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The Autoreclose function is a logic controller implemented in software. It takes inputs and processes them
according to defined logic to generates appropriate outputs. The logic is controlled by user prescribed settings and
commands. The controlling logic is complex and so, in order to facilitate its design and understanding, it is
decomposed into smaller logic functions which, when combined together implement the complete scheme. This
section concludes with a summary of:
● the logic inputs to the Autoreclose function,
●
the logic outputs from the Autoreclose function
● the Autoreclose operating sequence
●
the high-level design of the system logic functionality
3.1 AUTORECLOSE LOGIC INPUTS FROM EXTERNAL SOURCES
Logic inputs control the operation of the Autoreclose function. The logic inputs are mapped using DDB signals in
the PSL.
Generally the inputs are from external equipment connected to opto-isolated inputs. They can also come from
communications inputs, and some are internally derived.
This section provides an overview of the logic inputs originating from external sources.
3.1.1 CIRCUIT BREAKER HEALTHY INPUT
For circuit breakers to close, it needs energy. This energy usually comes from a spring (spring-charged circuit
breakers) or from gas pressure (gas pressurised circuit breakers). After closing, it is necessary to re-establish
sufficient energy in the circuit breaker before it can be closed again.
DDB signal inputs to the Autoreclose function allow the health of circuit breakers to be mapped to the logic. when
asserted, these signals demonstrate that there is sufficient energy available to close and trip the circuit breaker
before initiating a circuit breaker close command. If the signal indicating the health of the circuit breaker is low,
and remains low for a defined period set in the circuit breaker healthy timer, the circuit breaker locks out and stays
open.
If the circuit breaker healthy signal is not mapped in the PSL, the DDB signal defaults to high so that Autoreclose
may proceed.
3.1.2 INHIBIT AUTORECLOSE INPUT
A logic input can be used to inhibit the Autoreclose function. The signal is mapped to the DDB signal Inhibit AR in
the PSL.
Energising the input inhibits any auto-switching of connected circuit breakers. Any Autoreclose in progress is reset
and inhibited but not locked out. This function ensures that auto-switching does not interfere with any manual
switching. A typical application is on a mesh-corner scheme where manual switching is being performed on the
mesh, for which any Autoreclose would cause interference.
For products that are capable of single-phase tripping and Autoreclose, if a single-phase Autoreclose cycle is in
progress and a single pole of the circuit breaker is tripped when the inhibit Autoreclose signal is raised, the circuit
breaker is instructed to trip all phases, ensuring that all poles are in the same state (and avoiding a pole stuck
condition) when subsequent closing of the circuit breaker is attempted.
3.1.3 BLOCK AUTORECLOSE INPUT
External inputs can be used to block the Autoreclose function. If Autoreclose is in progress when the signal is
asserted, it forces a lockout.
Typically this feature is used where Autoreclose may be required for some protections functions but not required
for others. An example is on a transformer feeder, where Autoreclose can be initiated from the feeder protection
but blocked from the transformer protection.
Chapter 7 - Autoreclose P54A/B/C/E
128 P54xMED-TM-EN-1