ABB Relion 670 Series Applications Manual page 153

1MRK 511 401-UEN Rev. K
IN>Dir : Operate residual current release level in % of IB for directional comparison scheme. The
setting is given in % of
directional measurement. The output signals, STFW and STRV can be used in a teleprotection
scheme. The appropriate signal should be configured to the communication scheme block.
8.4.4.2
nd
2 harmonic restrain
If a power transformer is energized there is a risk that the current transformer core will
saturate during part of the period, resulting in a transformer inrush current. This will give a
declining residual current in the network, as the inrush current is deviating between the
phases. There is a risk that the residual over-current function will give an unwanted trip. The
inrush current has a relatively large ratio of 2
used to create a restrain signal to prevent this unwanted operation.
At current transformer saturation a false residual current can be measured by the protection.
Here the 2
2ndHarmStab : The rate of 2
restrain signal. The setting is given in % of the fundamental frequency residual current.
8.4.4.3 Parallel transformer inrush current logic
In case of parallel transformers there is a risk of sympathetic inrush current. If one of the
transformers is in operation, and the parallel transformer is switched in, the asymmetric
inrush current of the switched-in transformer will cause partial saturation of the transformer
already in service. This is called transferred saturation. The 2
of the two transformers will be in phase opposition. The summation of the two currents will
thus give a small 2
significant. The inrush current of the transformer in service before the parallel transformer
energizing, will be a little delayed compared to the first transformer. Therefore, we will have
nd
high 2
the normal 2
Power System
IEC05000136 V1 EN-US
Figure 69: Application for parallel transformer inrush current logic
BlkParTransf function is activated, the 2
If the
the residual current measured by the relay is larger than a selected step current level. Assume
that step 4 is chosen to be the most sensitive step of the four step residual overcurrent
protection function EF4PTOC. The harmonic restrain blocking is enabled for this step. Also the
same current setting as this step is chosen for the blocking at parallel transformer energizing.
The settings for the parallel transformer logic are described below.
BlkParTransf : This is used to On blocking at energising of parallel transformers.
Bay control REC670
Application manual
IB and must be set below the lowest INx> setting, set for the
nd
harmonic restrain can prevent unwanted operation as well.
nd
harmonic current content for activation of the 2
nd
harmonic current. The residual fundamental current will however be
harmonic current initially. After a short period this current will however be small and
nd
harmonic blocking will reset.
IN>
IN>
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nd
harmonic component. This component can be
nd
harmonic of the inrush currents
en05000136.vsd
nd
harmonic restrain signal will latch as long as
Section 8
Current protection
M15282-90 v7
nd
harmonic
M15282-97 v6
147