1MDU07205-YN rev. F
REF601 CEI
User’s manual
26
The relay can measure earth current by internal calculation and also by external core
balance current transformer input. Separate earth fault input is available in relay which
can be connected to core-balance current transformer of 1A secondary.
The operate time characteristic for low stage and high stage has only defi nite time
(DT) . The instantaneous stage always operates with the DT characteristic. In the DT
mode, the function operates after a predefi ned operate time and resets when the
fault current disappears.
4.2.2 Principle of Operation
REF601 has earth fault protection with low set and high set module. Earth fault modules
operates the protection as soon as fault current exceeds the set value of current. It
supports only DMT timing while highset supports to DMT timings.
As the fault current exceeds the set value, trip time counting is started and start LED
on front panel of relay glows ON. If fault current falls down below the drop-off value
of set current for 40 ms before trip time gets complete, start LED will be turned off
and trip count will become zero. Trip time will start from zero next time when the fault
current exceeds the set value again. After a healthy trip, Start LED will be turned off
and again if fault current exceeds threshold, start LED will be turned ON again
In case of healthy fault generation, after trip time get elapsed relay generates the
trip command which operates the Trip relay contacts as per user selected product
variant. Two LED indications on front plate of relay i.e. Trip (common trip indication)
and Trip Io and one signaling contact (XK2.1 –XK2.2) will also be generated for user
as Trip indication.
4.3 Three Phase Inrush Detector
The transformer inrush detection is used to coordinate transformer inrush situations
in distribution networks.
Transformer inrush detection is based on the following principle: the output signal is
activated once the numerically derived ratio of second harmonic current I_2H and
the fundamental frequency current I_1H exceeds the set value.
The operate time characteristic for the function is of defi nite time (DT) type. When
applying overcurrent protection to the MV side of the power transformer, it is neces-
sary that the protection system remains inoperative during transformer energization,
when a large primary current fl ows for a short period during switch on. The REF601
employs the most proven technique of blocking based on measured value of second
harmonic content to make the protection immune to magnetizing inrush.
Protection Functions
To Next Page
Loading...
