GE Multilin DFF, Инструкция по эксплуатации, Страница: 8 / 74

OPERATING PRINCIPLES
GEK-106166E DFF Digital Feeder Relay 7
2. OPERATING PRINCIPLES AND SETTINGS
DFF relay measures frequency by detecting the voltage zero crossings and measuring the time between them. When
the frequency is detected to be below the setting, the relay starts counting for how many consecutive half-periods
(semi cycles) it continues below the setting. There is a setting called “
SEMICYCLES SET ” to adjust the number of
half-periods for the unit to pickup.
It is possible that the frequency transiently restores and goes above the underfrequency threshold. If this occurs, the
DFF freezes the counter to pickup and starts counting the number of semi cycles to reset the unit. If the count of semi
cycles to reset reaches the value set in the setting “
SEMICYCLES RESET ” then the unit is reset. On the other hand,
if the frequency goes again below the threshold, the DFF will continue the count of semi cycles to set, from where it
was left.
If the “
SEMI CYCLES SET ” count is reached the pickup signal of the unit is activated and the relay starts the count of
the time delay set independently for each frequency unit.
When the time delay expires, the trip signal of the unit is activated.
The “
SEMICYCLES SET ” and “ SEMICYCLES RESET ” settings are common for the eight frequency units.
The time delay ( TIME DELAY and RESET TIME ) are independent for each one of the eight units.
The relay provides the
PICKUP signal and the TRIP signal for each one of the eight units as internal digital signals, to
allow the user to configure the output contacts as required for each application.
GE INTRO software must be used to change the factory default configuration of output contacts or LEDs.
The following functional block diagram shows the operation of the relay, as described above, and shows the PICKUP
and TRIP signals for each unit.
Drawing: 301A8000
FIGURE 2.1. DFF FUNCTIONAL BLOCK DIAGRAM