What should be include 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 an 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, cut-outs, 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.?