Upol = -3U
0
or
IN>Dir
RCA
Operation
-3U
2
IEC05000135-5-en.vsdx
IEC05000135 V5 EN-US
Figure 94: Relay characteristic angle given in degree
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 (3U
0
or U
2
)
•
Current (3I
0
· ZNpol or 3I
2
·ZNpol where ZNpol is RNpol + jXNpol), or
•
both currents and voltage,
Dual (dual polarizing, (3U
0
+ 3I
0
· ZNpol) or (U
2
+ I
2
· ZNpol)).
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 (3U
0
) can be below 1% and it is then necessary to use current
polarizing or dual polarizing. Multiply the required set current (primary) with the minimum
impedance (ZNpol) and check that the percentage of the phase-to-earth voltage is definitely
higher than 1% (minimum 3U
0
>
UPolMin setting) as a verification.
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
0
· ZNpol. The ZNpol can be defined as
(ZS
1
-ZS
0
)/3, that is the earth return impedance of the source behind the protection. The
maximum earth-fault current at the local source can be used to calculate the value of ZN as
U/(√3 · 3I
0
) Typically, 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
INx> or the product
3I
0
· ZNpol is not greater than 3U
0
. If so, there is a risk for incorrect operation for faults in the
reverse direction.
IPolMin: is the minimum earth-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.
UPolMin: Minimum polarization (reference) polarizing voltage for the directional function,
given in % of
UBase/√3.
1MRK 505 370-UEN D
Section 7
Current protection
Busbar protection REB670
161
Application manual
Содержание REB670 Series
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