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University of IdahoDepartment of Electrical and Computer EngineeringBuchanan Engineering, Room 213PO Box 441023Moscow, ID 83844-1023
December 5, 2012
Civil Engineering DepartmentP.O. Box 441022Moscow, Idaho 83844-1022
Attention: Dr. Jim LiouSubject: Pelton Wheel Development Project Interim Design Report
Please find enclosed the Pelton Wheel Development Project team’s interim design report. This report details the concepts and ideas considered for the project, design decisions that were made, and a detailed explanation of the system architecture that has been developed so far.
Additional information can be found on the design team’s website:<http://seniordesign.engr.uidaho.edu/2012-2013/peltonwheel/index.html>
We would also like to express our appreciation to you for providing us with the opportunity to work on this project, as well as your continued support and valuable input into our design development process. If you have any questions or concerns, please feel free to contact us.
Sincerely,
The Pelton Wheel Development Project Team
Enclosure: Interim Design Reportcc: Dr. Joe Law, Dr. Brian Johnson
Pelton Wheel Development Project December 4, 2012
University of Idaho
Pelton Wheel Development Project
Interim Design Report
Phil Spinden, Jennifer Jones, Ian Haynes & Kenneth Fletcher
12/4/2012
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Pelton Wheel Development Project December 4, 2012
Front Matter
Table of Contents
Front Matter..................................................................................................................................3
Executive Summary....................................................................................................................... 4
Report Body...................................................................................................................................5
Background....................................................................................................................................5
Problem Definition.........................................................................................................................6
Project Plan....................................................................................................................................8
Concepts Considered...................................................................................................................10
Concept Selection........................................................................................................................14
System Architecture.................................................................................................................... 16
Future Work.................................................................................................................................19
Appendices.................................................................................................................................. 21
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Pelton Wheel Development Project December 4, 2012
Executive Summary
The Pelton Wheel Development Project team is designing and fabricating a new tank
and frame for the Pelton turbine used in the Civil Engineering Hydraulics laboratory. In addition
to fabricating a new tank, we are attaching additional components including an electrical
generator, resistive load, and a torque transducer to measure the power transfer between the
turbine output and the generator input.
The two pelton wheels that are currently implemented in the Hydraulics Laboratory
(located in the basement of Buchanan Engineering Laboratory Building) both have distinct
disadvantages.
For this reason, rather than modify either existing solutions, our team chose to recycle
components from the more powerful pump and turbine assembly, and integrate it with a new,
more efficient tank design.
This new solution will be safer, more efficient, more aesthetically pleasing, and increase
the learning outcome of future students.
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Pelton Wheel Development Project December 4, 2012
Report Body
Background
Pelton wheels are a high head, low flow, high velocity turbine. Currently, they are used
in renewable energy by integrating them with existing renewable power systems (wind
turbines, large streams, etc.). For this reason, the Civil Engineering Department at University of
Idaho has a Pelton Wheel Laboratory as part of their Hydraulics curriculum.
Unfortunately, the quality of the two existing Pelton Wheels leaves much to be desired.
First, the current operational assembly is a smaller, integrated package. It is in working order,
but has fewer measurable quantities. This reduces the overall learning value for students as
they are unable to directly measure Energy transfer through the system. In addition, the
system’s small size makes it inefficient.
The second Pelton wheel assembly is an older, more robust, system. However, it is
currently inoperable and suffers from several design flaws. The tank is old, top heavy, and
deteriorating. For these reasons, our team designed a new tank, frame, and mounting assembly
to be used with the older three phase motor/pump assembly and turbine.
In this new assembly, students will be able to measure quantities necessary to analyze
power transfer and energy flow through the system. Concerns for the student’s safety and
learning experience made it necessary to take this ambitious approach to improving the
laboratory setup.
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Pelton Wheel Development Project December 4, 2012
Problem Definition
At a fundamental level, the goal of the Pelton Wheel Development Project is to improve
the existing implementation of a Pelton wheel inside the Civil Engineering hydraulics laboratory.
To this end, our team has several specific tasks in order to achieve this overarching goal of
improving the laboratory and the learning value that students gain from it.
First and foremost is the design of a new mobile tank frame. It is to be constructed with
angle iron and metal sheeting that support the tank and additional loading components on the
top of the assembly. The parts for this task have been ordered, designed for, and are ready for
fabrication and welding.
Going forward, the first task that must be tackled in the new semester is fabrication and
the welding of the new assembly. In parallel with this, design and further specification of the
electrical load must be completed. The depth and automation level of this solution is directly
tied in to our budget limitations, as well as time constraints.
The rough budget for the Pelton Wheel Development Project is altogether about $4,000.
The University of Idaho Civil Engineering Department has committed $2,000 to our project,
while the Shell Grant has given an estimate of up to $2,000. We have already bought some
mechanical components for the system. The new tank with shipping cost $380 and framing
parts so far have cost $260. Additional framing components will cost another $100. The most
expensive part of the design is the torque transducer, which will cost about $1,700. The
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Pelton Wheel Development Project December 4, 2012
generator will be about $300 and the microcontroller and electrical load components will be
around $100.
Total spending so far has been $640 taken from the CE Department money. The torque
transducer will be purchased with the Shell Grant money, using $1,700 of their offered budget.
The rest of the materials (generator, frame components, microcontroller, and electrical load)
will cost about $500. This will leave about $860 leftover from the CE Department budget.
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Pelton Wheel Development Project December 4, 2012
Project Plan
A list of design parameters for both the tank and torque transducer has been compiled
and verified. Mechanical components have been purchased and the new tank will be
fabricated, primarily due to efforts by Ken and Phil, by February. Meanwhile, Ken, Ian, and
Jenny, will be designing loading logic that allows for fast and precise variations in induced
torque. Simulations of the generators performance will be developed by Ian and Phil prior to
implementation to rate the resistive elements in the array, the wires transferring the power to
the load architecture, and the relays that will be used to implement the control logic. Once this
has been accomplished the loading system can be purchased and tested. Ken, Ian, and Jenny,
will monitor the interactions of the control system and load architecture and compare the
results to expectations. The design will then be revised as needed to maximize system
performance. Once the design has been finalized the system can be mounted on the assembly
and used in demonstrations.
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Pelton Wheel Development Project December 4, 2012
Concepts Considered
Mechanical:
The two primary options for the pelton wheel lab station were to modify one of the
existing solutions or to create a new solution that would suit our needs. There were two
existing lab stations which were available to be modified: an older and larger model, or a
newer, smaller model.
The older model was a long, shallow, two-part tank mounted on a tubular metal chassis.
The pump was mounted under the upper part of the tank, and the turbine was solidly mounted
on top of the upper tank above the pump. Output power and torque were obtained by
measuring the force from a lever arm on a brake clamped and tightened on the output shaft.
Flow rate was measured by a v-notch gauge. Trundle bearings on the pump allow the
mechanical power produced by the pump motor to be measured. A wattmeter is available for
measuring the electrical power into the motor.
While testing was not possible on this lab station due to a missing force gauge, our client
informed us that in prior tests the overall efficiency of this station was low, mainly due to poor
tank and pump design and placement. This lab station would not have been difficult to modify
as there was a lip on the inside of the top of the tank, allowing for easy mounting of additional
components. The long, narrow shape of this lab station would require that a generator be
mounted axially along the tank, with the electrical load further down the length of the tank.
The newer lab station is shorter, with a larger cross section. The tank, frame, and pump
compartment form an integrated structure, while the turbine is mounted to a plate which can
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Pelton Wheel Development Project December 4, 2012
be repositioned over the trough the water falls in. As with the older model, torque is measured
with a brake, however this one is a band tightened around the pulley from both ends rather
than clamped to the pulley. Flow measurement is very imprecise as it is done by timing how
long it takes for a smaller reservoir to fill to a specified level. Power into and out of the pump
cannot be directly measured.
The pump motor on this lab station is 580W, according to the nameplate, however the
pelton wheel produces approximately 38W of power at most, for an overall system efficiency of
less than 10%. Modification of this assembly would be more difficult due to the integrated
nature of the tank and frame. The generator and electrical load could be placed in a number of
configurations as there is more free space on the top of the assembly.
In addition to modifying the two existing solutions, we considered building a new
tank/chassis assembly that existing components, as well as future components, could be
integrated into.
The tank for the new assembly had multiple options, each with their own advantages
and disadvantages. A short, wide tank would provide more stability to the final design, as it
would have a wider footprint and a lower center of gravity. However, a taller tank would
provide better net positive suction head to the pump, as well as reduce the chance of a vortex
forming which could allow introduction of air into the pump inlet. A custom tank design was
briefly considered as it could allow for inclusion of the advantages of both, however it was
quickly ruled out due to cost.
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Pelton Wheel Development Project December 4, 2012
The main options for the material for the frame were flat metal strips, metal tubing, and
angle iron. The metal strips were the cheapest option but provided the least support. The
metal tubing was more expensive than the flat metal, however provided more support. The
round sides would present challenges in mounting the tank. The angle iron provided the
greatest deal of support and ease of mounting the tank; however it was the most expensive.
There were two main geometric arrangements considered for the chassis. The first had
the pump mounted sideways next to the tank at the bottom of the assembly, with a metal
frame holding the tank and the turbine/generator assembly in place. This option reduces the
height to improve stability while maintaining the pump near the bottom of the assembly.
Alternately, a two-level frame was considered which would allow the pump to be underneath
the tank. This option provides more space for the motor controller, as well as allowing for
pump to be positioned so a longer run of straight piping could be provided to the pump inlet.
Electrical:
One of the primary concerns of our client is coupling an electrical torque transducer
between the turbine and load. Knowing that this would a necessary component, we had to
constrain our design decisions (as well as budget) to match these needs. Since the electrical
rotary torque transducer will have an output, we knew having some control logic, to handle
inputs like torque and possibly a venture flow-meter, would be desirable.
Moreover, this torque transducer must be coupled to an electrical generator. The
purpose of this generator is to act as the loading device on the turbine. This is in place of the
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Pelton Wheel Development Project December 4, 2012
manual braking arm which was discussed earlier. The generator will be acting as an electrical
load on the turbine; a way to manually adjust load in real-time is a necessary solution.
Since our project had a wide operating range of speeds, it was desirable to select a
machine with a large speed bandwidth, as well as a linear torque-versus speed output
characteristic. This is desirable since the lab requires students to vary load, and the relationship
between torque and speed of the pelton turbine is also linear. With these considerations in
mind, the two main machine types considered were a synchronous induction machine, as well
as a direct current permanent magnet machine. The consideration for each machine is further
discussed in the following section.
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Pelton Wheel Development Project December 4, 2012
Concept Selection
Mechanical:
The main decision made for the project was that a new tank and chassis assembly was
wanted. Both of the existing solutions had significant disadvantages, and they would have
given a final product that both our team and our client would likely be unsatisfied with. The
older lab station had more learning potential. More quantities could be measured, but the tank
was deteriorating and required repairs and extensive cleaning. The new lab station was in good
condition but was very limited in the measureable quantities. Thus it was decided to design a
new assembly despite the additional work that would be required.
The tank selected for the final design was the taller one. Although it was not ideal for
stability, the increased pump efficiency was deemed to be more important. As stated earlier,
the custom tank design was not considered due to the significant increase in price. A
rectangular tank was chosen as it would be much easier to mount than a cylindrical tank. In
addition to the shape, a thicker tank was chosen to meet client specifications.
A two-level frame was chosen for the final design. While this was counterproductive to
our goal of increased stability, it was necessary as our client strongly desired increased pump
efficiency, including a longer run of straight pipe leading into the inlet, necessitating that the
pump be mounted below the tank. Angle iron was chosen for the portion of the frame holding
the tank as it could be arranged in such a way as to easily hold the tank with minimal amounts
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Pelton Wheel Development Project December 4, 2012
of material. It was decided that the lower frame would be made out of the metal tubing as it is
cheaper than the angle iron and did not need to interface with a flat surface.
Electrical:
As discussed previously, it was necessary for students to operate in a wide speed range
(from 0 rpm non-moving turbine to no load conditions). For this reason, an optimal solution
would have a linear torque speed characteristic. This is desirable since the lab requires students
to vary load, and the relationship between torque and speed of the pelton turbine is also linear.
For these reasons, a direct current permanent magnet brush machine was selected. They are
very robust machines with all the characteristics desired. A synchronous induction machine
would have been a better simulation of the large pelton wheels used in industry. However, this
solution was not practical for cost and size considerations (small scale) of our project.
In order to control the load level of our project, as well as the output current, a
microcontroller will be used in conjunction with relays. Do to availability, low cost, and
familiarity with the PIC32MX7 Cerebot™, our team plans to do initial load testing and design
with this board using the MPLab Integrated Development Environment.
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Pelton Wheel Development Project December 4, 2012
System Architecture
Mechanical systems:
Once the tank shape and frame components had been selected, the main mechanical
considerations were providing adequate suction head, improving stability, ensuring the frame
can support the assembly, providing adequate area to mount components, and preventing
vortex formation and air introduction.
No data was available for the required net positive suction head for the pump, so a
direct calculation was not possible. Therefore, the tank height was selected based on the
height of the existing tanks. Our client informed us that the older tank, which was
approximately 1ft tall, was not sufficient for this purpose. The newer lab station, approximately
30 inches tall, had no evidence of cavitation when in use. Due to the lack of data on the pump,
the minimum tank height was unknown; however a tank height of 30 inches was selected, as
although this may have not been the minimum, it was sufficient to prevent cavitation.
In order to improve the stability, two things were done. First, the base of the assembly
was made wider. The goal was to make it larger than the existing solution while still being
narrow enough to be maneuverable through doors. An upper limit of 2 ½ feet was established
for the entire assembly, and the width of the main frame was decided to be 24 inches. Second,
the center of gravity was lowered by making the tank as close to the ground as possible. The
lower bound for this was determined by providing sufficient space for the piping to run under
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Pelton Wheel Development Project December 4, 2012
the tank for improved pump efficiency. The wheels and lower frame are approximately 14
inches high, which is a significant improvement over the existing solution, which had the tank
more than 2 feet above the ground.
A statics analysis was conducted to determine the stresses on the main frame beams.
While there were smaller sizes that could support the weight, 1.5 inch angle iron was selected
as smaller sizes would have caused difficulties in providing enough space for the tank to rest on.
The corner posts on the tank will extend 2 inches above the tank to attach the upper assembly
consisting of the turbine, generator, and electrical load. The lower frame is made of 1.5 inch
steel tubing (sized to match the angle iron), and extends 1 foot to the rear of the tank to
provide a place to support the motor controller and pump. The lower frame is 8 inches high to
provide room for the pipe to pass under the tank.
The final mechanical concern was preventing air introduction into the pump inlet. There
are two main mechanisms that would cause air introduction are entrained air from the water
plunging into the tank, and formation of an air core vortex in the tank. In order to counter this,
a flow spreader and a vortex breaker were included. The flow spreader is a slanted plate
mounted below the turbine, extending into the water into the tank. Water falls onto the plate
and runs down into the water in the tank rather than plunging directly into the tank from the
turbine. The vortex breaker is a pair of crossed thin metal plates positioned on top of the pipe
inlet which prevents the circular water motion that would lead to a vortex.
Electrical systems:
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Pelton Wheel Development Project December 4, 2012
At a rudimentary level, adding an electrical generator will have increased value to
students by allowing them to see energy transfer and power flow through the entire system
(electrical mechanical hydraulic mechanical electrical). On top of this, being able to
manually adjust mechanical loading by varying the electrical load on the generator should give
a better applications understanding from a student’s view.
The specific torque transducer selected for the project was justified based on the worst
case possible scenario. This was used assuming maximum efficiency in all components, as well
as maximum torque. This worst case scenario is shown in graphical format in Figure 4 of
appendices. Adding this torque transducer, as well as the electrical generator, satisfies to basic
requirements of the project directly from our client. The quantitative analysis of the torque
requirements is shown in the calculations on Figure 3a & b.
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Pelton Wheel Development Project December 4, 2012
Future Work
Next Semester
Going forward, the team is prepared to begin fabricating the new tank frame and
chassis. In addition to construction the frame, the new tank will need to be slightly modified
from its manufactured dimensions. This will incorporate how we are going to remount and
reassemble the three phase induction motor and pump assembly.
Ideally, mechanical construction and mounting will not extend far into the semester.
With that in mind, the team plans for the mechanical aspect of the new assembly to be
completed by early February of the New Year. This leaves the remainder of the semester to
begin debugging and testing the electrical load on the physical assembly.
At a minimum, we would like to have a working assembly with an adjustable load. A
baseline assembly would be a manually adjustable rheostat configuration to electrically load
the machine. If team ideals are realized, we’ll have implemented a microcontroller to sense and
measure voltage and current (with the load being adjustable using pushbuttons). This setup
would incorporate the use of relays and an LED display.
Future Phases of Work
There will still be plenty of work for future teams to improve upon after our team is
finished next semester. Namely, this includes further automation and implementation in
regards to real time data acquisition.
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Pelton Wheel Development Project December 4, 2012
More specifically, our client had requested a change-order at preliminary design review.
This involved integrating real-time data acquisition into a program called LabView™. Due to the
lateness of this request and the number of team members qualified to incorporate this
solution; it is a tertiary item. For this reason, this would be a great project for future Computer
Engineers or Computer Scientists who could improve upon the data acquisition and interfacing
with a PC lab station.
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Pelton Wheel Development Project December 4, 2012
Appendices
Figure 1: Moment and Force calculations
Figure 2: Moment and Force diagrams
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Pelton Wheel Development Project December 4, 2012
Figure 3a: Torque and Power calculations
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Pelton Wheel Development Project December 4, 2012
Figure 3b: Torque and Power calculations
Figure 4: Power and Torque as a function of Speed
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Pelton Wheel Development Project December 4, 2012
Figure 5: New Tank Design
Figure 6: Team Schedule
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