ABB RELION 670 Series Applications Manual page 430

Section 20
Requirements
The high remanence type CT must fulfill
³
E E
a l a lre q
EQUATION1667 V1 EN-US
The low remanence type CT must fulfill
³
E E
a l a lre q
EQUATION1668 V1 EN-US
where
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
equal to required secondary e.m.f. E
³
E E
a l a lre q
EQUATION1668 V1 EN-US
20.1.6.2 Breaker failure protection
The CTs must have a rated equivalent limiting secondary e.m.f. E
the required rated equivalent limiting secondary e.m.f. E
424
æ
I
= × × × +
0.5 I s n R
ç
f ma x CT
I è
pn
æ
I
= × × × +
0.2 I s n R
ç
f ma x CT
I
è
pn
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
I =1 A and S =0.150 VA/channel for I
r R
æ
I
= × × × +
0.2 I s n R
ç
f ma x CT
I
è
pn
ö
S
+
R R
÷
L
2
I ø
n
ö
S
+
R R
÷
L
2
I
ø
n
=5 A.
r
below:
alreq
ö
S
+
R R
÷
L
2
I
ø
n
alreq
1MRK 505 337-UUS A
=0.020 VA/channel for
R
that is larger than or
al
that is larger than or equal to
al
below:
Application manual
(Equation 95)
(Equation 96)
(Equation 97)
M11621-3 v5