where:
I
kmax
Maximum primary fundamental frequency fault current for internal close-in
faults (A)
I
tmax
Maximum primary fundamental frequency fault current for through fault
current for external faults (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
In substations with breaker-and-a-half or double-busbar double-breaker arrangement, the
through fault current may pass two main CTs for the line differential protection without
passing the protected line. In such cases and if both main CTs have equal ratios and
magnetization characteristics the CTs must satisfy equation
sr
R
al
alreq
tfdb
ct
L
2
pr
r
I
S
E
E
I
R
R
I
I
æ
ö
³
=
×
×
+
+
ç
÷
è
ø
EQUATION1411 V2 EN-US
(Equation 564)
where:
I
tfdb
Maximum primary fundamental frequency through fault current that passes two main CTs (one-and-
a-half or double-breaker) without passing the protected line (A)
If a power transformer is included in the protected zone of the line differential protection the
CTs must also fulfill equation
.
sr
R
al
alreq
rt
ct
L
2
pr
r
I
S
E
E
30 I
R
R
I
I
æ
ö
³
=
× ×
×
+
+
ç
÷
è
ø
EQUATION1412 V2 EN-US
(Equation 565)
where:
I
rt
The rated primary current of the power transformer (A)
23.1.6.2
Distance protection
M11619-3 v5
The current transformers must have a rated equivalent limiting secondary e.m.f. E
al
that is
larger than the maximum of the required rated equivalent limiting secondary e.m.f. E
alreq
below:
Section 23
1MRK 505 343-UEN B
Requirements
736
Application manual
Содержание Relion 670 series
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