Guide for Design of Substation Structures Prepared by
Substation Structure Design Guide Subcommittee, of the Committee on Electrical Transmission Structures (CETS)
DEFINITION INSIDE THE FENCE
OUTSIDE THE FENCE
Leon Kempner, Jr., Chair George T. Watson, Co-chair
Wendelin H. Meuller, Secretary
Reyes M. Barraza Martin L. de la Rosa Rulon Fronk Rodney N. Hutcherson Massoud Khavari Paul M. Legrand II William L. Magee Jean-Robert Pierre Wayne P. Schumm Albert J. Tharnish
Terry G. Burley Harry V. Durden Jr. James M. Hogan Gary A. Johnston Steve M. Krohn Denis R. Lemelin Kenneth C. Malten Craig H. Riker David Tennent Chung J. Wong
DOCUMENT HISTORY: Started in 1991 First Draft 1994 Projected Completion 2006 (Oct. 30 2006) The Committee Membership Represented
• Utilities • Manufacturers • Consulting firms • Academic Institution • Research Institutions • General interest Individuals
PAST COMMITTEE MEMBERS AND OTHERS Richard X. Byrne
Michael F. Banat
Steven Groom
Don G. Heald
Donald Laird
Warren Crossman
James T. Kennedy
M. Kescharvarzian
Jerry Tang
Bing C. Chan
(Trudy) P. Germann
David Insinger
Husein Hasan
Peter Moskal
Don Lott
William J. Hamilton
Joe Shepherd
Jean-Bernard Dastous
M.P. Singh
Alain Peyrot
Brian C. Koch
Gary C. Violette
Alan J. King
Mircea Iordanescu
Tom Teevin
M. E. Kozlowski
Gary Engmann
Alan B. Peabody
Don Lott
Elwood Treadwell
Jake M. Kramer
Surrendar Menrai
M. R. Kazemi
TS Spangenberg, Jr
David Ackermann
Hank Page
Subir Roy
Brad Kemp
Dale Beason
OTHERS
Rapheal O. Peters
Gino Stagliano
Clayton L. Clem
Magdi F. Ishac
Long Shan
F.C. Shainauskas
Brian Goplen
Patrick A. Calizar
Lon C. Spencer
Jean-Robert Pierre
Dick Standford
J. R. Clayton
Curt Hinkel
Dan McIntyre
Herman Kwan
Carl Johnson
BACKGROUND INFORMATION: 9
Comprehensive document for the design of outdoor Electrical Substation Structures
9
Specific guidelines for 4-kV and above
9
Reference Existing Design Codes and Standards
Companion Documents: z
IEEE 693 “Recommended Practice for Seismic Design of Substations,” 1997 IEEE 693 addresses electrical equipment and its "first support” requirements. First support could be a pedestal for a current transformer (CT) or a support beam for a capacitor bank. The Substation Structure Design Guide will reference IEEE 693 and provide seismic requirements for structures not covered by IEEE 693.
z
IEEE 605, Rigid Bus Structures, Latest Edition Draft 8
Existing Industry Design Guides: - RUS/REA Bulletin 65-1, Rural Substations - Western Area Power Admin., Draft Doc. 1984 - NEMA SG6, Section 36, Outdoor Substations, (Structures, Pole-top Frames and Other Parameters) - Company Design Guides
STATUS: Completed PEER Review Committee: Chair: Henry W. Ho Hanna Essa Abdallah, Duane R. Alston Michael Brown Kamran Khan Otto J. Lynch William B. Mills Jerry Tang, Hay Yin Yu.
Level 1 comment: Represents a reviewer’s request to change the document per the reviewer’s submitted change (221/108) Level 2 is a reviewer’s general comment for the Substation Structure Design Guide subcommittee consideration (60/14)
STATUS: • Complete Editorial Review • Complete a companion Document Coordination Review (IEEE 693 and IEEE 605) • Ready for submittal to ASCE for publication • Should be available early next year, 2007, or sooner
CONTENTS: 1. INTRODUCTION 2. ELECTRICAL EQUIPMENT & STRUCTURE TYPES 3. LOADING CRITERIA FOR SUBSTATION STRUCTURES 4. DEFLECTION CRITERIA 5. METHOD OF ANALYSIS
6. DESIGN (ASD and USD) STEEL WOOD CONCRETE ALUMINUM SEISMIC BASEPLATE RIGID BUS DESIGN SPECIAL DESIGN CONSIDERATIONS
7. CONNECTIONS TO FOUNDATIONS (NOT FOUNDATION DESIGN) Foundations in substations should be designed according to accepted practice, the same as foundations designed for other structures. IEEE 691, “Guide for Transmission Structure Foundation Design and Testing,” is one source of information regarding the design of utility type structure foundations. 8. QUALITY CONTROL AND QUALITY ASSURANCE 9. TESTING 10. CONSTRUCTION AND MAINTENANCE
WORKSHOP SCHEDULE: Three Sections with short breaks in between Session 1: Introduction, Chapters 1 (Into.) and 2 (Structure/Equipment Types) Session 2: Chapters 3 (Loading), 4 (Deflections), and 5 (Analysis) Session 3: Chapters 6 (Design), 7 (Connections to Foundations), 8 (Quality Control/Assurance, 9 (Testing), and 10 (Construction and Maintenance)
1. INTRODUCTION
PARTS OF A SUBSTATION Parts of a substation can be grouped into several categories: (a) Site Related Facilities (b) Bus & Equipment “Outdoor” (c) Relay, Control, Metering, and Communications (d) Control House In general, in substations there is a site on which is located the major circuit bus and equipment as well as a control house. The control house contains protection, control, metering, and communication equipment as well as equipment related to the ancillary power systems (station service, 125vdc, etc.)
BUS AND EQUIPMENT - OUTDOOR The typical switchyard or substation contains the following components: (a) Bus (b) Outdoor Equipment Switching Power Transformers Instrument Transformers Reactive Power Compensation Lightning and Surge Protection (c) Grounding Grid (d) Conduit and/or Trench (e) Lighting, power distribution, and yard phone (f) Support Structures
yard phone booth
SUBSTATIONS The three functions of a transmission network are fulfilled through the different types of substations shown below. A single substation may perform more than one of these functions:
Types of Substations: - Substations Attach to Power Stations - Interconnect substations - Step-down (EHV/HV, EHV/MV, HV/MV) substations
Basic Structure of a Substation: - Substation Bus - Switchgear - Power Transformer - Control Protection and Monitoring Equipment - Communications Equipment
SUBSTATIONS IEEE DEFINITION (1) An area or group of equipment containing switches, circuit breakers, buses, and transformers for switching power circuits and to transform power from one voltage to another or to one system to another (ac/dc) (2) An assemblage of equipment for the purposes other than generation or utilization, through which electric energy in bulk is passed for the purpose of switching or modifying its characteristics. (A substation is of such size or complexity that it incorporates one or more buses, a multiplicity of circuit breakers, and usually is either the sole receiving point of commonly for more than one supply circuit, or it sectionalizes the transmission circuits passing through it by means of circuit breakers.)
2. ELECTRICAL EQUIPMENT & STRUCTURE TYPES
PURPOSE DEFINITIONS ELECTRICAL EQUIPMENT AND SUPPORTS PHOTOGRAPHS
SUBSTATION DESIGN SUPPORT STRUCTURES Switchyard Support Structures: Switchyard supports provide support for the switchyard equipment and bus at the elevations needed to provide adequate electrical clearance from finish grade to the bus or equipment live parts. Supports are also used to terminate outgoing transmission or distribution line conductors within the switchyard. The structures include the various stands for disconnect switches, instrument transformers, bus support insulators, surge arresters, and termination structures for overhead or underground transmission and distribution lines. The foundations for the structures are included with the supports.
Typical Substation Structure Material Types LATTICE STEEL
WOOD
CONCRETE
ALUMINUM
STEEL TUBE
BOX STRUCTURE TYPE OF CONSTRUCTION
Box Structure: The box structure is generally applied at 138 kV and below. It requires the least amount of land area and utilizes layers of bus, disconnect switches and related equipment, one above the other, connected with vertical bus runs, and supported on a common structure.
GAS INSULATED SUBSTATION CONSTRUCTION Gas Insulated: Gas insulated construction consists of completely enclosed buses and equipment insulated with SF6 gas. Because of the excellent insulating properties of this gas, very compact phase spacing. Gas insulated substations are generally installed for one or more of the following reasons: 1. Land area for the substation is extremely limited. 2. Environmental contamination is severe. 3. Site Environment, such as deep snow, etc. Since gas-insulated substations are shipped as factoryassembled units or modules, field erection time and cost are minimized.
Disconnect Sw.
Current Transf.
SUBSTATION
Dead Tank PBC
EQUIP.
Live Tank PBC Rigid Bus Bushing Wave Trap
Power Transf.
OUTDOOR EQUIPMENT
Lightning Arrester
Instrument Transf. PT
SUBSTATION DESIGN OUTDOOR EQUIPMENT S w itch ing E qu ip m e nt-T he fu nct io n o f sw itc hing equ ip m e nt is to co nnect and d isco n nect e le m e nts o f the substatio n o r utilit y syste m fro m the rest o f the su bstatio n o r utilit y syste m . S o m e eq u ip m e nt used, such as the c ircu it breaker, are capable o f interru pting (d isco nne cting) the very large qu a nt it ies o f cu rrent asso c iated w ith fau lts. C ertain equ ip m e nt can sw itc h (co nnect o r disco n ne ct) norm a l le ve ls o f lo ad current w herea s other equ ip m e nt can o n ly be o perated if little o r no current is flo w ing. E q uip m e nt can be o perated electrica lly fro m a re m o te lo catio n o r can o nly be o perated m a nua lly at the equ ip m e nt lo catio n
SUBSTATION DESIGN BUS
Bus: The function of bus is to interconnect the high voltage portions of the various components of the switchyard to form the required bus configuration for the substation. The parts of a bus layout includes rigid or strain bus conductors, the fittings used to connect the bus conductors to the switchyard equipment, and the insulators that support the bus conductors. RIGID BUS
FLEXIBLE BUS
Strain bus
SUBSTATION DESIGN OUTDOOR EQUIPMENT
DISCONNECT SWITCH
SUBSTATION DESIGN OUTDOOR EQUIPMENT
CIRCUIT BREAKER
SUBSTATION DESIGN OUTDOOR EQUIPMENT
CIRCUIT SWITCHER
SUBSTATION DESIGN POWER TRANSFORMATION EQUIPMENT
500/230KV XFMR - SINGLE PHASE UNITS WITH SPARE
SUBSTATION DESIGN INSTRUMENT TRANSFORMERS CURRENT TRANSFORMER (CT)
POTENTIAL TRANSFORMER (PT)
SUBSTATION DESIGN INSTRUMENTATION TRANSFORMERS Instrument Transformers: The functions of instrument transformers is to provide low voltage or low current inputs that can be used with protective relays and metering equipment. These inputs are proportional to the voltage or current which exist in the substation buses or equipment. The equipment can include potential transformers (PTs), coupling capacitor voltage transformers (CCVTs), current transformers (CTs), and bushing current transformers (BCTs).
SUBSTATION DESIGN POWER SYSTEM CONTROL: REACTIVE POWER EQUIPMENT SHUNT CAPACITOR BANK
SHUNT REACTOR BANK
SUBSTATION DESIGN REACTIVE POWER EQUIPMENT Reactive Power Compensation Equipment: Large quantities of capacitive or reactive power are used for power factor improvement or voltage control. They limit fault current on buses or distribution lines, and supply low impedance tuned paths to ground for harmonic voltages (which are “nuisance” voltages occurring at frequencies above 60 hertz). The typical equipment used for reactive power compensation includes capacitor banks and reactors, installed individually or in combinations.
Series Capacitors 9Used (typically at 230kV and above) to improve power transfer capability by compensating for voltage drop along a transmission line. 9If desired, load distribution between lines can be enhanced. 9Series capacitors can also force more power to flow over the line with larger conductors when parallel lines have different conductor sizes.
SUBSTATION DESIGN LIGHTNING AND SURGE PROTECTION ROD GAPS
LIGHTNING ARRESTOR
SUBSTATION DESIGN LIGHTNING AND SURGE PROTECTION Lightning and Surge Protection: The purpose of lightning and surge protection equipment is to protect the switchyard and control building from being struck by lightning, and to protect the insulation system of the switchyard equipment from transient, high voltages entering the substation from the transmission or distribution systems. These transient voltage waves can be caused by lightning strikes to the transmission or distribution lines, or from switching of the transmission system. The equipment for lightning and surge protection include the shielding masts and wires installed within the switchyard, rod gaps, and the surge arresters installed within the switchyard.
TYPICAL SUBSTATION LAYOUT
SUBSTATION LAYOUT DIAGRAMS
SUBSTATION LAYOUT DIAGRAMS THREE PHASE ACTUAL ARRANGEMENT
EQUIVALENT SINGLE LINE DIAGRAM
SUBSTATIONS
TYPES OF SUBSTATIONS
SUBSTATIONS:
Substation Types
- Generating Station to transform generating voltage to network voltage
SUBSTATIONS:
Substation Types
- Transmission Switching Station to switch interconnect portions of the utility system
SUBSTATIONS:
Substation Types
- Transmission Substation which can step-down or step-up voltage to interconnect the network
SUBSTATIONS:
Substation Types
- Distribution Substation to step-down voltage to the distribution level
SUBSTATIONS:
Substation Functions
- Isolate a faulted line or other component from the rest of the utility system
SUBSTATIONS: Substation Functions - To step-up or step-down voltage levels
SUBSTATIONS: Substation Functions - To allow for maintenance of line or equipment
SUBSTATIONS:
Substation Functions
- To allow for the addition of capacitors or reactors for electrical system control
SUBSTATIONS: Substation Functions - To allow for operational voltage, current, power and frequency measurements
SUBSTATIONS: Substation Functions - To allow control of power flows by switching lines in and out
SESSION 2: Chapter 3, Loading Chapter 4, Deflections Chapter 5, Analysis
3. LOADING CRITERIA FOR SUBSTATION STRUCTURES • INTRODUCTION • BASIC LOADING CONDITIONS Dead Loads Equipment Operating Loads Wire Tension Loads Extreme Wind Loads Combined Ice and Wind Loads Earthquake Loads Short Circuit Loads Construction and Maintenance Loads Wind Induced Oscillations Deflection Loads NESC Loads State and Local Regulatory Loads • APPLICATION OF LOADS • LOAD FACTORS AND COMBINATIONS • ALTERNATE DESIGN LOADS AND LOAD FACTORS • SERVICEABILITY CONSIDERATIONS • EXAMPLES
Wind Wind Maps Maps ASCE 7-05
3 Second Gust
F = Q kz V2 IFW GRF Cf A Where: F = Wind force in the direction of wind, pounds, (Newtons). Q = Air Density Factor, default value = 0.00256, (0.613 SI), defined in Section 3.2.5.1. kz = Terrain Exposure Coefficient, defined in Section 3.2.5.2. V = Basic Wind Speed, 3-second gust wind speed, mph, (m/s) defined Section 3.2.5.3. IFW = Importance Factor, defined in Section 3.2.5.4. GRF= Gust Response Factor (Structure and Wire), defined in Section 3.2.5.5. Cf = Force Coefficient, defined in Section 3.2.5.6. A = Projected wind surface area normal to the direction of wind, square feet (square meters).
(
G SRF = 1 + 3 .6 (ε ) E S (B S )
0 .5
)/ k
v
2
(Eq. 3-3) Where: ε = 0.75 Wire Supporting Structures (Dead-end and Line Termination)
ε = 1.00 Flexible Non-Wire Supporting Structures, < 1 Hertz For Rigid, Non-supporting Wire Structures, GSRF = 0.85
Table 3-4a Structure Response Factor, GSRF, Wire Supporting Structures, ε = 0.75 Height, h (ft)
Exposure B
Exposure C
Exposure D
≤ 33
1.17
0.96
0.85
> 33 to 40
1.15
0.95
0.84
> 40 to 50
1.12
0.94
0.84
> 50 to 60
1.08
0.92
0.83
> 60 to 70
1.06
0.91
0.82
> 70 to 80
1.03
0.89
0.81
> 80 to 90
1.01
0.88
0.81
> 90 to 100
1.00
0.88
0.80
Table 3-4b GSRF, Flexible Non-wire Supporting Structures, < 1Hertz, ε = 1.0 Height, h (ft)
Exposure B
Exposure C
Exposure D
≤ 15
1.59
1.20
1.02
> 15 to 33
1.48
1.15
0.99
> 33 to 40
1.37
1.11
0.96
> 40 to 50
1.33
1.08
0.95
> 50 to 60
1.28
1.06
0.94
> 60 to 70
1.25
1.05
0.93
> 70 to 80
1.22
1.03
0.92
> 80 to 90
1.19
1.02
0.91
> 90 to 100
1.17
1.00
0.90
Ice Ice Maps Maps
ASCE 7-05
Ice-Sensitive Substation Structures Not all structures or structural components have to consider ice loads in design. Consideration should be given to only ice-sensitive structures. In addition, ice loads may be applied to only selected components in ice-sensitive structures. For example, in dead end structure design, the ice load on the conductor is included in design, but the ice load on the structure is often neglected. Ice-sensitive structures are structures for which the load effects from atmospheric icing control the design of part or all of the structural system. Typically in a substation ice-sensitive structures include equipment, and rigid bus.
Seismic Seismic Maps Maps
Relative Seismic Hazard Map (USGS)
NEHRP - 2003
Maximum Considered Earthquake Ground Motion (1) The spectral response acceleration obtained from the 0.2 second map, Ss (short periods) and the 1.0 second map S1 (2) Acceleration-based Site Coefficient Fa (at 0.2 second period) and velocity-based Site Coefficient Fv (at 1.0 second period)
SDS = (2/3) (Fa) (Ss) SD1 = (2/3) (Fv) (S1) Sa = SDS For substation structure periods T > (SD1/SDS) use, Sa = SD1/T
Structure Seismic Design Force:
Sa FE = W IFE R Where: FE R IFE
= Seismic Design Force, Lateral Force applied at the Center of Gravity of the structure/component = Structure Response Modification Factor
W
= Importance Factor, Earthquake Loads = Dead Load (Including all rigidly attached equipment or conductor
Sa
Flexible attachments, such as conductors, need not be included) = Design Spectral Response Acceleration
Structure-Response Modification Factor, R Structure/Component Type Moment-Resisting Steel Frame Trussed Tower Cantilever Support Structures Tubular Pole Steel and Aluminum Bus Supports Station Post Insulators Rigid Bus (Aluminum and Copper) Structures with Natural Frequency Great Than 25Hz
USD 4.5 3.0 2.0 1.5 2.0 1.0 2.0 1.3
ASD 6.0 4.0 2.7 2.0 2.7 1.3 2.7 1.7
The Importance Factors, IFE Structures and Equipment Essential to Operation
1.25
Anchorage for Structures and equipment Essential to operation
2.0
All other structures (or equipment)
1.0
The selection of the appropriate Importance Factor (IFE) is the responsibility of the design engineer. The Importance Factors, IFE, specified in this section are the recommended valves for Ip used in IEEE 693 for foundation analysis.
TWO EXAMPLES IN THE DOCUMENT FOR DETERMINING STRUCTURE LOADS LINE TERMINATION STRUCTURE
69 KV DISCONNECT SWITCH SUPPORT
FIRST SUPPORT
EXAMPLES OF FIRST SUPPORT
Deflection Loads Where the structural designer has not developed specific loading conditions for deflection analysis, the following minimum load conditions may be used as a basis for deflection analysis. A load factor of 1.0, applied to the dead weight, is used with the deflection load cases.
Wind Load for Deflection Calculations Wind Deflection Load Conversion Factors 5-year mean recurrence Wind Deflection Load Conversion Factor
0.78
Ice and Wind Combined Load for Deflection Calculations Ice Thickness Deflection Conversion Factors 5-year mean recurrence Ice Thickness Deflection Conversion Factor Wind Deflection Load Conversion Factor
0.50 0.50
Other Deflection Considerations If the electrical equipment is expected to operate during extreme winds, then the unfactored extreme wind should be used for deflection calculations. If the electrical equipment is expected to operate during extreme icing, then unfactored extreme icing loads should be used for deflection calculations. Loads resulting from bus short circuit and earthquake events should not be considered in deflection analysis.
RIGID BUS DESIGN Bus Loading - Horizontal Bus Forces Fault Force on a cylindrical surface:(IEEE 605 formula) The magnetic fields produced by fault currents cause forces on the bus conductor. The bus conductor and its supports must be strong enough to withstand these forces. Decrement Factor Formula:
Fsc
=
C (Df 2Isc )2 (D)
C = 5.4 X 10-7 for English units Fsc = short circuit current unit force lbf/ft Isc = Symmetrical short circuit current D = conductor spacing center to center = constant based on type of short circuit and conductor location Df = decrement factor
Structure/Equipment Structure/Equipment Support Support Loads Loads
Loading Conditions
Wire Loaded Structures
Switch and Other Interruption Rigid Bus Equipment Supports Supports Supports
NESC*
Y
N
N
N
Extreme Wind/Hurricane
Y
Y
Y
Y
Extreme Ice and Wind
Y
Y
Y
Y
Seismic
Y
Y
Y
Y
Short Circuit
N
Y
Y
N **
Construction & Maintenance
Y
Y
Y
Y
Operational
N
Y
N
Y
Deflection
Y
Y
Y
Y
* Other Codes
** Design Should Consider if significant (rigid bus connected equipment)
APPLICATION OF LOADS The following loading conditions should be considered for checking substation structure stresses: 1. 2. 3. 4. 5.
NESC (other State or Local Regulatory Codes), Sections 3.2.12 and 3.2.13 Extreme Wind, Section 3.2.5 Combined Ice and Wind, Section 3.2.6 Earthquake, Section 3.2.7 Short Circuit (combined with other load conditions when considered appropriate), Section 3.2.8 6. Construction and Maintenance, Section 3.2.9 7. Equipment Operational Loads, Section 3.2.2 The following loading conditions should be considered for checking substation structure deflections: 1. Wind, Section 3.2.11.1 2. Combined Ice and/or Wind (Operational), Section 3.2.11.2 3. Equipment Operation Loads, Section 3.2.2.2
Ultimate Strength Design Cases and Load Factors LOAD CASES
LOAD FACTORS AND COMBINATIONS
Case 1
1.1 D + 1.2 W IFW + 0.75 SC + 1.1 TW
Case 2
1.1 D + 1.2 IWIFI+ 1.2 WI(1.0)+ 0.75 SC + 1.1 TW
Case 3
1.1 D + 1.0 SC + 1.1 TW
Case 4
1.1 D + 1.25 E (or EFS)IFE + 0.75 SC + 1.1 TW
D = Structure and Wire Dead Load; W = Extreme Wind Load; WI = Wind Load in combination with Ice; Iw = Ice Load in combination with Wind; E = Earthquake; EFS = Reactions from First Support; Tw = Horizontal Wire Tension for the appropriate load condition; SC = Short Circuit; IF = Importance Factors (IFW, IFI, IFWI, and IFE).
Allowable Stress Design 9Load Factors should be 1.0 Load Combinations A particular structure may not have all the individual load components listed in the load combination equations. It is the responsibility of the design engineer to determine whether a load case and/or load combination is appropriate. The combining of short circuit loads with other loads (wind, ice, and earthquake) should be considered and the level of short circuit load used in combination with other loads determined by the owner. These load combinations do not imply that only these four loads cases are adequate for the design of a substation structure. Variations of these or other loads cases may be required to account for conditions, i.e., wind direction, short circuit fault location, etc., applicable to the Utilities service region.
4. DEFLECTION CRITERIA Class A structures: support equipment with mechanical mechanisms where structure deflection could impair or prevent proper operation. Examples are group operated switches, vertical reach switches, ground switches, circuit breaker supports, and circuit interrupting devices.
4. DEFLECTION CRITERIA Class B structures: Support equipment without mechanical mechanisms, but where excessive deflection could result in compromised phase-to-phase or phase-to-ground clearances, unpredicted stresses in equipment, fittings, or bus. Examples are support structures for rigid bus, surge arresters, metering devices (such as CT’s, PT’s, and CCVT’s), station power transformers, hot-stick switches/fuses, and wave traps.
4. DEFLECTION CRITERIA Class C structures: Support equipment relatively insensitive to deflection, or are stand-alone structures that do not support any equipment. Examples are support structures for flexible (stranded conductor) bus, masts for lightning shielding, and dead-end structures for incoming transmission lines. Deflection limitations for these structures are intended to limit "P-delta" stresses, wind-induced vibrations, and visual impact. (Not in SG6).
SUMMARY OF STRUCTURE DEFLECTION LIMITATIONS Maximum Structure Deflection as a Ratio of Span Length, L (3) Member Type
Deflection Direction
Structure Classes Class A
Class B
Class C**
Horizontal (1)
Vertical
L/200
L/200
L/100
Horizontal (1)
Horizontal
L/200
L/100
L/100
Vertical (2)
Horizontal
L/100
L/100*
L/50
* NEMA SG6, SECTION 36, 2000 1/50 ** NEMA SG6, SECTION 36, NO CLASS C REQUIREMENT (1) Spans for horizontal members shall be the clear span between vertical supports, or for cantilever members, the distance to the nearest vertical support. Deflection shall be the net displacement, horizontal or vertical, relative to the member support points. (2) Spans for vertical members shall be the vertical distance from the foundation connection to the point of investigation. Deflection shall be the gross, horizontal displacement relative to the foundation support. (3) Loading Criteria for deflection Limitations, Section 3.2.1
SPAN LENGTH DEFINITIONS HORIZONTAL MEMBER SPAN
VERTICAL MEMBER SPAN
CLASS A STRUCTURES 1/100 OF THE VERTICAL SPAN
EXAMPLES • Group Operated Switches • Vertical Reach Switches • Ground Switches • Breaker Supports • Circuit Interrupting Devices.
1/200 OF THE HORIZONTAL SPAN (ANY DIRECTION)
CLASS B STRUCTURE
EXAMPLES • Support structures for rigid bus • Lighting/surge arresters • Metering devices (such as CT’s, PT’s, and CVT’s) • Station power transformers • Hookstick switches/fuses • Line/wave traps
1/100 OF THE VERTICAL SPAN (ANY DIRECTION)
1/200 OF THE HORIZONTAL SPAN (VERTICAL DIRECTION) 1/100 OF THE HORIZONTAL SPAN (HORIZONTAL DIRECTION)
CLASS C STRUCTURES 1/50 OF THE VERTICAL SPAN
EXAMPLES • Support structures for flexible (stranded conductor) bus • Masts for lightning shielding • Dead-end structures for incoming transmission lines.
1/100 OF THE HORIZONTAL SPAN (ANY DIRECTION)
MULIPLE CLASS STRUCTURE
LIN E END
CLASS DEFLEC TIO N C
SW ITC H CLASS DEFLEC TIO N A
Rotational limitations Some equipment and rigid bus designs may be sensitive to rotation of supporting members in addition to the deflection of the member. Equipment manufacturers should be consulted as to any rotational limits which may be necessary to ensure reliable operation. Lightning masts and other tall, slender structures In certain cases the structure type, design loads, and the lower deflection limits for Class C structures can result in a flexible (low stiffness) structure. These structures can be subject to potentially damaging wind-induced oscillations. Such structures can be susceptible to fatigue cracking and failure. Rigid Bus Conductor Deflection Criteria In order to obtain an acceptable appearance, it is recommended that the vertical deflection of rigid bus conductors (aluminum or copper tubing or shapes) be limited to L/200 of the span length. This criterion should be applied with the dead weight of the rigid bus, with dampers and no ice.
5. METHOD OF ANALYSIS STRESS CRITERION VS. DEFLECTION CRITERION MODEL Truss and Frame Models Finite Element Model STATIC ANALYSIS METHOD - OVERVIEW Approximate Analysis First Order and Second Order Elastic Analysis First Order Inelastic Analysis DYNAMIC ANALYSIS METHOD - OVERVIEW Steady State Analysis Eigenvalue Analysis - Natural Frequencies and Normal Modes Response Spectrum Analysis ANALYSIS METHOD - RECOMMENDATION Static Analysis Earthquake Analysis Dynamic Analysis of Short Circuit Events
Session 3: Chapter 6, Design Chapter 7, Connections to Foundations Chapter 8, Quality Control and Quality Assurance Chapter 9, Testing Chapter 10, Construction and Maintenance
6. DESIGN •
GENERAL
•
STEEL
•
CONCRETE
•
ALUMINUM
•
WOOD
•
SEISMIC
•
BASEPLATE
•
RIGID BUS DESIGN
•
SPECIAL DESIGN CONSIDERATIONS
6. DESIGN: GENERAL 9 Specific guidelines for member design and fabrication are not included in this guide. This guide refers to other documents for design guidelines and will note any exceptions. 9 Ultimate Strength Design (USD) and Allowable Stress Design (ASD), Ultimate strength design is recommended. 9 Ultimate Strength Design (USD): Factored design loads with stress levels up to yield strength or buckling capacity of the material and strength resistance factors, also referred to as LRFD. 9 Allowable Stress Design (ASD): Unfactored design loads and limits stress levels to a value which is less than the yield strength of the material. The 1/3 increase in the allowable stress for short duration loads, such as wind and seismic events, is not recommended for substation structures.
6. DESIGN: STEEL 9 ANSI/ASCE (1997) Standard 10, Design Transmission Structures (ASCE Standard 10)
of
Latticed
Steel
9 The American Institute of Steel Construction Load and Resistance Factor Design (LRFD) Manual , 2005 Edition 9 The ASCE/SEI Standard 48 (2005) , Design of Steel Transmission Pole Structures
6. DESIGN: CONCRETE 9 Reinforced Concrete Structures ACI 318 Building Code Requirements of Reinforced Concrete 9 Prestressed Concrete Structures PCI Design Handbook, Precast and Prestressed Concrete by the Prestressed Concrete Institute 9 Prestressed Concrete Poles ASCE Guideline for the Design and Use of Prestressed Concrete Poles
6. DESIGN: ALUMINUM 9 Aluminum structures should be designed and fabricated in accordance with the Aluminum Association “Specifications for Aluminum Structures,” using stresses for building type structures.
6. DESIGN: WOOD Ultimate Strength Design 9 IEEE Standard 751, Design Guide for Wood Transmission Structures 9 National Electric Safety Code (NESC) 9 National Standard ANSI O5.1 can be used for wood pole stresses with the NESC 0.65 reduction factor (Grade B Construction, Table 253-1) Allowable Stress Design 9 International Building Code (IBC), 2003
6. DESIGN: SEISMIC A structure defined by IEEE 693 as a “first support” is the single structural element upon which the equipment is supported. The first support can be a steel pedestal supporting a cantilever type piece of equipment, such as a surge arrester. The first support can also be a structural member (component) within a support structure.
6. DESIGN: SEISMIC 9 Allowable Stress Design The 1/3 increase in allowable stress for seismic loads is not recommended for substation structures.
6. DESIGN: BASE PLATE DESIGN 2
2
1
3 2
1
1 3
1
2
3 (a)
3 (b)
2 1 1
1
2 1 3
3 (c)
(d)
tmin
⎛ 6 = ⎜ ⎜ b F or F ⎝ eff y b
(
)
⎞ ⎟ (BL c + BL c +...+BL c ) 1 1 2 2 k k ⎟ ⎠
ASCE Standard 48, Design of Steel Transmission Pole Structures
6. DESIGN: RIGID BUS DESIGN 9 Rigid bus design should be approached as a system
requiring both an electrical and design engineer 9 Ultimate Strength Design (LRFD) of rigid bus design systems. 9 Short Circuit Load Obtained From IEEE 605 9 Design guidance per IEEE 605, but with ASCE Substation Document Loading, Load Factors, etc. 9 Seismic design per ASCE Substation Document
6. DESIGN: SPECIAL DESIGN CONSIDERATIONS • •
Structures for Air Core Reactors Wind Induced Vortex Shedding
•
Galvanizing Steel Considerations
•
Painted or Metallized Steel Considerations
•
Member Connection Design
•
Bolted Connections in Steel
• Welded Connections in Steel • Welded Connections In Aluminum • Concrete Structure Connections • Connections in Wood Structures • Weathering Steel Structures • Bolted Connections in Weathering Steel • Guyed Substation Structures
7. CONNECTIONS TO FOUNDATIONS •
INTRODUCTION
•
ANCHOR MATERIALS
•
ANCHOR ARRANGEMENTS
•
ANCHORS CAST-IN PLACE
•
DRILLED CONCRETE ANCHORS INSTALLED IN EXISTING CONCRETE
•
EXAMPLES
7. CONNECTIONS TO FOUNDATIONS 9 Anchor Bolt Design (Headed Anchors or Straight Length Deformed Reinforcing Bars) 9 Ultimate Strength Design approach to calculate the required cross sectional area of an anchor bolt is based on: ACI 349 “Code Requirements for Nuclear Safety” , ASCE 10 "Design of Latticed Steel Transmission Structures," and Shipp, J.G, Haninger, “Design of Headed Anchor Bolts,” Engineering Journal, American Institute of Steel Construction. 1983. Also references ACI 355. 9 Cast-in-place headed bolts are the recommended anchor bolt type 9 Design Considerations – Concrete: ACI 318 Appendix D 9 Stub angle and direct embedded structures can also be used in substations. These types of anchorage are covered by ASCE 10 (Latticed Steel Structures) and ASCE 48 (Tubular Pole Structures)
ANCHOR MATERIALS • ASTM F1554, and bolts manufactured from ASTM A36 Steel
• Straight Deformed Reinforcing Bars, ASTM A615 or A706 • In seismically active regions recommend ductile bolts • Minimum bolt size is 0.75 in. diameter • When smaller bolt sizes are used, it is recommended that the allowable bolt stresses exceed the applied stresses by not less than a factor of two (2)
ANCHOR ARRANGEMENTS
Base Plate Supported by Anchor Bolts with Leveling Nuts
Anchor Bolts with Base Plate on Concrete or Grout
Allows for adjustment of the base plate during erection
Large Shear Transfer Applications
9 Base Plate Supported By Anchor Bolts With Leveling Nuts If the clearance between the base plate and concrete exceeds two times the bolt diameter, then a bending stress analysis of the bolts is required (ASCE Standard 48, Design of Steel Transmission Pole Structures).
ANCHORS CAST-IN PLACE
Smooth bar hook bolts are not recommended because of less predictable behavior in tension tests
EXAMPLE OF A HOOK BOLT PULL-OUT FAILURE
DESIGN CONSIDERATIONS 9 Anchor Bolts With Base Plate on Concrete Or Grout TENSION AREA
Pu Aa = fdt
As = Aa + Av
SHEAR AREA FOR COMPRESSION
Av =
Vu - ( μ )(Pcm) [(φ )(fy )]
SHEAR AREA FOR UPLIFT
Vu Av = [(φ )(fy )]
REQIURED DIAMETER
d =
( 2)
1 ⎛ Αs ⎞ 2 ⎜ ⎟ + ⎝ π⎠
⎛ 0.974 ⎞ ⎜ ⎟ ⎝ n ⎠
DESIGN CONSIDERATIONS 9 Base Plate Supported By Anchor Bolts With Leveling Nuts
As = Aa + Ab + Av
Mu
Ab
⎛ 5⎞ = ⎜ ⎟ ( h)(Vu ) ⎝ 8⎠ 1 ⎧ 2⎫ 3 ⎡ ⎤ ⎪ 5hVu ⎪ = ⎨π ⎢ ⎥ ⎬ 2 f φ y ⎦ ⎪ ⎪ ⎣ ⎩ ⎭
Av = Vu
[(φ)( f )] y
REQUIRED DIAMETER
d =
( 2)
⎛ ⎜ ⎝
As ⎞ 1 2 ⎛ 0.974 ⎞ ⎟ + ⎜ ⎟ π⎠ ⎝ n ⎠
ANCHORAGE DESIGN CONSIDERATIONS - CONCRETE 9 Tensile Capacity Of Concrete (ACI 318) 9 Design Of Side Cover Distance For Tension (ACI 318) 9 Design Of Side Cover Distance For Shear (ACI 318) 9 Anchor Bolt Embedment Length (ACI 318)
ANCHORAGE DESIGN CONSIDERATIONS - CONCRETE
9
Localized Bearing Failure ASCE “Wind Loads and Anchor Bolt Design for Petrochemical Facilities” Bearing Plate Requirements
⎛ fy ⎞ ⎟⎟ Aplate = Abolt + As (0.11)⎜⎜ ⎝ f 'c ⎠ If the calculated value for Aplate is smaller than the area of the nut or bolt head, then a bearing plate is not required.
EXAMPLES 1.
BASE PLATE ON CONCRETE
2. BASE PLATE ON LEVELING NUTS 3. BASE PLATE ON LEVELING NUTS IN A DRILLED PIER
8. QUALITY CONTROL AND QUALITY ASSURANCE •
GENERAL QC = Fabricator, QA = Purchaser
•
STEEL STRUCTURES
•
ALUMINUM STRUCTURES
•
CONCRETE STRUCTURES
•
WOOD STRUCTURES
•
SHIPPING
•
HANDLING AND STORAGE
General Topics Materials Welding Fabrication Inspection Visual Inspection Specific Inspection Methods Of Welds Test Assembly Structure Coating Wood Treatment
9. TESTING
• • • •
•
Full-scale structural proof tests are rarely performed on substation structures. Full-scale testing should be considered when a standard and/or large quantities, or if it is a unique structural system. Component testing (a section of the tower, connections, etc.) may be cost effective for substation structures. Structural testing guidance can be found in the following documents: (1) ASCE Standard, ANSI/ASCE 10, "Design of Latticed Steel Transmission Structures" (1997). (2) ASCE Standard 48, "Design of Steel Transmission Pole Structures" (2005). (3) ASCE "Guide for the Design and Use of Concrete Poles" (1987). Seismic response (dynamic loading) requires that the support structure and equipment be seismically tested/evaluated as a system. Seismic tests are performed in accordance with IEEE 693, 2005.
10. CONSTRUCTION AND MAINTENANCE •
CONSTRUCTION Engineer(s) should anticipate construction loads imposed on the structure.
•
MAINTENANCE Engineer(s) should consider accessibility of equipment for maintenance and/or operation.
•
WORKER SAFETY All structures and equipment inaccessible with bucket trucks or small ladders, should be considered for climbing with a fall protection device. IEEE-1307, “Trial Use Guide for Fall Protection of the Utility Industry,” is one source of information for worker safety during climbing of utility structures.
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