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2.1.7
Countermeasures for Magnetising Inrush
GRD150 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
2.1.7.1 Inrush Current Detector
Inrush current detector ICD detects second harmonic inrush current during transformer
energisation and blocks the following definite time overcurrent protections.
- OC1 to OC4
- DOC1 to DOC4
- EF1 to EF4
- DEF1 to DEF4
- SEF1 to SEF4
- DSEF1 to DSEF4
- NOC1 and NOC2
- DNOC1 and DNOC2
- BCD
The blocking can be enabled or disabled by setting the scheme switches [∗∗∗∗-2F].
The ICD detects the ratio ICD-2f between a second harmonic current I2f and a fundamental
current I1f in each phase current, and outputs if its ratio is larger than the setting value. Figure
2.1.60 shows the characteristic of ICD element and Figure 2.1.61 shows ICD block scheme.
I
/I
2f
1f
ICD-2f(%)
0
ICD
[∗∗∗∗-2F].
+
ICDOC
Figure 2.1.60
ICD Element Characteristic
A
≥1
OP. BLOCK
&
B
C
Figure 2.1.61
⎯
68
|I
|/|I
|≥ICD-2f(%)
2f
1f
|I
|≥ICDOC
1f
I
1
Definite time
overcurrent
ICD Block Scheme
⎯
6 F 2 S 0 8 4 2
&
ICD
∗
&
OC
D
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