Breaker Failure Protection - ABB REL650 Applications Manual

1MRK 506 334-UUS A
18.1.6.2
Application manual
where:
I Maximum primary fundamental frequency current for close-in forward and reverse
kmax
faults (A)
I Maximum primary fundamental frequency current for faults at the end of zone 1
kzone1
reach (A)
I The rated primary CT current (A)
pn
I The rated secondary CT current (A)
sn
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 wire and additional load (W). In solidly grounded
L
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 The burden of an IED current input channel (VA). S
R
and S
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
a = 3 for the primary time constant T
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
k = 6 for the primary time constant T

Breaker failure protection

The CTs must have a rated equivalent secondary e.m.f. E
the required secondary e.m.f. E
=0.250 VA/channel for I =5 A
r r
p
below:
alreq
Section 18
Requirements
=0.010 VA/channel for I
R
£ 50 ms
> 50 ms
p
£ 30 ms
p
> 30 ms
p
that is larger than or equal to
al
=1 A
r
493