b o n n e v i l l e p o w e r a d m i n i s t r a t i o n line spacer cart psu capstone proposal...

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N

Line Spacer Cart PSU Capstone Proposal

Joshua Ponder


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Agenda

Overview History Current Issues Capstone Project Scope Contact Info



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Overview:

What is a “spacer cart”?• Vehicle designed to “drive” along high tension wires to facilitate/aid in

repair/replacement of various line hardware. (3 Models: 31” and 2 - 58”)• Frame is welded chrome-moly steel tubing (WLL 400 Lbs) Same for all models. • Power Plant - 4.6/10.7 HP 4-stroke gasoline engine driving (1) Eaton Model 7/11,

Variable Radial Ball Piston Pump, 7.2/17.5 GPM, 3600 RPM, 4/20 HP.• Drivetrain – Hydrostatic Drive 2 wheels, Eaton ‘H’ Series, 1800 psi, 996in/lb, 15 GPM• Safety features – None. (No Brakes, No redundancies)• All parts are fully conductive – Everything MUST let the electricity flow through it!• Parts used in repairs/replacements are attached to cage or hung over the sides.



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How are they used?:



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How are they used?: (cont)

Cart is hung on the line:• Lineman climbs nearest tower, scales out onto the line and assists placement of

wheels onto the cable bundle.• Cart is hoisted to the lines by a small crane.

– The lineman assists in placement of the wheel sets onto the lines, attaching and detaching picking hooks.

• Lineman gets into the cart and attaches a rope brake.– A rope brake is a rope that runs from the cart back to a transmission tower. If the cart were to loose traction or

break-down, the rope can be used to stop the cart and/or pull the cart back to a position that it can be removed from the lines by a crane.

• Tools and repair parts are hoisted into the cart and subsequently hung over the side for space.

• Lineman starts the cart and drives out to the point of interest on the line to perform work.

• During the work process, more weight is added to the cart as old hardware is removed. New pieces of hardware are removed from their positions hanging outside of the cage.

• When work is completed, the above pre-work process is reversed.



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Why do we need to work on lines?

Fiber Outage Report (Example)• Consolidation of handwritten logs / data dump out of TLM Apps

– Establish report covering all outages since 2003– Define the root cause for outages– Present root causes graphically for management



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Conductors a.k.a. “Lines”

Conductors:• Carry the power from point A to point B.• Range in size and construction• Can be an All Aluminum Conductor (AAC)• Also Aluminum Conductor Steel Reinforced (ACSR)• Very few are copper• Range in size from ½” to 2 ¼” diameter. • Pictured is Chukar, 1.602” diameter, capable of carrying 1453

amps. (230,000VAC * 1453 Amps ~ 333 MW)• Generally made by winding multiple wires together in a spiral

pattern within a circular envelope.• Majority of the power is carried by the “skin” of the conductor.• Generally hung with between 22-45 kips of tension.



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Conductor Angles and Tension

• All conductors are hung with a catenary; or shape similar to a x^2 graph. The angle and depth of the catenary are functions of the line span (distance from tower to tower), required line tension (harmonics), and minimum height above ground or water.

• Often, especially in river crossings, the catenary height can vary from ½-2x the supporting towers heights. This angle causes multiple issues with spacer carts. One example is creep, the cart drifts backwards down the lines at idle or when stopped.

• To date, no maximum angle or “safe operating envelope” for the spacer carts has been determined.



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Line hardware

Spacer/Damper:• Used to maintain spacing between individual conductors of a

single “phase”.– Generally on 500kV lines there are conductors per phase,

three phases per circuit.• Dampen out high frequency vibrations and oscillations.

– As wind passes over the profile of the conductor, the boundary layer causes an airfoil shaped envelope of air to form around the line, this in turn causes lift. The conductor rises slightly and changes tension within the line. When the wind speed/direction changes slightly, the airfoil shaped envelope around the line falls apart, the lift is lost and the line “falls” back into position momentarily increasing line tension. This cycle repeats and causes line “galloping”.

– Over the span of months or years these cycles induce fatigue in line suspension hardware at transmission tower and eventually the suspension hardware fails.

– By placing spacers at specified intervals, the natural harmonics formed by the tension and span length are reduced/or eliminated.



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Line hardware

Stockwell Damper:

• Used to dampen out harmonics on single or double conductor lines.– Serves same function as spacer damper without holding line spacing– Has own “natural frequency” and is paired by placing in correct

spacing patterns.

• Dampen out high frequency vibrations and oscillations caused by wind. – Prime example of a “vibration reducer.”– By placing dampers at specified intervals, the natural harmonics

formed by the tension and span length are reduced/or eliminated.



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Line hardware

Armor Rod:• Protective coating around the

conductor at attachment points• Coating is made of individual pre-

formed spiral patterned pieces• Armor rod is made from various

materials such as extruded steel or prepregnated fiberglass

• Lowers bending moments, minimizes conductor surface damage, and reduces fatigue within the conductor.



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Spacer Cart History: Work originally accomplished via “Boson's Chair”

• Imagine hanging out over I-84 during a “light breeze” 200-300 feet up replacing nuts and bolts without dropping anything.

• Roughly 15 years ago, a round of spacer dampers were manufactured with a design flaw. These dampers were installed across BPA’s system. Shortly after these spacer dampers started failing in large quantities.

• Around the same period, lineman at British Columbia Hydro mocked up a 4 wheeled suspended cart that could ride along the lines to aid in this kind of work. It used a gasoline motor, manual transmission and a mechanical driveline to 2 of the wheels.

• BPA borrowed a cart from B.C. Hydro and copied it.• Cart has been through multiple revisions/improvements. • No revision control, no formal engineering evaluations.• Several revisions later, the cart became hydrostatically driven;

however the body has remained unchanged.



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Current Issues: Structural issues:

• HIGHEST PRIORITY – Arm Integrity• Rear non-driven arms experience

issues passing over armor rod, spacer dampers, damper weights, etc..

• These items have a vertical lip ranging from ¼” -1”.

• The rear wheels effectively do not “climb” over the lips, therefore the lineman have to build up momentum such that the cart wheels “bounce” over the lips.

• This action induces enormous momentary shock loads in the rear arm assemblies and their respective attachment points.

• Fixes such a adding short sleeving chrome-molly tubes of a slightly larger diameter over the weak or highly-impacted area have resulted in moving the point of impact to just after the end of the reinforcing outer sleeve.



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Current Issues:



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Current Issues:

Structural Issues: • Cross Arm Bar Assembly:

• Holds drive and idler wheels parallel to one another

• Critical to prevent bending in rear wheels when overcoming obstacles such as armor rod

• Straight bar that slides into concentric tubes welded to right and left wheel assemblies

• Bar is held in place with a cotter pin

• If the wheel assembly “candy canes” are bent, this bar becomes very difficult to install

• This causes the lineman to stop using them, which perpetuates arm assembly damage.



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Current Issues:


Cross Bar Arm Assembly – Cotter Pin Connections


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Current Issues:

Pincher Wheels: • Used to keep contact pressure between

drive/idler wheels and the conductor• Necessary to keep cart under control on a

large catenary• Currently a bolt is used as a tensioner to

drive the pincher wheel upward into the conductor – Static Tension Pressure

• Assembly is captive in square stock mounted to the arm upright.

• Can be moved by swinging 90˚ out of plane

• Not user friendly, not dynamic, unable to help resist lateral loads.



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Current Issues:

Pincher Wheels – In stowed/folded position.



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Capstone Project Scope

The scope of work for the PSU team would revolve around addressing the issues described above. This means that a design of new arms or a retrofit/reinforcement of the existing arms needs to be planned, prototyped, built and tested. The new arm design would include a user-friendly way of operating the cross-arm bar assembly (‘bolt-action’ type of motion?). Additionally, the new arms would include a redesigned set of pinch-wheels, which would also be more user-friendly. The PSU team would be able to use the BPA test lab for destructive testing, as well as have interactions with a variety of different BPA specialists including engineers, linemen, foremen and shop managers.



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Contact Information


Joshua Ponder - [email protected]

Kevin Machtelinckx (BPA-TELM) – [email protected]

b o n n e v i l l e p o w e r a d m i n i s t r a t i o n line spacer cart psu capstone proposal...

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