Table of Contents
Advertisement
Section 24
Requirements
24.1.6.2
804
This can give the CT manufacturer a possibility to optimize the relation between the
resistance of the CT winding and the area of the iron core.
If the CT shall be specified as a class PX the following relation between the knee point
e.m.f. E
and R
shall be fulfilled:
k
ct
E
k
³
24.4
(
)
×
+
0.8 R
2.8
ct
EQUATION2544 V2 EN-US
Transformer differential protection
The current transformers must have a rated equivalent limiting secondary e.m.f. E
that is larger than the maximum of the required rated equivalent limiting secondary
e.m.f. E
below:
alreq
I
×
³
=
×
E
E
30 I
s n
nt
a l
a lre q
I
pn
EQUATION1672 V1 EN-US
I
×
³
= ×
×
E
E
2 I
s n
tf
a l
a lre q
I
pn
EQUATION1673 V1 EN-US
where:
I
The rated primary current of the power transformer (A)
rt
I
Maximum primary fundamental frequency current that passes two main CTs and
tf
the power transformer (A)
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 wire and additional load (W). The loop
L
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.
S
The burden of an IED current input channel (VA). S
R
A and S
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
E
k
³
or
19.5
+
R
2.8
ct
æ
ö
S
×
+
+
R
R
R
ç
÷
CT
L
2
I
è
ø
n
æ
ö
S
+
+
R
R
R
ç
÷
CT
L
2
I
è
ø
n
=0.150 VA/channel for I
=5 A
R
r
1MRK 502 071-UUS A
(Equation 294)
SEMOD54689-4 v4
al
(Equation 295)
(Equation 296)
=0.020 VA/channel for I
=1
R
r
Application manual
Advertisement
Table of Contents
