Busbar sizing for substations

Hasala DharmawardenaEngineer – DesignsLTL Projects PVT. LTD.

Assumptions

Sizing is relevant only forAl – E91E (6063 T6)Tubular

No structures are attached to the busbar

Busbar

Contents

1. Minimize bending moment at joints

2. Span width specific requirements

3. Post Insulator Sizing

1. Bending Moments

For equal Span width, the position of minimum bending

depends only on

• Length of a Span

• The Number of Spans

• The Type of support – e.g. Fixed , Pin

Assumptions

S= Slip fit Support

F= Fixed Support

E=Expansion Support

Points of Zero Bending Moment

Workings of the excel sheet

Example outputInput are showed in RED boxes

2. Deflection and Stress

Deflection caused by the weight of the tubeshould be less than 150th of

the length

Total stresses on the tube

should be less than the yield

stress

Both should be

simultaneously satisfied

Prerequisites

1. Wind Forces

2. Short circuit Forces

Wind forces

IdCKGVFW2

Where K is a constant depending on height and

exposure , G a constant depending on wind speed,

V wind velocity and d external diameter of the tube.

Short Circuit Forces

D

IF SCSC

4

2

10

6.1

Where Isc is the maximum Short circuit current and

D is the conductor centerline to centerline spacing

2.1 Deflection

33

5

384

G

BD F

YJECL

Where L is the maximum span length, Y maximum

deflection, J cross section moment of inertia and F bus unit

weight.

2.2 Fiber Stress

T

AS F

SFKCL

'

•Where L is the maximum span length, FA maximum fiber

stress of 6063 - T6, S section modulus, K is a constant

which depends on support type and number of supports

and FT is the total force

•Combines both wind forces and gravitational forces

2.2 Fiber Stress ctd…

Total force FT is given by

])[( 22GSCWT FFFF

Workings of the excel sheet

Select maximum possible span width to be the minimum of Ls and LD , If not change Di and Do or If possible the span width to be within the bounds defined

by the above conditions.

Secondary CalculationLD

Primary CalculationLS

Get Input dataSpan Width Number of Spans

Example output

Input are showed in RED boxes

Example output ctd …

Input are showed in RED boxes

3. Post Insulator

Total insulator cantilever load is calculated by assuming

vertically mounted insulator with horizontal bus.

Furthermore the effective weight of the mass transmitted

to one bus support depends on the bus configuration and

support conditions.

3. Post Insulator ctd…)]

)()(

2[

i

SBfi

i

WBfiWIIS H

FHH

H

FHHFKF

Where FIS is the load on the insulator, FWI is the wind force on the PI, FSB is the short circuit force transmitted to the PI, FWB is the wind force transmitted to the PI.

Example output

Thank You