ABB Relion 670 Series Applications Manual page 590

Section 24
Requirements
24.1.6.3 Non-directional inverse time delayed phase and residual overcurrent
protection
The requirement according to Equation
high set instantaneous or definitive time stage is used. In this case Equation is the only necessary
requirement.
If the inverse time delayed function is the only used overcurrent protection function the CTs must
have a rated equivalent limiting secondary e.m.f. E
rated equivalent limiting secondary e.m.f. E
³
E E
a l a lre q
EQUATION1679 V1 EN-US
where
I
op
I
pr
I
sr
I
n
R
ct
R
L
S
R
Independent of the value of I
³
E E
a l a lre q ma x
EQUATION1680 V1 EN-US
where
I
kmax
24.1.6.4 Directional phase and residual overcurrent protection
If the directional overcurrent function is used the CTs must have a rated equivalent limiting
secondary e.m.f. E
e.m.f. E
alreq
584
æ
I
×
= × × +
20 I s n R R
ç
op
CT L
I
è
pn
The primary current set value of the inverse time function (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 cable 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
the maximum required E
op
æ
I
×
= × +
I R R
s n
ç
k ma x
CT
I
è
pn
Maximum primary fundamental frequency current for close-in faults (A)
that is larger than or equal to the required rated equivalent limiting secondary
al
below:
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135 and Equation 136
that is larger than or equal to the required
al
below:
alreq
ö
S
+
R
÷
2
I
ø
n
=5 A
r
is specified according to the following:
al
ö
S
+
R
÷
L
2
I
ø
n
1MRK 511 401-UUS F
does not need to be fulfilled if the
=0.020 VA/channel for
R
Bay control REC670
Application manual
M11339-3 v5
(Equation 135)
(Equation 136)
M11624-3 v6