Distribution Automation Handbook
The selectivity diagram is a set of specific time/current curves which shows all the time/current curves, that is, the operating characteristics of the relays of the concerned chain of protection relays.
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Start by identifying the key components: contacts, coils, and connection points. This includes AC schematics, DC schematics, logic diagrams, data tables and singl line diagrams that prominently feature relaying. There are other types of drawings that will be discussed but are not the subject of this paper including wiring. Selective short-circuit protection can be achieved in different ways, such as: Time-graded protection Time- and current-graded protection A straightforward way of obtaining selective protection is to use time grading. This handbook covers the code of practice in protection circuitry including standard lead and device numbers, mode of connections at terminal strips, colour codes in multicore cables, dos and donts in execution.
