Trip Decision Example; Trip Decision Test - GE L90 Instruction Manual

9.2 OPERATING CONDITION CHARACTERISTICS
Assume the following settings:
• Slope 1: S = 10%
1
• Slope 2: S = 10%
2
• Breakpoint: BP = 5 pu secondary
• Pickup: P = 0.5 pu
Assume the following local and remote currents:
• Local current: I
local
• Remote current: I
remote
The assumed condition is a radial line with a high resistance fault, with the source at the local end only, and through a resis-
tive load current. The operating current is:
Since the current at both ends is less than the breakpoint value of 5.0, the equation for two-terminal mode is used to calcu-
late restraint as follows.
where = 0, assuming a pure sine wave.
The trip condition is shown below.
The use of the
CURRENT DIFF PICKUP
settings are discussed in the Current differential section of chapter 5.
The following figure shows how the L90 settings affect the restraint characteristics. The local and remote currents are 180°
apart, which represents an external fault. The breakpoint between the two slopes indicates the point where the restraint
area is becoming wider to override uncertainties from CT saturation, fault noise, harmonics, etc. Increasing the slope per-
centage increases the width of the restraint area.
9
9-18
= 4.0 pu 0°
= 0.8 pu 180°
2 2
I I_L I_R 4.0 0
op
2 2 2
I 2 S I_L
Rest 1
2 2
2 0.1 4
0.8328
2
I
10.24
Op
----------- - ----------------- -
1
0.8328
2
I
Rest
,
CURRENT DIFF RESTRAINT 1
L90 Line Current Differential System
2
0.8 180 10.24
2 2 2
2 S I_R 2P
1
2 2 2
2 0.1 0.8 2 0.5
12.3 1 Trip
,
CURRENT DIFF RESTRAINT 2
9 THEORY OF OPERATION

9.2.2 TRIP DECISION EXAMPLE

(EQ 9.34)
(EQ 9.35)
0

9.2.3 TRIP DECISION TEST

(EQ 9.36)
, and
CURRENT DIFF BREAK PT
GE Multilin