![GE Multilin 889 Instruction Manual Download Page 262](http://html.mh-extra.com/html/ge/multilin-889/multilin-889_instruction-manual_123014262.webp)
4–132
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION
CHAPTER 4: SETPOINTS
MAXIMUM TIME
Range: 0 to 1000 s in steps of 1 s
Default: 600 s
The negative sequence overcurrent
Maximum Time setting
defines the maximum time
that any value of negative sequence current in excess of the pickup value is allowed to
persist before a trip is issued. This setting can be applied to limit the maximum tripping
time for low level unbalances.
NOTE
NOTE:
Small power system transients or switching device operation can generate spurious
negative sequence current that can result in the false operation of the Current Unbalance
element. In order to prevent false operation of the element, minimum time is set to a fixed
value of 250 ms.
RESET TIME
Range: 0.00 to 1000.00 s in steps of 0.01 s
Default: 227.00 s
This setting defines the linear reset time of the trip element time accumulator. It is the
maximum reset time from the threshold of tripping based on the generator unbalance
inverse curve. The reset time has an accumulator/integrator to represent the thermal
memory counter which increments linearly if generator unbalance current is above
threshold, and decrements linearly if it below threshold. The "Unbal DPO" operand is set
to high when thermal memory counter resets to zero.
TRIP OUTPUT RELAY
Range: Do Not Operate, Operate
Default: Do Not Operate
Any assignable output relay can be selected to operate upon the generator unbalance
operation. The operation of these general relays is programmed by the user. Each relay
can be selected to become either energized or de-energized when operated, and to
operate as latched, self-resetting or pulsed.
ALARM FUNCTION
Range: Disabled, Alarm, Latched Alarm
Default: Disabled
This setting enables the generator unbalance Alarm functionality.
When the Alarm function is selected and the element operates, the "ALARM" LED flashes;
it self-resets when the operating conditions are cleared.
When the Latched Alarm function is selected and the element operates, the "ALARM"
LED flashes during the operating condition, and is steadily lit after the conditions are
cleared. The "ALARM" LED can be cleared by issuing a Reset command. Output relay #1
"Trip" will not operate if the Alarm or Latched Alarm setting is selected.
ALARM PICKUP
Range: 0.00 to 100.00 % FLA in steps of 0.01
Default: 3.00 % FLA
This setting specifies a pickup for the alarm function. The definite time overcurrent curve
would normally be used to generate an alarm to prompt an operator to take some
corrective action. This element would typically be set at a safe margin below the trip
pickup setting.
ALARM DELAY
Range: 0.00 to 600.00 s in steps of 0.01 s
Default: 0.50 s
This setting specifies a time delay for the alarm function. This is the minimum operate
time of the alarm element. This is set to prevent nuisance alarms during system faults.