ABB REG670 - Page 567

Voltage band limit check will be ignored for the START output if the
EnaVoltCheck setting is disabled. The voltage band limits are set with the settings
UHighLimit and ULowLimit.
The output VOLTOK is activated only if the system positive-sequence voltage
falls within the voltage band limits and the EnaVoltCheck setting is enabled.
To avoid oscillations of the START output signal, a hysteresis has been added with
current input comparison and voltage input comparison. It is also possible to block
FTAQFVR completely by activating the binary input BLOCK and its function is to
reset all the binary outputs of FTAQFVR and freeze the accumulation time.
Time counters
FTAQFVR uses two time counters.
1. Individual event time: The individual event time counter registers the time
passing if the system frequency falls within the frequency band limits each time.
It resets when the frequency comes out of the frequency band limits and also
when the BLOCK binary input is activated and start from zero when a new start is
activated.
2. Accumulation time: The accumulation time counter registers the time passing
whenever the START output is activated. It holds the registered time value even
when the START signal is deactivated and continues from the registered value
when the START signal is reactivated.
The registration of accumulation time is frozen at its present value when the input
HOLDACC or BLOCK is activated. The accumulation time can be set to the
initTimeAcc parameter value by activating the LOADINT input with the LHMI and it
can be reset to zero by activating the RESETACC input. The RESETACC input can be
activated by a binary input. The accumulated time ACCTIME is provided as a service
output.
The last completed individual event time is updated in the LASTEVTD output. This
output holds the last completed individual event time until the next event to complete.
Trip logic
The individual event and accumulation timer values are compared to the tCont and
tAcclLimit settings respectively. If these counter values exceed their limit values,
TRIPCONT and ACCALARM outputs will be activated. The TRIPACC output is
activated if both the ACCALARM and START signals are activated. A common TRIP
signal is generated when either TRIPCONT or TRIPACC is activated.
1MRK502052-UEN B Section 10
Frequency protection
561
Technical manual