What Structural EngineersShould Know about

Substation Rigid Bus Design

Minnesota Power Systems Conference

November 8, 2017

Paul Somboonyanon, P.E., P.Eng

Agenda

• Substation Rigid Bus System• Design Guide• Design Methods• IEEE 605 vs. Rigid Bus Model• Rigid Bus Modeling• Summary• Q&A

Substation Rigid Bus System

Substation Rigid Bus SystemBus Conductor

Insulator

A-Frame

Bus Structure

• Insulator Arrangements

Single Double Delta

Substation Rigid Bus System

Design Guide

• IEEE 605 Design Guide

“IEEE Guide for Bus Design in Air Insulated Substations”

providing:

– Electrical design aspects

– Structural design aspects

• IEEE 605 Design Guide – Loads

Gravity

Extreme Wind (ASCE 7-05)

Ice

Design Guide

• IEEE 605 Design Guide – Loads

Ice with Wind (ASCE 7-05)

Thermal

Earthquake (IEEE 693-05)

Design Guide

• IEEE 605 Design Guide – Loads

Short Circuit

Design Guide

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

𝑖𝑖𝑠𝑠𝑠𝑠 𝑡𝑡 = 2 𝐼𝐼𝑠𝑠𝑠𝑠[cos 2𝜋𝜋𝜋𝜋𝑡𝑡 + 𝛿𝛿 − 𝑒𝑒 �−𝑡𝑡𝑇𝑇𝑎𝑎 cos 𝛿𝛿 ]

AC Component Decaying DC Component

Eq. (17)

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

Additional resources: CIGRE 105, CIGRE 214, and IEC 60865

𝐹𝐹 𝑡𝑡 =𝜇𝜇

4𝜋𝜋𝑟𝑟2𝑖𝑖1 𝑡𝑡 𝑖𝑖2 𝑡𝑡 [𝑑𝑑1 ⊗ 𝑢𝑢𝑟𝑟 ⊗ 𝑑𝑑2 ] Eq. (13)

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

Design Guide

• IEEE 605 Design Guide – Short Circuit Load

Design Guide

• IEEE 605 Design Guide – Short Circuit LoadIEEE 605 Eq.

Rigid Bus Design

• Design Methods:

1. IEEE 605 Design Guide

2. Static Rigid Bus Modeling

3. Simplified Dynamic Approach

4. Dynamic Rigid Bus Modeling

Rigid Bus Design

• Design Methods – IEEE 605

Step 1: gather information

Step 2: go through each design criteria– Bus deflection limit– Bus stress limit– Insulator cantilever strength limit

Step 3: obtain “Allowable Span Length”

Rigid Bus Design

L ≤ Allowable Span

L ≤ Allowable Span

• Design Methods – IEEE 605

Rigid Bus Design

• Design Methods – Static Rigid Bus Modeling

Analyzing rigid bus system using FEA software by checking

– Insulator strengths

– Bus stress and deflection

– Thermal expansion effect

– Joint deflection

Rigid Bus Design

• Design Methods – Static Rigid Bus Modeling

Rigid Bus Design

• Design Methods – Simplified Dynamic Approach

“Analytical Techniques to Reduce Magnetic Force from High Fault Current on Rigid Bus”

By T.A. Amundsen, J.L. Oster, and K.C. Malten

considering:– dynamic property of bus span

Rigid Bus Design

• Design Methods – Simplified Dynamic Approach

Pros: Cons:

Easy to implement Load reduction varies by span length

Potentially provide more cost saving

No established design guideline of OLF

Rigid Bus Design

• Design Methods – Dynamic Rigid Bus ModelingIEEE 605 Eq.

Rigid Bus Design

• Design Methods – Dynamic Rigid Bus Modeling

Pros: Cons:

Provide more accurate results Complex analysis

Potentially provide more cost saving Time consuming

No established design guideline for OLF

• Comparison of Design Limitations

* with design assumption

IEEE 605 vs. Rigid Bus Model

Design Features IEEE 605 Model

– Insulator arrangements

• Single

• Double *

• Single

IEEE 605 vs. Rigid Bus Model

• Comparison of Design Limitations (Continued)

Design Features IEEE 605 Model

– Check insulator strengths

• Cantilever

• Torsional

• Tensile

• Compressive

Design Features IEEE 605 Model

– Check bus conductor fiber stress and deflection

• Simple arrangement

• Complex arrangement

IEEE 605 vs. Rigid Bus Model

• Comparison of Design Limitations (Continued)

• Comparison of Design Limitations (Continued)

IEEE 605 vs. Rigid Bus Model

Design Features IEEE 605 Model

– Provide detailed results

– Include bus structures/foundations

– Allow quick modifications

Rigid Bus Modeling

• Model Considerations– Bus Fitting Types

Rigid Slip Expansion

Rigid Bus Modeling

• Model Considerations– Bus Fitting Releases – Rigid

Rigid

x y

z

* Releases in relation to insulator local axes

Rigid Bus Modeling

• Model Considerations– Bus Fitting Releases – Slip

x y

z

Slip * Releases in relation to insulator local axes

Rigid Bus Modeling

• Model Considerations– Bus Fitting Releases – Expansion

x y

z

Expansion * Releases in relation to insulator local axes

Rigid Bus Modeling

• Model Considerations– Load Combinations

1. DL + Extreme Wind + Short Circuit

2. DL + Combined Wind/Ice + Short Circuit

3. DL + Seismic + Short Circuit

4. DL + Thermal

Rigid Bus Modeling

• Model Considerations– Load Combinations Approach

• LRFD - checking insulator strengths

• ASD - checking bus stress, bus deflection, and joint deflection

Rigid Bus Modeling

• Model Considerations– Load Combinations - Overload Factor (OLF)

LoadsOverload Factor (OLF)

IEEE 605 ASCE 113* Utility Std

DL or Ice 1.0 1.1 1.5

Wind or Seismic 2.5 1.2 2.0

Short Circuit 1.0 0.75 1.0

Thermal 1.0 1.0 1.0

* ASCE 113 Section 6.9.4 recommends reducing insulator strengths by 50% when using LRFD load combinations

Rigid Bus Modeling

• Model Considerations– Impact of Overload Factor to Cantilever Strength

Maximum

Rigid Bus Modeling

75%95%

69%

Maximum Insulator Strength Usage

IEEE Std 605 ASCE 113 Utility Std

1.2.3.

• Model Considerations– Impact of Overload Factor to Cantilever Strength

• Model Considerations– Welded Connections

Rigid Bus Modeling

IEEE 605, Section 6.6.1.4

• Model Considerations– ANSI C37.32 Table 4

Rigid Bus Modeling

Rigid Bus Modeling

• Model Considerations– Joint Deflection at Expansion Fitting

Summary

• IEEE 605 is a great source for substation rigid bus design.

• Different design methods are available.• Rigid bus modeling provides more accurate

results but several factors should be considered.