ABB Relion 670 Series Applications Manual page 493

1MRK 505 370-UUS Rev. K
I
fmax
I
pr
I
sr
I
n
R
ct
R
L
S
R
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
required secondary e.m.f. E
³
E E
a l a lre q
EQUATION1668 V1 EN-US
21.1.6.2 Breaker failure protection
The CTs must have a rated equivalent limiting secondary e.m.f. E
required rated equivalent limiting secondary e.m.f. E
³
E E
a l a lre q
EQUATION1677 V1 EN-US
where:
I
op
I
pr
I
sr
I
n
R
ct
R
L
S
R
Busbar protection REB670
Application manual
Maximum primary fundamental frequency fault current on the busbar (A)
The rated primary CT current (A)
The rated secondary CT current (A)
The nominal current of the protection IED (A)
The secondary resistance of the CT (W)
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 grounded systems. The resistance of a single secondary wire should be
used for faults in high impedance grounded systems.
The burden of an IED current input channel (VA). S
A and S =0.150 VA/channel for I
R
below:
alreq
æ
I
= × × ×
0.2 I s n R
ç
f ma x CT
I
è
pn
æ
I
×
= × × +
5 I s n R
ç
op
CT
I
è
pn
The primary operate value (A)
The rated primary CT current (A)
The rated secondary CT current (A)
The nominal current of the protection IED (A)
The secondary resistance of the CT (W)
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.
The burden of an IED current input channel (VA). S
I =5 A
r
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=5 A.
r
ö
S
+ +
R R
÷
L
2
I
ø
n
below:
alreq
ö
S
+
R R
÷
L
2
I
ø
n
=0.020 VA/channel for I
R
=0.020 VA/channel for I =1
R r
that is larger than or equal to
al
that is larger than or equal to the
al
=1 A and S =0.150 VA/channel for
r R
Section 21
Requirements
(Equation 97)
M11621-3 v5
(Equation 98)
487