ABB REL650 series, Applications Manual

Page: 500 / 516

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
(Equation 180)
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
18.1.6.3 Non-directional instantaneous and definitive time, phase and residual
overcurrent protection
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 1.5 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1678 V1 EN
(Equation 181)
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 18
1MRK 506 334-UUS A
Requirements
494
Application manual