive time, phase and residual
overcurrent protection
The CTs must have a rated equivalent limiting secondary e.m.f. E
or equal to the required rated equivalent limiting secondary e.m.f. E
æ ö
S
+ +
R R R
ç ÷
CT L
2
è I ø
n
1MRK 511 401-UUS A
that is larger than
al
below:
alreq
=0.020 VA/channel for I =1 A and S
R r
that is larger than
al
below:
alreq
Bay control REC670 2.2 ANSI
Application manual
M11621-3 v5
(Equation 128)
=0.150
R
M11622-3 v5