Toshiba GRL150-100 Series Instruction Manual page 46

2.10 Countermeasures for Magnetising Inrush
GRL150 provides the following two schemes to prevent incorrect operation from a magnetising
inrush current during transformer energisation.
- Protection block by inrush current detector
- Cold load protection
2.10.1 Inrush Current Detector
Inrush current detector ICD detects second harmonic inrush current during transformer
energisation and blocks the following protections:
- DIF
- OC1 to OC4
- EF1 to EF4
- SEF1 to SEF4
The ICD is used to protect a line with an in-zone transformer ('Teed' transformer) as shown in
Figure 2.10.1.1.
Note: DIFI1 should be set to take account of the transformer load current.
The blocking can be enabled or disabled by setting the scheme switches [DIF-ICD] and
[OC-ICD].
The ICD detects the ratio ICD-2f between second harmonic current I2f and fundamental current
I1f in each phase current, and operates if its ratio is larger than the setting value. Figure 2.10.1.2
shows the characteristic of the ICD element and Figure 2.10.1.3 shows the ICD block scheme.
When ICD operates, the local terminal DIF, OC, EF and SEF elements are blocked, and the signal
ICD_BLK-S is sent to the remote terminal for blocking the remote terminal DIF element. The
ICD_BLK-S is assigned to 2051:COM4-S by PLC function. The scheme logic of each element is
shown in the previous sections.
ICD-2f(%)
GRL150
Figure 2.10.1.1 Protection with In-zone Transformer
I /I
2f 1f
0
ICDOC
Figure 2.10.1.2 ICD Element Characteristic
⎯ 45 ⎯
Transformer
|I |/|I |≥ICD-2f(%)
2f 1f
|I |≥ICDOC
1f
I
1f
6 F 2 S 0 8 2 8
GRL150
&
ICD