Download Report




Electrical diagrams are drawings in which lines, symbols, letter and number combinations are used to represent electrical circuits.  In some plants, electrical diagrams may also be called prints, or blue prints

Electrical drawings are valuable tools for

 Making new electrical installations  Locating electrical problems  Modifying existing circuits


Symbols are used to standardize the reading of electrical diagrams. Electrical diagrams use a variety of symbols to represent component in electrical circuit Two tables that are helpful in understanding electrical diagrams are:  

American standard device function number

 Identifies the general function of electrical devices in terms of number designation

Standard diagram abbreviation table

 Lists abbreviations that are used to identify components

Drafting Practices Using Graphical Symbols

( a) The orientation of a symbol on a drawing does not alter the meaning of the symbol.

This is true even if the symbol is drawn backwards. A symbol is made up of all its various parts.

(b) The weight (or width) of a line does not affect the meaning of the symbol. In some cases a heavier line may be used for emphasis.

(c) Symbols are not drawn to scale. They can be drawn to any size compatible with the scale of the drawing.

(d) Arrowheads can be drawn closed or open, except when showing a "protective gap" (a gap placed between line parts and the ground which limits the maximum over-voltage that may occur.)

(e) The standard symbol for a terminal (o) can be added to any one of the graphic symbols where connecting lines are attached. This added terminal symbol is not a part of the graphic symbol itself.

(f) In order to make a drawing simpler, graphic symbols for devices such as relays or contactors may be drawn in parts. However, if this is done the drawing must show how the parts are related.

(g) Most often, it does not matter at which angle a connecting line is drawn to meet a graphic symbol.

(h) Broken lines with short dashes: - - - - - - , may be used to show paths or equipment that will be added to the circuit later, or those which are connected to the circuit but are not part of it.

(i) If details such as type, impedance, and rating are to be given, they should be drawn next to a symbol. If abbreviations are used, they should be in accordance with the American Standard Abbreviations for Use on Drawings. Letters that are joined together and use parts of graphic symbols are not abbreviations.

Information found on electrical diagrams Title block

Title block is usually located in the bottom right hand corner of an electrical diagram  It contains information that identifies the diagram


The notes on an electrical diagram usually give detailed information about certain parts of the diagram and/or list other reference that may be needed


Legend identify symbols and designations that are used on electrical diagrams 

Some times, the legend is a part of the diagram sheet but, in many cases ,it is separate sheet Suffix Letters

Suffix letters are used with device function number for various purpose. In order to prevent possible conflict, any suffix letter used singly, or any combination of letters, denotes only one word or meaning in individual equipment For purpose of clarification, these suffix letter have been classified in several groupings

Types of Diagrams

One-Line Diagram

A one-line diagram, which is also called a single-line diagram, is the most commonly used diagram in an industrial power system.


  Interpreting the scope of a proposed installation of a power system.

Serving as a basis to produce project drawings.

  Analyzing power system problems.

Determining which circuit interrupters must be opened to safely isolate electrical apparatus.

Characteristics  A one line diagram uses  Single lines  Standard graphical symbols  Standard nomenclature  A one line diagram shows the power path of an electrical circuit or a system of circuit  A one line diagram also shows the component devices or a parts of a power system  The multiple conductors of power circuits and control circuits are shown as single lines

               SUB – 91, SUB – 82 UNIT SUB – XY (TYPICAL) DG BUILDING (TYPICAL) A0, A1, B0, B1.C0 – Substation 91, Substation – 82 respectively.

– A typical Unit Substation.

– A typical Emergency Diesel Generator Building.

– 230 kV SF6 Circuit Breakers A2, A3, B2, B3, C2 GILBS 1, GILBS 2 A4, A5, B4, B5 A6, B6, C6 A6.1, B6.1 T21, T22 – 34.5 kV Circuit Breakers.

– SF6 Gas Insulated Load Break Switch Assembly.

– 34.5 kV SF6 Load Break Switches – 4.16 kV Vacuum Circuit Breakers.

– 4.16kV Vacuum Circuit Breakers / Vacuum Contactors A7, A7.1, A7.2, B7, B7.1, C.7 – 480V Air Circuit Breakers.

A8 A 9 T11, T12 – 480V Emergency Automatic Transfer Switch (EATS) ─ 480 V MCCB – 34.5kV / 4.16 kV Distribution Transformers.

− 34.5kV / 480V Distribution Transformers.

Three-Line diagram

Purpose Three line diagram provides detailed information pertaining to three phase circuitry that is not shown on a one-line diagram

 Three-line diagrams help plant maintenance and operations personnel to understand power system operations  They are also used to develop metering and protective relay wiring drawing


A three-line diagram represents power system components using the same standardized symbols as a one line diagram plus an additional set of standardized symbols that are also used in schematic and wiring diagrams

Unlike one-line diagram, a three-line diagram shows every conductor of a power circuit as an individual line

Schematic Diagrams


Schematic diagrams shows circuit elements and internal connections in an arrangement that allows a technician to interpret the function and operational logic of an electrical control circuit


 Schematic diagrams are composed using the same standardized symbols as one line, three-line, and wiring diagrams.  Schematic diagrams show all terminals and connections of functional devices.

 Figure shows a typical schematic diagram of a motor circuit and its associated one-line diagram.

Types of Schematic diagrams

 

Internal Schematic Diagrams


show only the internal circuits of a single physical device. Figure (a) is an example of an internal schematic diagram. It represents the internal circuits of a protective relay.

External Schematic Diagrams


show the internal circuits of physical devices but additionally show the external circuits that conduct input and output signals into and out of the devices. Figure (b) shows the elements of the same relay that is shown in Figure (a) but also shows the external circuit that connect this relay to other physical devices


 

Elementary Diagrams


show all of the operational elements and all of the circuits of a complete electrical control system. An elementary diagram is often used to represent the complete control circuit of an electrical substation.

Ladder Diagrams


are commonly used for understanding and designing system control logic. A ladder diagram is a top-down logical line schematic: logical because it moves from power input at the top through sequential operations. Figure shows a ladder diagram that represents a generator control circuit.

Wiring Diagrams

 A wiring diagram uses standardized symbols to show the physical devices of an electrical control panel and lines to show the wires that connect these devices to each other.


 Wiring diagrams are used by equipment manufacturers to install wires in electrical equipment such as switchboard and panels.  They are also used to show the necessary interconnection wiring between electrical equipment.

 For example, one type of wiring diagram, called an interconnection diagram, is used to show the wiring between two or more switchboards.


     Wiring diagrams show functional devices in their correct relative physical locations. Standardized and non-standard symbols are used to represent these functional devices. Lines are used to represent single conductors. Multiple conductors that are bundled together or that are installed in the same channel are shown as a single line with radial branches to show the locations where single conductors or other bundles leave the path of the main-trunk bundle. Each representation of a conductor is labeled with an identifying number (conductor number).

Logic Diagrams

Logic diagrams show the logic for complex circuits, processes, or devices. Logic diagrams utilize block-type and standardized logic-function symbols to represent highly complex functions that are performed either by integrated processing modules or by individual devices



Logic diagrams enable the equipment users to understand the related logic functions of devices or processes without requiring specific knowledge of their internal operations



     Logic diagrams utilize rectangular shaped blocks and standardized logic-function symbols to represent highly complex functions, processes, or devices. Each block contains a written description or a logic symbol that indicates the function of the block. On a logic diagram, straight lines represent the paths of process-control signals. The points where these signal paths are illustrated as entering or leaving a block represent the input and output signals of the block.

Logic diagrams are also used to represent the functions of an integrated control system that comprises several physically separated devices and electrical circuits.

Numbering System Format

Major Electrical Equipment The following numbering system shall be used for major electrical equipment in the primary power distribution system, power supplies to process equipment, essential power distribution systems, instrument power supplies, and supervisory systems.

The format is “XX-XX-XXXXXX” and is composed of the following parts:

 Note 1: The equipment category code shall consist of two to five letters and is a unique code for each piece of electrical equipment.  Note 2: The WBS (Work Breakdown Structure) unit number shall be per the requirements of specification.

 Note 3: The voltage number is a two-digit number that identifies the voltage level as follows: 01 - 230 kV 10 - 34.5 kV 20 - 13.8 kV 30 - 4.16 kV and 2.4 kV 40 - 480 V and below

 Note 4: The serial number is a two-digit number that starts at 01. Each piece of electrical equipment has a unique serial number for its category and substation. Substations do not have serial number.

 Note 5: A single letter (usually starts at A) is used to identify two or more identical pieces of equipment in the same service, such as a shared serial number by two transformers connected to the same double ended switchgear or a shared serial number by two battery chargers connected to a set of battery.



1. ESWG-83-2001A

ESWG -Essential Switchgear 83 -WBS unit number 20 -The voltage level of this equipment is 13.8 kV 01 -The first equipment in this series of this type of equipment A -Connected to bus A

2. XFR-70-1001B

XFR -Power Transformer 70 -WBS unit number 10 -The voltage level of this equipment is 34.5 kV 01 -The first equipment in this series of this type of equipment B -Connected to bus B

3. MCC-84-4003B1 or MCC-84-4003B2

MCC Motor Control Center 84 WBS unit number 40 The voltage level of this equipment is 480 volts 03 The third equipment in this series of this type of equipment B Connected to bus B 1 or 2 The first or the second MCC connected to bus B

4. SUB-82

SUB Substation 82 WBS unit number Note that substations do not have a voltage number or serial number.

Minor Electrical Equipment

The following numbering system shall be used for minor electrical equipment such as lighting panelboards, terminal boxes and other equipment not listed as major equipment: The format is “XXX-XX-X” and is composed of the following parts:

Note 1: The equipment category code shall consist of two to four letters and is a unique code for each type of minor electrical equipment. Note 2: The WBS (Work Breakdown Structure) unit numbers refer to the requirements of specification.

Note 3: Each type of minor electrical equipment has a unique letter designation assigned to it. All distribution panels shall be considered one type of minor electrical equipment and shall not share common letter designation.


1. ELP-82-A

ELP -Essential Lighting Panel 82 -WBS unit number A -Unique letter designation

2. PP-82-B

PP -Power Panel 82-WBS unit number B -Unique letter designation