GE Multilin DFF Instruction Manual page 10

GENERAL SETTINGS DESCRIPTION
•
RELAY STATUS: The relay can be switched in or out of service (NO SERV / IN SERV)
•
FREQUENCY: Defines the nominal frequency of the network ( 50 Hz / 60 Hz )
•
NOMINAL VOLTAGE: Defines the secondary phase-phase Vac nominal voltage applied to the relay.
•
INHIBIT V: The relay incorporates an inhibit voltage element with a user settable threshold INHIBIT V.
•
SEMICYCLES SET: The DFF includes a counter that increments in semi cycles during an underfrequency
situation. For example 5 semi cycles of 50Hz is equivalent to 50ms delay. This acts as a time delay to filter
spurious variations in the input signal to the frequency unit. The counter is initially frozen if the frequency restores
and it is reset by the operation of the SEMICYCLES RESET counter. This counter activates the Frequency
Element pick up signal when the count exceeds the SEMICYCLES SET threshold.
•
SEMICYCLES RESET: The DFF includes a counter that increments in semi cycles when the frequency restores.
This counter resets the SEMICYCLES SET counter when the count exceeds the SEMICYCLES RESET
threshold.
•
PHASE VT RATIO: Defines the ratio of the HV phase voltage transformer.
•
GROUND VT RATIO: Defines the ratio of the HV zero sequence voltage transformer.
SETTINGS FOR EACH INDIVIDUAL FREQUENCY ELEMENT (for example 81 N1)
• The FUNCTION TYPE setting adjusts the operation of the frequency unit as absolute frequency or rate of change
of frequency (df/dt).
• The 81 PICKUP is the pickup value for the unit if it is set as FREQ and for the underfrequency supervision
element if it is set as df/dt.
• The TIME DELAY is the intentional time delay of the unit to produce a trip after pick up.
• dF/dT is the instantaneous value of the rate of change of frequency that will produce a trip if the FUNCTION
TYPE is set as df/dt, and the supervision elements have operated.
• RESET TIME is the time the frequency units maintain the tripping signal after the condition that caused the trip
has disappeared.
OPERATION IN FREQ MODE:
Select the setting FUNCTION TYPE as FREQ. (The setting value of dF/dT is now ignored). The operation time of
this unit will depend on the setting of TIME DELAY. The pickup will occur once the adjusted "number of semi-cycles"
expire, (common setting for all units), and the trip will take place when the time delay ends (note that tripping
conditions should persist during all the time delay).
OPERATION IN DF/DT MODE:
To adjust a unit as rate of change select the setting FUNCTION TYPE as dF/dT.
In order to issue a trip in this operating mode the frequency has to be lower than the adjusted value in setting 81
PICKUP AND the rate of change of frequency must be more negative than the setting value of dF/dT.
GEK-106166E
OPERATING PRINCIPLES
DFF Digital Feeder Relay 9