IW93-2 HESG440356R1 HESG216678/B ABB distributed control system industrial DCS module card

Description

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Directional protection is based on the ability to correlate the circuit-breaker’s behavior with the
direction of the fault current.
Two different trip times can be set on the PR123 trip unit depending on the current direction:
– a time (t7Fw) for a direction of current concordant (Fw) with the reference direction set;
– a time (t7Bw) for a direction of current discordant (Bw) with the reference direction set.
Reference
direction
A current threshold only (I7) can be set on the PR123 trip unit.
If the fault current is discordant (Bw) with the reference direction, the protection shall intervene
when the threshold I7 is reached within the set time t7Bw (provided that the functions S and I
have not been set as to intervene before function D).
If the fault current is concordant (Fw) with the reference direction, the protection shall intervene
when the threshold I7 is reached within the set time t7Fw (provided that the functions S and I
have not been set as to intervene before function D).
Moreover, if function I is active and the short-circuit current exceeds the set value I3
, the circuitbreaker will trip instantaneously independently of the direction of the current.
The reference direction set by ABB is from the top of the circuit-breaker (the zone where the trip
unit is located) towards the bottom.
In this way, all the quantities measured by the PR123 trip unit can be evaluated as they actually
flow through the installation. Furthermore, in the wiring diagram of the system, the reference
direction to carry out a selectivity study and consider the
tripping directions Bw or Fw
correctly still remains from top
to bottom.
In the following wiring diagram the reference directions
are shown in red. By considering the circuit-breakers supplied as in the figure above, it
can be seen that for QF2 this
is the default direction,
whereas for QF1 the direction
has been inverted by means
of the software.
The figure above shows the actual configuration the circuit-breakers have in the system. The
red arrow shows the reference direction set by default on the circuit-breaker.
If the power supply direction of the circuit-breaker is from top to bottom (supply from G2), the
reference direction must remain the one set by ABB.
If the power supply direction of the circuit-breaker is from bottom to top (supply from G1), the
new PR123 trip unit allows the default setting to be inverted by operating on its software.