Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
9.12.1.1
APPLICATION EXAMPLE
The following setting example illustrates how to select the characteristic angle for the phase directional
unit. ABC phase rotation is assumed.
90-
α
α
α
90 -
I
A
V
A
V
C
V
B
α
ZI
I
A
V
A
U
BC
Figure 9-51. Application example
Assume a simple case with a line open at one end and with a A phase to ground fault without fault
resistance. If the line impedance is Zl
α
, the fault current I
A
lags the voltage V
A
with an angle
α
. The
phase directional unit does not use the phase voltage for polarization but the voltage between the other
two un-faulted phases, i.e. V
CB
which is displaced from the faulted phase voltage by 90 degrees. If the
angle between the operating and polarizing vector falls within the set characteristic angle
α
+/- 90
degrees, a forward operation is obtained.
Consequently, the characteristic angle
θ
for a line with positive sequence angle
α
should be set to:
θ
= 90 -
α
or ANG_67 = 90
°
-
∠
ZL1.
August 1, 2009
9-57
973.334.3100
