The activation of the
BLOCK
input resets Timer and deactivates the
START
and
OPERATE
outputs.
Blocking logic
There are three operation modes in the blocking functionality. The operation
modes are controlled by the
BLOCK
input and the global setting Configuration >
System > Blocking mode which selects the blocking mode. The
BLOCK
input can be
controlled by a binary input, a horizontal communication input or an internal signal
of the protection relay's program. The influence of the
BLOCK
signal activation is
preselected with the global setting
Blocking mode.
The
Blocking mode setting has three blocking methods. In the "Freeze timers"
mode, the operation timer is frozen to the prevailing value. In the "Block all" mode,
the whole function is blocked and the timers are reset. In the "Block OPERATE
output" mode, the function operates normally but the
OPERATE
output is not
activated.
4.3.5.5
Application
HIxPDIF provides a secure and dependable protection scheme against all types of
faults. The high-impedance principle is used for differential protection due to its
capability to manage the through-faults also with the heavy current transformer
(CT) saturation.
For current transformer recommendations, see the Requirements for
measurement transformers section in this manual.
High-impedance principle
The phase currents are measured from both the incoming and the outgoing feeder
sides of the busbar. The secondary of the current transformer in each phase is
connected in parallel with a protection relay measuring branch. Hence, the relay
measures only the difference of the currents. In an ideal situation, there is a
differential current to operate the relay only if there is a fault between the CTs,
that is, inside the protected zone.
If there is a fault outside the zone, a high current, known as the through-fault
current, can go through the protected object. This can cause partial saturation
in the CTs. The relay operation is avoided with a stabilizing resistor (R
s
) in the
protection relay measuring branch. R
s
increases the impedance of the protection
relay; hence the name high-impedance differential scheme.
1MRS757644 H
Protection functions
620 series
Technical Manual
585
