2.Lecture on Hydraulic Turbine

Hydraulic Turbine A.1

University of Toronto

January, 2015

Hydraulic Turbine Hydraulic Turbine


Classification of Hydraulic Turbine

Key Operating Parameters

Energy Losses and Efficiency Analysis

Spiral Case and Draft Tube


Water energy Mechanical energy Electric energy

Hydraulic turbine Generator Power grid

| — Main shaft — | Different hydraulic turbines with different mechanism on energy conversion.

Classification of Hydraulic Turbine

Water energy = Potential energy +Kinetic energy


The energy for per unit water body utilized by hydraulic turbine is just the energy difference between the inlet (Section 1 ) and outlet (Section 2) of the runner (head loss temperately ignored).

)2

()2

(2

2222

2111

1 gVPZ

gVPZH

12

)()( 222

211

22

11

gHVV

H

PZPZ

and then yields


H

PZPZEP

)()( 22

11

gHVVEC 2

222

211

1 CP EE

1 , 0 CP EE

1 , 10 CPP EEE

Utilize kinetic energy of water completely--Impulse turbine

Utilize potential energy and kinetic energy of water simultaneously---Reaction turbine

Potential energy:

Kinetic energy:

(1) If

(2) If

It means


Hydraulic Hydraulic turbineturbine

ReactionReaction

ImpulseImpulse

FrancisFrancis

Axial flowAxial flow

Deriaz (Diagonal flow)Deriaz (Diagonal flow)

TubularTubular

PeltonPeltonCross flow (Banki)Cross flow (Banki)TurgoTurgo

Nagler (Propeller)Nagler (Propeller)

KaplanKaplan

StrafloStraflo

Half TubularHalf TubularBulbS-type

Pit

ReversibleReversible

Classification of hydraulic turbine:

FrancisFrancisAxial flowAxial flow

DeriazDeriaz


Reaction turbineFrancis turbine Radial inflow and axial outflow; high stability and efficiency with simple structure; optimal head 20～ 700m with wide application；max. unit capacity: 750MW (Three Gorge, etc.) and 1015MW (in construction)

1- Main shaft 2-Blades 3-Guide vanes



Runner of the Francis Turbine1-Runner crown 2-Blades 3-Bottom ring 4, 5-Wearing ring 6-Runner cone


Axial flow turbineAxial inflow and axial outflow; applicable head 3-80m. (1)Nagler Turbine (not adjustable blades): relatively low H with narrow variation; low capacity; and narrow region with high efficiency.(2)Kaplan Turbine (adjustable blades): relatively high H with wide variation; large capacity; and wide region with high efficiency.

1-Guide vanes 2-Blades 3-Wheel hub1-Guide vanes 2-Blades 3-Wheel hub


1-Blade 2-Pivot

3, 4-Bearing 5-Rotating arm

6-Connecting rod 7-Operating frame

8-Runner blade servomotor piston

9-Piston rod


Kaplan turbine of Gezhouba hydropower station in China with 11.3m diameter and 175.5MW unit capacity.

( One of the largest Kaplan turbines in the world)


Deriaz TurbineDiagonal inflow and outflow; applicable head 40～ 200m; similar to the axial flow turbine, basically with adjustable blades; not widely used.

1-Spiral case 2-Guide vanes

3-Blades 4-Draft tube


Tubular turbineNo spiral case; horizontal main shaft; applicable head 1 ～ 25m ， suitable for the hydropower stations with low head and large flow rate, especially for tidal power stations.Including straflo turbine (full tubular turbine) and half tubular turbine (bulb turbine, S-turbine and pit turbine).


Straflo turbine: the generator outside of the water channel, connected to the periphery of the runner.


S-turbine: placing the generator outside of the water channel with a jog and a shaft connecting the runner and generator; low efficiency.

Pit turbine: with a gear box for small hydropower stations.


Bulb tubular turbine: 1～ 25m, low head and large flow; widely used


Impulse turbine Pelton Turbine： vertical strike the runner at its tangent

lines; 300～ 1700m(large), 40～ 250m(small), high head and small flow; for example, Bieudron Hydropower Station, 1869m, 3423MW.

Turgo turbine: strike the runner at an angle to its tangent lines; 20～ 300m, relatively large flow, for medium and small hydropower stations.

Crossflow turbine： two strikes.


Crossflow turbine


Pelton Turbine

Turgo turbine


Runner of the Pelton turbine for

Mofangou II hydropower statio

n in China (13MW）

Subagu hydropower station, 1175.0m, 226MW


Reversible turbine(1) Pumped-storage power station (Francis turbine, Deriaz turbine)(2) Tidal hydropower station (Bulb tubular turbine with adjustable blades)


Main parameters of hydraulic turbine include:

• Head H

• Flow rate Q

• Output N

• Efficiency

• Rotational speed n

Key Operating Parameters


Gross head Hg:

Hg=ZR (reservoir water level) ZT (tail water level)

Operating head H (net head)： H=Hg-∑△hf (total friction loss) - ∑△hj (total local loss)

Several specified head:

(1) Max. head (1) Max. head HHmaxmax: Mainly for strength design of turbine’s

structure

(2) Min. head (2) Min. head HHminmin: Designed for turbine’s reliable and stabl

e operation

Head


(3) Average head (3) Average head HHavav : Turbine basically operating close to this head (high efficient area)

(4) Rated head (4) Rated head HHrr : Relative to rated output (mainly based on the weighted average head and the development mode)

(5)Weighted average head :(5)Weighted average head : Also locating in the high Also locating in the high efficiency areaefficiency area

i

iia T

THH

ii

iiia NT

NTHHor


Flow rate /discharge

QQ: : the water volume passing through the turbine in the water volume passing through the turbine in unit timeunit time

Rated flow rate (Qr): the specified flow rate with rated head Hr, rated speed nr and rated output Nr.


nn: the rotational speed of runner in unit time: the rotational speed of runner in unit time, , r/minr/min 。。In general, the turbine and generator are with rigid connection, their rotational speeds are synchronous, except for some small turbines.

60nPf for grid frequency f=50 Hz, then P

n 3000

P is the number of generator’s magnetic poles, and then the synchronous speed nsyn is obtained.

Rotational speed

nr=nsyn for main shaft of turbine connected to generator directly, and nrnsyn for connection with a gear box.


Power and efficiency

QH.QHN w 819

Output of turbine Output of turbine NN ：： considering the energy loss, N <Nw, define

wN

N

Based on the theorem of momentum moment

(kW) (W) 955060

2 nMnMMN

QHN 81.9

Input power Input power NNww ：： total energy of water flow passing through the turbine in unit time.

Rated output Rated output NNrr [KW][KW]: the output power of main shaft wit: the output power of main shaft wit

h h rated head Hr [m], rated flow rate Qr [m3/s], rated rotational speed nr [r/min].

%)96~%90(QHN


Installed CapacityIn general, installed capacity means output power of the generator.

gg NN %98~96g

(1) Output of the turbine (N)

(2) Capacity of the unit (Ng)

(3) Shaft power (N)

Three key conceptions easy to be confused are


Efficiency of the turbine

WNN

， NW - N is the energy losses.

• According to the energy characteristics, energy losses in According to the energy characteristics, energy losses in the turbine include: hydraulic loss, volume loss (flow rate the turbine include: hydraulic loss, volume loss (flow rate loss) and mechanical loss.loss) and mechanical loss.

• The corresponding efficiencies include: hydraulic The corresponding efficiencies include: hydraulic efficiencyefficiencyηηHH ，， volume efficiencyvolume efficiencyηηvv and mechanical and mechanical

efficiencyefficiencyηηm.m.

Energy Losses and Efficiency Analysis


(1) Hydraulic loss(1) Hydraulic lossΔΔHH and hydraulic efficiency and hydraulic efficiencyηηHH

When the flow passes through the turbine, including the spiral case, stay ring, guide vanes, runner and draft tube, the hydraulic loss inevitably exits due to friction, shock, vortex and flow separation.

HHHe

HH

QH)HH(Q e

H

Effective head

Hydraulic efficiencyHydraulic efficiencyηηHH


(2) Volume loss (2) Volume loss ΔΔQQ and volume efficient and volume efficient ηηvv

qQQe

Considering the hydraulic loss and volume loss, the power transferred from the water to the runner is defined as effective power.

eee HQ)HH)(qQ(N

The volume efficiency is QQ

QqQ

QHH)qQ( e

e

eV

Due to the leakage of flow rate,Due to the leakage of flow rate, the effective flow rate of the turbine


(3) Mechanical loss (3) Mechanical loss NNmm and mechanical efficiency and mechanical efficiency ηηmm

Turbine’s output is me NNN

Mechanical efficiency is ee

mem N

NN

NN

Finally

HVmHVmeememW QHHQHQNQHNN

The total efficiency of the turbine is defined as

mVH

—obtained by model test and further theoretical conversion.


Optimum operating condition of the turbine

Shock loss and vortex loss

Eff

icie

ncy

Vol. loss Mech. loss

Hydraulic loss (friction loss, local loss and outlet loss)

Output N


Optimum operating condition:

The condition with the highest efficiencyηmax ;

The controlling energy loss is hydraulic loss ;

The controlling hydraulic loss is water shock loss

for inlet water flow and vortex loss for outlet flow.

Therefore, the optimum operating condition is basically

defined as that with min. hydraulic loss due to water

shock and vortex.


Classification of spiral cases(1) Concrete spiral case: Reinforced concrete; steel lining; prestressed concrete. Suitable for the hydropower stations with lower head, H≤40m, especially for run-of-river hydropower stations.

(2) Metal spiral case ： H ＞ 40m

a. plate-welded spiral case： widely used; whole-buried and additional soft cushion.

b. cast-steel spiral case： for the high head hydropower stations with turbine’s diameter D1＜ 3m.

Spiral Case and Draft Tube


Plate-welded spiral case

Plate-welded spiral case Cast spiral case

Nose end

detail

c. cast spiral case ： similar to cast-steel spiral case. High rigidity; partial buried; load bearing directly; reduction of the height of power house.

Plate-welded spiral case


Cross section of spiral casesMetal spiral case: circular (inlet section); sections close to nose end: Circular section is modified into oval section with the same area to improve the stress condition.


Four typical inlet sections of concrete spiral case:

m≥n: reduce the height of power house and shorten the length of main shaft.

Concrete spiral case: trapezoidal section


Function of draft tube

Sketch for function analysis of draft tube(1) Without draft tube (2) With draft tube

Datum


Based on the Bernoulli equation , we can obtain

)22

( 52

255

222

2 hgV

gVHEEE AB

where includes the static vacuum (static head) and dynamic vacuum (reduce the Kinetic energy by diffusion)

ΔE is just the recycled kinetic energy by draft tube.

2ppE a

Pressure head at turbine’s outlet reduced.


Then, the functions of draft tube are:Then, the functions of draft tube are:

(1)Collect and drain the water flow from runner’s outl(1)Collect and drain the water flow from runner’s outlet to downstream;et to downstream;

(2) If (2) If HH22 ＞＞ 0, utilize this potential energy of the water f0, utilize this potential energy of the water f

low;low;

(3) Recycle part of kinetic energy of water flow from r(3) Recycle part of kinetic energy of water flow from runner’s outlet.unner’s outlet.


The static head H2 depends on turbine’s installed elevation and is not concerned with the performance of draft tube, and then, the recycling coefficient of kinetic energy for draft tube ηw is

gV

hgV

gV

w

2

222

22

52

255

222

The total hydraulic losses of draft tube include the kinetic energy loss at its outlet and internal hydraulic loss.

gV

hgVh w 22

22

52

255

: the total hydraulic loss efficient of draft tube.w


The following equation is satisfied

ww 1

For the low head axial flow turbines, the kinetic energy

at the outlet of draft tube may be equal to 40 ％ H; whil

e for high head turbines, it is less than 1.0 ％ H. Theref

ore, the performance of draft tube is more important fo

r low head turbines.


Types of draft tube

(1) Vertical (1) Vertical conical draft tubeconical draft tube: η

w=80％ ~85％ ; suitable for sma

ll turbines.

(2) Bend conical draft tube:(2) Bend conical draft tube: ηw=4

0％ ~60％ ; often used for small horizontal turbines.

(3) Elbow draft tube:(3) Elbow draft tube: better hydraulic performance, better hydraulic performance, ηw=75

％ ~80％ ; widely used.

Bend conical draft tubeBend conical draft tube


Elbow draft tubeElbow draft tube



Local deformation of draft tube:Local deformation of draft tube:

(1) If the bottom rock excavation of power house is (1) If the bottom rock excavation of power house is limited and the height of draft tube should not be limited and the height of draft tube should not be reduced, the bottom of horizontal diffusion is allowed reduced, the bottom of horizontal diffusion is allowed to have a reasonable upwarping,to have a reasonable upwarping,ββ≤6°~12°.≤6°~12°.


(2) Considering the asymmetry of spiral case, especially (2) Considering the asymmetry of spiral case, especially for the concrete spiral case, the asymmetric draft for the concrete spiral case, the asymmetric draft tube can be recommended to reduce the possible tube can be recommended to reduce the possible width of power house. In this case, the center line of width of power house. In this case, the center line of draft tube is deviated from the center line of draft tube is deviated from the center line of turbine. turbine.

Unit’s center line


(3) The horizontal diffusion of draft tube is often designed (3) The horizontal diffusion of draft tube is often designed with high and narrow sections, which is more suitable with high and narrow sections, which is more suitable for the underground power houses to improve the rock for the underground power houses to improve the rock stability .stability .


(4) In some cases, the length of draft tube increases (4) In some cases, the length of draft tube increases mainly for the underground hydropower stations.mainly for the underground hydropower stations.

(5) The length of (5) The length of draft tube draft tube increases in some increases in some cases to meet the cases to meet the requirement of requirement of the detailed the detailed arrangements of arrangements of auxiliary power auxiliary power house.house.


Thank you!

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2.Lecture on Hydraulic Turbine

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