single line diagram (sld) or, one line diagram

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 • Coordination studies • Load flow studies • Safety evaluation studies • All other engineering studies • Electrical safety procedures • Efficient maintenance

WHAT SHOULD BE IN A SINGLE LINE DIAGRAM (SLD)? A typical package of single line diagram shall include:

• Incoming lines showing voltage and size • Incoming main fuses, cutouts, switches, and main/tie breakers • Power transformers (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 switchgear 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. 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).

M

2x1c

,120

.0 m

m2

Cu.

R=2

73.4

65 K

WY=

273.

220

KWB=

272.

445

KWTL

=819

.130

KW

R=5

5.29

6 KW

Y=55

.060

KW

B=54

.275

KW

TL=1

64.6

30 K

W

R=9

8.67

0 KW

Y=98

.670

KW

B=98

.660

KW

TL=2

96.0

00 K

W

R=9

8.67

0 KW

Y=98

.660

KW

B=98

.670

KW

TL=2

96.0

00 K

W

1x1c

ECC

240

mm

2 BYA

/NYY

(or

10-1

2 m

m d

ia b

are

copp

er w

ire

1x4c

240 m

m2 B

YA/N

YY1x

1c E

CC 2

40 m

m2 B

YA/N

YY (o

r10

-12

mm

dia

bar

e co

pper

wir

e1x

1c E

CC 2

40 m

m2 B

YA/N

YY (o

r10

-12

mm

dia

bar

e co

pper

wir

e

600

A (a

djus

tabl

e)M

CCB

Sample of load schedule (DB Schedule) (You can follow it or prepare it as your own style)