# GE UR Series Instruction Manual Page 294

Line differential relay.

8.2 OPERATING CONDITION CALCULATIONS
>
I _L
BP
7.
If
and
4
2
(
(
I
-- - S 2
=
rest
3
2
2 P
<
I _L
BP
8.
If
and
2
I
=
rest
Characteristics of differential elements can be shown in the complex plane. The operating characteristics of the L90 are
fundamentally dependant on the relative ratios of the local and remote current phasor magnitudes and the angles of
σ
as shown in the following figure (RESTRAINT CHARACTERISTICS).
rem
The main factors affecting the trip-restraint decisions are:
1.
Difference in angles (+ real represents pure internal fault when currents are essentially in phase, – real represents
external fault when currents are 180° apart).
2.
The magnitude of remote current.
3.
The magnitude of the local current.
4.
Dynamically estimated errors in calculations.
5.
Settings.
The following figure also shows the relay's capability to handle week-infeed conditions by increasing the restraint ellipse
when the remote current is relatively small (1.5 pu). Therefore, uncertainty is greater when compared with higher remote
currents (3 pu). The characteristic shown is also dependant on settings. The second graph shows how the relay's trip-
restraint calculation is made with respect to the variation in angle difference between local and remote currents. The char-
acteristic for 3 terminal mode is similar where both remote currents are combined together.
8
8-20
<
>
I _R1
BP
I _R2
BP
and
2
2
2
2
(
)
)
(
I _L
BP
S 1
I _R1
+
2
-- - σ
(
σ
σ
)
+
+
+
loc
rem1
rem2
3
>
<
I _R1
BP
I _R2
BP
and
4
2
2
2
(
(
)
(
(
-- - S 1
I _L
S 2
I _R1
+
3
2
2
-- - σ
(
σ
σ
)
2 P
+
+
+
loc
rem1
rem2
3
L90 Line Differential Relay
, then
2
2
2
2
)
(
(
S 2
I _R2
BP
+
, then
2
2
2
2
)
)
(
)
BP
S 1
I _R2
+
+
8 THEORY OF OPERATION
2
2
)
)
(
)
)
2 S 1
BP
+
+
2
2
(
)
)
S 1
BP
+
GE Power Management
σ
/
loc #### This manual is also suitable for:

L90 