Single-line diagram (SLD) is also known as a one-line diagram. It is a high-level diagram that shows how incoming power is distributed to the equipment. It is the first step in preparing a critical response plan, allowing you to become thoroughly familiar with the electrical transmission system layout and design.
The single-line diagram also becomes your lifeline of information when updating or responding to an emergency. An accurate single-line diagram ensures optimum system performance and coordination for all future testing and can highlight potential risks before a problem occurs.
An effective single-line diagram will clearly show how the main components of the electrical system are connected, including redundant equipment and available spares. It shows a correct power distribution path from the incoming power source to each downstream load – including the ratings and sizes of each piece of electrical equipment, their circuit conductors, and their protective devices.
Whether you have a new or existing facility, the single-line diagram is the vital roadmap for all future testing, service, and maintenance activities. As such, the single-line diagram is like a balance sheet for your facility and provides a snapshot of your facility at a moment in time.
2. Scope of SLD
To give you an accurate picture of your electrical system, the single-line diagram information normally includes:
- Incoming lines (voltage and size)
- Incoming main fuses, potheads, cutouts, switches, and main/tiebreakers
- Power transformers (rating, winding connection, and grounding means)
- Feeder breakers and fused switches
- Relays (function, use, and type)
- Current/potential transformers (size, type, and ratio)
- Control transformers
- All main cable and wire run with their associated isolating switches and potheads (size and length of run)
- All substations, including integral relays and main panels and the exact nature of the load in each feeder and on each substation
- Critical equipment voltage and size (UPS, battery, generator, power distribution, transfer switch, computer room air conditioning)
3. Uses & Significance
Single-line diagrams are used by several trades including Electrical, Mechanical, HVAC, and plumbing, but the electrical one-line diagram is the most common. HVAC and plumbing riser diagrams are essentially one-line diagrams, but they go by different names.
An electrical single-line diagram is a representation of a complicated electrical distribution system into a simplified description using a single line, which represents the conductors, to connect the components. Main components such as transformers, switches, and breakers are indicated by their standard graphic symbol. The overall diagram provides information on how the components connect and how the power flows through the system.
4. Flow Diagram of SLD
Few parameters are considered while designing the flow of a single-line diagram to keep it simple & readable:
- Remember to use a single line to represent multiple conductors.
- Diagrams should start at the top of the page with the incoming source of a system’s power.
- Electrical symbols must be used while drawing the single-line diagram to make it simple & concise.
- No physical location or size representation is required of the electrical equipment only ratings and breakers sizes with the other equipment to be used should be written.
5. Designing of SLD
To Design a single-line diagrams for your facility Some steps need to be taken:
- Create an inventory of all the utilities & equipment used in the building.
- Verify its existence and that they are adequately available.
- Confirm loads are connected to emergency/standby feeders.
- Verify potential single points of failure.
- Evaluate design redundancy of critical systems
- Make a report that outlines the findings by site along with recommended actions.
- Provide a copy of the single-line electrical diagram in AutoCAD format
- An up-to-date single-line diagram is vital for a variety of service activities including:
- Short circuit calculations, Coordination studies, Load flow studies, Safety evaluation studies, All other engineering Studies, Electrical safety procedures & Efficient maintenance, etc.
6. Calculations Requirements for SLD
6.1. Identify the appropriate symbols:
To draw and understand a single-line diagram you first need to be familiar with the electrical symbols. This chart shows the most frequently used symbols. For electric power networks, an appropriate selection of graphic symbols is the most important step.
6.2. Draw the required system:
To draw the electrical single line diagram first we need all the information on electrical equipment and the supply of receiving power. The most important information to include is:
- Incoming service voltage
- Equipment rated current
- Identification of names of equipment
- Bus voltage, frequency, phases, and short circuit current withstand ratings
- Cable sizes, runs of cables, and lengths
- Transformer connection type, kVA, voltages, and impedance
- Generator voltage and kW
- Motor HP
- Current and Voltage ratios of instrument transformers
- Relay device numbers
6.3. Related calculations:
To represent the three-phase system in a single line diagram various other cal. are required:
- Calculation Of generator reactance
- Calculation Of transformer reactance
- Calculation Of transmission-line reactance
- Calculation Of reactance of motors and other equipment etc.
7. Software’s used
AutoCAD Electrical has a schematic library and a single line diagram sub-library. This enables the user to place two different representations down of the same component.
ETAP Single-Line Diagram / View is an intelligent user interface to model, validate, visualize, analyze, monitor, and manage electrical power systems, from high to low voltage AC and DC networks.
It is a low voltage electrical installation design software developed by Schneider Electric. it is a user-friendly software that helps you optimize equipment and costs while managing operating specifications, all along with the design of your power distribution projects.
7.4 Microsoft Visio
Visio Professional or Visio Plan 2 are used to create electrical and electronic schematic diagrams.
8. Benefits of SLD:
- Help identify fault locations which identify when to perform troubleshooting & simplify troubleshooting
- Identify potential sources of electric energy during the distribution process.
- Accurate single line diagram will further ensure the safety of personnel work
- Meets compliance with applicable regulations and standards
- Ensure safe, reliable operation of the facility