ABB REL670 2.2 IEC, Applications Manual

Page: 888 / 908

The low remanence type CT must fulfill
sr R
al alreq f max ct L
2
pr r
I S
E E 0.2 I R R
I I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1535 V2 EN-US
(Equation 537)
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
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 wire 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
=0.020 VA/channel for I
r
=1
A and S
R
=0.150 VA/channel for I
r
=5 A.
The non remanence type CT
CTs of non remanence type (for example, TPZ) can be used but in this case the CTs
within the differential 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:
sr R
al alreq f max ct L
2
pr r
I S
E E 0.2 I R R
I I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1536 V2 EN-US
(Equation 538)
25.1.6.2 Distance protection
M11619-3 v5
The current transformers must have a rated equivalent limiting secondary e.m.f. E
al
that is larger than the maximum of the required rated equivalent limiting secondary
e.m.f. E
alreq
below:
k max sr
R
al alreq ct L
2
pr r
I I
S
E E a R R
I
I
×
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1080 V2 EN-US
(Equation 539)
Section 25
1MRK 506 369-UEN B
Requirements
882 Line distance protection REL670 2.2 IEC
Application manual