The expanded principle wiring diagram (referred to as the expanded diagram) is to draw the AC and DC circuits, current and voltage circuits, coils and contacts of relays and other electrical appliances of the secondary equipment in their respective circuits according to the sequence of operation and working principle, which also indicates the wiring and operation principle of relay protection, signal system, and operation control. For beginners, this kind of principle wiring diagram is not easy to understand, but it is convenient for use in construction and operation.
Characteristics of the expanded principle wiring diagram:
(1) Relays and other electrical appliances are not represented as a whole, so the function description of each circuit should be annotated separately beside the circuit.
(2) DC voltage bus or AC voltage bus is represented by thick lines to distinguish from other circuits.
(3) Relays and other electrical equipment are marked with text symbols specified by national standards. The numbers added before and after the text symbols represent the component numbers, which are consistent with the numbers on the aggregated principle wiring diagram.
(4) The connecting wires between relays and other electrical appliances should be given digital labels, called circuit designations. The national standard for secondary circuit designations is "Circuit Labels on Power System Diagrams".
(5) Various small buses are given text labels. The text labels of small buses are marked according to the national standard "Graphical Symbols for Electrical Diagrams".
(6) In the expanded principle wiring diagram, some electrical contacts are shown in another diagram or used in other installation units, so the source should be indicated on the diagram. For introduced contacts or circuits, it should also be indicated where they come from.
