SINGLE LINE DIAGRAM - The Bangladesh Accord on Fire and

SINGLE LINE DIAGRAM (SLD) Or, ONE LINE DIAGRAM
The single-line diagram is the blueprint for electrical system analysis. It is the first step in
preparing a critical response plan, allowing you to become thoroughly familiar with the
electrical distribution system layout and design in your facility.
WHY IT’S REQUIRED?
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. It needs to change as your
facility changes to ensure that your systems are adequately protected.
To make all the changes documented in a common file, making the electrical system easily
understandable for any technical person inside/outside of the factory.
An up-to-date single-line diagram is vital for a variety of service activities including:
Short circuit calculations
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Coordination studies
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Load flow studies
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Safety evaluation studies
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All other engineering studies
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Electrical safety procedures
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Efficient maintenance
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WHAT SHOULD BE IN A SINGLE LINE DIAGRAM (SLD)?
A typical package of single line diagram shall include:
Incoming lines showing voltage and size
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Incoming main fuses, cutouts, switches, and main/tie breakers
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Power transformers (rating, winding connection and grounding means)
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Feeder breakers and fused switches rating and type.
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Relays (function, use and type)
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Current and / or potential transformers with size, type and ratio
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Control transformers rating.
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All main cable and wire runs with their associated isolating switches
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All substations, including integral relays and main panels with total load of each feeder and
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each substation
Critical equipment voltage and size (UPS, battery, generator, power distribution, transfer
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switch, computer room air conditioning)
A summary load schedule for the LT switchgear panel.
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A load schedule for each distribution panels and switch board.
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Rating and dimension of bus bar.
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All outgoing cables with cable size and type with rating and type of their associated isolating
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switches (e.g. circuit breaker).
Length and voltage drop of all outgoing cables.
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Rating of PFI , changeover, ATS, generators with associated protection and isolating switch
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All earthing cable rating (size, type etc.)
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All connected load with their individual load capacity.
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All spare switches (outgoing circuit breaker) shall be mentioned.
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Earthing system must be included with dimension of earthing pit, boring, earth electrode size,
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earth lead and ECC cable size and type.
Here is given an example of a typical LT panel one line diagram or Single line diagram (try to follow it
as best as possible).
1x1c ECC 240 mm2 BYA/NYY (or
10-12 mm dia bare copper wire
600 A (adjustable)
MCCB
R=55.296 KW
Y=55.060 KW
B=54.275 KW
TL=164.630 KW
2x1c,120.0 mm2 Cu.
1x1c ECC 240 mm2 BYA/NYY (or
10-12 mm dia bare copper wire
R=273.465 KW
Y=273.220 KW
B=272.445 KW
TL=819.130 KW
M
R=98.670 KW
Y=98.670 KW
B=98.660 KW
TL=296.000 KW
1x1c ECC 240 mm2 BYA/NYY (or
10-12 mm dia bare copper wire
1x4c 240 mm2 BYA/NYY
R=98.670 KW
Y=98.660 KW
B=98.670 KW
TL=296.000 KW
Sample of load schedule (DB Schedule) (You can follow it or prepare it as your own style)