Phase Differential - GE 489 Instruction Manual

4.6 S5 CURRENT ELEMENTS
T

PHASE DIFFERENTIAL

T
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The 489 percentage differential element has a dual slope characteristic. This allows for very sensitive settings when fault
4
current is low and less sensitive settings when fault current is high (more that 2 × CT) and CT performance may produce
erroneous operate signals. The
current. The delay can be fine-tuned to an application so it still responds very fast, but rides through normal operational dis-
turbances.
The differential element for phase A will operate when
where: I
operate
I
restraint
k characteristic slope of the differential element in percent
=
I = phase current measured at the output CT
A
I = phase current measured at the neutral end CT
a
Differential elements for phase B and phase C operate in the same manner.
4-26
ð
PHASE DIFFERENTIAL
ENTER
TRIP: Off
ESCAPE
ASSIGN TRIP
ESCAPE
RELAYS (1-4): 1---
MESSAGE
DIFFERENTIAL TRIP
ESCAPE
MIN. PICKUP: 0.10 x CT
MESSAGE
DIFFERENTIAL TRIP
ESCAPE
SLOPE 1: 10%
MESSAGE
DIFFERENTIAL TRIP
ESCAPE
SLOPE 2: 20%
MESSAGE
DIFFERENTIAL TRIP
ESCAPE
DELAY: 0 cycles
MESSAGE
DIFFERENTIAL TRIP MIN PICKUP
= I – I = operate current
A a
I I
–
A a = restraint current
= -------------------- -
2
< ×
1 if I
slope = 2 CT ; slope
R
1.2
1
0.8
OPERATE
REGION
0.6
0.4
0.2
0
0 0.5 1 1.5
Figure 4–4: DIFFERENTIAL ELEMENTS
489 Generator Management Relay
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to 4
Range: 0.05 to 1.00 × CT in steps of 0.01
Range: 1 to 100% in steps of 1
Range: 1 to 100% in steps of 1
Range: 0 to 100 cycles in steps of 10
value sets an absolute minimum pickup in terms of operate
> ×
I k I
operate restraint
≥ ×
2 if I
= 2 CT
R
Slope 2 = 20%
Slope 1 =10%
Minimum Pickup = 0.10 x CT
2 2.5 3 3.5 4
I (multiples of CT)
restraint
4 SETPOINT PROGRAMMING
4.6.8 PHASE DIFFERENTIAL
4.5 5 5.5
GE Power Management