Ct Wiring And Setting Of Earth Fault Detection; Ct Wiring Of 2 Phase Ct; Earth Fault Current Detection Wiring; 2 Phase Ct Wiring - Toshiba GRE110 Instruction Manual

2.2.5 CT Wiring and Setting of earth fault detection

On the models 400, 401 and 402, the earth fault current input may be connected either in the
residual circuit of the phase CTs, or alternatively a dedicated earth fault CT may be used. In the
case of connection in the residual circuit of the phase CTs, the settings of the phase CT ratio OCCT
and the earth fault CT ratio EFCT should be equal. On the other hand, where a dedicated earth fault
CT or only earth fault CT (no 3 phase CT) are applied, then the settings of OCCT and EFCT may
NOT be equal. The connection methods are illustrated in figure 2.2.10.
The maximum setting value of the earth fault protection is 20.00A in case of elements EF1 and
EF2, and 100.00A for EF3 and EF4. However, it should be noted that, in the case that a dedicated
earth fault CT connection is used, the measuring range of earth fault current is limited to 20A
maximum.
TB1
Ia
1
2
Ib
3
4
Ic
5
6
7
Ie
8
Residual
current
(a)for Residual current
detection wiring

2.2.6 CT Wiring of 2 phase CT

When applying 2 phase CT's for the main circuit, the relay input wiring is as shown in Figure
2.2.11. This wiring derives phase B vector current from phase A and phase C vector current as
shown in Figure 2.2.12. If zero phase current occur or 3 phase current is unbalanced, the phase B
current measurement value will not be correct.
When applying 2 phase CT's, the earth fault current input cannot be connected to the residual
circuit of the phase CT's. This wiring is NOT for models 820 and 821.
Ia
Ic
from
Zero-phase
current
transformer
Figure 2.2.11 2 phase CT wiring
TB1
Ia
Ia
Ib
Ib
Ic
Ic
Ie
Ie
from
Zero-phase
current
transformer
(b)for Zero-phase current
transformer wiring
Figure 2.2.10

Earth fault current detection wiring

TB1
1
2
3
4
5
6
7
Ie
8
 22 
1
Ia
2
3
Ib
4
5
Ic
6
7
Ie
Ie
8
from
Zero-phase
current
transformer
(c)for only Zero-phase
current transformer wiring
Ia
Ib Ia+Ic
Ic
Ie
Ic
Figure 2.2.12 Phase B composition of vectors
6 F 2 T 0 1 7 2
TB1
1
Ia
2
3
Ib
4
5
Ic
6
7
Ie
8
Ia
Ib=-(Ia+Ic)