STNW3014 Standard for Busbar Design · 2020-06-26 · Energex Limited ABN 40 078 849 055 Ergon Energy Corporation Limited ABN 50 087 646 062 B.3.3.2. Wind load on busbar (F w) The

Joint Standard Document between Energex and Ergon Energy

Energex Limited ABN 40 078 849 055 Ergon Energy Corporation Limited ABN 50 087 646 062

Substation Standard

Standard for Busbar Design

These standards created and made available are for the construction of Energy Queensland

infrastructure. These standards ensure meeting of Energy Queensland’s requirements. External

companies should not use these standards to construct non-Energy Queensland assets.

If this standard is a printed version, to ensure compliance, reference must be made to the Energy

Queensland internet sitehttp://www.ergon.com.au/ to obtain the latest version.

Approver Carmelo Noel

If RPEQ sign off required insert details below.

Energy Queensland

Certified Person Name and Position Registration Number

John Lansley

Engineering Manager Substation Standards

RPEQ 6371 (Electrical)

Paul De Sousa Roque

Senior Line Structure Engineer

RPEQ 10013 (Mechanical)

Abstract: This standard provides guidance on the selection of busbar type and application.

Keywords: Busbar, Conductor, Connection, Support, Insulator, SS-1-3.2.

http://www.ergon.com.au/


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For definitive document version and control detail, please refer to the information stored on the

Process Zone.

Document approvals

Name Position title Signature Date

Carmelo Noel GM Asset Standards

John Lansley Manager Substation Standards

Stakeholders / distribution list

Name Title Role


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Table of Contents

1 Overview .............................................................................................................................. 1

1.1 Purpose ................................................................................................................... 1

2 References ........................................................................................................................... 1

2.1 Energy Queensland controlled documents ............................................................... 1

2.2 Other documents ..................................................................................................... 1

3 Legislation, regulations, rules, and codes ............................................................................. 2

4 Definitions, acronyms, and abbreviations.............................................................................. 3

4.1 Definitions ................................................................................................................ 3

4.2 Acronyms and abbreviations .................................................................................... 3

5 General procedure ................................................................................................................ 4

6 Design requirements ............................................................................................................ 4

7 Evaluation of conductor size for current rating ...................................................................... 4

7.1 Basic data and standard conditions ......................................................................... 4

7.2 Skin effect ................................................................................................................ 7

7.3 Proximity effect ........................................................................................................ 7

7.4 Corona inception voltage ......................................................................................... 7

7.5 Rating tables for standard sizes of busbars ............................................................. 7

8 Rigid busbar mechanical design ........................................................................................... 9

8.1 Loads on rigid busbar and support insulators ......................................................... 10

8.1.1 Permanent loads .............................................................................................. 10

8.1.2 Exceptional loads ............................................................................................. 10

8.2 Busbar mechanical data ........................................................................................ 10

8.2.1 Basic data ........................................................................................................ 10

8.2.2 Busbar mechanical strength ............................................................................. 11

8.2.3 Support insulator mechanical strength ............................................................. 11

8.2.4 Evaluation of natural frequency ........................................................................ 11

8.2.5 Busbar end supports ........................................................................................ 12

8.3 Maximum busbar span length based on allowable vertical deflection ..................... 12

8.4 Maximum busbar span lengths based on conductor allowable fibre stress ............ 12

8.5 Maximum busbar span length based on insulator cantilever strength .................... 13

9 Documentation required ..................................................................................................... 14

Annex A Formulae and assumptions for calculation of conductor current ratings ................. 15

A.1. Formulae Used ...................................................................................................... 15


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A.1.1. Continuous current rating (I) ......................................................................... 15

A.1.1.1. Power dissipation due to radiation of 1 meter of conductor (PR) ............ 15

A.1.1.2. Power dissipation due to convection of 1 meter of conductor (PC) ......... 15

A.1.1.3. Power gained through solar radiation of 1 meter of conductor (PS) ........ 17

A.1.1.4. AC Resistance of 1 meter of conductor (R) ............................................ 18

A.2. Combined proximity effect and skin effect .............................................................. 18

A.3. Calculation of corona onset .................................................................................... 20

A.3.1. Conductor corona onset gradient .................................................................. 20

A.3.2. Conductor maximum voltage gradient ........................................................... 20

A.3.2.1. Three phase single conductors .............................................................. 20

A.3.2.2. Three phase bundle conductors ............................................................. 21

A.4. Short time current rating ........................................................................................ 22

Annex B Busbar mechanical strength and maximum span length calculations ..................... 23

B.1. Data used in calculation of maximum span lengths ................................................ 23

B.2. Maximum span length based on allowable deflection ............................................. 25

B.2.1. Simple-simple end supports (Lvss) ................................................................. 25

B.2.2. Simple-fixed end supports (Lvsf) .................................................................... 25

B.2.3. Busbar maximum cantilever span based on allowable deflection (Lvc) .......... 26

B.3. Maximum span length based on conductor allowable fibre stress .......................... 26

B.3.1. Simple-simple or simple-fixed end supports (LSs) ......................................... 26

B.3.2. Maximum busbar cantilever length based on allowable fibre stress .............. 27

B.3.3. Total load acting on the busbar conductor (FT) ............................................. 27

B.3.3.1. Combined busbar and anti-vibration conductor gravitational weight (FGtotal)27

B.3.3.2. Wind load on busbar (Fw) ....................................................................... 28

B.3.3.3. Short-circuit mechanical load on busbar (Fsc) ......................................... 28

B.4. Maximum span length based on end insulators torsional strength (Lb) ................... 29

B.5. Maximum span length based on insulator cantilever strength (Le) .......................... 29

B.6. Maximum busbar spans with exceptional short-circuit current and X/R values ....... 30

B.7. Thermal Expansion Load ....................................................................................... 39

B.7.1. Thermal Expansion (ΔL) ............................................................................... 39

B.7.2. Load due to thermal expansion (FTE) ............................................................ 39

Annex C Wind Induced Vibration and Resonance ................................................................ 40

C.1. General .................................................................................................................. 40

Annex D Standard palm terminal sizes and current rating .................................................... 42


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1 Overview

1.1 Purpose

This standard provides the current ratings and mechanical limits of outdoor, air insulated busbars

to be adopted within Energy Queensland. This standard also details methods of calculating their

thermal ratings and determining mechanical loads on conductor and support insulators.

2 References

2.1 Energy Queensland controlled documents

Document number or location

(if applicable)

Document name Document type

(NA000000R100) Plant Rating Guidelines Ergon Energy Guideline

Energex Plant Rating Manual Energex Guideline

(STNW3013) Substation Standard Clearances

in air

Energy Queensland Substation

Standard

2.2 Other documents

Document number or location

(if applicable)

Document name Document type

(AS/NZS 1170.0, 2002)

(Standards Australia)

Structural design actions. Part 0: General

principles Standard

(AS/NZS 1170.2, 2011)


Structural design actions. Part 2: Wind

actions Standard

(AS 1531, 1991)


Conductors – Bare overhead – Aluminium

and aluminium alloy Standard

(AS/NZS 1664.2, 1997)


Aluminium Structures – Part 2: Allowable

stress design Standard

(AS 1746, 1991)


Conductors - Bare Overhead - Hard-drawn

Copper Standard

(AS 2067, 2016)


Substations and high voltage installations

exceeding 1 kV a.c Standard

(AS 4398.1, 1996)


Insulators – Ceramic or glass – Station

post for indoor and outdoor use – Voltage

greater than 1000 V a.c

Standard

(AS 62271.1, 2012)


Common specifications for high voltage

switchgear and controlgear standards Standard

(AS 62271.301, 2005)


High voltage switchgear and controlgear

Part 301: Dimensional standardization of

terminals

Standard

(IEC 60287-1-1, 2014)

(IEC) Electric cables – calculation of current

rating – Part 1-1: Current rating equations Standard





(100% load factor) and calculation of

losses - General

(IEC 60865-1 Ed.3.0, 2011)

(IEC)

Short-circuit Currents - Calculation of

Effects - Part 1: Definitions and

Calculation Methods

Standard

(IEC 60909-0, 2016)

(IEC)

Short-circuit currents in three-phase a.c.

systems - Part 0: Calculation of currents

(IEEE 80, 2000)

(IEEE)

IEEE Guide for Safety in AC Substation

Grounding Standard

(IEEE 605, 2008)

(IEEE)

IEEE Guide for Bus Design in Air

Insulated Substations Standard

(TB601, 2014)

(Cigre)

Guide for thermal rating calculations of

overhead lines Technical Brochure

(Morgan, Finlay, & Derrah, 2000)

IEE Proceedings science,

measurement and technology, 147

(4), 169-171.

(New formula to calculate the skin effect in

isolated tubular conductors at low

frequencies)

Technical Journal

3 Legislation, regulations, rules, and codes

Legislation, regulations, rules, and codes

(National Electricity Rules, 2015) (AEMC)

(Queensland Electricity Act, 1994) (Qld Govt)

(Queensland Electricity Regulation, 2006) (Qld Govt)

(Queensland Electrical Safety Regulation, 2013) (Qld Govt)

(Queensland Work Health and Safety Act, 2012) (Qld Govt)





4 Definitions, acronyms, and abbreviations

4.1 Definitions

For the purposes of this standard, the following definitions apply:

Term Definition

Albedo The incident solar radiation reflected from the ground. (TB601, 2014)

Cantilever A long projection supported at only one end.

Fixed Support Support which does not permit angular movement of the conductor at the

supported point. (AS 3865, 1991)

Emissivity The ratio of power radiated by a material body to the power radiated by a

blackbody at the same temperature. (IEEE 605, 2008)

Load The value of a force appropriate to an action.

Shall Indicates that a statement is mandatory.

Should Indicates a recommendation advisable (non-mandatory).

Simple Support Support which permits angular movement of the conductor. (AS 3865, 1991)

Solar absorptivity The ability of a conductor to absorb heat from solar radiation. (IEEE 605, 2008)

4.2 Acronyms and abbreviations

The following abbreviations and acronyms appear in this standard.

Term, abbreviation or

acronym

Definition

AC Alternating Current

AAC All-Aluminium Conductor

AAAC All-Aluminium Alloy Conductor

DC Direct Current





5 General procedure

The procedure for the design of a busbar comprises a series of steps listed below and, elaborated

on in the subsequent clauses:

1. Obtain busbar design requirements.

2. Evaluate conductor size for current ratings.

3. Determine busbar mechanical design.

4. Complete required documentation.

6 Design requirements

This section provides the required parameters for design and mechanical evaluation of busbar,

insulators, and supports. The following parameters are critical for design of both rigid and flexible

busbar arrangements:

Busbar operating voltage.

Maximum load current.

Maximum short-circuit current.

Busbar operating temperature.

Location of the substation.

Electrical and safe working clearances.

Span length between supports.

Electrical connections.

Mechanical loads on the busbar and support insulators: pull of connections etc.

7 Evaluation of conductor size for current rating

Conductor continuous current rating calculations are based on the methods presented in Cigre

Technical Brochure: Guide for thermal rating calculations of overhead lines (TB601, 2014).

Conductor short time current rating calculations are based on the methods used in IEEE Guide of

safety in AC substation grounding (IEEE 80, 2000). Detailed rating formulas and assumptions are

presented in Annex A.

7.1 Basic data and standard conditions

Current ratings given in Table 9

Table 9, Table 10, Table 11,Table 12 and Table 13 are calculated from the following standard site

conditions and conductor properties, they have been utilised to give a conservative conductor

continuous current rating.

Table 1 Standard site conditions

Site Condition Value

Region Ergon Energex

Summer noon (day 356) ambient temperature 40˚C 35˚C

Winter 6pm (day 172) ambient temperature 20˚C 15˚C





Site Condition Value

Busbar & connections continuous operating temperature 90˚C 90˚C

Busbar short time (fault) temperature (AS 2067, 2008) 250˚C 250˚C

Wind speed (NA000000R100, 2015) 1m/s 0.5m/s

Wind yaw angle to conductor axis

(NA000000R100, 2015) 45˚ 90˚

Site latitude (Tropic of Capricorn) -23.5˚ -23.5˚

Site albedo (reflectance) of ground surface

(NA000000R100, 2015) 0.2 grass 0.2

Site height above sea level 1000m 1m

Clearness Ratio 1.0 1.0

Conductor azimuth to the sun (degrees from north-south) 90˚ 90˚

Table 2 Aluminium 6101-T6 conductor electrical properties

Conductor property Value

DC Volume resistivity at 20˚C

(Aluminium Electrical Conductor Handbook, 1989) 0.031347×10

-6 Ω/m

Constant mass temperature coefficient of resistance at 20˚C

(Aluminium Electrical Conductor Handbook, 1989) 0.00363 per ˚C

Thermal capacity per unit volume

(TCAP) (IEEE 80, 2000) 2.6 J/cm

3

Solar absorption coefficient – new

(less than 1 year old) (NA000000R100, 2015) 0.5

Emissivity coefficient – new

(less than 1 year old) (NA000000R100, 2015) 0.5

Table 3 AAAC 1120 conductor electrical properties


DC Volume resistivity at 20˚C 0.0293x10-6

Ω/m

Constant mass temperature coefficient of resistance at 20˚C (AS 1531, 1991) 0.0039 per ˚C

Table 4 AAC conductor electrical properties



Ω/m






Table 5 Bare copper hard drawn stranded conductor properties



Ω/m


Table 6 AAAC 1120 stranded conductor properties (AS 1531, 1991)

Conductor

Name

Nominal overall

diameter (mm)

Cross sectional

area (mm2)

DC resistance at

20˚C (Ω/m)

Combined skin and

proximity effect

Neon 18.8 210 14.2 ×10-5

1.00

Oxygen 23.8 337 8.84 ×10-5

1.00

Sulphur 33.8 673 4.44 ×10-5

1.03

Twin Oxygen 47.6 674 4.42 ×10-5

1.00

Twin Sulphur 67.6 1346 2.22 ×10-5

1.04

Table 7 AAC stranded conductor properties (AS 1531, 1991)

Conductor

Name

Nominal overall

diameter (mm)

Cross sectional

area (mm2)

DC resistance at

20˚C (Ω/m)

Combined skin and

proximity effect

Mars 11.3 77.3 37 ×10-5

1.00

Saturn 21 262 11 ×10-5

1.00

Triton 26.3 409 7.06 ×10-5

1.01

Uranus 29.3 506 5.72 ×10-5

1.02

Venus 33.8 673 4.29 ×10-5

1.04

Table 8 Bare copper hard drawn stranded conductor properties (AS 1746, 1991)

Conductor Nominal overall

diameter (mm)

Cross sectional

area (mm2)

DC resistance at

20˚C (Ω/m)

Combined skin and

proximity effect

19/2.14 10.5 68.3 27.5 ×10-5

1.00

19/2.75 13.8 113 16 ×10-5

1.00

37/2.50 17.5 182 9.96 ×10-5

1.00

37/3.00 21 262 6.91 ×10-5

1.01

61/2.75 24.8 500 5 ×10-5

1.03

If there is a requirement to rate the conductor outside the values listed in Table 9

Table 9, Table 10, Table 11,Table 12 and Table 13, the above conditions and properties can be

obtained from site specific conditions and conductor manufacturers.





7.2 Skin effect

Skin effect coefficients have been calculated for all conductors listed in this standard in accordance

with the methods used in IEC Electric cables – calculation of the current rating – Part 1-1: Current

rating equations (100% load factor) and calculation of losses – General (IEC 60287-1-1, 2006) and

(Morgan, Finlay, & Derrah, 2000). Skin effect is negligible for all tubular and stranded conductors

listed within this standard with the exception of sulphur stranded conductor. A skin effect coefficient

of 1.03 has been used in Table 11 and Table 12 in calculating the current rating of sulphur

conductor. For detailed calculation of skin effect refer to Annex A.

7.3 Proximity effect

Proximity effect coefficients have been calculated by the method used in IEC Electric cables –

calculation of the current rating – Part 1-1: Current rating equations (100% load factor) and

calculation of losses – General (IEC 60287-1-1, 2006). A proximity effect coefficient of 1.01 has

been taken in the calculation of twin sulphur current rating listed in Table 11 and Table 12. The

spacing between twin conductors is assumed to be 114mm. For detailed calculation of proximity

effect refer to Annex A.

7.4 Corona inception voltage

The conductor corona inception voltage shall be above the installation highest operation voltage.

All tubular conductors provided in this standard have a corona inception voltage well above 220kV.

All stranded conductors provided in this standard have a corona inception voltage above 132kV

when installed as a singular conductor per phase. Refer to Annex A if design requires the

installation of non-standard conductors or higher corona inception voltages.

7.5 Rating tables for standard sizes of busbars

Current ratings for a range of standard busbar sizes, not including connections, are listed in Table 9

Table 9, Table 10, Table 11, Table 12 and Table 13. In order to minimise the number of fittings,

these standard sizes should be used unless there is a special requirement to use a non-standard

conductor. If non-standard conductors are to be installed refer to Annex A for calculation of current

ratings. During design, busbar connection types shall be considered as they limit current and may

affect the overall busbar rating.

Table 9 Continuous and short time current ratings of 6101-T6 tubular busbars

Busbar

size Dia x

wall (mm)

CSA

(mm2)

Standard

Conditions

Continuous Current Rating (A)

(Operating temperature 90˚C)

Short time current

rating (kA)

(at 250˚C)

Summer Noon Winter 6pm 1sec 3sec

40 x 3 348 Energex 827 1019 23 13

80 x 4 955 Energex 1622 2042 89 51.4

100 x 4 1206 Ergon 1866 2353 112 64

100 x 6 1772 Ergon 2261 2852 165 95





Busbar

size Dia x

wall (mm)

CSA

(mm2)

Standard

Conditions



Short time current

rating (kA)

(at 250˚C)

125 x 6 2243 Ergon 2719 3461

209 120 Energex 2775 3556

Table 10 Continuous and short time current ratings of copper tubular busbars

Busbar

size Dia x

wall (mm)

CSA

(mm2)

Standard

Conditions



Short time current

rating (kA)

(at 250˚C)


25.4 x

1.63 122

Energex 578 705 15 8

38.1 x

1.63 187

Energex 790 937 23 13

50.8 x

4.88 704

Energex 1646 2042 86 50

Table 11 Continuous and short time current ratings of stranded busbars

Conductor

Name

Wind

Speed

(m/s)



Short time current rating

(kA)

(at 250˚C)


Neon 1 562 736 20 11

Oxygen 1 752 997 32 18

Sulphur 1 1134 1535 64 37

Twin

Oxygen 1 1504 1994 64 37

Twin

Sulphur 1 2258 3054 128 74

Table 12 AAC Continuous and short time current ratings of stranded busbars

Conductor

Name

Wind

speed

(m/s)



Short time current rating (kA)

(at 250˚C)


Mars 0.5 309 371 7 4

Saturn 0.5 658 796 24 14





Conductor

Name

Wind

speed

(m/s)




(at 250˚C)

Triton 0.5 867 1054 38 22

Uranus 0.5 989 1205 48 27

Venus 0.5 1182 1444 64 37

Table 13 AAC Continuous and short time current ratings of stranded copper busbars

Conductor

Wind

speed

(m/s)




(at 250˚C)


19/2.14 0.5 358 428 8 4

19/2.75 0.5 500 601 13 8

37/2.50 0.5 671 809 22 12

37/3.00 0.5 841 1018 32 18

61/2.75 0.5 1029 1250 44 25

8 Rigid busbar mechanical design

This section provides an outline of the mechanical loads to consider in the design of a busbar, also

providing permissible busbar span lengths for standard conductors listed in Section 7. If non-

standard conductors or span lengths are required, refer to Annex B for methods of calculation.

Mechanical design is based on allowable stress design in accordance with Standards Australia

Aluminium structures Part 2: Allowable stress design (AS/NZS 1664.2, 1997).

8.1 Loads on rigid busbar and support insulators

The loads to consider in the mechanical busbar design are the permanent loads and exceptional

loads. It should be noted that the loads and their intensity can vary according to substation location

and application requirements.

8.1.1 Permanent loads

The permanent loads that shall be considered during design are:

Dead loads: includes the weight of the structure, the weight of components and connections of

the bus and the weight of an inserted anti-vibration conductor. When determining the portion of

the busbar to be supported in a multiple support bus section the following has been applied to

simplify calculations:

o The inner insulators support half of the adjacent spans on either side.

o The outer insulators support half of the adjacent span and the overhang portion.

Tension loads from strained conductors.





Thermal loads: if a section of busbar has two or more fixed supports, there will be a

longitudinal load acting on the fixed supports due to thermal expansion of the busbar caused

by short-circuit current. In calculating the thermal load, the insulator support posts/structure

can be considered as having infinite stiffness. This conservative approach will provide some

built-in safety factor for the insulators. To eliminate thermal load, a common practice is use of

only one fixed support in a busbar section, the remaining is of simple type.

8.1.2 Exceptional loads

The exceptional loads that shall be considered during design are:

Wind loads: loads on busbars are considered as uniformly distributed acting horizontally.

Loads on insulators are considered as concentrated acting horizontally at the middle.

Electromagnetic loads (short-circuit loads): for flat configuration busbars this load is considered

as uniformly distributed acting horizontally. The lateral deflection of the busbar creates an

accompanying longitudinal deflection of the busbar support insulators. This longitudinal load

will vary from a minimum at centre of the bus system to a maximum at the end support. This

load could be minimised by using no more than one fixed support in a busbar section.

Other exceptional loads include earthquake and ice loads, in Energy Queensland’s geographical

area earthquakes and icing conditions seldom occur and therefore can be neglected.

Formulae for calculating various types of load are given in Annex B.

8.2 Busbar mechanical data

8.2.1 Basic data

Evaluation of busbar and insulator mechanical strength should be based on the following physical

and mechanical properties.

Table 14 Aluminium 6101-T6 conductor mechanical properties (Aluminium Electrical Conductor

Handbook, 1989)


Specific gravity 2.703

Coefficient of linear expansion (1/°C) 23 x 10-6

Ultimate tensile strength MPa 200*

0.2% proof stress MPa 172*

Modulus of Elasticity MPa 68,950

*These are minimum values, typical values are slightly higher.

Table 15 Copper conductor mechanical properties


Specific gravity 8.92

Coefficient of linear expansion (1/°C) 17 x 10-6

Ultimate tensile strength MPa 405*

0.2% proof stress MPa 200*

Modulus of Elasticity MPa 124000

*These are minimum values, typical values are slightly higher.





8.2.2 Busbar mechanical strength

Evaluation of the busbar mechanical strength should be based on the following criteria:

The load deflection is important from an appearance standpoint. Deflection should be limited to

30mm or 1/150 of the span length, whichever is smaller.

Maximum fibre stress in the busbar due to maximum resultant load on the busbar should not

exceed 50% of the 0.2% proof stress of the busbar material. This allows for reduction in

strength due to welds. The stress in a rigid busbar should be evaluated for the worst case of

the load combination: dead load + wind load + short-circuit load.

8.2.3 Support insulator mechanical strength

Bending moments on the support insulators should be evaluated for the worst case of load

combination: busbar dead load + wind load on conductor and insulator + short-circuit load +

thermal expansion load.

Dead weight, wind load on conductors, short-circuit load on the busbar and thermal expansion load

if applicable will act at the union of the conductor and insulator as a concentrated load. Wind load

on the insulator is considered as concentrated and acts at the middle.

Outermost insulators should be checked for torsional strength by performing calculations using the

formula in Annex B.4.

Standard porcelain insulators are of designation C6-xxx of Standards Australia Insulators –

ceramic or glass – station post for indoor and outdoor use – voltages greater than 1000Va.c Part 1:

Characteristics (AS 4398.1, 1996). They shall have a cantilever strength of 6kN, and a minimum

torsional strength in accordance with Section 3 of AS 4938.1.

8.2.4 Evaluation of natural frequency

Natural frequency of each span should be calculated separately with the appropriate choice of end

fixing supports. The formulae relating to natural frequency are given in Annex C.

The natural frequency of the busbar shall not be:

Similar to the frequency of eddy shedding.

Similar to the natural frequency of the insulator/post support unit as the busbar could be

subjected to very high amplification of ground motion.

Similar to the power frequency.

Wind induced vibration can be attenuated by placing a continuous length of stranded conductor

loosely inside the tubular busbar. The stranded conductor shall be restrained at one end to prevent

migration within the busbar. The damping cable used shall be between 10% and 33% of the bus

conductor weight and be the made of the same material to prevent galvanic corrosion. Audible

noise generated by the stranded damping cable inside the bus conductor should be taken into

account during design.

8.2.5 Busbar end supports

End supports for a busbar span range from simple to fixed. At least one simple end connection

shall be installed on each span to ensure the effects of thermal expansion are minimised. If the end

supports of the busbar are unknown, simple-simple end supports should be assumed as this is the

most conservative in span calculation.





8.3 Maximum busbar span length based on allowable vertical deflection

The allowable vertical deflection of the busbar conductor shall be limited to 30mm or 1/150 of the

span length, whichever is the smaller. The vertical deflection is measured from the busbar

attachment point at the insulators to the mid span point. For the case with an inserted anti vibration

conductor, a conductor weight of 19/3.75 AAAC (Neon) has been used in this calculation. It is

assumed that the conductor is inserted for the whole length of the busbar. Table 16 lists the

maximum busbar span lengths based upon allowable vertical deflection.

Table 16 Maximum busbar span length with 30mm vertical deflection at no load

Busbar

size

(mm)

Maximum span length (m)

End supports

Simple-simple Simple-fixed Cantilever

No AAAC With AAAC No AAAC With AAAC No AAAC With AAAC

40 x 3 5.7 4.7 7.1 5.9 3.2 2.7

80 x 4 8.2 7.5 10.2 9.3 4.6 4.2

100 x 4 9.1 8.7 11.3 10.9 5.1 4.9

100 x 6 9.0 8.7 11.2 10.9 5.1 4.9

125 x 6 10.1 9.9 12.6 12.3 5.7 5.6

8.4 Maximum busbar span lengths based on conductor allowable fibre stress

Maximum busbar span lengths based on conductor allowable fibre stress shown in Table 17 for

various regions, exposure conditions and types of support are calculated based on the following

assumptions:

An anti-vibration 19/3.75 (Neon) AAA conductor is inserted. The results will not be noticeably

different from those without an inserted conductor, especially where wind and short-circuit

horizontal loads are high.

The short-circuit levels and spacing between phases for various voltages are indicated in

Annex B.

Wind speeds at various regions and terrain conditions are given in Annex B.

Wind load and short-circuit load act simultaneously.

An allowable stress design factor of safety of 1.65 is applied (AS/NZS 1664.2, 1997).

Three-phase R.M.S. short-circuit current is 20 kA, refer to Annex B if the design site has a

higher short-circuit value.

Site X/R ratio is 5.5 refer Annex B if the design site has a higher X/R value.

The exposure categories listed in Table 17 are defined by Standards Australia Structural design actions Part 2: Wind actions (AS/NZS 1170.2) with exposure category 2 deemed as the most extreme. If exposure conditions are unknown use values of exposure category 2 (shaded cells in Table 17).

Table 17 Maximum busbar spans based on conductor allowable fibre stress

Syst.

Volt

(kV)

Busbar

size

(mm)


End Supports

Simple-Simple and Simple-Fixed Cantilever

Region A (non-cyclonic) and exposure category

A2 A3 A4 A2 A3 A4

33 40 x 3 2.7 2.7 2.7 1.3 1.3 1.3

80 x 4 6.1 6.2 6.3 3 3.1 3.1





66 100 x 4 8.7 8.9 9.2 4.3 4.4 4.6

100 x 6 10.3 10.6 10.8 5.1 5.3 5.4

110 &

132

100 x 4 9.7 10.0 10.3 4.8 5.0 5.1

100 x 6 11.5 11.8 12.2 5.7 5.9 6.1

125 x 6 14.2 14.6 15.1 7.1 7.3 7.5

Region B (non-cyclonic intermediate) and exposure category

B2 B3 B4 B2 B3 B4

33 40 x 3 2.5 2.6 2.6 1.2 1.3 1.3

80 x 4 5.7 5.8 6 2.8 2.9 3

66 100 x 4 8.0 8.2 8.5 4.0 4.1 4.2

100 x 6 9.5 9.8 10.1 4.7 4.9 5.0

110 &

132

100 x 4 8.8 9.1 9.4 4.3 4.5 4.7

100 x 6 10.4 10.8 11.2 5.1 5.4 5.6

125 x 6 12.6 13.1 13.8 6.3 6.6 6.9

Region C (cyclonic) and exposure category

C2 C3 C4 C2 C3 C4

33 40 x 3 2.4 2.5 2.6 1.2 1.2 1.3

80 x 4 5.5 5.6 5.8 2.7 2.8 2.9

66 100 x 4 7.6 7.9 8.1 3.8 3.9 4.0

100 x 6 9.0 9.3 9.6 4.5 4.6 4.8

110 &

132

100 x 4 8.0 8.4 8.9 4.0 4.2 4.4

100 x 6 9.5 10.0 10.5 4.7 5.0 5.3

125 x 6 11.7 12.2 12.9 5.8 6.1 6.4

8.5 Maximum busbar span length based on insulator cantilever strength

Maximum span lengths based on insulator cantilever strength shown in Table 18 for various

regions and exposure conditions are calculated based on the assumptions made in Section 8.4

with the following additions:

Insulator cantilever strength is 6kN.

No torsional strength of the insulators is considered in Table 18, however Appendix B4

includes formulae for calculation of torsional load for a fixed/simple beam.

Insulator dimensions are to Standards Australia Insulators – ceramic or glass – station post for

indoor and outdoor use – voltages greater than 1000Va.c Part 1: Characteristics (AS 4398.1,

1996). Surface area of an insulator exposed to wind pressure is taken at the produce of its

given height and diameter.

No thermal load and longitudinal load are taken into account.

An allowable stress design strength reduction factor of 2 is used to allow for the effect of the

dynamic nature of short-circuit load on the support insulator.

Table 18 Maximum busbar spans based on insulator cantilever strength

System

volt

(kV)

Busbar

size

(mm)

Maximum permissible span length (m)

Region and exposure category

A2 A3 A4 B2 B3 B4 C2 C3 C4

33 40 x 3 8.2 8.4 8.6 7.3 7.6 7.9 6.7 7.1 7.4

80 x 4 7.0 7.3 7.6 6.1 6.4 6.8 5.5 5.9 6.2

66 100 x 4 9.0 9.5 10.1 7.3 7.9 8.5 6.4 7.0 7.6

100 x 6 9.0 9.5 10.1 7.3 7.9 8.5 6.4 7.0 7.6

110 & 100 x 4 10.6 11.5 12.6 7.7 8.7 9.7 6.2 7.1 8.2





132 100 x 6 10.6 11.5 12.6 7.7 8.7 9.7 6.2 7.1 8.2

125 x 6 9.9 10.8 11.8 7.3 8.2 9.1 6.0 6.8 7.7

The above span lengths are applicable to multiple-span busbars, for a single span the length is

double. If exposure conditions are unknown use values of exposure category 2 (shaded cells in

Table 18)

9 Documentation required

Documentation on the design of a busbar shall take the form of a design report and is to include,

but not be limited to the following:

Values for the critical design factors, the methods used and assumptions made in

ascertaining these values.

Details on calculations used in the design process.

A drawing or series of drawings detailing the layout of busbars.





Annex A Formulae and assumptions for calculation of conductor

current ratings

A.1. Formulae Used

A.1.1. Continuous current rating (I)

The formulae used for the calculation of continuous current carrying capacity are presented in

Cigre Technical Brochure: Guide for thermal rating calculations of overhead lines (TB601, 2014).

Conductor continuous current rating is calculated by the equation below:

√[

]

Where:

I = The continuous current rating of the conductor (A)

PR = Power dissipation due to radiation of 1 meter of conductor (W/m) refer A.1.1.1

PC = Power dissipation due to convection of 1 meter of conductor (W/m) refer A.1.1.2

PS = Power gained through sFreyolar radiation of 1 meter of conductor (W/m) refer A.1.1.3

R = AC Resistance of one meter of conductor (Ω) refer A.1.1.4

A.1.1.1. Power dissipation due to radiation of 1 meter of conductor (PR)

Where:

D = Diameter of the conductor (mm)

σB = Stefan-Boltzmann constant 5.67x10-8

εs = Solar absorptivity of the conductor surface (0.5 new (less than 1 year old), 0.85 weathered

(more than one year old))

Ts = Conductor operating temperature (˚C)

Ta = Site ambient Temperature (˚C)

A.1.1.2. Power dissipation due to convection of 1 meter of conductor (PC)

Where:


Ta = Site ambient temperature (˚C)

λf = Thermal conductivity of the air (W/k·m)





Tf = Temperature of the air film in contact with the conductor surface (˚C)

Nuδ = Nusselt number dependent upon wind direction (smooth conductors)

Nuδ = Nusselt number dependent upon wind direction (stranded conductors)

δ = Wind angle of attack relative to the conductor (deg)

Nu90 = Nusselt number at 90˚ wind angle of attack relative to the conductor

B = constant dependent upon Re (see Table 19)

n = constant dependent upon Re (see Table 19)

Re = Reynolds number

V = Wind speed (m·s-1)

D = Diameter of the conductor (mm)

vf = Kinematic viscosity of the air film (m2·s-1)

µf = Dynamic viscosity of air film (kg·m-1·s-1)

γ = Mass density of air film

y = Site height above sea level (m)

Table 19 Coefficients dependant on the value of Re

Smooth Conductors Stranded Conductors

Rs ≤ 0.05

Stranded Conductors

Rs > 0.05

Re B n Re B n Re B n

35 –

5000 0.583 0.471

100 -

2650 0.641 0.471

100 –

2650 0.641 0.471

5000 -

50000 0.148 0.633

2650 -

50000 0.178 0.633

2650 -

50000 0.048 0.800

50000 -

200000 0.0208 0.814

Where:





D = Conductor diameter (mm)

d = Diameter of wires in the outermost layer of the conductor (mm)

A.1.1.3. Power gained through solar radiation of 1 meter of conductor (PS)

Where:

αs = Solar absorptivity of the conductor surface (0.5 new (less than one year old), 0.85 weathered

(greater than one year old))

D = Conductor diameter (mm)

IT = Global solar radiation (W·m-2)

(

) (

)

F = Albedo or ground reflectance (0.2 grass, 0.3 sand)

IB(y) = Direct solar radiation intensity adjusted to site height above sea level (W·m-2)

[ (

)]

y = Site height above sea level (m)

IB(0) = Direct solar radiation intensity at sea level (W·m-2)

Ns = Atmosphere clearness ratio (1.0 for a standard atmosphere, < 0.5 for cloudy or overcast sky)

Hs = Solar altitude (deg)

φ = Site latitude, negative for southern hemisphere (deg)

δs = Solar declination

[

]

N* = Day of the year

Z = Hour angle of the sun (deg)

Time = Time of the day given in hours (0 – 24)

ɳ = Angle of the solar beam with respect to the conductor axis (deg)

γc = Azimuth of the conductor positive from south through west (deg)

γs = Azimuth of the sun positive from south through west (deg)





(

)

Id = Diffuse solar radiation intensity (W·m-2)

A.1.1.4. AC Resistance of 1 meter of conductor (R)

( )

α20 = Conductor material constant mass temperature coefficient of resistance at 20˚C (specified by

the conductor supplier)


Sk = Combined skin and proximity effect refer Annex A.2.

Rdc(20) = The DC resistance of the conductor at 20˚C (specified by the supplier for stranded

conductors) for tubular conductors see the following formula (Ω·m-1)

20 = Conductor material resistivity at 20˚C (Ω·m)

D = Conductor diameter (m)

D1 = Tubular conductor inner diameter (m)

A.2. Combined proximity effect and skin effect

The formulae used in the calculation of conductor combined skin and proximity effect are

presented in in IEC Electric cables – calculation of the current rating – Part 1-1: Current rating

equations (100% load factor) and calculation of losses – General (IEC 60287-1-1, 2006) and

(Morgan, Finlay, & Derrah, 2000). Combined skin and proximity effect for stranded conductor is

calculated by the formulae below:

Where:

Sk = Combined skin and proximity effect

Ys = Conductor skin effect factor

xs = Skin effect variable

ks = Skin effect coefficient equal to 1 for conductors listed in this standard

Rdc =Conductor DC resistance at operating temp (Ω·m-1) refer A.1.1.4

f = Frequency (Hz)

Yp = Conductor proximity effect factor





(

)

dc = Conductor diameter (mm)

S = Distance between conductor axis (mm)

xp = Proximity effect variable

kp = Proximity effect coefficient equal to 1 for conductor listed in this standard

Skin effect factors for tubular conductor are calculated by the following formulae presented in

(Morgan, Finlay, & Derrah, 2000):

Where:

√

t = Conductor tube thickness (mm)

D2 = Conductor diameter (mm)

f = Frequency (Hz)

Rdc =Conductor DC resistance (Ω·m-1) refer A.1.1.4





A.3. Calculation of corona onset

The formulae for the calculation of conductor corona onset gradient and conductor maximum

surface voltage gradient are presented in IEEE Guide for bus design in air insulated substations

(IEEE 605, 2008). Designers shall ensure the conductor selected for application has a corona

onset gradient that is greater than the conductor maximum surface voltage gradient as calculated

below.

A.3.1. Conductor corona onset gradient

√

Where:

Ec = Corona onset gradient (kV·cm-1)

E0 = Empirical constant (30kV·cm-1 peak value or 21.1kV·cm-1 rms value)

C = Empirical constant (0.301cm-1)

m = Conductor irregularity factor (0.7)

(0.2 for extreme irregularities or deposition to 0.85 clean, common range of 0.6 to 0.85)

rc = Conductor outside radius (cm)

Da = Relative air density

(

)

T = Site ambient temperature (40˚C)

T0 = Reference temperature value (25˚C)

PP0 =Reference pressure value

A = Site altitude (1.0 km)

A.3.2. Conductor maximum voltage gradient

A.3.2.1. Three phase single conductors

⁄

Where:

Em = Maximum voltage gradient at the surface of the conductor (kV·cm-1)

d = Conductor diameter (cm)

Ea = Average voltage gradient at the surface of the conductor (kV·cm-1)





V1 = 110% line to ground voltage (kV)

he = Equivalent distance from centre of the conductor to the ground plane for the three phases (cm)

√

h = conductor centre distance from the ground (cm)

D = Phase to phase spacing for the three phases (cm)

A.3.2.2. Three phase bundle conductors

Em = Maximum voltage gradient at the surface of the conductor (kV·cm-1)

Ea = Average voltage gradient at the surface of the conductor (kV·cm-1)

(

)

V1 = 110% line to ground voltage (kV)

n = number of subconductors in bundle (2)

r = Conductor radius (cm)

he = Equivalent distance from centre of the conductor to the ground plane for the three phases (cm)

√

re = Equivalent single-conductor radius of bundle subconductors

s = Distance between subconductors (11.4 cm)

d = Conductor diameter (cm)

g = Bundle number constant (equal to 1 for bundles of 1, 2 and 3. And equal to 1.12 for bundles of

4)





A.4. Short time current rating

The conductor short time current ratings listed in Table 9 and Table 10 are calculated by the

methods presented in IEEE Guide of safety in AC substation grounding (IEEE 80, 2000). The

following formulae are used to calculate conductor short time current rating:

√(

) (

)

Where:

I = RMS current (kA)

Amm2 = Conductor cross sectional area (mm2)

TCAP = Thermal capacity per unit volume (2.6 J/cm3 for aluminium)

Tm = Conductor maximum allowable temperature (250˚C)

Tc = Conductor operating temperature (90˚C)

tc = Duration of fault current (1 or 3 seconds)

αr = Thermal coefficient of resistivity at the reference temperature 20˚C

r = Conductor resistivity at the reference temperature 20˚C (µΩ·cm)

K0 = Variable





Annex B Busbar mechanical strength and maximum span length

calculations

B.1. Data used in calculation of maximum span lengths

The following tables list the data and factors used in the calculation of the loads applied to a rigid

busbar structure.

Table 20 Busbar wind load calculation data Standards Australia Structural design actions Part 2:

Wind actions (AS/NZS 1170.2, 2011)

Region Region A

(non-cyclonic)

Region B

(non-cyclonic)

Region C

(cyclonic)

Exposure &

Terrain category 2 3 4 2 3 4 2 3 4

Regional wind

speed VR (m/s) 48 48 48 63 63 63 73 73 73

Wind direction

multiplier (Md) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Terrain/height

multiplier (Mzcat) 0.91 0.83 0.75 0.91 0.83 0.75 0.91 0.83 0.75

Design wind

speed Vdes (m/s) 43.7 39.8 36.0 57.3 52.3 47.3 66.4 60.6 54.7

Boundaries of regions A, B and C are indicated in Figure 1.

Table 21 Terrain category descriptions as per Standards Australia Structural design actions Part 2:

Wind actions (AS/NZS 1170.2, 2011)

Category Description

Category 2

Open terrain, including grassland, with well-scattered obstructions having heights

generally from 1.5m to 5m, with no more than two obstructions per hectare, e.g.

farmland and cleared subdivisions with isolated trees and uncut grass.

Category 3

Terrain with numerous closely spaced obstructions having heights generally from

3m to 10m. The minimum density of obstructions shall be at least the equivalent of

a 10 house-size obstructions per hectare, e.g. suburban housing or light industrial

estates.

Category 4 Terrain with numerous large, high (10m to 30m tall) and closely-spaced

constructions, such as large city centres and well-developed industrial complexes.

Table 22 Standard short-circuit site data

System nominal voltage (kV) 66 110 & 132

Short-circuit level (kA) 25 25

X/R ratio 5.5 5.5

Spacing between phases (m) 1.8 2.6

If the design requires higher short-circuit or X/R values refer to B.6





Figure 1 Wind regions

Standards Australia Structural design actions Part 2: Wind actions (AS/NZS 1170.2, 2011)





B.2. Maximum span length based on allowable deflection

The formulae used for the calculation of busbar maximum span based on allowable deflection are

presented in IEEE Guide for bus design in air insulated substations (IEEE 605, 2008). Busbar

maximum span based on allowable deflection is calculated by the equations below:

B.2.1. Simple-simple end supports (Lvss)

(

)

⁄

Where:

Lvss = The simple-simple busbar allowable span based on the vertical deflection limit (m)

Y = The Young’s modulus of the conductor material (N/m2)

δmax = The vertical deflection limit (m)

J = The bending moment of inertia of the conductor cross section (m4)

(

)

Do = The conductor outside diameter (m)

Di = The condutor inside diameter (m)

FG = The conductor gravitational weight by unit length (N/m)

(

)

wc = The specific weight of the conductor material (N/m3)

Fi = The anti-vibration conductor gravitational weight by unit weight (N/m)

wic = The anti-vibration conductor unit weight (kg/m)

B.2.2. Simple-fixed end supports (Lvsf)

(

)

⁄

Where:

Lvsf = The simple-fixed busbar allowable span based on the vertical deflection limit (m)

(For description and calculation of figures not listed see B.2.1)





B.2.3. Busbar maximum cantilever span based on allowable deflection (Lvc)

(

)

⁄

Where:

Lvc = The busbar allowable cantilever span based on the vertical deflection limit (m)

(For description and calculation of figures not listed see B.2.1)

B.3. Maximum span length based on conductor allowable fibre stress

The formulae used for the calculation of busbar maximum span based on conductor allowable fibre

stress are presented in IEEE Guide for bus design in air insulated substations (IEEE 605, 2008).

Busbar maximum span based on conductor allowable fibre stress is calculated by the equations

below:

B.3.1. Simple-simple or simple-fixed end supports (LSs)

√

Where:

LSs = The allowable busbar span base on the conductor maximum fibre stress simple-simple or

simple-fixed end supports (m)

σallowable = The allowable stress of the conductor material (N/m2)

Ps = The conductor material 0.2% proof stress (Mpa) refer 8.2.1

SF = The allowable stress design safety factor, equal to 1.65


J = The bending moment of inertia of the conductor cross section (m4)

(

)

Di = The conductor inside diameter (m)

FT = The total load acting on the conductor by unit length (N/m) refer B.3.3





B.3.2. Maximum busbar cantilever length based on allowable fibre stress

Maximum busbar cantilever length is calculated as half of the maximum allowable stress span

length with simple-simple end supports refer B.3.1.

B.3.3. Total load acting on the busbar conductor (FT)

The formulae used for the calculation of total load acting on the busbar conductor are presented in

IEEE Guide for bus design in air insulated substations (IEEE 605, 2008). Total load acting on the

busbar conductor is calculated by the equations below:

√

Where:

FGtotal = The combined busbar conductor and anti-vibration conductor gravitational weight by unit

length (N/m) refer B.3.3.1

Fw = The wind load by unit length (N/m) refer B.3.3.2

Fsc = The short-circuit mechanical load by unit length (N/m) refer B.3.3.3

B.3.3.1. Combined busbar and anti-vibration conductor gravitational weight (FGtotal)

Where:

Fg = The busbar conductor gravitational weight by unit length (N/m)

(

)

wc =The specific conductor weight (N/m3)

Fi = The anti-vibration conductor gravitational weight by unit length (N/m)

Wci = The anti-vibration conductor unit weight (kg/m)

Table 23 Typical anti-vibration conductor unit weight as per Olex 2015

Conductor Unit weight (wci)

Neon 0.576 kg/m

Oxygen 0.924 kg/m

Sulphur 1.86 kg/m





B.3.3.2. Wind load on busbar (Fw)

The formulae used for the calculation of wind load acting on the busbar conductor are presented in

Standards Australia Structural design actions Part 2: Wind actions (AS/NZS 1170.2, 2011). Wind

load is calculated by the equations below:

Where:

Ap = The density of air, taken as equal to 1.2 kg/m3

Cdyn = The structure dynamic response factor, equal to 1

Do = The outside diameter of the busbar conductor (m)

Az = The reference area factor, equal to 0.8

Vdes = The design wind speed (m/s), for standard values refer B.1

VR = The site regional wind speed (m/s) refer B.1

Md = The wind direction multiplier, equal to 1

Ms = The shielding multiplier, equal to 1

Mt = The topographic multiplier, equal to 1

Mzcat = The terrain/height multiplier, dependent upon site characteristics and location refer B.1

Cfig = The busbar conductor aero-dynamic shape factor

Kar = The aspect ratio correction factor for individual member loads, equal to 1

Ki = The angle of inclination correction factor, equal to 1

Cd = The drag force coefficient for the busbar conductor

As per (AS.NZS 1170.2:2011 Table E3)

B.3.3.3. Short-circuit mechanical load on busbar (Fsc)

The formulae used for the calculation of short-circuit mechanical load acting on the busbar

conductor is presented in IEC Short-circuit Currents - Calculation of Effects - Part 1: Definitions

and Calculation Methods (IEC 60865-1 Ed.3.0, 2011) and IEC Short-circuit currents in three-phase

a.c. systems – Part 0: Calculation of currents (IEC 60909-0, 2016). Short-circuit mechanical load is

calculated by the equations below:

√

Where:

Ik3 = The site maximum predicted r.m.s. 3-phase short-circuit current (A) refer B.1

D = The busbar phase spacing from conductor centres (m) refer (STNW3013, 2013)





k = The peak short-circuit constant

R = The site real impedance (Ω) refer B.1

X = The site reactive impedance (Ω) refer B.1

B.4. Maximum span length based on end insulators torsional strength (Lb)

The formulae used for the calculation of busbar maximum span based on insulator torsional

strength is presented by transforming the formulae for fixed - simple moment of a beam.

Where:

ꞷ = Fw + Fsc (N)

L = Length of Busbar (m)

T = Torque (Nm)

√

Where:

Lb = Maximum span length based on end insulators torsional strength (m)

T = maximum torsional strength of the insulator at the rated voltage (Nm)

Fw = Wind load on busbar (N)

Fsc = Short Circuit load on busbar (N)

B.5. Maximum span length based on insulator cantilever strength (Le)

The formulae used for the calculation of busbar maximum span based on insulator cantilever

strength are presented in IEEE Guide for bus design in air insulated substations (IEEE 605, 2008).

Busbar maximum span based on insulator cantilever strength is calculated by the equations below:

[

[ ]

]

Where:

Le = The maximum span length based on insulator cantilever strength (m)

Ht = The support insulator height (m)

Fis = The support insulator cantilever strength (N)


Fw = The wind load acting on the busbar by unit length (N/m) refer B.3.3.2





Fsc = The short-circuit load acting on the busbar by unit length (N/m) refer B.3.3.3

SF = The insulator cantilever safety factor, equal to 2 due to the dynamic effect of short-circuit load

Fwci = The wind load acting on the support insulator by unit length (N/m)

Ap = The density of air, taken as equal to 1.2 kg/m3

Cdyn = The structure dynamic response factor, equal to 1

Doi = The outside diameter of the support insulator (m)

Vdes = The design wind speed (m/s), for standard values refer B.1

VR = The site regional wind speed (m/s) refer B.1

Md = The wind direction multiplier, equal to 1

Ms = The shielding multiplier, equal to 1

Mt = The topographic multiplier, equal to 1

Mzcat = The terrain/height multiplier, dependent upon site characteristics and location refer B.1

Cfigi = The support insulator aero-dynamic shape factor

Kar = The aspect ratio correction factor for individual member loads, equal to 1

Ki = The angle of inclination correction factor, taken as equal to 1

Cdi = The drag force coefficient for the support insulator.

B.6. Maximum busbar spans with exceptional short-circuit current and X/R

values

The following tables list the maximum busbar spans for both the allowable stress method and

support insulator cantilever strength method for sites which have a short-circuit current rating or

X/R value greater than 20kA and 5.5. The span lengths have been calculated using worst case

wind speed and exposure values.

Table 24 Maximum busbar span based on allowable stress and varying short-circuit conditions.

(100x4mm busbar, 66kV, region C2)

3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 10.6 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5

5 10.4 10.3 10.3 10.2 10.2 10.2 10.2 10.2 10.2 10.2 10.2

7.5 10.0 9.9 9.8 9.8 9.8 9.8 9.8 9.7 9.7 9.7 9.7





10 9.6 9.4 9.4 9.3 9.3 9.2 9.2 9.2 9.2 9.2 9.2

12.5 9.1 8.9 8.9 8.7 8.7 8.7 8.6 8.6 8.6 8.6 8.6

15 8.6 8.4 8.3 8.2 8.1 8.1 8.0 8.0 8.0 8.0 8.0

17.5 8.1 7.9 7.7 7.6 7.6 7.5 7.5 7.5 7.4 7.4 7.4

20 7.6 7.4 7.2 7.1 7.1 7.0 7.0 6.9 6.9 6.9 6.9

22.5 7.2 6.9 6.7 6.6 6.6 6.5 6.5 6.5 6.4 6.4 6.4

25 6.8 6.5 6.3 6.2 6.1 6.1 6.1 6.0 6.0 6.0 6.0

27.5 6.4 6.1 5.9 5.8 5.8 5.7 5.7 5.6 5.6 5.6 5.6

30 6.0 5.7 5.6 5.5 5.4 5.3 5.3 5.3 5.3 5.2 5.2






(100x6mm busbar, 66kV, region C2)

3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5

5 12.3 12.2 12.2 12.2 12.2 12.1 12.1 12.1 12.1 12.1 12.1

7.5 11.9 11.8 11.7 11.7 11.6 11.6 11.6 11.6 11.6 11.6 11.6

10 11.4 11.2 11.1 11.1 11.0 11.0 11.0 10.9 10.9 10.9 10.9

12.5 10.8 10.6 10.5 10.4 10.3 10.3 10.3 10.2 10.2 10.2 10.2

15 10.2 10.0 9.8 9.7 9.7 9.6 9.6 9.5 9.5 9.5 9.5

17.5 9.6 9.4 9.2 9.1 9.0 8.9 8.9 8.9 8.8 8.8 8.8

20 9.1 8.8 8.6 8.5 8.4 8.3 8.8 8.8 8.8 8.8 8.2

22.5 8.5 8.2 8.0 7.9 7.8 7.8 7.7 7.7 7.6 7.6 7.6

25 8.0 7.7 7.5 7.4 7.3 7.2 7.2 7.2 7.1 7.1 7.1

27.5 7.6 7.2 7.0 6.9 6.8 6.8 6.7 6.7 6.7 6.6 6.6

30 7.1 6.8 6.6 6.5 6.4 6.4 6.3 6.3 6.2 6.2 6.2






(100x4mm busbar, 110/132kV, region C2)

3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 10.6 10.6 10.6 10.6 10.6 10.6 10.6 10.6 10.6 10.6 10.6

5 10.5 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4

7.5 10.2 10.2 10.1 10.1 10.1 10.1 10.1 10.0 10.0 10.0 10.0

10 9.9 9.8 9.8 9.7 9.7 9.7 9.6 9.6 9.6 9.6 9.6

12.5 9.5 9.4 9.3 9.3 9.2 9.2 9.2 9.2 9.1 9.1 9.1

15 9.1 9.0 8.9 8.8 8.7 8.7 8.7 8.7 8.6 8.6 8.6

17.5 8.7 8.5 8.4 8.3 8.3 8.2 8.2 8.2 8.1 8.1 8.1

20 8.3 8.1 8.0 7.9 7.8 7.8 7.7 7.7 7.7 7.6 7.6

22.5 7.9 7.7 7.5 7.4 7.4 7.3 7.3 7.2 7.2 7.2 7.2

25 7.5 7.3 7.1 7.0 6.9 6.9 6.8 6.8 6.8 6.8 6.8

27.5 7.1 6.9 6.7 6.6 6.5 6.5 6.5 6.4 6.4 6.4 6.4

30 6.8 6.5 6.4 6.3 6.2 6.1 6.1 6.1 6.0 6.0 6.0







3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5

5 12.4 12.4 12.4 12.4 12.4 12.4 12.4 12.3 12.3 12.3 12.3

7.5 12.1 12.1 12.0 12.0 12.0 12.0 12.0 11.9 11.9 11.9 11.9

10 11.7 11.7 11.6 11.5 11.5 11.5 11.5 11.4 11.4 11.4 11.4

12.5 11.3 11.2 11.1 11.0 11.0 10.9 10.9 10.9 10.9 10.9 10.8

15 10.8 10.7 10.5 10.5 10.4 10.4 10.3 10.3 10.3 10.3 10.2

17.5 10.3 10.1 10.0 9.9 9.8 9.8 9.7 9.7 9.7 9.7 9.6

20 9.8 9.6 9.5 9.4 9.3 9.2 9.2 9.1 9.1 9.1 9.1

22.5 9.3 9.1 8.9 8.8 8.7 8.7 8.6 8.6 8.6 8.6 8.5

25 8.9 8.6 8.5 8.3 8.2 8.2 8.1 8.1 8.1 8.1 8.0

27.5 8.4 8.2 8.0 7.9 7.8 7.7 7.7 7.6 7.6 7.6 7.6

30 8.0 7.8 7.6 7.4 7.4 7.3 7.2 7.2 7.2 7.2 7.1







3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 15.6 15.6 15.6 15.6 15.6 15.6 15.6 15.6 15.6 15.6 15.6

5 15.4 15.4 15.4 15.3 15.3 15.3 15.3 15.3 15.3 15.3 15.3

7.5 15.1 15.0 15.0 14.9 14.9 14.9 14.9 14.9 14.9 14.8 14.8

10 14.6 14.5 14.4 14.4 14.3 14.3 14.3 14.3 14.3 14.2 14.2

12.5 14.1 14.0 13.8 13.8 13.7 13.7 13.6 13.6 13.6 13.6 13.6

15 13.6 13.4 13.2 13.1 13.0 13.0 12.9 12.9 12.9 12.9 12.8

17.5 13.0 12.7 12.6 12.4 12.4 12.3 12.2 12.2 12.2 12.2 12.1

20 12.4 12.1 11.9 11.8 11.7 11.6 11.6 11.5 11.5 11.5 11.4

22.5 11.8 11.5 11.3 11.1 11.0 11.0 10.9 10.9 10.8 10.8 10.8

25 11.2 10.9 10.7 10.5 10.4 10.3 10.3 10.2 10.2 10.2 10.2

27.5 10.7 10.4 10.1 10.0 9.9 9.8 9.7 9.7 9.6 9.6 9.6

30 10.2 9.8 9.6 9.4 9.3 9.2 9.2 9.1 9.1 9.1 9.0





Table 29 Maximum busbar span based on insulator cantilever strength and varying short-circuit

conditions. (100x4 & 6mm busbar, 66kV, region C2, 6kN insulator cantilever strength)

3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 12.7 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6 12.6

5 12.1 12.0 12.0 11.9 11.9 11.9 11.9 11.8 11.8 11.8 11.8

7.5 11.3 11.1 11.0 10.9 10.9 10.8 10.8 10.8 10.8 10.7 10.7

10 10.3 10.1 9.9 9.8 9.7 9.7 9.6 9.6 9.5 9.5 9.5

12.5 9.3 9.0 8.8 8.6 8.5 8.5 8.4 8.4 8.3 8.3 8.3

15 8.3 8.0 7.7 7.5 7.4 7.4 7.3 7.3 7.3 7.2 7.2

17.5 7.3 7.0 6.7 6.6 6.5 6.4 6.3 6.3 6.2 6.2 6.2

20 6.5 6.1 5.9 5.7 5.6 5.5 5.5 5.4 5.4 5.3 5.3

22.5 5.7 5.4 5.1 5.0 4.9 4.8 4.7 4.7 4.6 4.6 4.6

25 5.1 4.7 4.5 4.3 4.2 4.2 4.1 4.1 4.0 4.0 4.0

27.5 4.5 4.2 3.9 3.8 3.7 3.6 3.6 3.6 3.5 3.5 3.5

30 4.0 3.7 3.5 3.4 3.3 3.2 3.2 3.1 3.1 3.1 3.0






conditions. (100x4 & 6mm busbar, 110/132kV, region C2, 6kN insulator cantilever strength)

3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4 10.4

5 10.1 10.1 10.0 10.0 10.0 10.0 9.9 9.9 9.9 9.9 9.9

7.5 9.6 9.5 9.4 9.4 9.4 9.3 9.3 9.3 9.3 9.3 9.3

10 9.0 8.9 8.7 8.7 8.6 8.6 8.5 8.5 8.5 8.5 8.5

12.5 8.3 8.1 8.0 7.9 7.8 7.7 7.7 7.7 7.6 7.6 7.6

15 7.6 7.4 7.2 7.1 7.0 6.9 6.9 6.9 6.8 6.8 6.8

17.5 6.9 6.7 6.5 6.3 6.2 6.2 6.1 6.1 6.1 6.0 6.0

20 6.3 6.0 5.8 5.6 5.5 5.5 5.4 5.4 5.4 5.3 5.3

22.5 5.6 5.4 5.1 5.0 4.9 4.9 4.8 4.7 4.7 4.7 4.7

25 5.1 4.8 4.6 4.5 4.4 4.3 4.3 4.2 4.2 4.2 4.1

27.5 4.6 4.3 4.1 4.0 3.9 3.8 3.8 3.7 3.7 3.7 3.7

30 4.1 3.9 3.7 3.6 3.5 3.4 3.4 3.3 3.3 3.3 3.3






conditions. (125x6mm busbar, 110/132kV, region C2, 6kN insulator cantilever strength)

3-Phase RMS

short-circuit

current (kA)


X/R Ratio

5.5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30

2.5 10.1 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0

5 9.8 9.7 9.7 9.7 9.6 9.6 9.6 9.6 9.6 9.6 9.6

7.5 9.3 9.2 9.1 9.1 9.0 9.0 9.0 9.0 9.0 9.0 9.0

10 8.7 8.6 8.5 8.4 8.3 8.3 8.3 8.2 8.2 8.2 8.2

12.5 8.1 7.9 7.7 7.6 7.6 7.5 7.5 7.5 7.4 7.4 7.4

15 7.4 7.2 7.0 6.9 6.8 6.8 6.7 6.7 6.6 6.6 6.6

17.5 6.7 6.5 6.3 6.2 6.1 6.0 6.0 5.9 5.9 5.9 5.9

20 6.1 5.8 5.6 5.5 5.4 5.4 5.3 5.3 5.2 5.2 5.2

22.5 5.5 5.2 5.0 4.9 4.8 4.8 4.7 4.7 4.6 4.6 4.6

25 5.0 4.7 4.5 4.4 4.3 4.2 4.2 4.1 4.1 4.1 4.1

27.5 4.5 4.2 4.0 3.9 3.8 3.8 3.7 3.7 3.6 3.6 3.6

30 4.1 3.8 3.6 3.5 3.4 3.4 3.3 3.3 3.2 3.2 3.2





B.7. Thermal Expansion Load

Thermal expansion in the busbar and load exerted on outermost fixed support insulators due to

thermal expansion can be calculated from the following formulae presented in (IEEE 605, 2008):

B.7.1. Thermal Expansion (ΔL)

( )

Where:

ΔL = The change in busbar span length due to thermal expansion (m)

α = The coefficient of linear expansion of the busbar conductor material (1/˚C)

Li = The busbar span length at the initial temperature (m)

Ti = The initial installation temperature (˚C)

Tf = The final installation temperature (˚C)

B.7.2. Load due to thermal expansion (FTE)

Where:

FTE = The thermal expansion load at the conductor’s ends (N)

Ac = The cross-sectional area of the busbar conductor (m2)

S = The thermal stress (N/m2)

E = The busbar conductor modulus of elasticity (N/m2)

ε = The strain under thermal expansion





Annex C Wind Induced Vibration and Resonance

C.1. General

Vibration of tubular busbar may be induced by steady light winds producing eddies, which are

alternately shed from opposite sides of the tube. The frequency of eddy shedding (fa) is related to

the wind velocity and tube diameter by the following formula presented in (IEEE 605, 2008):

Where:

C = The Strouhal number, equal to 0.19 for cylinders

V = The wind velocity (m/s)


When the frequency of the eddy shedding coincides with the natural frequency of the conductor,

wind induced vibration of the conductor may occur. To ensure there is an allowance for installation

variations the ratio of the eddy shedding frequency to the conductor natural frequency is outside

the range of 0.5 to √2 as below:

√

Where:

fa = The frequency of eddy shedding (Hz)

fb = The natural frequency of the conductor (Hz)

The natural frequency of a conductor span is dependent on the manner in which the ends are

supported and on the conductor’s length, mass, and stiffness. The natural frequency of a

conductor span (fb) is calculated as follows:

√

Where:

L = The conductor span length (m)

E = The modulus of elasticity of the conductor material (N/m2)

m = The mass per unit length of the conductor (kg/m)

K = The dimensionless constant accounting for the type of the conductor end support:

K = 1.00 for simple-simple

K = 1.25 for simple-fixed

K = 1.51 for fixed-fixed





J = The moment of inertia of the conductor cross sectional area (m4)

(

)


Di = The conductor inside diameter (m)





Annex D Standard palm terminal sizes and current rating

All terminals shall comply with the details and dimensions shown in Table 32 and Figure 2, Figure

3, Figure 4 and Figure 5 which are adapted from Standards Australia: High voltage switchgear and

control gear Part 301: Dimensional standardization of terminals (AS 62271.301, 2005). Cross

hatched areas in Figure 2, Figure 3, Figure 4 and Figure 5 represent the minimum connection

contact surface area.

All palm terminals except numbers 6 and 11 may be used either as equipment palm terminals or as

conductor terminals. Terminal number 7 is intended for use as conductor palm terminal with

equipment palm terminal numbers 12, 13 and 14. Terminals 6 and 11 are intended for use as

conductor palm terminals.

Figure 2: Terminal palms 1 thru 6





Figure 3 Terminal palms 7 thru 9





Figure 4: Terminal palms 11 and 12





Figure 5: Terminal palms 13 and 14

Table 32 Palm Terminal characteristics and current rating (AS 62271.301, 2005)





Terminal

Number

Bolt hole

diameter

mm

Net contact

area

mm2

Minimum thickness

mm

Assigned current-rating

A

Copper Aluminium Copper Aluminium

1 14 780 4 6 200 80

2 14 1430 4 6 400 200

3 14 3670 6.3 12 800 630

4 14 4670 10 12 1250 800

5 14 9300 16 12 2500 1250

6 14 4270 10 12 1250 630

7 18 or 22 7730 16 20 2500 1250

8 18 or 22 15300 16 20 3150 2000

9 18 or 22 21000 - 20 - 3150

10 18 or 22 28100 - 20 - 4000

11 18 or 22 6430 - 20 - 1000

12 18 or 22 - - 20 - 2500

13 18 or 22 - - 20 - 3150 (3750)

14 18 or 22 33300 - 20 - 5000

STNW3014 Standard for Busbar Design · 2020-06-26 · Energex Limited ABN 40 078 849 055 Ergon Energy Corporation Limited ABN 50 087 646 062 B.3.3.2. Wind load on busbar (F w) The

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