2013 turbine manufacture pelton turbine

8/11/2019 2013 Turbine Manufacture Pelton Turbine

1/60

Design and Construction of a 10KW

Pelton Turbine

CompletedTurbineSonatubesK

igali


2/60

[email protected]

Page 1

CONTENTS

!"#$%#$& ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( )

*+%,-$./% 0-11234 ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( 5

) 62,783"-#9 ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( :

; %3& ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( ?

@ =%,A2#.,2B C%&.8# (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( D@() E#.$.2B C%&.8# F%/.%G (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( D@(; 6%21 !2B,-B2$."#& (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( )H@(@ 6%23.#8 0%B%,$."# ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( ))

5 =2#-I2,$-3.#8 (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( ))5() .#% 0A"-B9%3 6B",7& ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( ))5(; .#% 0J2,%3& (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( );5(@ .#% 0A2I$ ((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( );5(5 .#% F-##%3 KB2$%& (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( )@5(: .#% 6%23.#8 L"-&.#8 (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( )@5(M


3/60

[email protected]

Page 2

0$; :'7'2?, @22?7-'4'7( A2?BC7- ################################################################################################ D/0$; 1,?7 A2?BC7- @ ###################################################################################################################### D/0$; 1,?7 A2?BC7- E ####################################################################################################################### D/0$; 6,'F?(C*7 A2?BC7- @############################################################################################################### D/0$; 6,'F?(C*7 A2?BC7- E ############################################################################################################### D/0$; H'8(C*7 A2?BC7- ####################################################################################################################### D/0$; HB?7 @22?7-'4'7( ################################################################################################################## D/0$;%$G%%# %(O-.#"+ 2#9 F%#%G2>B% *#%384 !"1J2#4 (((((((((((((((((((((((((((((( @@K3.,% >3%27 9"G# &A%%$ I"3 $-3>.#% ,2&.#8 &.8#%9 >%$G%%# %(O-.#"+ 2#9 F%#%G2>B% *#%384 !"1J2#4 ( @@

RKK*VCEW ! S !"&$ 63%279"G# (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((( @5*(O-.#"+ .#%


4/60

[email protected]

Page 3

Document Control Sheet

Project: E.quinox Hydro Project

Report Title: Design and Construction of a 10KW Hydroelectric Pelton Turbine

Date: 1stSeptember 2013

Project Code: 0578

Name Date

Prepared by:Evan Lawson

1stSeptember

2013

Reviewed by:Matthew Wood 6thOctober 2013

Approved by:Rushabh Mehta 6thOctober 2013

Revision Date Description Prepared Reviewed Approved

Evan

Lawson

5thOctober

2013

Corrections and revisions EL MW RM


5/60

[email protected]

Page 4

EXECUTIVE SUMMARY

E.quinoxs ambitions as an organisation to develop a hydro system with a low cost self built Pelton turbine

and casing stem back as far as 2009 during the inception of the organisation. Only in the summer of 2013were these ambitions fully realised. After a year of design and manufacturing work an in-house low cost

Pelton turbine was manufactured and assembled at Imperial College London by a group of E.quinoxmechanical and civil engineers.

During the summer expedition of 2013 the turbine system was transported to Rwanda where it was installedat the E.quinox Rugaragara falls hydro station for testing purposes. Whilst on the ground an extensive

period of turbine casing design was undertaken. The Renewable Energy Company (REC), a subsidiary ofSonatubes Kigali, were contracted to manufacture the casing due to their previous experience with suchwork and designs. After collaboration and communication of the design via a series of technical

manufacturing drawings, REC were able to deliver a finished casing with two weeks.

Delivery of the casing and turbine to site followed, with a period of installation and testing programmes.Electrical installation of an asynchronous alternator and dump load was also performed in order to regulate

the turbine speed and measure the system electrical output.

Evaluation of the whole system has concluded in many positives coming from the overall design ethos of theproject. However likewise many recommendations for design changes and improvements have also beennoted and discussed here in detail. These design recommendations should be considered for the E.quinox

summer expedition 2014 with an envisaged aim to fully commission the system.


6/60

[email protected]

Page 5

1 BACKGROUND

Since e.quinoxs early history the idea of developing a pico hydro-electric power system has been high on

the organisations agenda. Accompanying these plans were proposals to mechanically engineer a turbinesystem in order to generate power from the hydro plant. In 2013 these ambitious goals were finally realised

with the design and construction of a 10KW Pelton turbine. The following is a brief breakdown of theorganisations historical involvement with turbine development as well as its shortcomings before finallyconstructing a Pelton turbine prototype.

During the e.quinox summer expedition of 2011, the then executive committee had ambitions to exploit a

site for hydropower development following a similar model to that of the solar energy kiosks alreadyinstalled in Rwanda. Such an infrastructure intensive project could not be handled by e.quinox alone and sothe committee sought a partnership with DHE (Dartmouth Humanitarian Engineering), a US based student

organisation with aims aligned with e.quinox vision. In that same year DHE had finished construction oftheir second pico hydro-electric system in Banda, Nyungwe, Southern Province, both of which with acapacity sub 1KW. One of the Banda sites was in 2011 upgraded with a Pelton turbine (figure 2) designed

and built by DHE in America, the turbine was shipped to Rwanda within travellers baggage allowance andthe casing was developed in country. This was e.quinoxs first exposure to a self-manufactured turbine. The

turbine previously operating at that site was an unconventional device made in Rwanda, whereby theturbine cups (arguably the most difficult to manufacture) were created from steel tubing cut in half andwelded together (figure 1).

Figure 1: DHE Early prototype turbine after one-yearservice, cups formed from middle cut steel tube.

Figure 2: DHE Pelton turbine prototype after installationwith inlet valve, mechanical deflector, shaft and three

stage pulley.

During 2011 and 2012 design and planning work commenced for e.quinox and DHEs collaborative 6KW

hydro-electric power system at the Rugaragara falls in Southern Province. Early design calculationssuggested that the proposed system tapped a potential 6KW of electrical power from the river in dry

weather flow conditions. Over the course of the design phase many options were evaluated for bothturbines and electrical generator devices. Principally a choice was necessary between Pelton and cross-flowturbines. A Pelton turbine design was chosen due to its improved efficiency in high head, high flow

situations characteristic of the site in question, despite the Pelton design being more complicated tomanufacture. Unfortunately, after exploring several avenues for the manufacture of a Pelton turbine, itwas decided that ultimately no 6KW capacity turbine would be installed during construction of the hydro

system in 2012. As a reliable alternative, it was decided that the DHE contingent would purchase a Stream

Engine Turgo turbine with combined induction generator. These compact units are manufactured in Canada


7/60

[email protected]

Page 6

by an external company (http://www.microhydropower.com/ ); the unit was shipped to Rwanda intravellers additional baggage allowance. Despite the unit being undersized for the full potential of the

site, an identical unit had run flawlessly at DHEs Banda site for over one year and was considered a crediblealternative. The 1KW capacity was also plenty to run a battery charging scheme of 120+ battery boxes aswas intended for the site. The stream engine was installed with the intention of being able to install a

larger capacity turbine at a future date, this included; additional plumbing outlets, oversized tailrace, andadditional space in the powerhouse.

Figure 3: Rugaragara falls hydro site, installed stream engine with one nozzle input. Note space and additionalplumbing allowed for future Pelton turbine installation.

Despite no turbine of 6KW capacity being installed during 2012, it has already been discussed thatsignificant efforts had been made in that direction during the build up to the 2012 expedition. InSeptember 2011 a mechanical engineering project was started within e.quinox to design and manufacture

our own Pelton turbine. Two 2nd year mechanical engineering students took up the project, fresh recruitsto the e.quinox hydro team. Initially design work progressed well, however significant problems were

encountered during manufacture. Due to a combination of lack of experience and a lack of time the projectwas never realised. The design was for a cantilevered shaft with a double set of bearings on the left side ofthe shaft and the turbine unit on the right. Later it was discovered that overall the turbine and shaft were

undersized, and in reality the cantilevered shaft design was unnecessarily complicated. The shaft and partof the bearing housings were the only parts to be manufactured. Only months before the expedition was

due to depart it was decided to put the Pelton turbine project on hold and explore other options. Weimmediately contacted a company based in Cornwall named Evans Engineering (http://www.evans-

engineering.co.uk) about the potential for having them build a 6KW Pelton turbine, casing, and inlet withtwo spear control valves. There were several issues associated with this plan, firstly due to the restrictedtime frame and the companies busy order books it was not possible to turn something around in theallotted time, secondly the added logistics of shipping a very heavy and very large mechanical unit to

Rwanda needed to be considered. Evans Engineering were able to offer us a 10KW Pelton system that wasstored at their workshops but had a single broken stainless steel cup. The total quoted cost for this unit,

including casing and spear valves was 13,000. This was largely in excess of our budget (3000) and did notincorporate the costs of shipping such a large volume and heavy unit to Rwanda. Appropriately, this line ofenquiry was terminated.

Following our failed attempts to manufacture or buy a Pelton turbine system in the UK our attention

switched to having a system manufactured in Rwanda. During a previous surveying expedition in January2012, e.quinox team members had been informed of a location to purchase high pressure PVC pipe stock

named Sonatubes. Coincidentally whilst meeting the manager there, discussion was struck about a separate


8/60

[email protected]

Page 7

business he was running named the Renewable Energy Company, through which hydro turbines were beingmanufactured at the Sonatubes factory. No evidence of the quality of manufactured machines was

obtained. During our purchase of PVC penstock piping upon our return to Rwanda in the summer of 2012 ameeting was arranged between e.quinox, DHE, Fidele Claude (Sonatubes Manager), and Eugene Walliaula(Workshop Manager). It was agreed that a Pelton turbine could be produced, as well as a casing and two

spear valves for flow control. The design of the machine and unit was discussed but mostly left up to theworkshop manager Eugene who had allegedly produced these machines before. The total cost for themachine was quoted at 3000 (converted from RWF). Unfortunately due to major delays in the

manufacture, poor communication and poor manufacturing quality the agreement was cancelled. Manylessons were learnt from this experience, a non-exhaustive list follows. Ability to manufacture stainless

steel Pelton cups in East Africa is poor and limited, even in Kenya where Eugene attempted to have themmilled from bronze. A more viable alternative is to have these investment cast in the UK. Firm contractsneed to be created between e.quinox and the supplier, highlighting; expected manufacturing completion

dates, expected manufacturing tolerances and finished, penalty clauses, expected safe working practicesand communication procedures. The biggest mistake made in 2012 was the lack of a binding contract.Lastly a full set of working drawings with exact specifications and dimensions should be given. Allowing the

manufacturer free reign over the design is not appropriate, especially if your machine needs to meetcertain design standards, providing high quality manufacturing drawings avoids any ambiguity. We later

revisited Eugene at Sonatubes in January 2013 and discovered the extent of manufacturing that hadactually been completed (figure 4 and 5). Whilst the work appeared to be heading in an appropriatedirection, both the time frames and manufacturing quality achieved was not workable within our budget

and schedule.

Figure 4: Steel turbine casing manufactured bySonatubes in 2012.

Figure 5: Bronze Pelton cup prototypes manufacutredby Sonatubes in Nairobi, Kenya.

The many lessons learnt over the two previous years had culminated in a vast array of organisational

knowledge pertaining to the ups and downs of producing Pelton turbine machines. With that in mind, inSeptember 2012, after successfully installing e.quinox first ever hydropower system, a fresh attempt wasmade at producing a turbine in the UK. A group of six mechanical engineers were enrolled to the project,

and worked from concept design through to manufacturing completion. The following report is a technicaldiscussion on the successful design and construction of a 10KW Pelton turbine for installation at theRugaragara falls hydropower system in rural Rwanda. It is intended as a guide for those intending to embark

upon a similar project, but is not a comprehensive design for a Pelton turbine because each must bespecifically tailored to the particular characteristics of the site at which it is to be installed.


9/60

[email protected]

Page 8

Figure 6: E.quinox Pelton turbine prototype during casing manufacture and before installation of stainless steelcups.

2 TEAM MEMBERS

The following Imperial College e.quinox team members were involved with the inception, design andconstruction of the Pelton turbine project.

Matthew Wood(MEng) Civil and Environmental Engineering E.quinox Alumni and Technical DevelopmentHead 2012- 2013. Matthew helped manage the design and manufacturing team to realise the aims of theproject both in the UK and Rwanda.

Joakim ScharpCivil and Environmental Engineering E.quinox Hydro Project Leader 2013 2014. Joakimhelped manage the design and manufacturing team to realise the aims of the project both in the UK andRwanda.

Finlay Mcphail (MEng) Civil and Environmental Engineering E.quinox Alumni and Hydro Project Leader2012 - 2013. Finlay helped manage the design and manufacturing team to realise the aims of the project

both in the UK and Rwanda.

Evan Lawson Mechanical Engineering Evan led the majority of design as well as mechanical installation

work in Rwanda and the UK. He was also responsible for a large part of the shaft and spacer manufacturingas well as final assembly. Evan also designed the entire power transmission system.

Rebecca TelfordMechanical Engineering Rebecca contributed largely to the design of the casing whilst inRwanda, as well as the design of the Pelton turbine in the UK. Rebecca also contributed much to the designand manufacture of the Pelton turbine especially the bearing housing.

Laura SanMiguel GimenoMechanical Engineering Laura especially contributed to the early stage designand calculations as well as making significant contributions to the manufacture of the Pelton turbine in theUK.

Dmitri IvanovMechanical Engineering Dmitri was fundamental to the early stage design and calculationsinvolved in the turbine project. Later he went on to contribute much to design revisions, CAD work and the

manufacturing of shoulder and internal spacers.


10/60

[email protected]

Page 9

Avtar Rekhi Mechanical Engineering Avtar contributed significantly to early stage design andmanufacturing work.

3 MECHANICAL DESIGN

3.1

Initial Design Review

To start the initial design phase, calculations were conducted to size the turbine and jets for the system.The engineering theory behind these was taken from the Micro Hydro Design manual. Based on theproperties of the stream flow and net head, it was possible to calculate the optimal diameter for the

runner plate and diameter of the jet nozzles. It was also important to select the correct number of jets andthe number of Pelton cups on the turbine; achieved using the same design calculations. Due to the changes

in flow during the wet and dry seasons, the efficiency of the system was calculated for varying streamflows, to ensure the system would work as intended throughout the year. Appendix D gives details of thecalculations and the resulting design parameters used to size the turbine.

During the early stages of the project, after the appropriate turbine system parameters had been

calculated, it was important for the team to brainstorm different mechanical design iterations beforechoosing the final form factor. Several critical decisions were made during this phase that led to the final

design; these are discussed and justified below.

In previous years a cantilevered turbine had been investigated and prototyped. Immediately this was ruledout due to the extra manufacturing complication it produces. Furthermore comparing a cantilevered systemwith a simply supported system shows that the former requires much larger shaft diameters to

accommodate the increased forces and moments. The knock on effect is to require larger bearings. Theincrease in cost of both materials and bearings is not proportional to the size, with larger parts costing

exponentially more. For these reasons a simply supported beam system was chosen.

Figure 7: Early complex design idea involving use of a catalogue shaft bolt to lock turbine against a shoulder.


11/60

[email protected]

Page 10

The difficult design problems are the need to axially and rotationally fix the runner plate onto the shaft.Rotational restraint is traditionally provided by an industry standard keyway, this was instantly recognised

as the appropriate solution for our design. More difficult is the problem of axial restraint. We developedmany different solutions each having a range of complexities and manufacturing issues. These included theuse of circlips and grub screws as well as catalogue locking shaft nuts. Finally the solution as described

below was chosen in which a shoulder is manufactured in the shaft around which spacers can be made tobolt the turbine around the shoulder.

Lastly a method of restraining the shaft axially between the bearings was required. Again although optionswere considered, by far the easiest way to achieve this is by machining a step down shoulder in either end

of the shaft. Bearings then abut these shoulders and the correct positioning of the bearing housings restrainthe shaft axially between the bearings.

3.2 Beam Calculations

The stresses developed in the turbine by self-weight as well as the design action of jet impact pressures

may be fully evaluated by calculation. Many aspects are very complex to derive meaningful solutions byhand unless significant simplifications are made. For example the stresses developed in the runner plates

are best modelled using finite element analysis. There is a dynamic element to the loading also as alternatecups are loaded causing the turbine to subsequently spin at large RPMs.

One of the more basic calculations to consider is the forces and moments developed in the shaft due to itbeing simply supported between two bearing blocks and then cantilevered beyond the bearings. An

idealisation of the system is given in the sketch below (Figure 8).

Figure 8: Idealization of turbine as a simply supported beam system.

The turbine is idealised as a simply supported beam of length L 1 with cantilevered length L2. The weight ofthe turbine itself is modelled as a load P1, the load due to the tension force imparted by the belt is

modelled as P2.A UDL w represents the self-weight of the shaft, theoretically this is not a uniform load, butfor simplification it is assumed that the variation is marginal and a load corresponding to an aluminiumshaft of 30mm diameter is used. The dynamic loads are ignored here as it is considered that if the turbine

is properly balanced then no dynamic loads are present. Note also that the beam is not rotationally

restrained along its longitudinal axis (along the shaft); hence the moment that would be introduced due to


12/60

[email protected]

Page 11

the jet hitting a cup at an eccentricity from the shaft is not present. Theoretically some frictionalresistance would cause a moment to be induced but this is considered negligible. The aim then is to check

that the design stresses developed in the beam do not exceed the material factors of safety for thealuminium shaft. From this a minimum design diameter for the shaft is calculated as 21.8mm. Refer toAppendix D for full calculations and load derivations.

3.3

Bearing Selection

The method used for selecting bearings follows that laid out by the hydro design manual. Firstly the bearing

type chosen was a deep groove ball bearing, as they can take a relatively high axial and radial load. Sealedbearings were chosen in order for them to be suitable for the damp environment of the kiosk. It was then

decided that the bearings should last for 1 year of constant use at 500rpm. Using equation (1), and thenapplying a safety factor of 10 to account for the environmental effects, we calculated the required staticand dynamic load requirements. The next step was to select a bearing with an inner race that would

accommodate the shaft diameter and shoulder step.

Table 1: Bearing parameters (Data Sheet: A$$JTXX-7(3&U"#B.#%(,"1XG%>XJX>2BBU>%23.#8&X5H??5)5X )

Parameter ValueBearing Type Deep Groove

Bore Type Parallel

Cage Material Steel

Dynamic Load Rating 20.6 (KN)

End Type Sealed

Inside Diameter 25 (mm)

Maximum Speed - Grease 8000 (RPM)

Maximum Speed - Oil 13,000 (RPM)

Number of Rows 1

Outside Diameter 62 (mm)

Race Type Plain

Race Width 17 (mm)Static Load Rating 11.2 (KN)

L10

=

C

P

!

"#

$

%&

10

3 B

n

!

"#

$

%&

(1)

Where: L10: Is the bearing life in hours

C: Is the radial rating of the bearings in N

P: Is the dynamic equivalent radial load applied to the bearing

B: is 106/60

n: is the rotation speed in rev/min

4 MANUFACTURING

The following section describes the manufacturing procedure for each of the components within the Pelton

turbine. CAD graphics of each of the components can be viewed in Appendix A Drawing 0578_012. Formanufacturing of the turbine casing see section 8.

4.1

Turbine Shoulder Blocks


13/60

[email protected]

Page 12

The shoulder Block is a set of three components designed to maintain the axial and rotational location ofthe runner wheels and the Pelton cups. The shoulder flange fits over the shoulder on the shaft and fixes the

runner plates to the other two components of the shoulder block via eight M6 bolts. For manufacturingdrawings of the three components see Appendix A drawing 0578_010.

The shoulder flange was manufactured from an 80 mm diameter aluminium cylinder that was cut down to40 mm length. A 30 mm diameter hole was drilled through the centre of the block, then the centre of the

block was bored out to a diameter of 50mm and a depth of 20 mm to make it flush with the shoulder on theshaft. Finally, 8 M6 holes were drilled into the spacer at 45-degree intervals, with a centre distance of32.50mm away from the centre of the spacer.

The second spacer was also manufactured from a 80mm diameter, 40mm long aluminium cylinder. A 30 mmhole was drilled trough the centre of the block, and 8 M6 holes were drilled unto the block as in theshoulder flange. A keyway 3.30mm deep was cut into the flange in accordance with British standard keyway

manufacturing practises and dimensions. Care was taken to ensure that the keyway had the same angularorientation as the M6 holes, to ensure that the keyways and the holes on the second and third spacers lineup correctly.

The third spacer was manufactured in the exact same manner as the second one, except that the length of

the space is smaller at 20 mm instead of 40mm.

4.2 Turbine Spacers

Eight internal spacers were cut from a 50mm aluminium bar of 20 mm diameter. Oversized spacers(approximately 43mm long) were cut from the bar using a band saw, before the spacers were trimmed

down to size on a lathe and an M8 clearance hole was drilled through the block. This process was repeatedon each of the eight spacers. The spacers were designed to add rigidity and stiffness to the mid section ofthe turbines runner plates.

4.3 Turbine Shaft

The turbine shaft was manufactured from a 50 mm diameter, 550mm long aluminium round bar. The shaftwas turned down to a length of 546mm and then the cuts were made as shown in Appendix A drawing0578_009. Care was taken to ensure that the cuts on each side of the central shoulder were completed in a

single session to ensure the concentricity of the shaft. In addition, to prevent the shaft from bending underits own weight during turning, the shaft needed to be supported at both ends. To accomplish this, a small

Figure 9: Turbine shoulder block and spacers (From left to right: Shoulder Block, Runner plate, Internal spacer,runner plate, external spacer, Note yellow blocks are bearings.)


14/60

[email protected]

Page 13

pilot hole was drilled into both ends of the shaft, to provide purchase for a rolling support.

4.4 Turbine Runner Plates

The runner plates (Appendix A Drawing 0578_007) pose an interesting manufacturing challenge due to the

necessity to achieve an exactly circular plate with a multitude of accurately located clearance holes. Theconsequences being that an off-circular plate would not balance correctly, and any hole misalignmentswould create assembly problems. A Solidworks 3D model of the runner plate was first created in order toaccurately locate all of the component holes. Before producing the plates in aluminium, an acrylic

prototype was made using a 3-axis CNC machine at the Imperial College Ideas Laboratory. To do this a .stlfile was produced from the 3D model, square sheets of acrylic with sides measuring 10mm greater than the

diameter of the runners were placed in the CNC machine to produce the prototypes. The objective ofprototyping in acrylic is to check the accuracy of the CAD model and identify any design short falls beforemanufacturing the final product from aluminium.

The aluminium runner plates were finally produced using a 2-axis CNC laser-cutting machine within the

department of mechanical engineering at Imperial College London. In order to achieve this a .dxf file wasgenerated from the 3D model and provided to the technicians along with a large sheet of laser grade

aluminium. The sheet, measuring 1.5m x 2.5m, was of a size the machine could accommodate whilst stillproviding enough material to produce four plates in one cutting session. Laser grade aluminium is nodifferent to standard grade aluminium in its makeup, except the former is coated in a protective film that

does not reflect the laser cutter and does not melt onto the metal sheet. Four runner plates were producedfrom 3mm thick aluminium, two of which will be used in service and the other two used as spares. Notethat the thickest material that can be processed on the laser cutter is 3mm. The laser cutting process was

complete in approximately 1hour and 30 minutes. However at least one week should be allowed in theprogramme schedule to account for technician and machine availability.

Several other options were considered for manufacture before finally choosing laser cutting. Conventional

CNC was considered using the facilities within the mechanical engineering departments teaching workshop.However the diameter of runner required was outside the working range of the machines. Use of anindexing head on a milling machine was also considered but considered to be too time consuming and

overly complicated. Furthermore locating the multitude of clearance holes for components by hand wouldhave been time consuming, as well as less accurate than an automated approach.

Anybody wishing to employ the services of the plastics CNC machine should contact:

Ingrid Logan Ideas Lab Head Technician [email protected]

Anybody wishing to employ the services of the laser cutting CNC machine should contact:

Graham Gosling Head of Mechanical EngineeringLaboratory Facilities

[email protected]

Paul Woodward Mechanical EngineeringTechnician

[email protected]

4.5 Turbine Bearing Housing

Two bearing housings were manufactured to support the turbine shaft and constrain the bearings (See

Drawing 0578_007 in Appendix A). These were manufactured out of two aluminium blocks, of dimensions100 x 128 x 51 mm. The large size of these blocks meant that they could not be sourced through theconventional route of Imperial College, Mechanical Engineering Stores. Instead they were purchased online

(www.aluminiumwarehouse.co.uk). The bearing housings had to be secured to the turbine casing, and weredesigned to rest on steel angle welded to the side of the casing. To secure the housings holes were drilled

through the entire block of material, so that they could be bolted to the casing. A hole was initially drilled


15/60

[email protected]

Page 14

through the centre of the block. This was then bored out to a diameter slightly larger than the end of theturbine shaft. This allowed the shaft to be slotted into both of the bearing housings. This hole was then

enlarged to the diameter of the bearing, but only to a depth of 27mm. The advantage of this was that itconstrained the bearings axially in one direction and the shoulders on the shaft constrained them in theother. An initial design idea was to then cut the bearing-housing block in half to allow easier assembly of

the turbine. This was later rejected as it was considered that cutting the bearing housing in half wouldinevitably lead to bearing misalignment problems, ultimately leading to a reduction in bearing life.

4.6 Temporary Support Stands

In order to accommodate the testing of the manufactured turbine it was necessary to have a stand to

secure the turbine to. This stand was also designed with the aim of developing into a future turbine testingrig system.

The priority in the design was to create something that was easy to manufacture, but was robust and heavyto act as resistance to any water jet impulses that may be used to spin the turbine. With this in mind we

approached the civil engineering structures laboratory at Imperial College London to source materials andget advice on a design. Kindly the technicians were able to donate to us three offcuts of steel I section

beam designated as UKC-152. Two stands were constructed in total. Each stand (figure 10) comprised of abottom horizontal I-section member with an I-section located at the midpoint and welded vertically to thetop flange. A steel capping plate was then welded onto the end of the vertical I-section. Lastly holes were

drilled in the bottom flange of the horizontal members to allow it to be secured to a base.

Figure 10: Turbine temporary support stands before drilling of top holes to receive turbine housing


16/60

[email protected]

Page 15

Figure 11: Fully assembled turbine test unit with support stands, induction generator, turbine cover and ELChousing.

As well as having two secure stands on which to test the turbine, it was also envisaged that the wholesystem would be contained on a self-contained rig (figure 11). Although not completely finished the rig that

was built consists of a sturdy wooden base frame on which the steel stands are bolted. The wooden base isframed internally for strength, and has detachable wheels to allow it to be transported easily. Between thetwo steel stands is an opening in the wooden frame in order to allow water to egress. To the side of thesteel stands and turbine an induction generator is bolted to the wooden frame as well as a housing for an

Electronic Load Controller (ELC). Between the steel stands is a precisely made clear acrylic box. It isenvisaged that this box will be used to contain the turbine and the water jets used to power the turbine.

The transparent nature of the box allows for easy observation of the behaviour of the turbine.

The rig has not yet been finished and requires further development of the transparent acrylic box as wellmounting of the jet nozzles. Experience taken from the development of the real casing (section 7) inRwanda should also be noted so as to not make similar mistakes when developing this rig in the UK.

4.7 Temporary Resin Pelton Cups

Early on in the design phase it was decided that a set of prototype cups were necessary for testing and inorder to guide further design. However the manufacturing of Pelton cups due to their intricacy is extremelydifficult and expensive, particularly when multiple cups must be manufactured from stainless steel. To this

extent it was decided instead to cast a complete set of prototype cups from resin. Resin was chosenbecause of its ductile properties and its ability to easily absorb and dissipate energy from an impact such asthat of a high power water jet.

However before resin casting of the prototype cups could commence, the difficulty still remained that we

did not have a master copy with which to make a mould from. To this extent we had two prototype Peltoncups produced (figure 12) on a 3D printer owned by the Imperial College Robotics Society. The CAD design

for the cup itself was found on an open source 3D printer models website (www.thingiverse.com) and foundto be of a suitable size for our design. Two cups were produced in total, one with a slightly finer internal

mesh structure that proved to be of a much stronger and finer design. Nevertheless before the printed


17/60

[email protected]

Page 16

master copies could be used to produce moulds they were covered in wax in order to smooth out anyanomalies left as residue from the 3D printing.

The moulds and resin cups were manufactured at the Imperial College Ideas laboratory where specialist

equipment for mixing and pouring resin and silicon is available. Much of the following describedmanufacturing was undertaken under the supervision and advice of the laboratory technician, Ingrid Logan,who has extensive experience working with resins and plastics. Firstly a small MDF formwork was created to

contain the master models and pour silicon around. Three screws were drilled through the bottom of theformwork upon which the flat base of the Pelton cup was attached using super glue. A silicon mix was thenproduced in a centrifuge by mixing silicon with a hardening agent (mixing in a centrifuge eliminates any air

bubbles). This mix was poured around the master cup until fully covered whilst allowing around 25mm ofsilicon above the model. The silicon was left to cure for 24 hours. Once cured the MDF formwork was

removed and the screws removed from the base using a cordless drill. In order to remove the master cupwhilst retaining the mould for future use a sharp knife was used to cut a wavy pattern through the mould tothe cup. The mould was cut on three out of four sides, the last side being left as a sort of hinge. Note that

the cutting of the mould and removal of the printed cup is a time consuming process. Lastly two holes weredrilled into the mould across the shoulder section. One hole would later be used to inject resin and a

second hole would be used to allow the egress of air. Two silicon moulds were made in order to speed up

the process of producing prototype cups.

Once the moulds were complete a resin was mixed, again in a centrifuge, by combining resin with ahardening agent. Much smaller quantities are required than that of the silicon for the mould. The resin is

then injected into one of the holes previously drilled into the mould. On the first attempt it was found thatresin was seeping out through the gap in the middle of the mould. To solve this problem the moulds weretightly wrapped in Clingfilm. Initially the amount of hardener agent used was insufficient as prototype cups

came out particularly malleable and soft. The ratios were changed as well as switching to a faster setting-hardening agent in order to speed up the manufacturing process.

The quality of the cups produced was largely mixed. Many were of sufficient quality but required some

touching up with a patching resin mix. All required a small amount of machining in order to remove somesurplus resin material. Overall the shoulder end of the cups was produced very well due to its blockynature, however the thinner top end of the cups where the arms come round to the front opening was

produced more poorly. Generally this occurred because air would easily get trapped at the tips of thesearms. In the future placing air holes above both of these locations would be recommended.

In total 20 resin prototype cups were made. Holes in the shoulders to attach the cups to the runner plates

were drilled using an HSS drill bit after casting. Drilling in this resin material should be carried out using adrill at a low speed and low torque. Anybody wishing to produce silicon moulds and resin prototypes shouldcontact Ingrid Logan (details above).

Figure 12: 3D printed Pelton cup with applied yellow wax and seated on screws within mould formwork.


18/60

[email protected]

Page 17

Figure 13: Silicon mould with visible Pelton cup silhouette and curved cut for mould release.

4.8 Stainless Steel Pelton Cups

Following the success of the resin cast cups it was decided to have the Pelton cups manufactured instainless steel (figure 14). After seeking the advice of several of the mechanical engineering technicians itwas decided that the preferred process was investment casting (also referred to as lost wax casting).

However Imperial College has no facility for any form of metal casting. As such the work was outsourced toa company in Devon named Investacast (http://www.investacast.com), which had previous experience withproducing Pelton cups.

There are several stages to this complicated process all of which are explained in detail on the Investacast

website (see above) with video explanations. Of particular note is that once the company have made themaster pattern or tooling from the prototype we sent, that tooling is kept and can be used again in thefuture. This seriously reduces the cost of any future Pelton cups that wish to be made as the production of

a tooling represents around 50% of the cost of the initial cups.

Despite being very happy with the quality of the casting work produced by Investacast ltd, we weredisappointed with the timeliness and quality of service given to us, especially considering the large cost of

the items. Communication with Chris Buckland at Investacast was slow and often-required chase up phonecalls by us. The delivery of the items was also five weeks late despite constant promises from Investacastthat they were on schedule.

Anybody looking to employee the services of an investment casting company should contact:

Chris Buckland Costing Engineer at InvestacastLtd (Ilfracombe Devon)

[email protected]

+44(0)1271 866200


19/60

[email protected]

Page 18

Figure 14: Stainless steel Pelton cups before tidying and shoulder hole machining.

5

MATERIALS

In the selection of an appropriate material for the construction of the Pelton wheel turbine, the two main

material properties required are corrosion resistance and high load bearing capabilities. Although stainlesssteel is perhaps the most attractive option for this application, it is among the most difficult materials to

work and manufacture, making it very costly and time consuming to produce turbine parts from.Consequently, aluminium was chosen to build the main body of the turbine due to its resistance tocorrosion, cheap cost and suitable structural properties. Its forgiving nature and ease of manufacturing

made it an ideal material to construct the organisations first turbine from. Ideally for long termdeployment the aluminium would be anodised to improve its corrosion resistant properties. The Pelton cups

were made from stainless steel, as described in section 4.8 due to it being of a comparable cost toaluminium when casting.

6 TRANSMISSION SYSTEM

Once the turbine design had been finalised, a method of linking the Pelton wheel to the alternator needed

to be developed. The transmission systems investigated were gear trains, pulleys and clutches, but a pulleysystem was settled upon due to its flexibility, simplicity and greater tolerance allowances. Furthermorepulley transmission systems were known to be available in Rwanda should replacements or repairs be

necessary to source in country.

The design rationale for the transmission system of our turbine follows the guidelines set out by The Micro

Hydro Design Manual.


20/60

[email protected]

Page 19

6.1 Preliminary Design Requirements

The transmission system needed to fulfil several design criteria. Primarily It needed to step up the rotation

speed of the system from 500 rpm to 1500 rpm. The reason for stepping the rotational speed up to 1500rpm is such that the four-pole alternator machine employed would be able to generate 50hz AC when

spinning around 1500 rpm. As the turbine was designed to spin at only 500 rpm it was necessary to step thesystem up using different pulley diameters. The estimated power output of the system was to be 10KW asper the turbine design. The alternator had not yet been sourced at this point and so a certain degree of

flexibility was required in the transmission design so as to allow for a range of diameters.

6.2 Design Rationale

From the Power and the speed ratio, we can calculate the approximate torque that the generator shaft willundergo, which is approximately 60Nm. From this, we could then calculate the minimum Pitch circle

Diameter (PCD) for the small (alternator side) pulley: 95mm. This means that the turbine side pulley willhave approximately a 300mm PCD.

From the turbine power, we can estimate the design power of our belts; they would have to be

conservatively rated for approximately 15KW. In addition, from this power rating and the maximum pulleyspeed of 1500 rpm, we could determine that an SPC or SPB cross section for the belt would be suitable forour transmission train.

It should be noted that the actual pulley is in fact comprised of two separate components: the actual

pulley, and a taper lock bush that lies directly on the shaft. This removes the need to provide axial locationfor the pulleys, but requires the sourcing of two separate parts. The taper lock bush provides an industrystandard friction fit through the use of a slotted cut in the bush construction (figure 15) as well as the

installation of two grub screws. Two grub screw slots are located either side of the slit in the bush,tightening the grub screws has a two fold affect, firstly it compresses the bush onto the axle creating a

friction fit, secondly it secures the taper lock bush component to the surrounding pulley. Conveniently athird grub screw location is provided, tightening the grub screw here releases the taper lock bush for easeof disassembly. There are different ISO series of taper lock bush, each of which have the same outer

diameter but have a range of different inner diameters to suit different axles. Make sure to match theinner diameter to the axle size and the outer diameter (or the series number) to the appropriate pulley.Note that although a friction fit is produced to axially restrain the pulley, a key is still required for

rotational restraint.

Figure 15: Taper lock bush being installed in a pulley.


21/60

[email protected]

Page 20

6.3 Pulley Selection

The pulleys taper lock bush and belts were initially sourced in the UK because the team were unsure as to

the availability of various and specific diameters of pulleys in Rwanda. The alternator shaft diameter wasinitially unknown and so this was sourced in the UK later. However, the convenience comes depending on

what ISO standardised size is chosen, the taper lock may have varying diameters but will fit the same ODpulley. Size ISO 1600 bushes come with inner bore diameters ranging from 14 to 42 mm, meaning that theyshould be able to fit the shafts of most alternators we will come across. A pulley of size 1600 and PCD

95mm was chosen, and the corresponding taper was to be selected later after the generator was sourced.All pulleys and taper lock bushes were sourced online in the UK from www.bearingboys.co.uk. They were

then transported to Rwanda in expedition members luggage.

For the pulley on the turbine side, the PCD must be 285 mm, which requires a 2012 size taper lock bush.The bush must also have an ID of 25mm. A summary of components is given in table 2:

Table 2: Turbine transmission system components list

Item Designation Inner BoreDiameter

(mm)

OuterDiameter

(mm)

Source

TurbinePulley

SPB300/1 V - 305.5 www.bearingboys.co.uk

AlternatorPulley

SPB100/1 V - 105 www.bearingboys.co.uk

Turbine TaperLock Bush

2012_25 25 - www.bearingboys.co.uk

AlternatorTaper Lock

Bush

1610_42 42 - RS Components

6.4

Tensioning Methods

When the system is set up, a method of tensioning the belt must be implemented, to prevent the belt fromdamaging itself while in use. Two options are available: Slide rails and jockeys. Slide rails were chosen due

to their simplicity and ease of manufacture on site. This was achieved using two steel channel sections witha rebate in the top flange to allow alternator bolts to slide along the length of the channel. A few beltswere initially sourced in the UK, these were B section v groove belts to match the purchased pulleys. An

initial inside diameter of 1524 mm was chosen but this proved too small for the final as built design.Instead we sourced longer belts in Kigali, these are available in abundance due to their application in the

automotive and agricultural machinery industries.

6.5 Implementation

6.5.1

Methodology

Firstly the alternator was sourced in order to determine the alternator shaft diameter (42mm). Once theshaft diameter was sent back to London, a taper lock bush was sourced form RS components and then sentto Rwanda via DHL. The transmission system was then assembled as described above. To prevent injury to

the operators, a grille was erected around the transmission system (figure 16) to prevent contact with anymoving components. The grille was constructed from flat sheets of stiff steel grillage material. It was bent

and cut into the appropriate shape to form a cover over all moving components. It was then bolted onto theturbine casing at its topside, and its bottom was drilled and screwed onto the concrete upstand.

6.5.2

Problems Encountered on the Ground

The casing design was largely unknown before leaving the UK, hence it was unknown what centre to centre

distance would be installed between turbine shaft and alternator shaft. The belts initially bought were too


22/60

[email protected]

Page 21

short but new belts were sourced in Kigali relatively easily. Furthermore the taperlock bush on the turbinewas initially slightly too lose due to manufacturing tolerances, this was later remedied by placing the

keyway. Lastly the taper lock bush on the generator side was not robust enough and fractured. Fortunatelythe pulley could still be attached to the generator due to its operation in compression.

Figure 16: Turbine casing with grating around transmission system

7

TURBINE CASING

7.1 Casing Design

A casing was designed in order to house the turbine during operation. This served several purposes,including: supporting the turbine and alternator; protecting people from moving parts and high-pressure

jets; and restricting spray from the turbine. The casing was composed of three components a base plate, atop casing and a bottom casing. The base plate was manufactured from 8mm thick plate steel and the rest

of the casing from 5mm thick plate steel. The base plate supported the rest of the casing, and has runnersmade from rolled steel channel section to allow the alternator to be laterally. The ability of the alternatorto slide relative to the casing meant the transmission belt between it and the turbine could be correctly

tensioned. A hole in the base above where the turbine was situated was also cut in the plate, to allow thewater to flush into the tailrace and exit the kiosk. The main body of the casing had to be designed in two

parts, due to the configuration of the bearing housings and turbine shaft such that the turbine could bemore easily assembled in situ. Steel angle was welded around the perimeter of the two casing halves toallow them to be bolted together and also bolted to the base plate. Two holes were cut in the casing for

installation of the spear valves and nozzle jets. These were located on the casing top and casing front,nozzle and valve assemblies were attached to the turbine casing using through bolts. Two more holes were


23/60

[email protected]

Page 22

drilled in the casing sides to allow the turbine shaft to be positioned through the casing. The casing wasfully sealed at joints using rubber gaskets. Lastly an access hole was cut in the side of the turbine casing; a

steel hatch was attached over the hole and secured with bolts. Lastly the entire casing was painted with atwo-coat epoxy paint.

7.2

Contractual ProcedureHistorically our dealings with Renewable Energy Company (REC) - Sonatubes have been fraught withdelays, unclear costs, and false promises. To this extent when dealing with REC in summer 2013 it was

imperative that a clear and firm contractual framework was laid out and agreed upon by both parties inorder to expedite manufacturing. A copy of the contract agreed upon between e.quinox and REC can be

found in Appendix B. A copy of the price breakdown agreed upon for the manufacturing can also be foundin Appendix B as signed by both parties.

It is important to note that lengthy contractual agreements are not common practice when engaging insmall business transactions within East Africa. The concept of a contractual agreement is rather western

and may be met with resistance by business owners in East Africa where handshake agreements are morecommon. When constructing such a contract it is important to include several key aspects. Firstly in order

to ensure that the manufacturing is delivered on time the contract must detail the expected programme ofworks with a specific expected due date and time. It may be necessary to include penalty clauses such thatany delay in works leads to a reduction in payment in order to incite punctual delivery of works. Without

these programme arrangements it is likely that the manufacturer will run far over schedule. In fact ourexperiences have taught us that the typical expected time for completion should be at least doubled inorder to allow for complications that mostly always occur.

Secondly notes on the expected specification and quality of works must be agreed. It is standard practice

that a full set of working drawings is provided to the manufacturer including the expected tolerances to bemet. Regular inspections of work should be undertaken such that these tolerances can be checked and

signed off before further work can progress. Without detailed technical drawings it is common thatmanufacturers will deviate largely from the expected works.

Communication is imperative to successful completion of any project. Clear procedures for communicationmust be provided within the contract. Not only does this mean highlighting primary and secondary methods

of communication (telephone and email details) but also the expected time frame within which a reply to acommunication must be made. Moreover the contract should highlight the fact that any changes or

requested deviations from the drawings provided should be communicated to the clients. Details should beprovided of the clients responsibilities to respond to such requests within a reasonable time frame.Remember that email communication within east Africa is slow as most people do not have regular access

to email, communication by telephone should always take precedent over email.

Lastly consider that the contract is a two-way document. It should consider both the manufacturers and theclients responsibilities. This should include such items as the scope of detail and specification the clientshould provide to the manufacturer and the timely order in which it should be delivered. Finally a specific

break down of costs should be provided, written out in a separate document and signed & stamped by both

parties. Full payment should not proceed until full delivery of the manufactured product as to the agreedspecification. Normally a deposit is made as a percentage of the total cost. As a rule of thumb for total costless than 1000 a 10% deposit should be given, for total cost greater than 2000 20% should be given.

All these details and any special arrangements should be provided in a clear and professional document.Upon agreement by both parties each page should be initialled and the last page signed, printed and dated.

Both parties should retain copies. A receipt should then be given for the deposit and a second receiptshould be obtained after full payment.

It is our experience that such contracts provide stability to a relationship between client and manufacturer

rather than a distinct binding legal framework. As in many cases within East Africa it is unclear as to whatprocedure to follow should there be any serious break of clauses. Regardless it is certain that following alegal dispute route would unearth a huge amount of unnecessary, costly and time consuming bureaucracy.

Rather it highlights in one easy document everything that the involved parties should be doing.


24/60


25/60

[email protected]

Page 24

Figure 18: Eugene (manufacturer) and Evan inspecting finished casing (swan neck absent)

Figure 17: Drilling holes in bearing housing mounting bracket


26/60

[email protected]

Page 25

7.4 Recommendations for Future Design

Despite being very pleased with the delivered product post manufacturing; after installation and testing,

evaluation has shown that several design changes are required to the turbine casing itself. These arediscussed below.

Firstly during installation gaskets were cut and added at the middle level intersection, and the intersection

between the base plate and the bottom section. Gaskets were also placed between the nozzle valves andthe swan. We found in some capacity most elements of the design caused some form of leak, some moremajorly than others. The base plate was placed down on the concrete upstand and secured using

mechanical fasteners anchored to the concrete. Mistakenly the base plate was grouted in post anchoring,this meant that grout had to be filled into very small gaps underneath the base plate. Several leaks were

eventually found to come from underneath the base plate itself where the grout had failed. In future thebase plate should be laid down on a bed of grout and then bolted down to the anchors. This helps create aseamless layer of grout around the entirety of the base plate to stop the ingress of water from inside the

tailrace. We also found that when the alternator is starting up and not necessarily spinning at its optimumrpm the vibrations induced in the base plate are large and caused a lot of the grouting to crack. This effectcould be reduced by using vibration mount pads, but also by using more anchoring bolts between the

concrete and the base plate.

Furthermore we found that along the short sides of the bottom section, the gasket between the angle andbase plate leaked profusely. This is considered to be because only two connecting bolts are placed at the

ends of these shorter angles. Ideally more holding down bolts would be used and would be spread evenlyalong the angle length. All together we found that actually having the bottom section be separable fromthe base plate is unnecessary and adds very little to the ease of construction. Future designs should

consider minimising the amount of separable connections and instead weld the bottom section directly tothe base plate.

More leaks were found at the middle level intersection coming from the gasket between the two angles.

This intersection could not be designed out, as it is necessary to be able to lift the top section off toperform maintenance on the turbine. A plethora of securing bolts have been designed all along the angles

in order to ensure a secure connection between both sections of the casing. However leaks around theperimeter showed that the gasket material wasnt of a high enough quality. The problem being that therubber used was not thick enough or compressible enough, such that when all the bolts are fully tightened,

parts of the gasket are still loose allowing water egress. Future designs should allow for a thicker and morecompressible gasket so that the rubber can take up any flaws/unevenness in the angles surface.

Furthermore at the intersection between the top and bottom of the case we found that when the turbine isstarting up, there is a lot of water splashing unevenly around the inside of the case causing water to egress

from around the shaft. This problem is eliminated when the turbine reaches full rpm and the jets are fullydeveloped. However it shows that a shaft seal is necessary on the inside of the casing to eliminate leakingduring start up. Moreover the same problem is encountered around the two shafts for the deflector plates

as leaking was seen around the bearing housings. Again designing in shaft seals could solve this.

Finally a more extensive problem was found in the swan design. To start with after installation and testingit was found that several leaks were present around the welds between the two parts of the swan neck.

Grinding down the welds solved this problem, followed by re-welding where holes were found and finallycovering the entirety of the welds with car body filler. However the more extensive problem was thatwhilst the swan neck fitted to its connections on the casing immediately after welding (figure 18), some

time later the welds had cooled causing shrinkage. When trying to refit the swan it was found that the boltholes between case and swan connections were up to 20mm misaligned. Using a special arrangement of

bolts and a lot of leverage eventually solved this problem. The situation is less than ideal and is very timeconsuming, taking around two hours to secure the swan; a job that should take 10 minutes. The solution isto ensure more accurate manufacturing and leaving the swan neck connected whilst allowing the welds to

cool.


27/60

[email protected]

Page 26

Figure 19: Swan neck after painting

8 ELECTRICAL DUMP LOAD

The turbine system installed during the 2013 summer expedition was calculated to have a maximum outputof 10KW, hence in order to test the turbine it required an outlet to dump the generated energy. Ultimatel

the turbine will be connected up to the internal charging system within the kiosk, the electrical system toachieve this was outside the scope of the 2013 summer expedition. Instead an alternator coupled with apassive load would be used to test the electrical output produced, and stop the turbine from running out of

control. The alternator was selected to support the theoretical maximum 10KW capacity of the hydrosystem. After inspecting several alternator options we chose a synchronous machine with the specificationsgiven in table 3. Synchronous machines of many different capacities and form factors were found, as were

induction generators. The machine cost 480,000 RWF in total and was sourced from a shop in Nyambogogowhich had a large store of alternators in a warehouse behind the shop, selling mainly motors and devices

for agriculture but also alternators and induction machines.


28/60

[email protected]

Page 27

Table 3: Synchronous Generator Specification

Property Value

Model (-) STC-10

Manufacturer (-) Elmega

Phase (-) 3 Phase ACConnection (-) Neutral Point Star Connected

Operational Phase Voltage (V) 230

Operational Line Voltage (V) 380

Frequency (Hz) 50

Power Factor (-) 0.8

Output (KVa, KW) 12.5,10

Current (A) 19.1

Pole Number (-) 4

Synchronous Speed (rpm) 1500

In a micro hydro system a common solution is to use heating elements as a dump load. Heating elements,much like those found in a kettle, are cheap and easy to come by and will reliably transfer excess electricalenergy to the surroundings. The dump load was designed as a three-phase AC load connected to thealternator in a star configuration with a neutral return line. The neutral line was left in to support a return

current which exists if the three loads are not balanced, which is entirely possible in the real world andespecially within the operating environment presented in a developing country such as Rwanda. The

impedance to be applied to each of the three phases was chosen so that it would allow the alternator torun at its operating voltage and current, whilst the power rating of each must be more than that of thecalculated power as a safety factor. The real power in KW is the useful power output, however the system

must be rated to the apparent power in KVA. The load on each branch of the star has a voltage of 219.4Vacross it and 12.1A running through it. This leads to a power of 4190.5VA dissipated in each load (leading toa total apparent power of just over 12.5KVA dissipated across all three branches). The resistance required

for this load is then 21.4/19.1 = 11.5 ohms.

After exploring the market we found a combination of electric water heating coils that could be combinedto create a load with the correct resistance and rating. The objective was therefore to find a combination

of water heaters, which could be turned into a load equivalent to approximately 11.5 ohms and rated at4.5-5KW. The solution we came up with was to use three 1000W heaters in parallel on each branch (figure20). Each heater had a resistance of 61.2 ohms and cost 1500RWf (approximately 1.50). This gave the load

a total resistance of 12.24 ohms with a current of 3.82A passing through each branch. This resistance isclose enough to not affect the operating voltage too much. And each water heater will see a power

dissipation of 838W, which is suitably lower than the rating of 1KW. These numbers will fluctuate due to avariety of factors, but using a safety factor of ~20% allows this to happen with jeopardising the safety ofthe system.

To implement this design the heating elements were wired up in parallel and positioned in the kiosk

tailrace so that the water exiting the turbine will carry away excess energy. This method is particularlysmart as it ensures that at any one point that electricity is being produced, there must also be water

present in the tail race in order to dissipate excess heat. The tailrace was retrofitted with a concrete weirto ensure that a pool of water backed up in the tailrace meaning the heater elements were constantlysubmerged. Three bespoke steel brackets were created to secure the water heater elements to the

underside of the concrete slab placed over the tailrace (figure 21). The dimensions of the brackets andheaters ensure that under full flow conditions only the metal heater element is fully submerged. Above thismetal element an HDPE plastic case contains the wire to element connections. This was stripped of

unnecessary electrical indicators such as LEDs before being glued and fully sealed using mastic for awatertight seal. The two wire lines that emerge from the heater elements enter an IP65 case. One wire

from every water heater element is connected to a common neutral. The second wires from the element ona branch are joined together to ensure a parallel connection and then spliced onto a single heavy gaugewire that goes back to one of the phases on the alternator, depending on which branch of resistors it is

(each branch is colour coded). The neutral also comprises heavy gauge wire and follows the same route


29/60

[email protected]

Page 28

back through the kiosk wall and into the alternator. The physical wiring in the kiosk follows the schematicgiven in figure 20.

Figure 20: Electrical circuit diagram for heater elements

Figure 21: Electrical dump load showing three rows of heater element resistors and IP65 case containing wiring


30/60

[email protected]

Page 29

9 TESTING

Due to time constraints, an in-depth testing of the rig could not be implemented. In particular, a stress

test could not be performed to estimate how the turbine would perform if it were run consistently duringthe year. Nevertheless, testing was attempted by running the turbine for short periods of time and

recording our observations. The plastic resin cups that were used in the absence of delivery of the stainlesssteel cups held up remarkably well during testing. The only shattered cup was the 3-D printed cup; theothers showed little sign of damage. This could be due to the fact that the incoming jets are not as focused

as expected, reducing the pressure forces acting on the cups. The plastic cups will have to be exchangedfor the stainless steel ones at some point regardless of this, as they will eventually oxidise and becomebrittle.

The turbine casing and the associated piping had severe leakage problems, specifically beneath the casing,

at the ball valve between the swan neck and the main pipe, and at the mid-section of the casing. The leakat the ball valve was the most significant one in terms of volume of water lost, but the others are not smallenough to be ignored. Initially, the leak under the casing was sealed using grout, but once the alternator

was installed, the entire system vibrated significantly during use, to the point that the grouting cracked. Inaddition to causing leakage problems, the excessive vibration may also cause structural problems later on.

The leak at the midsection of the casing is particularly troublesome, as it allows a noticeable amount ofwater into the bearings, potentially washing away their lubricant and significantly reducing their designlife.

The turbine RPM and power output were much lower than expected.

Table 4: Alternator RPM when connected to the dump load, and when disconnected.

Flow Condition Unloaded (RPM) Loaded (RPM)

Full Flow 1450 580

Half Flow 1050 430

Table 5: Voltage, current and calculated power of the 3 phases during loading.

Voltage (V) Current (A) Power (W)

50 0.05 2.5

The dump loads appeared to work, as they did indeed exhibit a temperature increase of approximately 10

degrees while above water and the turbine was run for approximately 5 minutes. When the loads weresubmerged, no noticeable temperature difference was noted assumedly showing that there is transfer ofenergy from the elements to the moving water of the tailrace. On a separate occasion, the test was

repeated in the presence of Leonardo Ialongo, an electrical engineer. It should also be noted that thesecond test was conducted after a period of rain, and that in this test, the settling tank reachedequilibrium such that the flow into the tank matched the output through the penstock and so full pipe flow

was observed through the penstock. In this test two of the phases were disconnected in an attempt toreduce the load on the alternator. Doing so increased the alternators speed, but also significantly increased

the heat produced by the heating elements that were still connected. This was to be expected as all theenergy produced was now being dumped over just three heater elements instead of nine.

Table 6: Alternator Speed and Voltage measurements

Flow Condition Alternator Speed (RPM) Voltage (V)

Full Flow 720 120

During the second experiment, no current readings were taken under the suggestion of Mr Ialongo, as heraised concerns that the potential design current could damage the multimeter, which was only rated to 10


31/60

[email protected]

Page 30

amps. Overall a lower power output was observed than the theoretical power output of the site, this maybe explained by a plethora of reasonings:

1)

The site was poorly rated in preliminary surveys.

2)

The tests were conducted in the dry season, where the volumetric flow of the water was too low.

This is potentially the most likely explanation, as the second test was conducted after a period ofrain, increasing the inflow of water into the settling tank.

3)

The settling tank was improperly calibrated. Occasionally the settling tank did not reach

equilibrium; it would empty faster than it would fill up. This would cause the flow in the pipe to go

from experiencing pipe flow, to open channel flow, reducing the potential pressure of the water jet

and overall power output.

4) Improper design of the conical input jet nozzles.

Although the issues discussed reduce the effectiveness of the turbine significantly, many of them have verysimple solutions. The following list is not meant to be an exhaustive list of solutions, but instead give anidea of what may be done to further improve the system.

1)

Vibrations in the turbine and alternator.

The vibrations of the turbine can be remedied in a number of ways. The most effective solutions wouldprobably be to anchor the baseplate of the turbine in more locations, specifically towards the edges of thebaseplate, as currently it is only anchored in the middle. Introducing dampeners under the baseplate to

absorb some of the vibrational energy may further improve the design. The vibrations of the turbine mayalso be reduced by increasing / reducing the weight of the rig depending on whether it is operating above

or below resonance.

2) Leaks

The different leaks in the casing and the housing would each have different solutions. The leaks beneaththe baseplate would need to be sealed off with silicone or an alternative viscous solid. The leak at the ball

valve requires a flexible pipe to reduce the angle between the two adjoining pipes. The leak at the mid-section of the baseplate can be resolved partially using improved gaskets, but the leaks in the bearinghousing will require that they be completely re-designed.

3) Low Power Output

The low power output of the turbine is not a problem that can be solved easily. The problem may be due inpart to the alternator not operating at the specified speed, or the low water flow rate or a number of other

reasons. More research should be done into understanding how generators work and what the realisticpower output of our site is.

10

FINANCES

This project consists of three key phases; manufacture of a testing support stand, manufacture of themechanical Pelton turbine, and manufacture of the turbine casing. To this extent the following costsummaries are provided for each phase of the project:

Table 7: Project finances summary

Phase Cost

Turbine Temporary Support Structure 151.25

Pelton Turbine Manufacture 2568.62

Turbine Casing Manufacture 1696.37

Total 3416.24


32/60

[email protected]

Page 31

A full cost break down for each phase can be found in Appendix C. By far the most expensive componentwithin the whole build was the investment casting of the Pelton cups in stainless steel by the external

company Investacast Ltd. This cost represents approximately 60% of the total cost given above. Otheroptions were explored for having the Pelton cups manufactured, however no other investment castingcompany gave a markedly lower quote price. Notably we compared quotes at Investacast ltd for aluminium

cups vs stainless steel cups. Surprisingly these were of comparable cost despite stainless steelmanufacturing usually being much higher due to higher material and machining costs.

Please also note that the costs supplied above do not include the cost of labour, fabrication tools, orworkshop space hire (with the exception of the Pelton cups and turbine case). This is because the majority

of the turbine manufacturing took place at Imperial College mechanical engineering student teachingworkshops by current students. Overall the cost represents roughly one quarter of the costs quoted by a

professional company to manufacture an entire system in the UK. This represents a significant step forwardin the development of a low cost Pelton turbine system for pico hydro systems, assuming that themanufacturing skills and facilities are available to those looking to undertake such a project.

11

CONCLUDING REMARKS

From the complexities of the project described in this report a plethora of conclusions may be derived.Nevertheless the overarching conclusion concerns the success of the project. The beginning of this report

describes the complex historical background to creating a turbine in Rwanda. The devotion of the team to

this years project, and their willingness to create a truly fantastic piece of engineering has led to the

success of this project. This years project has set the foundation from which improvements and further

developments to the turbine system can be made.

It is recommended that the turbine is re-manufactured with an emphasis on improving the design and

construction of the bearing housings. Ultimately the alignment of bolts through a 100 mm thick bearing

housing is difficult to achieve, and a potential redesign should be considered. Furthermore many of the

aluminium parts were created from non-anodized sheeting. It is recommended that after manufacture the

aluminium components be anodized for longevity of the product. Although stainless steel would be theideal material choice, its cost and the difficulty to manufacture make it prohibitive to the success of

creating a low cost turbine system.

Considering the casing, the robustness and durability of the design were a success. Our working relationship

with the casing manufacture was also very successful and overall delivered a product that was very close to

specification, something almost un-heard of in Africa. The main problems with the casing concern the

leaking at several key locations as previously described. Some additional time and alterations to the design

will remedy these issues, and potential solutions have already been given. The vibrations of the casing

caused by the alternator are of particular concern, however solutions have been presented here and the

use of damping connections may be necessary.

Thoughts and effort for the coming year will involve developing and testing solutions to the specificproblems identified. The teams attention will then turn to developing scheme plans to usefully harness the

electricity produced from the Pelton turbine. In the coming year design work will shift from mostly

mechanical engineering to the incorporation of a joint mechanical electrical engineering team workload

as the two disciplines must work together to realise the aims of providing direct power to the local villages.

Particular emphasis should be placed on the sustainable implementation of such plans, from an

environmental, economic and social point of view.


33/60

[email protected]

Page 18

APPENDIX A TECHNICAL DRAWINGS

List of Technical Drawings:

Turbine Casing Drawings:

0578_001: General Arrangement Drawing

0578_002A: Plan Drawing A

0578_002B: Plan Drawing B

0578_003A: Elevation Drawing A

0578_003B: Elevation Drawing B

0578_004: Section Drawing

0578_005: Swan Arrangement

0578_006: Kiosk Plumbing Arrangement

Pelton Turbine Drawings:

0578_007:Bearing Housing Manufacturing Drawing

0578_008: Runner Plates Manufacturing Drawing

0578_009: Shaft Manufacturing Drawing

0578_010: Shoulder Block/Spacer Block Manufacturing Drawing

0578_011: Pelton Cup Machine Drawing

0578_012: Turbine Graphics

DISCLAIMER:

As of 1stSeptember 2013, and to the Authors knowledge, the drawings presentedhere and their dimensions are accurate and representative of the as built state of

hydro the system. These drawings are specific to the site for which they weredesigned, and as such should not be used by external partners, persons or companiesin order to manufacture a Pelton turbine system for any other specification before

first consulting an expert.


34/60


35/60


36/60


37/60


38/60


39/60


40/60


41/60


42/60


43/60


44/60


45/60


46/60


47/60

[email protected]

Page 19

APPENDIX B - MANUFACTURING CONTRACTS

Turbine casing contract signed between e.quinox and Renewable EnergyCompany

Price break down sheet for turbine casing signed between e.quinox andRenewable Energy Company


48/60

!"#$%#&$!'

#$%&'()*+%&,(-*$#%)*.%/&()/&.#*).(

0 1*#.%'+(./(*,#''2'&.(

)*+, -./001023 +, 34 50 1-60 5037002 3*0 80-60/, 49 0:;6/4 30-1 -26 3*0 ?0207-580

@20/.> A41B-2> 4B0/-3+2. 9/41 C42-3 HFI*-+8D J4-K+1 CF*-/B -26 H-33*07 L446: )*0 9-5/+F-34/ +,

/0B/0,02306 5> @


49/60

!"#$%#&$!'

)*+),-). -/ ,/0-1,- )23450/* 56 107 ,8109): 1;) .):5;).


50/60

!"#$%#&$!'

#

$

%&

'()%*+'&,-)+.'

)* +,*-./0//123/ 4/3150 1./ 61+0/4 25 '.471.85 9/,4-.0 :8 :0 /;7/68/4 8+,:618/4 8- /?@+:,-; 10 0--, 10 ./10-,1235 7.168:6123/ A3/00 814/ /@+13 8-

&$I -* 814/ +7-, 4/3:9/.5 -* :8/>0 HF MF N -* !$I -* 814/ :, 7/.0-, 1*8/. 9:0+13 :,07/68:-, -* 8/,8 -* 81:,4/. -* 814/ +7-, ./6/:78 -* 873/8/ 1,4

*:,13:O/4 7.-4+68 1*8/. 1 9:0+13 :,07/68:-, 1,4 0


51/60

!"#$%#&$!'

#

$%&'()*+,-./(0/.

)*+,-*./,012 .3453+1+/6 7899 :1 1;51./12 /3 :1 *:91 /o complete a basic shake .34486683+8+> *+2 *-/10 8+6/*99*/83+ /?1 6@6/14 86 1;51./12 /3 :1 *:91 /3 78/?6/*+2

:*68. 6/0166 /16/6 *+*93>3,6 /3 * ABC DA9/84*/1 B848/ C/*/1E *+2 FBC DF..821+/ B848/ C/*/1E /3

684,9*/1 /?1 1;/0141 93*26 /?*/ 4*@ :1 1;51./12 3G10 /?1 6@6/14 98-1/841

3

4-)5+6-5.7&6-/(-&-8(.

H?1 6@6/14 86 1;51./12 /3 510-304 /3 2168>+ .08/108* -30 /?1 -806/ /73 43+/?6 *-/10

.34486683+8+>I J*89,01 3- /?1 6@6/14 *-/10 /?86 510832 86 /?1 01653+68:898/@ 3- 1IK,8+3;I

#$%&'()

e.quinox operates on the Zero principle for safety, this means zero ?*04 /3 51063++19 30

1+G803+41+/I H?1 -*:08.*/30 86 1;51./12 /3 1+6,01 *99 51063++19 8+G39G12 8+ /?1 -*:08.*/83+ *01

730L8+> 6*-19@ /?03,>?3,/ /?1 503M1./I

C51.8-8. 01K,80141+/6N

J,99@ 0*/12 71928+> 4*6L6 /3 501G1+/ 2*4*>1 /3 1@168>?/

O93G16 *+2 >3>>916 ,612 2,08+> *+@ >08+28+> 30 53986?8+>

J,99@ G1+/89*/12 *01*6 2,08+> 71928+> *+2 5*8+/8+>

F+@ 8+M,0816 /3 51063++19 7899 :1 .3+6821012 61083,6 :01*.?16 3- /?1 .3+/0*./I

C8>+*/,016N

)*//?17 P332N IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Q+ R1?*9- 3- SIK,8+3;I

=*/1N

S,>1+1 P*98*,9*N IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Q+ :1?*9- 3- T1+17*:91 S+10>@ U345*+@

=*/1N


52/60


53/60

[email protected]

Page 20

APPENDIX C COST BREAKDOWN

E.quinox Turbine Temporary Support Structure Finances

E.quinox Pelton Turbine Finances

E.quinox Turbine Casing Finances


54/60


55/60

!"#$ !"#$%&' )*+%, -."/01%

%&'()*'"+ -.&' !"#$%&' 2%3, 456

7*'%, 89:;9:*?%, >@

AB%&C%?, D@

/0*1'('#$ 21(' 3.&'$ 4.'*5 3.&'$

8 =8E8;F =8E8;F

< 89EG8; 1.'R *1? \*RB%"R >8; R'%%K ]01& OK*'%? )Y*+/#Q#Q#

N'%%K %Y N'*01K%RR R'%%K =;;++ T 6++ S 5++ 2N A#+O#1%1'R

>6 -B"%*?%? V*" Z01& !K*'%? N'%%K N'.??01Q 2N A#+O#1%1'R

>G -B"%*?%? V*" Z01& !K*'%? N'%%K N'.??01Q 2N A#+O#1%1'R

>6 T#&C @*RB%"R>6 ).'R

6;++ ?0*+ S ?@AB

%CD0(1.E F"5'.1 409%&B P1Q N'#"%R


56/60

!"#$ !"#$%&' )*+%, -."/01%

%&'()*'"+ -.&' !"#$%&' 2%3, 456

7*'%, 89:;9:*?%, >@

AB%&C%?, D@

/0*1'('#$ 21(' 3.&'$ 4.'*5 3.&'$

8 8E=F5=G 8E=F5=G

8 8H8F9=G 8H8F9=G

8 0J? K'%%J TJ*'% I /*K% 8;;;++ O 0J? K'%%J &B*11%J 8;;;++ O H;++ O =++

!*01'01N [J.% %T#OS T*01' *1? B*"?%1%"

\#J?01N ?#Q1 /#J'K \0J'0 >8; +%&B*10&

2013 turbine manufacture pelton turbine

Documents