Nd Harmonic Restrain; Parallel Transformer Inrush Current Logic - Hitachi Relion 670 Series Applications Manual

1MRK511407-UUS Rev. N
polMethod: Defines if the directional polarization is from
• Voltage (3V
• Current (3I
• Both current and voltage, Dual (dual polarizing, (3V
Normally voltage polarizing from the internally calculated residual sum or an external open delta is used.
Current polarization is useful when the local source is strong and a high sensitivity is required. In such
cases the polarizing voltage (3V
or dual polarization. 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 >VPolMin setting) as a verification.
0
RNPol, XNPol: The zero-sequence source is set in primary ohms as base for the current polarization.
The polarizing voltage is then achieved as 3I
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
· zero sequence source) is set. The setting is in primary ohms.
When the dual polarizing method is used, it is important that the setting Pickupx or the product 3I
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. A typical setting is 5-10% of IB.
VPolMin: Minimum polarization (reference) polarizing voltage for the directional function, given in % of
VBase/√3.
IDirPU: Operate residual current release level in % of IB for directional comparison scheme. The setting
is given in % of IB and must be set below the lowest INx> setting, set for the directional 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
component. This component can be 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
harmonic restrain can prevent unwanted operation as well.
2ndHarmStab: The rate of 2
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
Phasor measurement unit RES670
Application manual
or V )
0 2
· ZNpol or 3I ·ZNpol where ZNpol is RNpol + jXNpol), or
0 2
) can be below 1% and it is then necessary to use current polarization
0
. If so, there is a risk for incorrect operation for faults in the reverse
0
nd
harmonic current content for activation of the 2
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+ 3I · ZNpol) or (V
0 0
· ZNpol. The ZNpol can be defined as (ZS
0
0
Current protection
+ I · ZNpol)).
2 2
-ZS )/3, that is
1 0
) Typically, the minimum ZNPol (3
nd
harmonic
nd
harmonic restrain signal.
Section 8
·
0
M15282-90 v7
nd
M15282-97 v7
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