6.1.3 Connection examples for high impedance differential
protection
GUID-8C58A73D-7C2E-4BE5-AB87-B4C93FB7D62B v5
WARNING! USE EXTREME CAUTION! Dangerously high voltages might be
present on this equipment, especially on the plate with resistors. De-energize
the primary object protected with this equipment before connecting or
disconnecting wiring or performing any maintenance. The plate with resistors
should be provided with a protective cover, mounted in a separate box or in a
locked cubicle. National law and standards shall be followed.
6.1.3.1 Connections for three-phase high impedance differential protection
GUID-C12CCAAF-5AE5-4A9C-AC9C-F56A66FD2C14 v8
Generator, reactor or busbar differential protection is a typical application for three-phase
high impedance differential protection. Typical CT connections for three-phase high
impedance differential protection scheme are shown in figure 34.
L1
(A)
L2
(B)
L3
(C)
Protected Object
CT 1200/1
Star/Wye
Connected
L1
(A)
L2
(B)
L3
(C)
CT 1200/1
Star/Wye
Connected
7
8
9
1
0
1
1
1
2
1
2
3
4
5
6
AI01
(I)
AI02
(I)
AI03
(I)
AI04
(I)
AI05
(I)
AI06
(I)
7
6
X1
R4
R5
R6
1
2
12
1
2
11 12 13 14
U
U
U
R1
1
3
4
2
1
3
R2
2
4
1
3
R3
2
4
1 2 3 4 5 6 7
L1 (A)
L2 (B)
L3 (C)
N
3-Ph Plate with Metrosils and Resistors
2
3
5
4
X X
L1 (A)
L2 (B)
L3 (C)
N
1
IED
IEC07000193_4_en.vsd
AI3P
AI1
AI2
AI3
AI4
AIN
SMAI2
BLOCK
^GRP2L1
^GRP2L2
^GRP2L3
^GRP2N
TYPE
IEC07000193 V4 EN-US
Figure 34: CT connections for high impedance differential protection
Pos
Description
1 Scheme earthing point
It is important to insure that only one earthing point exist in this scheme.
2 Three-phase plate with setting resistors and metrosils. Protective earth is a separate 4 mm screw
terminal on the plate.
3 Necessary connection for three-phase metrosil set.
4 Position of optional test switch for secondary injection into the high impedance differential IED.
Section 6 1MRK 511 358-UEN A
Differential protection
92
Application manual
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