Trip Decision Example - GE UR Series Instruction Manual

8.2 OPERATING CONDITION CALCULATIONS
Settings: S1 = 10%, S2 = 10%, BP = 5 pu secondary, P = 0.5 pu
Assumed Current: I_ L= 4.0 pu ∠0°, I_ R= 0.8 pu ∠0°
The assumed condition is a radial line with a high resistance fault, source at the local end only, and through resistive load
current.
2
– (
I I _L I _R
= +
op
As the current at both ends is less than the breakpoint of 5.0, equation (1), for 2-terminal mode, is used to calculate
restraint.
2 2
( ⋅
I 2 S
=
Rest 1
( ⋅ (
2 0.1
=
0.76
=
σ
where = 0, assuming a pure sine wave.
2
I
10.2
Op > ⇒
----------- - 1 ---------- -
2 0.76
I
Rest
The use of the CURRENT DIFF PICKUP, CURRENT DIFF RESTRAINT 1, CURRENT DIFF RESTRAINT 2, and CUR-
RENT DIFF BREAK PT are discussed in the SETTINGS chapter.
The following figure shows how the relay's main settings are affecting the restraint characteristics. Remote and local cur-
rents are 180° apart which represent an external fault. The breakpoint between two slopes indicates the point where the
restraint area is becoming wider to override uncertainties coming from CT saturation, fault noise, harmonics etc. Increasing
the slope percentage makes the restraint area wider.
8
8-22
2 2
) ∠ ∠
4.0 0° 0.8 0° 10.2
= – =
2 2 2
⋅ ) ( ⋅ ⋅ )
I _L 2 S I _R 2 P
+ +
1
2 2 2 2
) ⋅ ) ( ⋅ ( ) ⋅ )
4 2 0.1 0.8
+
> ⇒
13.42 1 Trip
=
loc pu
20
OPERATE
16
10
BP=4, P=1, S1=20%, S2=40%
8
4
0
4 8
0
Figure 8–11: SETTINGS IMPACT ON RESTRAINT CHARACTERISTIC
L90 Line Differential Relay
2
σ
+
2
⋅ ( )
2 0.5 0
+ +
RESTRAINT
BP=8, P=2, S1=30%, S2=50%
BP=4, P=1, S1=30%, S2=50%
OPERATE
12 16
8 THEORY OF OPERATION

8.2.3 TRIP DECISION EXAMPLE

8.2.4 TRIP DECISION TEST
rem pu
20
831725A1.CDR
GE Power Management