Design of Pelton Wheel: Tuesday Group

49
Design & Analysis of Pelton Wheel Turbine P M V Subbarao Professor Mechanical Engineering Department Internal Details of the Machine….

Transcript of Design of Pelton Wheel: Tuesday Group

Page 1: Design of Pelton Wheel: Tuesday Group

Design & Analysis of Pelton Wheel Turbine

P M V SubbaraoProfessor

Mechanical Engineering Department

Internal Details of the Machine….

Page 2: Design of Pelton Wheel: Tuesday Group

Koyna Hydro Electric Project

Koyna Dam from the catchment area of about

891.78 Sq. Km

•Koyna river rises in the Mahabaleshwar, a famous hill station in the hill range of Sahyadri. •It flows in a north - south direction almost parallel to the Arabian Sea coast for a distance of 65 Kms.

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Details of Koyna Hydro Electric Project

• Number of units: 4• Capacity of each unit=250MW• Head

– Normal Head=415m– Maximum Head=510m

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Creation of Reservoir

Page 5: Design of Pelton Wheel: Tuesday Group

MORE ADAPTED TYPE OF TURBINA IN FUNCTION OF THE  SPECIFIC SPEED.

Specific Speed in r.p.m. Turbine type Jump height in m

Until 18 Pelton of an injector 800 From 18 to 25 Pelton of an injector 800 to 400 From 26 to 35 Pelton of an injector 400 to 100 From 26 to 35 Pelton of two injectors 800 to 400 From 36 to 50 Pelton of two injectors 400 to 100 From 51 to 72 Pelton of four injectors 400 to 100

Specific speed in rpm4

5H

PNN s

Page 6: Design of Pelton Wheel: Tuesday Group

Selection of Speed of A Turbo Machine

Hzfforz

Np

503000

Zp : Number of pairs of poles of the generator

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Questions to be Answered

• Is it possible to change number of units in Stage IV?

• What is the allowable speed of the generator for each unit, if number of units is 2, 5, 6 or 7?

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Page 11: Design of Pelton Wheel: Tuesday Group

Design of Any Selected Pelton Wheel Unit

• Different capacities for each sub-group.• Design for Normal Head.• Assume an overall efficiency: 90 – 94%• Calculate the required flow rate.

HgQP pelton

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General Layout of A Hydro Power Plant

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THE CONDUIT SYSTEM

• Water from the storage is diverted into the main conduit system through a 3,370ft long intake channel and an intake tower, trash racks and two intake gates each 21ftX8ft.

• The head race tunnel is 12,000ft long and 21ft in diameter. • It is concrete lined for the whole of the length expect for

the last 1600ft at the surge end where 17ft diameter steel lining is provided.

• The diameter of the tunnel, in the stretch of steel lining is reduced on ground of economy

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Open Channel Gravity Flow

hgDfVS

24 2

0

Channel Bed Slope

PADh

4

Pipe Material Absolute Roughness, emicron

(unless noted)drawn brass 1.5drawn copper 1.5commercial steel 45wrought iron 45asphalted cast iron 120galvanized iron 150cast iron 260wood stave 0.2 to 0.9 mm

concrete 0.3 to 3 mm

riveted steel 0.9 to 9 mm

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Design of Penstock

2

4 penstockpenstock dVQ

gHVpenstock 2In general

But maximum allowable value is 10 m/sMaximum allowable head loss in Penstock =2 to 4% of available head

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General Design of Under Ground Power Tunnels/Penstocks

Page 17: Design of Pelton Wheel: Tuesday Group
Page 18: Design of Pelton Wheel: Tuesday Group

penstock

penstockfriction gd

fLVHxh

24 2

gHkV penstockvpenstock 2,

Speed) Specific toalproportion(inversly 0.15 to2.0:, pestockvk

2

9.0Re74.5

7.3log

0625.0

hDk

f

Pipe Material Absolute Roughness, emicron

(unless noted)drawn brass 1.5drawn copper 1.5commercial steel 45wrought iron 45asphalted cast iron 120galvanized iron 150cast iron 260wood stave 0.2 to 0.9 mm

concrete 0.3 to 3 mm

riveted steel 0.9 to 9 mm

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Design of Penstock

Group No. Unit SizeMW

Qp Dp Head loss

1. 500

2. 333.3

3. 200

4. 166.7

5. 142.85

6. 125

7. 111.1

8. 100

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Distributor : Only for multi jet Wheel

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Design of Distributor

Q2

4 penstockpenstock dVQ

Penstock

Page 22: Design of Pelton Wheel: Tuesday Group

The Nozzle and Jet : A Key Step in Design

d0djet,VC

Free Surface Shape for Maximum Power

Page 23: Design of Pelton Wheel: Tuesday Group

Initial guess for Diameter of the Jet at the outlet, do

gHKdQ voo 24

2

83.081.0 vOK

It is important to find out the VC and outlet jet diameters/areas

Page 24: Design of Pelton Wheel: Tuesday Group

Geometrical Relations for Nozzle

dO

2dO – 2.4dO

5dO – 9dO

0.8dO – 0.9dO

1.2dO – 1.4dO

1.1dO – 1.3dO

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Performance Analysis of Nozzle-Spear Valve

Ideal Nozzle-spear Valve:

constant2

2

gzV

p

Along flow direction

frictiontotal ΔppVp -constant2

2

Real Nozzle-spear Valve:

Page 26: Design of Pelton Wheel: Tuesday Group

penstock

penstockfriction d

fLVp

24 2

2

9.0Re74.5

7.3log

0625.0

hDk

fPipe Material Absolute Roughness, e

micron(unless noted)

drawn brass 1.5drawn copper 1.5commercial steel 45wrought iron 45asphalted cast iron 120galvanized iron 150cast iron 260wood stave 0.2 to 0.9 mm

concrete 0.3 to 3 mm

riveted steel 0.9 to 9 mm

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Numerical Computation of Total Pressure Variation

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Efficiency of Spear Nozzle Valve

1001

inlettot

exittotinlettotvalvespear p

pp

Acceptable Range: 97.5% -- 99%

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Design of Penstock

Group No. Unit SizeMW

djet Head loss

1. 500

2. 333.3

3. 200

4. 166.7

5. 142.85

6. 125

7. 111.1

8. 100

valvespear

Page 30: Design of Pelton Wheel: Tuesday Group

Geometrical Relations for Nozzle

The values of α varies between 20 to 30° whereas β varies from 30 to 45°.

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Industrial Correlations for Jet Area variation with stroke

Optimal value of Outlet jet area, ao

2BsAsao

s is the displacement of spear

sinsin2 orA

2

2

sinsinsinsinB

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Computation of Variation Jet Area with stroke

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Mean Diameter of Pelton Runner

Mean diameter or Pitch circle diameter:Dwheel

Circumferential velocity of the wheel, Uwheel

gHU wheel 2

gHKUwheeluwheel 2

Page 34: Design of Pelton Wheel: Tuesday Group

Experimental values of Wheel diameter to jet diameter

Dwheel /djet,VC 6.5 7.5 10 20

Ns (rpm) 35 32 24 10

turbine 0.82 0.86 0.89 0.90

4 5H

PNN wheels

99.098.0 1 vK gHKQd

vVCjet 2

4

1,

Higher ratios are preferred for better efficiency.Modern wheels for high heads use ratios as high as 30!

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Optimal values of Wheel diameter to jet diameter

Ns

jet

wheeld

D

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Group No. Unit SizeMW

1. 500

2. 333.3

3. 200

4. 166.7

5. 142.85

6. 125

7. 111.1

8. 100

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Geometric Details of Bucket

The hydraulic efficiency depends more on the main bucket dimensions (length (A), width (B) and depth (C)).The shape of the outer part of its rim or on the lateral surface curvature also has marginal effect on hydraulic efficiency.

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Empirical Geometry of Bucket Shape

A

B

C

2i

e

S

I

IVII

III

V

DW

Page 40: Design of Pelton Wheel: Tuesday Group

Empirical Relations for Bucket Geometry

• A = 2.8 djet,VC to 3.2 djet,VC

• B = 2.3 djet,VC to 2.8 djet,VC

• C= 0.6 djet,VC to 0.9 djet,VC

i = 50 to 80

e is varied from section I to section V• I: 300 to 460

• II: 200 to 300

• III: 100 to 200

• IV: 50 to 160

• V: 00 to 50

Page 41: Design of Pelton Wheel: Tuesday Group

RWRP

dO, Vj,O

lj

wheel

wheel

Ojet

D

Dd

21

1cos

,

sin12,

wheelvO

wheelu

Rkk

Number of Buckets

Page 42: Design of Pelton Wheel: Tuesday Group

Maximum allowable angle between two successive buckets

2

Minimum number of buckets 360

z

Dr Taygun has suggested an empirical relation for z

155.0,

VCjet

wheel

dDz

Page 43: Design of Pelton Wheel: Tuesday Group

Group No. Unit SizeMW

1. 500

2. 333.3

3. 200

4. 166.7

5. 142.85

6. 125

7. 111.1

8. 100

Page 44: Design of Pelton Wheel: Tuesday Group

Absolute and Relative Paths of Jet : Orthogonal Interactions

e

VjetUblade

Ublade

Vrel,jet,exit

e

Vjet,exit

Page 45: Design of Pelton Wheel: Tuesday Group

1

coscoscos2

2

eaii

aid i

kVU

VU

2

1coscoscos2

ai

eiai

d Vi

kUVU

Define Blade Speed Ratio,

1

coscoscos2

ik e

id

Page 46: Design of Pelton Wheel: Tuesday Group

Approximate Velocity Triangles: Pelton Bucket

1cos2max, ed k riereb VVUmP

cos

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Start of Jet Bucket Interactions

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Sequence of Jet Bucket Interactions

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Bucket Duty Cycle

• Compute angles of onset and close of interactions.

• Select few locations during bucket jet interaction.• Compute mass of jet intercepted by the bucket and

corresponding blade exit angles.• Numerically integrate the work done by a bucket

per rotation.• Compute Average Power developed by bucket

and efficiency.