ABB REB670 Series - Breaker failure protection

I
fmax
Maximum primary fundamental frequency fault current on the busbar (A)
I
pr
The rated primary CT current (A)
I
sr
The rated secondary CT current (A)
I
r
The rated current of the protection IED (A)
R
ct
The secondary resistance of the CT (W)
R
L
The resistance of the secondary wire and additional load (W). The loop
resistance containing the phase and neutral wires, must be used for faults
in solidly earthed systems. The resistance of a single secondary wire should
be used for faults in high impedance earthed 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.
The non remanence type CT
CTs of non remanence type (for example, TPZ) can be used but in this case the CTs within the
differential zone must be of non remanence type. They must fulfill the same requirements as
for the low remanence type CTs and have a rated equivalent secondary e.m.f. E
al
that is larger
than or equal to required secondary e.m.f. E
alreq
below:
sr
R
al alreq f max ct L
2
pr
r
I
S
E E 0.2 I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1536 V2 EN-US (Equation 94)
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:
sr
R
al alreq op ct L
2
pr
r
I
S
E E 5 I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1380 V2 EN-US (Equation 95)
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
r
The rated 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 earthed systems. The resistance of a single
secondary wire should be used for faults in high impedance earthed 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
1MRK 505 370-UEN D Section 21
Requirements
Busbar protection REB670 453
Application manual