ABB RELION 650 SERIES, Applications Manual

Page: 248 / 262

sn
al alreq s tmax CT L
pn
I
E E 2 V 2 I (R R )
I
³ = × = × × × +
EQUATION-2431---ANSI V1 EN-US
(Equation 31)
where:
V
s
Set operate value to the voltage relay (V)
I
kmax
Maximum primary fundamental frequency fault current for through fault current for external faults (A)
I
pn
The rated primary CT current (A)
I
sn
The rated secondary CT current (A)
R
CT
The secondary resistance of the CT (Ω)
R
L
The resistance of the secondary cable from the CT up to a common junction point (Ω). The loop resistance
containing the phase and neutral wires, must be used for faults in solidly grounded systems and the
resistance of a single-phase wire should be used for faults in high impedance grounded systems.
All CTs to the same protection should have identical turn ratios. Consequently auxiliary CTs cannot
normally be used. The IED must be provided with separate cores.
16.1.6.2 Breaker failure protection
M11621-3 v4
The CTs must have a rated equivalent secondary e.m.f. E
al
that is larger than or equal to the
required secondary e.m.f. E
alreq
below:
s n R
a l a lre q CT L
2
pn n
op
I S
E E 5 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1677 V1 EN-US
(Equation 32)
where:
I
op
The primary operate value (A)
I
pn
The rated primary CT current (A)
I
sn
The rated secondary CT current (A)
I
n
The nominal 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 grounded systems. The resistance of a single
secondary wire should be used for faults in high impedance grounded 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
Section 16 1MRK 505 287-UUS B
Requirements
242 Busbar protection REB650
Application manual
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