What Structural Engineers Should Know about Substation Rigid Bus Design Minnesota Power Systems Conference November 8, 2017 Paul Somboonyanon, P.E., P.Eng
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.