GE 489 User Manual

4-26 489 Generator Management Relay
GE Power Management
4.6 S5 CURRENT ELEMENTS 4 SETPOINT PROGRAMMING
4
4.6.8 PHASE DIFFERENTIAL
The 489 percentage differential element has a dual slope characteristic. This allows for very sensitive settings when fault
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
DIFFERENTIAL TRIP MIN PICKUP
value sets an absolute minimum pickup in terms of operate
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:
= restraint current
I
A
= phase current measured at the output CT
I
a
= phase current measured at the neutral end CT
Differential elements for phase B and phase C operate in the same manner.
Figure 4–4: DIFFERENTIAL ELEMENTS

PHASE DIFFERENTIAL

[ENTER] for more
PHASE DIFFERENTIAL
TRIP: Off
Range: Off, Latched, Unlatched
ASSIGN TRIP
RELAYS (1-4): 1---
Range: Any combination of Relays 1 to 4
DIFFERENTIAL TRIP
MIN. PICKUP: 0.10 x CT
Range: 0.05 to 1.00
×
CT in steps of 0.01
DIFFERENTIAL TRIP
SLOPE 1: 10%
Range: 1 to 100% in steps of 1
DIFFERENTIAL TRIP
SLOPE 2: 20%
Range: 1 to 100% in steps of 1
DIFFERENTIAL TRIP
DELAY: 0 cycles
Range: 0 to 100 cycles in steps of 10
ENTER
ESCAPE
ð
ð
MESSAGE
ESCAPE
MESSAGE
ESCAPE
MESSAGE
ESCAPE
MESSAGE
ESCAPE
MESSAGE
ESCAPE
I
operate
kI
restraint
×>
I
operate
I
A
I
a
– operate current==
I
restraint
I
A
I
a
–
2
---------------------=
k characteristic slope of the differential element in percent=
slope 1 if
I
R
2CT×<= ; slope 2 if I
R
2CT×≥=
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Minimum Pickup = 0.10 x CT
Slope 1 =10%
Slope2=20%
OPERATE
REGION
I (multiples of CT)
restraint
I (multiples of CT)
operate

GE 489 Specifications

General

Brand	GE
Model	489
Category	Relays
Language	English