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1MRK 502 071-UUS A
24.1.6.3
24.1.6.4
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
In substations with breaker-and-a-half or double-busbar double-breaker arrangement,
the fault current may pass two main CTs for the transformer differential protection
without passing the power transformer. In such cases and if both main CTs have equal
ratios and magnetization characteristics the CTs must satisfy equation
equation 297.
æ
I
×
³
=
×
E
E
I
s n
R
ç
f
a l
a lre q
CT
I
è
pn
EQUATION1674 V1 EN-US
where:
I
Maximum primary fundamental frequency current that passes two main CTs without passing the
f
power transformer (A)
Breaker failure protection
The CTs must have a rated equivalent limiting secondary e.m.f. E
or equal to the required rated equivalent limiting secondary e.m.f. E
I
×
³
= ×
×
s n
E
E
5 I
op
a l
a lre q
I
pn
EQUATION1677 V1 EN-US
where:
I
The primary operate value (A)
op
I
The rated primary CT current (A)
pr
I
The rated secondary CT current (A)
sr
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 cable and additional load (W). The loop resistance containing the
L
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.
S
The burden of an IED current input channel (VA). S
R
VA/channel for I
=5 A
r
Restricted ground fault protection (low impedance differential)
The requirements are specified separately for solidly grounded and impedance
grounded transformers. For impedance grounded transformers the requirements for the
ö
S
+
+
R
R
÷
L
2
I
ø
n
æ
ö
S
+
+
R
R
R
ç
÷
CT
L
2
I
è
ø
n
Section 24
Requirements
295
that is larger than
al
below:
alreq
=0.020 VA/channel for I
=1 A and S
R
r
GUID-AFAFC587-6986-4FF4-A5E1-6F5DC0A72A6B v1
and
(Equation 297)
M11621-3 v5
(Equation 298)
=0.150
R
805
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