Overfrequency (81O) - GE 339 Instruction Manual

S3 PROTECTION

Overfrequency (81O)

NOTE:
NOTE
6–88
The 339 provides 2 Overfrequency Protection elements. Each element can be set to either
cause a trip or generate an alarm when the frequency of the input voltage (wye-
connected VT: Van; delta-connected VT: Vab) exceeds the pickup level for a specified time
delay. If it is desirable to have an alarm before a trip occurs, the user can set the function
of one Overfrequency element to ALARM, and the function of the other element to TRIP.
This feature may be useful for load shedding applications on large motors. It could also be
used to load shed an entire feeder if the trip was assigned to an upstream breaker.
The overfrequency feature is inhibited from operating unless the phase A voltage is above
30% of nominal. When the supply source is energized, the overfrequency delay timer will
only be allowed to time when the 30% threshold is exceeded and the frequency is above
the programmed pickup level. In the same way, when an overfrequency condition starts
the overfrequency delay timer and the phase A voltage falls below the 30% threshold
before the timer has expired, the element will reset without operating.
The following path is available using the keypad. For instructions on how to use the
keypad, please refer to Chapter 3 - Working with the Keypad.
When "VFD Not Bypassed" is asserted, frequency source is software calculated from the
phase A current. The overfrequency element is inhibited from operating unless this current
is above 10% of nominal. A minium voltage is not required.
PATH: SETPOINTS > S3 PROTECTION > OVER-FREQUENCY1(2)
OVERFREQ FUNCTION
Range: Disabled, Alarm, Latched Alarm, Trip
Default: Disabled
For details see Common
OVERFREQ PKP
Range: 40.00 to 70.00 Hz in steps of 0.01
Default: 60.50 Hz
This setting defines the Overfrequency pickup level, and it is usually set to a frequency
level considered dangerous for the stability of the system.
OVERFREQ DELAY
Range: 0.1 to 600.0 s in steps of 0.1
Default: 2.0 s
This setting specifies the time delay before overfrequency operation.
OUTPUT RELAY X
For details see Common
BLOCK 1 to 3
For details see Common
setpoints.
setpoints.
setpoints.
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS