ABB RELION REX640 Technical Manual page 358

Protection functions
Faulted
phases
B - C
C - A
U
C
Figure 215: Phasors in a single-phase earth fault, phase A to ground, and a two-
phase short circuit, phases B-C, are short-circuited when the polarizing quantity is
the positive-sequence voltage U 1
Network rotation direction
Typically, the network rotating direction is counter-clockwise and defined as "ABC".
If the network rotating direction is reversed, meaning clockwise, that is, "ACB",
the equations for calculating the angle difference needs to be changed. The
network rotating direction is defined with a system parameter
The change in the network rotating direction affects the phase-to-phase voltages
polarization method where the calculated angle difference needs to be rotated 180
degrees. Also, when the sequence components are used, which are, the positive
sequence voltage or negative sequence voltage components, the calculation of the
components are affected but the angle difference calculation remains the same.
When the phase-to-ground voltages are used as the polarizing method, the network
rotating direction change has no effect on the direction calculation.
358
Used Used Angle difference
fault polarizi
current ng
voltage
I -I U
B C 1
ANGLE B
I -I U
C A 1
ANGLE C
I U
A 1
U
A
I
I
B
C
U
B
A
The network rotating direction is set in the protection relay using the
parameter in the HMI menu Configuration > System > Phase rotation.
The default parameter value is "ABC".
_ ( U ) ( I I )
ϕ ϕ
= − −
1 B C
_ ( U ) ( I I )
= ϕ − ϕ −
C A
1
U
A
U
1
I
A
I
C
U
C
B
1MRS759142 F
o
90
ϕ
− −
RCA
(Equation 26)
o
150
− ϕ +
RCA
(Equation 27)
-90°
I - I
B c
-I
C
I
B
U
B
Phase rotation .
REX640
Technical Manual