ABB Relion REQ650, Руководство по применению

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Independent of the value of I
op
the maximum required E
al
is specified according to the
following:
sn R
al alreq max k max CT L
2
pn
r
I S
E E I R R
I I
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1077 V1 EN
(Equation 83)
where
I
kmax
Maximum primary fundamental frequency current for close-in faults (A)
16.1.6.4 Directional phase and residual overcurrent protection
If the directional overcurrent function is used the CTs must have a rated equivalent
secondary e.m.f. E
al
that is larger than or equal to the required equivalent secondary
e.m.f. E
alreq
below:
sn R
al alreq k max CT L
2
pn r
I S
E E I R R
I
I
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1078 V1 EN
(Equation 84)
where:
I
kmax
Maximum primary fundamental frequency current for close-in forward and reverse faults (A)
I
pn
The rated primary CT current (A)
I
sn
The rated secondary CT current (A)
I
r
The rated current of the protection IED (A)
R
CT
The secondary resistance of the CT ( W )
R
L
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 earthed systems. The resistance
of a single secondary wire should be used for faults in high impedance earthed systems.
S
R
The burden of an IED current input channel (VA). S
r
=0.010 VA/channel for I
r
=1 A and S
r
=0.250
VA/channel for I
r
=5 A
16.1.7 Current transformer requirements for CTs according to other
standards
All kinds of conventional magnetic core CTs are possible to use with the IEDs if they
fulfill the requirements corresponding to the above specified expressed as the rated
equivalent limiting secondary e.m.f. E
al
according to the IEC 61869-2 standard. From
different standards and available data for relaying applications it is possible to
approximately calculate a secondary e.m.f. of the CT comparable with E
al
. By
Section 16
1MRK 505 291-UEN A
Requirements
320
Application manual