What should need to inlcude in a Single Line Diagram (SLD)?

Single Line Diagram (SLD):

In Power System Engineering, a single line diagram is a simplified representation of a three phase power system. 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.

The single-line diagram provides the road map to enable proper maintenance of equipment, design redundancy, and protection of a electrical distribution system

Why SLD is Required?:

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

What should be in a SLD?:

A typical package of single line diagram shall include:

• Incoming main fuses, cutouts, switches, and main breakers rating, breaking capacity and breaker details. 

• Power transformers & Distribution transformer (rating, winding connection and grounding means) 

• Feeder breakers and fused switches rating and type.

• Relays (function, use and type) 

• Current and / or potential transformers with size, type and ratio 

• Control transformers rating. 

• All main cable and wire runs with their associated isolating switches 

• All substations, including integral relays and main panels with total load of each feeder and each substation 

• Critical equipment voltage and size (UPS, battery, generator, power distribution, transfer switch, computer room air conditioning) 

• A summary load schedule for the LT switch gear panel. 

• A load schedule for each distribution panels and switch board. 

• Rating and dimension of bus bar. 

• All outgoing cables with cable size and type with rating and type of their associated isolating switches (e.g. circuit breaker). 

• Length and voltage drop of all outgoing cables. 

• Rating of PFI , changeover, ATS, generators with associated protection and isolating switch 

• All earthing cable rating (size, type etc.) 

• All connected load with their individual load capacity. 

• All spare switches (outgoing circuit breaker) shall be mentioned. 

• Earthing system must be included with dimension of earthing pit, boring, earth electrode size, earth lead and ECC cable size and type.