Table of Contents
Advertisement
Section 6
Differential protection
•
Only one measuring circuit is utilized for all fault types (that is, no redundancy for multi-
phase faults)
•
Primary fault sensitivity varies depending on the type of fault and involved phase(s), see
Table
•
The load currents in the healthy phases might produce the stabilizing current when an
internal single phase to ground fault occurs. However, there is no problem for solidly
earthed systems with high earth-fault currents
•
No indication of faulty phase(s) in case of an internal fault
•
Not possible to fully utilize Open CT detection feature
6.1.6.2
Auxiliary summation CTs
Auxiliary Summation Current Transformer (that is, ASCT in further text) of the type SLCE 8 is
used with the summation principle of the IED. The principle drawing of one such ASCT is
shown in Figure 83.
IEC03000118 V1 EN-US
Figure 83: Principle ASCT drawing
The ASCT has three primary windings and one secondary winding. In further text, turn
numbers of these windings will be marked with N1, N2, N3 & N4, respectively (see Figure
more information).
There are three types of ASCT for REB670:
1.
ASCT type with ratio 1/1A, for balanced 3-Ph current input, shall be used with all main
current transformers with 1A rated secondary current (that is, 2000/1A)
2.
ASCT type with ratio 5/1A, for balanced 3-Ph current input, shall be used with all main
current transformers with 5A rated secondary current (that is, 3000/5A)
3.
ASCT type with ratio 2/1A, for balanced 3-Ph current input, shall be used with all main
current transformers with 2A rated secondary current (that is, 1000/2A)
Note the following:
•
main CT rated primary current is not important for ASCT selection
•
possible main CT ratio differences will be compensated by a parameter setting in the IED
•
rated secondary current of ASCT is 1A for all types. That means that secondary ASCT
winding should be always connected to the IED with 1A CT inputs, irrespective of the rated
secondary current of the main CT
136
24
Auxiliary Summation CT
type SLCE 8; X/1A
P1
N1
S1
P2
P3
N4
N2
P4
P5
N3
S2
P6
en03000118.vsd
1MRK 505 370-UEN D
M12136-4 v4
83
for
Busbar protection REB670
Application manual
Advertisement
Table of Contents
