Overfrequency - GE 339 Instruction Manual

CHAPTER 6: SETPOINTS

Overfrequency

339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
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.
PATH:
SETPOINTS > S3 PROTECTION > OVER-FREQUENCY1(2)
OVERFREQ FUNCTION
Range: Disabled, Alarm, Latched Alarm, Trip
Default: Disabled
The selection of Latched Alarm, Alarm, or Trip setting enables the Overfrequency
Function. If the operating condition is satisfied when Trip is selected as the function, the
logic operand ANY TRIP OP will be asserted, which in turn will activate the "TRIP" LED and
operate the "Trip" output relay. If Alarm is selected, the "ALARM" LED will flash upon
overfrequency operation, and will automatically reset when the activating condition
clears. If Latched Alarm is selected, the "ALARM" LED will flash upon overfrequency
operation, and will stay "ON" after the condition clears, until a reset command is
initiated. The TRIP output relay will not operate if the Latched Alarm or Alarm function is
selected. Any assignable output relays can be selected to operate when the setting
OVERFREQ FUNC is selected as Latched Alarm, Alarm, or Trip.
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 4 to 6 / OUTPUT RELAY 5 to 6
Range: Do not operate, Operate
Default: Do not operate
Any assignable output relay can be selected to operate upon Overfrequency operation.
When the SWITCHING DEVICE is selected as BREAKER, the assignable output relays will
be Output Relay 4 to 6. When the SWITCHING DEVICE is selected as CONTACTOR, the
assignable output relays will be Output Relay 5 to 6.
S3 PROTECTION
6–99