ABB Relion 670 Series Applications Manual page 156

Section 8
Current protection
In a normal transmission network a normal value of RCA is about 65°. The setting range is -180° to
+180°.
polMethod : Defines if the directional polarization is from
Voltage (3V
•
Current (3I
•
• both currents and voltage,
Normally voltage polarizing from the internally calculated residual sum or an external open delta is
used.
Current polarizing is useful when the local source is strong and a high sensitivity is required. In
such cases the polarizing voltage (3V
polarizing or dual polarizing. Multiply the required set current (primary) with the minimum
impedance (ZNpol) and check that the percentage of the phase-to-ground voltage is definitely
higher than 1% (minimum 3V
RNPol, XNPol : The zero-sequence source is set in primary ohms as base for the current polarizing.
The polarizing voltage is then achieved as 3I
that is the ground return impedance of the source behind the protection. The maximum ground-
fault current at the local source can be used to calculate the value of ZN as V/(√3 · 3I
the minimum ZNPol (3 · zero sequence source) is set. The setting is in primary 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.
8.4.3.2 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. Here
nd
the 2 harmonic restrain can prevent unwanted operation as well.
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.
150
or V )
0 2
· ZNpol or 3I ·ZNpol where ZNpol is RNpol + jXNpol), or
0 2
Dual (dual polarizing, (3V
) can be below 1% and it is then necessary to use current
0
> VPolMin setting) as a verification.
0
. If so, there is a risk for incorrect operation for faults in the
0
IB and must be set below the lowest INx> setting, set for the directional
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+ 3I · ZNpol) or (V
0 0
· ZNpol. The ZNpol can be defined as (ZS
0
1MRK 511 401-UUS F
+ I · ZNpol)).
2 2
-ZS )/3,
1 0
) Typically,
0
Pickupx or the product
IB .
M15282-90 v6
Bay control REC670
Application manual