ABB Relion 670 Series Applications Manual page 494

Section 21
Requirements
21.1.6.3 Non-directional instantaneous and definitive time, phase and residual
overcurrent protection
The CTs must have a rated equivalent limiting secondary e.m.f. E
required rated equivalent limiting secondary e.m.f. E
³
E E
a l a lre q
EQUATION1678 V1 EN-US
where:
I
op
I
pr
I
sr
I
n
R
ct
R
L
S
R
21.1.6.4 Non-directional inverse time delayed phase and residual overcurrent
protection
The requirement according to Equation
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
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
Table continues on next page
488
æ
I
×
= × ×
1.5 I s n R
ç
op
CT
I
è
pn
The primary operate value (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 =5 A
r
below:
alreq
æ
I
×
= × × +
s n
20 I R
ç
op
CT
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)
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below:
alreq
ö
S
+ +
R R
÷
L
2
I
ø
n
=0.020 VA/channel for I
R
100 and Equation 101
that is larger than or equal to the required rated equivalent
al
ö
S
+
R R
÷
L
2
I
ø
n
1MRK 505 370-UUS Rev. K
that is larger than or equal to the
al
=1 A and S =0.150 VA/channel for
r R
does not need to be fulfilled if the high set
Busbar protection REB670
M11622-3 v5
(Equation 99)
M11339-3 v5
(Equation 100)
Application manual