ABB Relion REC670, Applications Manual

Page: 638 / 658

24.1.6.1 Breaker failure protection
M11621-3 v5
The CTs must have a rated equivalent limiting secondary e.m.f. E
al
that is larger than
or equal to the required rated equivalent limiting 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 128)
where:
I
op
The primary operate value (A)
I
pr
The rated primary CT current (A)
I
sr
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
=0.020 VA/channel for I
r
=1 A and S
R
=0.150
VA/channel for I
r
=5 A
24.1.6.2 Non-directional instantaneous and definitive time, phase and residual
overcurrent protection
M11622-3 v5
The CTs must have a rated equivalent limiting secondary e.m.f. E
al
that is larger than
or equal to the required rated equivalent limiting secondary e.m.f. E
alreq
below:
Section 24
1MRK 511 401-UUS A
Requirements
632 Bay control REC670 2.2 ANSI
Application manual