Basic concepts and auto-check for clearing procedures

Safety when working in presence of electricity is a universal goal. Finding practical methods to achieve this safety, however, is not always easy or obvious. Maintenance personnel must take the necessary steps to assure that the system or portion of the system on which they plan to work is in an electrically safe working condition. The accepted, reliable way to provide safety is to de-energize the equipment first, then to connect the equipment to ground so that it cannot be re-energized. Complexity of the electrical system normally determines the level of detail planning required for system clearing procedures. Complex power distribution systems that may have several sources into an area require several switching steps to isolate a portion of the system. It is necessary to use more elaborate clearing procedures and written switching instructions for systems together with a single-line diagram. The instructions and/or procedures should include verifying that the power has been removed (by live line testing or other means) followed by the placing of grounds and locking/tagging of isolating devices. The clearing procedures should be completely written, checked and understood by all persons involved before applying them to any portion of the power distribution system. This paper considers the subject from both European and American points of view. It investigates the basic concepts and definitions to give prominence to operating bonds and to help the procedure-project. It proposes some simple rules, a graphical representation and an algebraic model of electrical status to allow an auto-check of the clearing procedure