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Spacer Cart
MECHANICAL/STRUCTURAL ISSUE
ANALYSIS AND REDESIGN
Product Design Specifications Report - Winter 2016
Sponsor company:Bonneville Power Administration
Contact Engineer:Kevin Machtelinckx
Academic Advisor:Huafen Hu, Ph.D.
Group member:Bao Phan
Carlos Jiménez
Robert Lawrence
Austin Ferrante
Mackenzie Larson-Weber
Sam Levin
Stephen Randall
Joshua Ponder
Table of Contents:
●Introduction………………………..………………………………………….Page 3
●Purpose of document……………….………………………………………….Page 4
●Mission Statement……………….………………………………………….Page 4
●Project Plan………………………..………………………………………….Page 4
●Customers Identification
○External Customers……….………………………………………….Page 7
○Internal Customers……….………………………………………….Page 7
●Customers Feedback and Interview………………………………………….Page 8
●Project Design Specification……….………………………………………….Page 9
●Conclusion………………………..………………………………………….Page 12
●Appendix…………………………………………………………………...Page 13
List of Exhibits:
- Spacer Carts Mechanical/Structural Issues Analysis and Redesign, Machtelinckx, Kevin, October 2015, BPA Internal Report.
Introduction:
Since the United States established a power grid, power transmission lines have required maintenance. On modern high voltage power transmission lines, maintenance is often performed via a ‘Spacer Cart’ which is hung on the transmission lines themselves and can drive itself along the lines using an onboard motor. There are several companies which design and sell these carts, but all have their own advantages and drawbacks, none of them are completely ideal. BPA (Bonneville Power Administration), using their own fabrication shop and in-house expertise, created their own ‘Spacer Cart’ for use in transmission line repair.
However, though the ‘Spacer Cart’ they have created is capable of performing its intended job, several details in regards to usability and safety were not addressed during its initial design, therefore they have requested the help of a Portland State Capstone team in evaluating and addressing different aspects of the ‘Spacer Cart’ design.
Purpose of Document:
The purpose of this PDS (Product Design Specification), as its name implies, is to define the scope of the project and the requirement(s) due at final product delivery by the Portland State University (PSU) Capstone Team, as defined by the customer, Bonneville Power Administration (BPA). The document will outline a set of specifications that will be addressed by the Capstone team, each specification being ranked in regard to its level of importance to the customer.
Mission Statement:
The purpose of the project is the re-design of the spacer cart currently in use by BPA. Overall project scope is limited to addressing safety/functionality limitations with the current design. The goal of the new design is to reduce stresses in the frame caused by impacts sustained during normal operation, and to address access and ease of use issues experienced with both the supporting crossarms which connect and bring the suspension arms in-line, and the pinch wheel assemblies which increase driving wheel traction with the conductors. These new designs must all pass design envelopes specified by BPA for line clearance. BPA would like a prototype available to them for testing by June 1, 2016.
Project Plan:
Owing to the fact that there are several separate design goals and a large team, the team has separated into 3 subgroups, each tasked with a single design goal: the frame redesign, the pinch wheel redesign, and the crossarm redesign. Table 1 below illustrates the tentative dates and milestones for the project.
Table 1: Project Milestones
Plan DatesProject Tasks / Start Date / End Date
External Search / 1/25/16 / 2/1/16
PDS Report and Presentation / 2/2/16 / 2/2/16
Internal Search / 2/1/16 / 2/8/16
Concept Evaluation and Selection / 2/8/16 / 2/12/16
Detailed Design / 2/12/16 / 2/26/16
Design Review with BPA / 2/29/16 / 2/29/16
Design Modifications / 2/29/16 / 3/4/16
Final Design Review with BPA / 3/7/16 / 3/7/16
Progress Report and Presentation / 3/8/16 / 3/8/16
Fabrication / 3/14/16 / 4/11/16
Laboratory Testing / 4/18/16 / 4/22/16
Redesign (if needed) / 4/22/16 / 4/29/16
Final Design Fabrication / 5/2/16 / 5/30/16
Field Testing / 6/1/16 / 6/1/16
Documentation / 6/1/16 / 6/6/16
Final Presentation and Project End / 6/8/16 / 6/8/16
Graph 1: Spacer Cart project timeline
Customer(s) Identification:
External Customers:
●Linemen at BPA (end users)
○Interest: A ‘Spacer Cart’ with features that are easier to use while performing maintenance on the lines, such as the crossarm assembly and the pinch wheel assembly.
●Fabrication Shop at BPA
○Interest: Completed drawings and assembly instructions for fabricating components of the ‘Spacer Cart’ per BPA drawing specification.
●Maintenance Department at BPA
○Interest: Re-designed features on the ‘Spacer Cart’ that are durable and easy to maintain.
●Kevin Machtelinckx, Project Engineer at BPA
○Interest: A completed ‘Spacer Cart’ that meets all of BPA’s specifications.
Internal Customers:
●Portland State Capstone Program
○Interest: Completion of the Capstone project by meeting all sponsor expectations and specifications.
●Dr. Faryar Etesami, Mechanical Engineering Professor overlooking Capstone Projects
○Interest: Completion of design process, planning and execution following the guidelines and parameters established in the Capstone program. Completion of the Capstone project by meeting all sponsor expectations and specifications.
Customers Feedback and Interviews:
Initial interview with Kevin Machtelinckx, our primary BPA contact, was held on November 20, 2015 at the BPA site in Vancouver. The project team met with Kevin, as well as several other employees of BPA to discuss the mechanical and structural issues of the ‘Spacer Carts’. Our team also also performed a physical inspection of the current ‘Spacer Cart’ design, discussed the scope of work to be accomplished, and received a document detailing the current mechanical and structural issues from Kevin M. A follow up meeting was held at the BPA facility on January 13, 2016, in order to discuss, in more detail, the issues with the ‘Spacer Carts’ to allow the Capstone team time to review the discussed project scope and provided documentation. The Capstone team also detailed design envelope requirements with regard to the Product Design Specifications during this meeting.
Product Design Specification:
Table 2: PDS - Performance
PerformanceRequirements / Primary Customer / Metrics & Targets / Metric / Target / Target Basics / Verification
Angle of Incline / BPA / Cart must climb/descend a line at an angle. / degrees / 35 / Customer Defined / Site Testing
Weight Rating / BPA / Working Load Limit / lbs / 550 / Customer Defined / Site Testing
Pincher Wheels / BPA / Must traverse on wire and pass armor rod lip / inches / ½ / Customer Defined / Site Testing
Table 3: PDS - Safety
SafetyRequirements / Primary Customer / Metrics & Targets / Metric / Target / Target Basics / Verification
Structural Frame / BPA / Frame to withstand vibrations and impact load under working weight limit
(Impact Loads to be provided by BPA) / Physical Testing / 550 / Withstand / support all loads (Static / Dynamic) associated with normal cart operation and WLL / Lab Testing
Safety Factor / BPA / Establish safety factor based on industry standards
(applicability to be defined by BPA) / Specified applicable design criteria / N/A / Customer/ Project Team Decision / Customer Interview
Table 4: PDS - Environment and Ergonomics
Environment and ErgonomicsRequirements / Primary Customer / Metrics & Targets / Metric / Target / Target Basics / Verification
Crossbar Redesign / BPA / Crossbars should be redesigned to be easier for technicians to remove / Operation Efficiency / BPA Foreman Approval / Ease of Use / Site Testing
Wind, Rain and Cold Environment / BPA / Cart must withstand use in wind, rain and cold environments / Duration-Years / 5 / Corrosion Resistance / Field Use
Operational Design Envelope / BPA / All physical modifications must fall within operational envelope restrictions / Design envelope standard
Appendix A / All modifications fall within design envelope restriction / Specified Design Envelope / Physical Inspection
Table 5: PDS - Maintenance and Parts
Maintenance and PartsRequirements / Primary Customer / Metrics & Targets / Metric / Target / Target Basics / Verification
Frame Reinforcement / BPA / Years in service without frame repair / Years / 5 years / Customer Defined / Site Testing, FEA analysis
Table 6: PDS - Installation
InstallationRequirements / Primary Customer / Metrics & Targets / Metric / Target / Target Basics / Verification
Pinch Wheel Assembly / BPA / Pinch Wheel mechanism to be installed easily / Operation Efficiency / BPA Foreman Approval / Ease of Operation / Site Testing
Cross-Arm Bar Assembly / BPA / Cross-arm bar assembly to be easy to use while on the line / Operation Efficiency / BPA Foreman Approval / Ease of Operation / Site Testing
Table 7: PDS - Cost
CostRequirements / Primary Customer / Metrics & Targets / Metric / Target / Target Basics / Verification
Cost must not exceed original spacer cart production cost by a significant amount / BPA / N/A / N/A / A relative value / BPA will decide what cost(s) are acceptable. / Record keeping of budget expendi-
tures and production costs
Conclusions:
This document has outlined the specifications for the redesign of BPA’s spacer cart. The main goal of the redesign is to address stress issues in the frame and increase ease of use on some of the features. Secondary goals of the project are both to make the cart lighter and cheaper if possible. We have met with Bonneville employees and engineers to discuss the specific goals and outline a rubric of guidelines to follow during our design process. Also defined in this report is a progress goal timeline which has been shared with BPA to update them on our project milestones. For this project we will need to create 3D and 2D CAD models of our design ideas for fabrication, perform FEA analysis utilizing the dynamic/static loading scenarios the cart will undergo during operation, and verify all of our design criteria through physical failure testing with a fabricated prototype. Fabrication will be done by BPA which will save the project team labor hours and allow deeper focus on design goals. One of the project’s largest challenges is prototype fabrication will take several weeks, therefore the project team must be certain that the design is sound before delivery to BPA for fabrication. Given the aggressive timeline specified there might exist only one shot to make a working prototype and meet final delivery deadlines. By splitting into “sub-teams” focused on specific design areas/criteria, the large task of redesigning the cart has been pared down to more manageable sub-tasks. This has allowed the large project team to collaborate on design ideas while assigning individuals a specific task/goal to accomplish.
Appendix:
Section A. Design Envelope Restrictions
Figure 3: Design change limit envelope - Axial view
Figure 4: Design change limit envelope - Transverse view