ABB REB670 - Busbar Protection

21.1.6.1 Busbar protection
SEMOD129059-4 v6
The CT can be of high remanence or low remanence type and they can be used
together within the same zone of protection. Each of them 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:
The high remanence type CT must fulfill
sn
R
al alreq fma x CT L
2
pn n
I
S
E E 0.5 I R R
I I
³ = × × × + +
æ ö
ç ÷
è ø
EQUATION1667 V1 EN-US (Equation 90)
The low remanence type CT must fulfill
sn
R
al alreq f max CT L
2
pn n
I
S
E E 0.2 I R R
I I
³ = × × × + +
æ ö
ç ÷
è ø
EQUATION1668 V1 EN-US (Equation 91)
where
I
fmax
Maximum primary fundamental frequency fault current on the busbar (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 wire 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.
The non remanence type CT
CT
s of non remanence type (for example, TPZ) can be used but in this case the CTs
within the dif
ferential zone must be of non remanence type. They must fulfill the same
requirements as for the low remanence type CTs and have a rated equivalent secondary
e.m.f. E
al
that is larger than or equal to required secondary e.m.f. E
alreq
below:
Section 21 1MRK 505 370-UUS A
Requirements
528 Busbar protection REB670 2.2 ANSI
Application manual