ABB RELION 670 Series Applications Manual page 173

1MRK 505 337-UUS A
When the dual polarizing method is used it is important that the setting
ZNpol is not greater than 3V
direction.
IPolMin : is the minimum ground-fault current accepted for directional evaluation. For smaller
currents than this value the operation will be blocked. 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 IBase 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.
7.3.2.3 2nd 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 overcurrent function will give an unwanted trip. The inrush current has a
relatively large ratio of 2nd harmonic component. This component can be used to create a restrain
signal to prevent this unwanted function.
At current transformer saturation a false residual current can be measured by the protection. Also
here the 2
2ndHarmStab : The rate of 2nd harmonic current content for activation of the 2nd harmonic
restrain signal. The setting is given in % of the fundamental frequency residual current.
HarmRestrainx : Enable block of step x from the harmonic restrain function.
7.3.2.4 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.
Application manual
. If so, there is a risk for incorrect operation for faults in the reverse
0
IBase and must be set below the lowest INx> setting, set for the directional
nd
harmonic restrain can prevent unwanted operation.
Pickupx or the product 3I
nd
harmonic of the inrush currents of the two
nd
Section 7
Current protection
·
0
IBase .
M15282-90 v5
M15282-97 v5
harmonic current
nd
harmonic
167