Phase Overcurrent - GE Multilin 489 Instruction Manual

CHAPTER 5: SETPOINTS
5.6.5

Phase Overcurrent

1 PHASE
OVERCURRENT
Note
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
PATH: SETPOINTS S5 CURRENT ELEM.
[ ] PHASE OVERCURRENT
TRIP: Off
ASSIGN TRIP
MESSAGE
RELAYS (1-4): 1---
ENABLE VOLTAGE
MESSAGE
RESTRAINT: No
VOLTAGE LOWER
MESSAGE
LIMIT: 10%
PHASE OVERCURRENT
MESSAGE
PICKUP: 10.00 x CT
CURVE SHAPE:
MESSAGE
ANSI Extremely Inv.
FLEXCURVE TRIP TIME
MESSAGE
AT 1.03 x PU: 65535 ms
↓
FLEXCURVE TRIP TIME
MESSAGE
AT 20.0 x PU: 65535 ms
OVERCURRENT CURVE
MESSAGE
MULTIPLIER: 1.00
OVERCURRENT CURVE
MESSAGE
RESET: Instantaneous
If the primary system protection fails to properly isolate phase faults, the voltage
restrained overcurrent acts as system backup protection. The magnitude of each phase
current measured at the output CTs is used to time out against an inverse time curve. The
489 inverse time curve for this element may be either ANSI, IEC, or GE Type IAC standard
curve shapes. This allows for simplified coordination with downstream devices. If these
curve shapes are not adequate, FlexCurves™ may be used to customize the inverse time
curve characteristics.
The voltage restraint feature lowers the pickup value of each phase time overcurrent
element in a fixed relationship (see figure below) with the corresponding input voltage to a
minimum pickup of 0.15 × CT. The
tripping prior to primary protection clearing a fault when voltage restraint is enabled and
severe close-in fault has occurred. If voltage restraint is not required, select "No" for this
setpoint. If the VT type is selected as "None" or a VT fuse loss is detected, the voltage
restraint is ignored and the element operates as simple phase overcurrent.
A fuse failure is detected within 99 ms; therefore, any voltage restrained overcurrent trip
should have a time delay of 100 ms or more or nuisance tripping on fuse loss could occur.
For example, to determine the voltage restrained phase overcurrent pickup level under the
following situation:
•
PHASE OVERCURRENT PICKUP:
PHASE OVERCURRENT
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to
4
Range: No, Yes
Range: 10 to 60%. Seen only if
VOLTAGE RESTRAINT
Range: 0.15 to 20.00 × CT in steps of
0.01
Range: See Table 5–1: 489 Overcurrent
Curve Types on page –29.
Range: 0 to 65535 ms Seen only if
CURVE SHAPE
Range: 0 to 65535 ms. Seen only if
CURVE SHAPE
Range: 0.00 to 1000.00 in steps of 0.01
Range: Instantaneous, Linear
setpoint prevents very rapid
VOLTAGE LOWER LIMIT
"2.00 × CT"
ENABLE
is "Yes"
is "Flexcurve"
is "Flexcurve"
5–35