Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.3.6.6
690
Timer calculates the start duration START_DUR value, which indicates the
percentage ratio of the start situation and the set operating time. The value is available
in the Monitored data view.
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.

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
measuring branch. R increases the impedance of the protection relay; hence the name
s
high-impedance differential scheme.
1MRS759142 C
) in the protection relay
s
REX640
Technical Manual