ABB RELION 670 SERIES REG670 - Transformer Differential Protection

This can give the CT manufacturer a possibility to optimize the relation between the
resistance of the CT winding and the area of the iron core.
If the CT shall be specified as a class PX the following relation between the knee point
e.m.f. E
k
and R
ct
shall be fulfilled:
( )
³ ³
× + +
k k
ct ct
E E
24.4 or 19.5
0.8 R 2.8 R 2.8
EQUATION2544 V2 EN-US (Equation 294)
24.1.6.2 Transformer differential protection
SEMOD54689-4 v4
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:
sn
R
al alre q CT L
2
pn n
nt
I
S
E E 30 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1672 V1 EN-US (Equation 295)
sn
R
al a lreq CT L
2
pn n
tf
I
S
E E 2 I R R
I I
³ = × × + +
æ ö
×
ç ÷
è ø
EQUATION1673 V1 EN-US (Equation 296)
where:
I
rt
The rated primary current of the power transformer (A)
I
tf
Maximum primary fundamental frequency current that passes two main CTs and
the power transformer (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
Section 24 1MRK 502 071-UUS A
Requirements
804 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual