Sequential Trip - GE Multilin 489 Instruction Manual

CHAPTER 5: SETPOINTS
5.4.8

Sequential Trip

SEQUENTIAL
Note
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
The active group can be selected using the
assigned digital input (shorting that input will activate the alternate set of protection
setpoints, Group 2). In the event of a conflict between the
setpoint or the assigned digital input, Group 2 will be activated. The LED indicator on the
faceplate of the 489 will indicate when the alternate setpoints are active in the protection
scheme. Changing the active setpoint group will be logged as an event. Independently, the
setpoints in either group can be viewed and/or edited using the
setpoint. Headers for each setpoint message subgroup that has dual settings will be
denoted by a superscript number indicating which setpoint group is being viewed or
edited. Also, when a setpoint that has dual settings is stored, the flash message that
appears will indicate which setpoint group setting has been changed.
PATH: SETPOINTS S3 DIGITAL INPUTS
ASSIGN DIGITAL
[ ] INPUT: None
SEQUENTIAL TRIP TYPE
MESSAGE
Low Forward Power
ASSIGN TRIP
MESSAGE
RELAYS (1-4): 1---
SEQUENTIAL TRIP
MESSAGE
LEVEL: 0.05 x Rated
SEQUENTIAL TRIP
MESSAGE
DELAY: 1.0 s
If an input is assigned to the tachometer function, it may not be used here.
During routine shutdown and for some less critical trips, it may be desirable to use the
sequential trip function to prevent overspeed. If an input is assigned to the sequential trip
function, shorting that input will enable either a low forward power or reverse power
function. Once the measured 3-phase total power falls below the low forward power level,
or exceeds the reverse power level for the period of time specified, a trip will occur. This
time delay will typically be shorter than that used for the standard reverse power or low
forward power elements. The level is programmed in per unit of generator rated MW
calculated from the rated MVA and rated power factor. If the VT type is selected as None,
the sequential trip element will operate as a simple timer. Once the input has been shorted
for the period of time specified by the delay, a trip will occur.
The minimum magnitude of power measurement is determined by the phase CT minimum
of 2% rated CT primary. If the level for reverse power is set below that level, a trip will only
occur once the phase current exceeds the 2% cutoff.
Users are cautioned that a reverse power element may not provide reliable indication
when set to a very low setting, particularly under conditions of large reactive loading on
the generator. Under such conditions, low forward power is a more reliable element.
setpoint or the
ACTIVATE SETPOINT GROUP
ACTIVATE SETPOINT GROUP
EDIT SETPOINT GROUP
SEQUENTIAL TRIP
Range: None, Input 1 to Input 7.
Range: Low Forward Power, Reverse
Power
Range: Any combination of Relays 1 to
4
Range: 0.02 to 0.99 × Rated MW in
steps of 0.01
Range: 0.2 to 120.0 s in steps of 0.1
5–25