ABB RELION 670 Series Applications Manual page 172

Section 7
Current protection
7.3.2.2 Common settings for all steps
AngleRCA : Relay characteristic angle given in degree. This angle is defined as shown in figure 86.
The angle is defined positive when the residual current lags the reference voltage (Vpol = 3V
ANSI05000135 V3 EN-US
Figure 86: 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
•
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. Setting is in primary ohms.
166
RCA
Operation
IDirPU
or V )
0 2
· ZNpol or 3I ·ZNpol where ZNpol is RNpol + jXNpol), or
0 2
Dual (dual polarizing, (3V
VPolMin setting) as a verification.
>
0
V pol = 3V or V
0 2
en 05000135-4- ansi. vsd
+ 3I
0
) can be below 1% and it is then necessary to use current
0
· ZNpol. The ZNpol can be defined as (ZS
0
1MRK 505 337-UUS A
· ZNpol) or (V + I · ZNpol)).
0 2 2
) Typically,
0
Application manual
M15282-81 v9
or V )
0 2
-ZS )/3,
1 0