A sectionalizer is a protective device, used in conjunction with a recloser, or breaker and reclosing relay, which isolates faulted sections of lines. The sectionalizer does not interrupt fault current.
Instead, it counts the number of operations of the interrupting device upstream and opens while the interrupting device is open.
Reclosing relays and automatic sectionalizing equipment are used together to isolate a faulted portion of a distribution circuit. After the downstream line sectionalizer has operated, the reclosing relay at the substation should have one autoreclosing cycle left to re-energize the unfaulted section of the circuit.
It should be noted that line sectionalizers are not intended to operate at any time when the circuit is actually energized. The line sectionalizer operates its contacts only during the time that the circuit is de-energized.
The actual making and breaking of the current is accomplished by the circuit breaker. If the sectionalizing sequence is to be successful, the autoreclosing times associated with the feeder breakers need to coordinate with the line sectionalizer on the distribution circuit.
Various types of sectionalizing equipment and numerous sectionalizing schemes exist on distribution systems. The intent here is to discuss two of these sectionalizing schemes and the coordination required between the reclosing relay and the sectionalizing equipment.
The pulse-counting sectionalizing scheme utilizes a downstream line sectionalizer that counts the number of high current pulses that pass through it. After a predetermined number of high current pulses (typically two), it will open on the next loss of voltage when the feeder breaker opens.
The sectionalizer resets after a high current pulse if it detects no further high current pulses within its reset time. Therefore, if proper sectionalizing is to occur for a permanent fault beyond the sectionalizer, the autoreclosing time of the reclosing relay associated with the feeder breaker needs to be less than the reset time of the sectionalizer.
The reclosing relay should have one autoreclose attempt left after the sectionalizer opens to re-energize the unfaulted portion of the circuit. In the scheme shown in Figure 1, the autoreclosing sequence of the reclosing relay associated with the feeder breaker is 20 s, 20 s, and then lockout (R20 R20). The downstream sectionalizer is set to count two current pulses before opening and has a reset time of 25 s.
Sectionalizer Scheme
A three-phase loop sectionalizing scheme (shown in Figure below) consists of two distribution circuits each containing a normally closed three-phase automatic line recloser (used as a sectionalizing switch) and a normally open three-phase recloser as a tie switch installed between the two circuits.
The three-phase line recloser opens after a 50 s delay for loss of any phase potential on its source side and the tie switch closes after a 55 s delay for loss of all three-phase potentials on either side of it. The feeder breaker autoreclosing sequence has to be less than the delayed opening of its associated line recloser for loss of potential.
This allows the feeder breaker to restore the circuit to normal in the event of a momentary fault between it and the line recloser. For faults beyond the line recloser, unlike as described in the previous example of the current-pulse counting scheme, the overcurrent function of the tie recloser is coordinated with the three-phase reclosers and will open the tie recloser, and the feeder breaker will remain closed.
The tie recloser has autoreclosing functions to lockout for overcurrent operations; however, it will not autoreclose for a loss of potential operation and has to be closed manually or via SCADA.
thanks for the info
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