Thanks to this function, it is also possible to obtain selectivity in meshed and ring networks.
By means of zone selectivity with function D “Zone selectivity D”, which can only be set to [On]
when zone selectivity “S” and “G” are set to [Off] and there is an auxiliary power supply, it is possible to coordinate the behaviour of the various PR123 devices, by cabling the trip unit buses in a suitable way.
In fact, each trip unit has 4 signals available:
– two input signals (one in a concordant and one in a discordant direction) by means of which the trip unit receives the “block” signal from other trip units
– two output signals (one in a concordant and one in a discordant direction) by means of which the trip unit sends a “block” signal to other trip units.
The circuit-breakers which do not receive a “block” signal (coordinated in the direction of the current) will send the opening command within a time equal to “t7sel”.
The circuit-breakers which receive the “block” signal will open within the backward or forward time according to the direction of the current.
If function I is activated and the short-circuit current exceeds the set value (I3), the circuit-breaker will open instantaneously and independently of the directions and of the signals received.
For safety reasons, the maximum duration of the “block” signal is 100ms more than the selected T7sel for the CB which send the “block” signal.
If, after this time and for any reason, the circuit-breakers due to trip have not yet opened, the “block”
signal falls on the other circuit-breakers which will command opening within the setted T7sel.
A shielded twisted pair cable (not supplied; ask ABB for information) can be used to carry out the cabling. The shield should only be earthed on the trip unit of the circuit-breaker on the supply side.
• The maximum length of the cabling for zone direction selectivity, between two units, is 300 metres.
• A maximum number of 20 circuit-breakers can be connected to the outputs (OUT Bw or OUT Fw) of a trip unit.
The figure below shows the connections necessary to activate the “blocks” between the vari-ous trip units. In particular:
1) in the case of a fault in A, circuit-breaker QF1 is passed through by a current from busbar B1;
this current flows in a direction discordant with the one set. The OUT Bw bus of QF1 “blocks”
the IN Fw bus of circuit-breaker QF2 and the IN Bw bus of circuit-breaker QF3: in fact, the current flows through QF2 in the same direction as the set-ting, whereas QF3 is passed through by a current discor-dant with the setting (the ac-tive “block” signals are indi-cated by wider arrows).
Reference Direction
Direction (OUT-IN) Arrow Bw Bw
ABB SACE 6/17
2) in the case of a fault in B, circuit-breaker QF2 is passed through by a current from busbar B1;
this current flows in a direction discordant with the one set. The OUT Bw bus of QF2 “blocks”
the IN Fw bus of circuit-breaker QF1 and the IN Bw bus of circuit-breaker QF3: in fact, the current flows through QF1 in the same direction as the set-ting, whereas QF3 is passed through by a current discor-dant with the setting (the ac-tive “block” signals are indi-cated by wider arrows).
QF3 +
Direction (OUT-IN) Arrow Bw Bw
Bw Fw Fw Fw
Reference Direction
Direction (OUT-IN) Arrow Bw Bw
Bw Fw Fw Fw
3) in case of a fault in C, circuit-breakers QF1 and QF2 are passed through by a current flowing in the same direction as the one set, whereas QF3 is passed through by a current with discor-dant direction. No circuit-breaker is “blocked” and con-sequently all the circuit-break-ers affected by the fault will trip according to the time set-tings of protections “S” and/
or “I”.
ABB SACE
4) in the case of a fault in D, circuit-breaker QF3 is passed through by a current from busbar B1;
this current flows in the same direction as the one set. The OUT Fw bus of QF3 “blocks” the IN Fw bus of circuit-breakers QF1 and QF2: in fact, both circuit-breakers are passed through by fault currents con-cordant with the direction set (the active “block” signals are indicated by wider arrows).
QF3 +
Direction (OUT-IN) Arrow Bw Bw
Bw Fw Fw Fw
Reference Direction
Direction (OUT-IN) Arrow Fw Fw
Fw Bw Bw Fw
The following example analyses a network with a bus-tie and takes the behavior of the protection devices in the presence of faults into consideration:
1) Fault in B1 with the bus-tie closed: only circuit-breakers QF1 and QF3 must interrupt the fault: in particular, circuit-breaker QF3 is passed through by a current from busbar B2 (therefore in the same direction as the one set); the OUT Fw bus sends a “block” signal to the IN Fw bus of circuit-breaker QF2 (passed through by a current flowing from trans-former TM2 and consequently in a direction concordant with the one set), and to the IN Bw bus of circuit-breaker QF5 (passed through from a current flowing from the motor and consequently in a direction dis-cordant with the one set).
1SDC200320F0001
ABB SACE 6/19
6
2) Fault in the motor: in this case, only circuit-breaker QF5 must interrupt the fault. Circuit-breaker QF5 is passed through by a current flowing from busbars B1 and B2, in a direction concor-dant with the one set; therefore, the OUT Fw bus of QF5 “blocks” both the IN Fw bus of QF2 (passed through by a current flowing from TM2 and consequently in a direction concordant with the one set) as well as the IN Bw bus of QF3 (which is passed through by a current flowing from TM1 and consequently in a direction discordant with the one set). Similarly, circuit-breaker QF3 is also passed through by a current flowing from TM1 in a direc-tion discordant with the one set: consequently, the OUT Bw bus of QF3 “blocks” the IN Fw bus of QF1 (passed through by a current flowing from TM1 and therefore in a direction concordant with the setting).
3) Fault on the supply side of transformer TM2: in this case, only circuit-breaker QF2 must inter-rupt the fault. Circuit-breaker QF2 is passed through by a current flowing from TM1 and from the motor, in a direction discordant with the one set; as a consequence the OUT Bw bus of QF2 “blocks”:
– the IN Bw bus of QF5 (passed through by a current flowing from the motor and consequently in a direction discordant with the one set)
– the IN Bw bus of QF3 (passed through by a current flowing from TM1 and consequently in a direction discordant with the one set).
Similarly, circuit-breaker QF3 is also passed through by a current flowing from TM1 in a direction discordant with the one set; therefore its OUT Bw bus “blocks” the IN Fw bus of QF1 (passed through by a current flowing from TM1 and therefore in a direction con-cordant with the one set).
Reference Direction
Direction (OUT-IN) Arrow Fw Fw
Fw Bw Bw Bw Bw Fw
Reference Direction
Direction (OUT-IN) Arrow Fw Fw
ABB SACE
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