Electrical interlock design for complex high-power switching networks

The paper reviews the derivation of interlock logic and the resultant interlock circuits for conventional double-busbar substations. These methods are then shown to be inadequate when the number of operating constraints on each switch and the degree of network interconnection are increased. A new method of deriving the interlock logic that can be converted directly into hard-wired form is then presented. The application of this method to the Dinorwic pumped storage scheme is given as an example. The ways by which conflicts between safety and operating requirements can be overcome are then described. Finally, the methods by which such complex interlock logic may be checked are discussed and examples given of the application of decision tables to this task.