Autoreclose-circuit design for large substations using logic sequence switching

Well established logic-switching-constraint techniques are utilised in an alternative method of employing counters to design control circuits applicable to power-system sequence switching. Counting techniques have already been employed in autoreclose schemes, but the paper postulates a new method of using these for the design of schemes of autoreclose in large electricity substations. A development of the use of logic switching constraints previously used elsewhere is shown to be more reliable than more cumbersome and less scientific intuitive methods. In this way it is possible to define all the operational conditions to be satisfied after a complex series of faults. Reduction of the problem to a number of constituent sequences enables attention to be focused on the control requirements for any individual fault condition. An appropriate sequence is decided by the action of a master selector circuit, since it will be shown that it is possible to group fault conditions in which the initial sequence is identical. When the desired control-sequence-constraint equations have been synthetised, a practical circuit may take the form of electromagnetic or semiconductor logic devices. In order to verify the methods adopted, the authors have developed a logical controller which is capable of satisfying all the autoreclose requirements applicable to a typical 4-switch-mesh substation. Standardised control circuits are developed which may be applied to each corner of the mesh, with provision for correct functioning under simultaneous fault conditions in its own and adjacent corner zones. Such control circuits have been built and tested by the authors, and constructional details relevant to the construction of such circuits are given.