pw interim design report r3-1

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


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


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.


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.


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


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.


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.


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


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.


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


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.


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


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.


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


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:


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.


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.


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.


Appendices

Figure 1: Moment and Force calculations

Figure 2: Moment and Force diagrams


Figure 3a: Torque and Power calculations


Figure 3b: Torque and Power calculations

Figure 4: Power and Torque as a function of Speed


Figure 5: New Tank Design

Figure 6: Team Schedule

pw interim design report r3-1

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