Introduction to Electrical Diagrams

Electrical Diagrams Introduction

• Electrical diagrams represent electrical circuits using shapes, lines, symbols, numbers and letters.
• Electrical diagrams illustrate the connections between devices, showing signal, power, and control connections.
• Electrical diagrams are used for building new installations and troubleshooting electrical problems.
• Electrical diagrams aid in modifying existing circuits and servicing (testing) the devices.
• Electrical diagrams are also known as prints or blue prints in some plants.

Electrical Diagrams: Uses

• Electrical diagrams provide information on the relative positions, functions, and arrangement of devices and terminals to assist in:
  • Making new electrical installations.
  • Locating and troubleshooting electrical problems.
  • Modifying existing circuits or servicing equipment.

Electrical Diagrams: Introduction

• Diagrams are a universal language for communicating information about simple and complex mechanisms, systems, and processes.
• They convey information from the drafting table to the technician, more efficiently than words alone.
• Symbols and notes condense a large amount of information into a compact format on a single diagram.

Electrical Diagrams: Types

• Different types of electrical diagrams are available, each providing specific information:
  • Single Line Diagrams: show the flow of electrical circuits and connections in a simplified manner.
  • Schematic Diagrams: illustrate the electrical connections and components in their proper positions, regardless of physical location.
  • Wiring Diagrams: depict the physical arrangement of devices and their connecting wires and cables.
  • Block Diagrams: present the major components and their relationships in a system, showing the overall concept of the operation.
  • Layout Drawing: show the physical location of devices and systems in a facility.

Electrical Diagram Symbols and Abbreviations

• Standardized symbols are used in electrical diagrams, adhering to either ANSI or IEC guidelines.
• It is important to maintain consistency with one standard within a diagram for universal readability.

Protection Device Function Symbols and Abbreviations

• Two methods for indicating protection relay functions are commonly used:
  • ANSI Standard: utilizes a numbering system for different functions.
  • IEC: employs graphical symbols.
• Device function numbers are standardized by IEEE and used in several countries.

Single Line Diagrams

• Represent the flow of electrical circuits using single lines and graphic symbols, disregarding physical relationships.
• Depict the arrangement of equipment in a substation in a simplified manner, using internationally recognized symbols.
• Typically represent three-phase connections with a single line.
• Often include main data for HV equipment.
• Include instrument transformers, protection, measurement, and control equipment with their secondary wiring.

Three Line Diagrams

• Provide detailed information about three-phase circuitry that is not included in a one-line diagram.
• Utilize standardized symbols consistent with one-line diagrams.
• Show each conductor in a power circuit as a separate line.
• Schematic diagrams are detailed versions of single line diagrams, illustrating components in their proper electrical position, regardless of physical location.

Schematic Diagrams

• Display circuit functions in a definite sequence, typically read from left to right and top to bottom.
• Employ standard electrical symbols and device numbers to represent components or parts of components.
• Present components in their relaxed or de-energized state, showing the condition when no power is applied.
• Include labels for all symbols and numerical details like ratings, resistance, and capacitance values.

Wiring Diagrams

• Show the relative positions of components in the circuit and how conductors are connected.
• Classified into internal and external diagrams:
  • Internal Wiring Diagrams: illustrate the physical arrangement of devices and accessories within a panel or switchgear assembly.
  • External Wiring Diagrams: depict the physical arrangement of panels and their interconnecting wiring.
• Used for panel or switchgear construction, modifications, and rewiring.
• Assist in troubleshooting by showing the relative positions of devices and terminals.

Panel or Switchgear Component Identification

• Each device in a panel is assigned an arbitrary alphabetical or double-letter identifier.
• Each terminal block, fuse block, resistor, or other accessory is also assigned a letter identifier.
• Terminal points on each device are assigned numerical identifiers, determined by the manufacturer or owner.

Block Diagrams

• Represent the major components and their electrical or mechanical relationships in a simplified block format.
• Lines between blocks indicate connections.
• Illustrate the overall operation and arrangement of key components and the progression of a signal or current flow.
• Typically used with textual descriptions to explain component interactions and overall system operation.
• Simplify the system, providing the general concept without detailed operation.