7.6.8
Second harmonic blocking element
A harmonic restrain of the Four step residual overcurrent protection function EF4PTOC
51N_67N can be chosen. If the ratio of the 2nd harmonic component in relation to the
fundamental frequency component in the residual current exceeds the pre-set level
defined by parameter setting
2ndHarmStab
. Any of the four residual overcurrent stages
can be selectively blocked by parameter setting
HarmRestrainx
. When 2nd harmonic
restraint feature is active the EF4PTOC 51N_67N function output signal 2NDHARMD
will be set to logical value one.
a
b
a>b
BLOCK
AND
I
OP
Extract second
harmonic current
component
Extract
fundamental
current component
X
2ndHarmStab
a
b
a>b
a
b
a>b
0.07*IBase
IEC13000015-1-en.vsd
2NDHARMD
UseStartValue
IN1>
IN2>
IN3>
IN4>
a
b
a>b
|I
OP
|
t
t=70ms
OR
AN
D
BlkParTransf=On
q
-1
OR
2ndH_BLOCK_Int
IEC13000015 V1 EN
Figure 104:
Second harmonic blocking
1MRK 506 335-UUS A
Section 7
Current protection
231
Technical manual
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