ABB Relion 670 Series Applications Manual page 135

1MRK 511 407-UUS Rev. J
V/(√3 · 3I
ohms.
When the dual polarizing method is used, it is important that the setting
3I · ZNpol is not greater than 3V
0
reverse direction.
IPolMin : is the minimum ground-fault current accepted for directional evaluation. For smaller
currents than this value, the operation will be blocked. A typical setting is 5-10% of
VPolMin : Minimum polarization (reference) polarizing voltage for the directional function, given in
VBase /√3.
% of
IDirPU : Operate residual current release level in % of IB for directional comparison scheme. The
setting is given in % of
measurement. The output signals, PUFW and PUREV can be used in a teleprotection scheme. The
appropriate signal should be configured to the communication scheme block.
8.2.3.2
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
signal to prevent this unwanted operation.
At current transformer saturation a false residual current can be measured by the protection. Here
nd
the 2 harmonic restrain can prevent unwanted operation as well.
2ndHarmStab : The rate of 2
signal. The setting is given in % of the fundamental frequency residual current.
8.2.3.3 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
transformers will be in phase opposition. The summation of the two currents will thus give a small
nd
2 harmonic current. The residual fundamental current will however be 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 high 2
initially. After a short period this current will however be small and the normal 2
blocking will reset.
Phasor measurement unit RES670
Application manual
) Typically, the minimum ZNPol (3 · zero sequence source) is set. The setting is in primary
0
0
IB and must be set below the lowest INx> setting, set for the directional
nd
harmonic component. This component can be used to create a restrain
nd
harmonic current content for activation of the 2
© Copyright 2017 Hitachi Power Grids. All rights reserved
. If so, there is a risk for incorrect operation for faults in the
nd
harmonic of the inrush currents of the two
Section 8
Current protection
Pickupx or the product
IB .
M15282-90 v7
nd
harmonic restrain
M15282-97 v6
nd
harmonic current
nd
harmonic
129