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1MRK 505 370-UEN D
I
fmax
I
pr
I
sr
I
r
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
than or equal to required secondary e.m.f. E
³
E
E
al
EQUATION1536 V2 EN-US
21.1.6.2
Breaker failure protection
The CTs must have a rated equivalent limiting secondary e.m.f. E
to the required rated equivalent limiting secondary e.m.f. E
³
E
E
al
EQUATION1380 V2 EN-US
where:
I
op
I
pr
I
sr
I
r
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 rated 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 earthed systems. The resistance of a single secondary wire should
be used for faults in high impedance earthed systems.
The burden of an IED current input channel (VA). S
I
=1 A and S
=0.150 VA/channel for I
r
R
æ
I
=
×
×
×
sr
0.2 I
R
ç
alreq
f max
I
è
pr
æ
I
= ×
×
×
sr
5 I
R
ç
alreq
op
ct
I
è
pr
The primary operate value (A)
The rated primary CT current (A)
The rated secondary CT current (A)
The rated 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 earthed systems. The resistance of a single
secondary wire should be used for faults in high impedance earthed systems.
The burden of an IED current input channel (VA). S
channel for I
=5 A
r
=5 A.
r
below:
alreq
ö
S
+
+
R
R
÷
ct
L
2
I
ø
r
ö
S
+
+
R
R
÷
L
2
I
ø
r
=0.020 VA/channel for I
R
=0.020 VA/channel for
R
that is larger
al
that is larger than or equal
al
below:
alreq
=1 A and S
=0.150 VA/
r
R
Section 21
Requirements
(Equation 94)
M11621-3 v5
(Equation 95)
453
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