ABB REC670 Applications Manual page 178

Section 8
Current protection
172
RCA
IDirPU
ANSI05000135 V3 EN-US
Figure 67: 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 (3V or V )
0 2
• Current (3I · ZNpol or 3I
0
• both currents and voltage, Dual (dual polarizing, (3V
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 (3V
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-ground voltage is definitely higher than 1% (minimum 3V
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
defined as (ZS -ZS )/3, that is the ground return impedance of the source behind the
1 0
protection. The maximum ground-fault current at the local source can be used to
V pol = 3V or V
0
Operation
en 05000135-4- ansi. vsd
·ZNpol where ZNpol is RNpol + jXNpol), or
2
) can be below 1% and it is then
0
1MRK 511 401-UUS A
2
+ 3I · ZNpol) or (V
0 0 2
>VPolMin setting)
0
· ZNpol. The ZNpol can be
0
Bay control REC670 2.2 ANSI
Application manual
+ I ·
2