ABB REL650 - Breaker Failure Protection

where:
I
kmax
Maximum primary fundamental frequency current for close-in forward and reverse
faults (A)
I
kzone1
Maximum primary fundamental frequency current for faults at the end of zone 1
reach (A)
I
pn
The rated primary CT current (A)
I
sn
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 wire and additional load (W). In solidly grounded
systems the loop resistance containing the phase and neutral wires should be used
for phase-to-ground faults and the resistance of the phase wire should be used for
three-phase faults.
In isolated or high impedance grounded systems the resistance of the single
secondary wire always can be used.
S
R
The burden of an IED current input channel (VA). S
R
=0.010 VA/channel for I
r
=1 A
and S
r
=0.250 VA/channel for I
r
=5 A
a This factor is a function of the primary time constant for the dc component in the
fault current.
a= 2 for the primary time constant T
p
£ 50 ms
a = 3 for the primary time constant T
p
> 50 ms
k
A factor of the primary time constant for the dc component in the fault current for a
three-phase fault at the set reach of zone 1.
k = 4 for the primary time constant T
p
£ 30 ms
k = 6 for the primary time constant T
p
> 30 ms
18.1.6.2 Breaker failure protection
The CTs must have a rated equivalent secondary e.m.f. E
al
that is larger than or equal to
the required secondary e.m.f. E
alreq
below:
1MRK 506 334-UUS A Section 18
Requirements
493
Application manual