Raabe J. Hydro power - the design, use, and function of hydromechanical, hydraulic, and electrical еquipment

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flotion simplifies to curl

201.

The axial component

this vectorial equation rer?ds

Inserting

and

from (10.6-36) gives the following quadratic partial differential

fluation for the stream functions

and

Y2:

fie other components of curl

yield similar relations for the stream functions. They

facilitate the elimination of one stream function so as to have ultimately one partial differential

quation for one of the stream functions

and

Y2.

fie development of improved computer hardware stimulated the creation of corresponding com-

~uter programs. The progress in numerical turbomachinery analysis was shown in a review by

lopikse

(10.1831. It can be considered as a prerequisite of a computer-aided blading of hydroturbo-

a trend of the future.

Starting from

Wu,

Bosman

et al. demonstrate the feasibility of obtaining flow details through

turbomachine blade passages by working iteratively with existins two-dimensional computer pro-

grams, which solve alternately blade to blade and shroud to hub streamsheets

[10.184].

Novak

et al. (10.1851 present a system, which is also modeled after the work of

ll,ir,

and which

comprises two coordinated computer programs, one providing solutions on

axisymmetric blade-to-

blade surfaces and the second on streamsheets roughly parallel to the blades.

this context. the method of

Adler

and

Krimertnan

has to be mentioned [10.186]. They used a finite

clement method, to solve modified

equations. The method allows for non-axisymmetric blade-

to-blade surfaces and uses iteratively the results known from the families of face-to-face and hub-

to-shroud calculations.

All known streamsurface methods suffer from the constraint, that the surfaces cannot pass across the

edges of the blade passage and that the blade-to-blade surfaces which are split at the inlet edge shall

meet

in corresponding points at the outlet. After

Bosnlan

[10.187] the stream surface techniques

become totally inadequate when applied to centrifugal impellers and radial turbines, where devia-

lions of the blade-to-bladc surfaces from surfaces of revolution are large enough to make the

distinction between the families of blade-to-blade and shroud-to-hub faces impossible.

Since according to

[10.187] there seems to be no easy way

overcome the limitations, the usefulness

streamsurface methods for the prediction of real flow effects in turbomachines is questionable.

the

last few years another strong trend has been towards fully 3 dimensional methods,

which solve the fluid dynamic equations with respect to velocity and pressure.

an example for recent finite element methods the procedure proposed by

Pfoertner

[10.188]

may

mentioned. He solves the equations

motion (Cap. 5.3) and continuity

(see

5.2)

for an incompressible 3-dimensional flow. The computational domain used (see

Fig.

10.6.7) consists here of one blade passage with its adjacent regions upstream and

downstream of the rotor channel.

nis

domain is automatically divided into tetrahedron elements

two steps (see

Fig.

10.6.7).

Preliminary division into bricks with

nodes given by the

families of bladewise, streamwise and

pitchwise oriented surfaces.

Subdivision

the bricks into

tetrahedra, so as to obtain elements which are as near as

Possible to regular tetrahedra.

Fig.

10.6.7.

Coniputational domain for

3-dimc'nsio11:il

finite

element calcula-

tions

rclntive flow in

pump

rotors

after

P'rtnrr.

[lo.]

881.

Inserting a reasonable initial state in the momentum equation and coniinility yields residuals in each

tetrahedron. Integrating the weighted residuals of

thc elcrncnt's volume and summing up all the

elements gives

resulting residual.

procedure follows which makes

the

luttcr as small as possible.

Thus the continuity and momentum equation are best

satisfied.

The minimization

effected by a so-called conjugate gradient algorithm. Together with

gradient

projecting technique, the latter is used to satisfy the

boundiiry condition

[10.188].

These projection

techniques allow the

fornlulation of linear Ktshs betmen

aWc

ncxfsl variables as, e.g. all the

vclocity components in a peripheral oriented surface.

This procedure can bc used to satisfy addi-

tional side conditions such

as a satisfaction of continuity over the whole passagc or a useful

corldition for the outlet plane. Hence it is possible to prescribe a dcsircd attenuation of any pitch-

periodic non-uniformity on thc distribution of the velocity components downstream of tho rotor.

This method of

Pjbertner

has been successfully applied to a variety

geometric configurations such

as radial

ar,d

scmi-axial punlp impellers, Francis turbine runners. coliical guide vanes for bulb

turbiges etc.

Ribcut

[lo.

1891

treats the three dimensio~al divergent and rotational flow in turbomachines. Using

potential theory a quasi three dimensional

method is

developed,

which yields high numerical

accuracy. The method includes the influence of the casing and blade boundary layers on the cascade

circulation.

l'hc usc of two vortex sheets. representing thc boundary surf:~ce. allows the calculation

of stalled flows and secondary vorticity. The velocities of

computcd divergent flow agrce fairly well

wit11 the measurements.

careful analysis of the meridionai component

relative eddy in mixed

flow

machines was given

Lcwis

and

Fuirhairn

[10.190].

10.7.

Computer aided design of hydroturbines

10.7.1. Introduction

computer aided design

(CAD)

is utilized by industry to modernize the design process.

The

drawing board is replaced

a video display unit. Simultaneously rules are drawn

for designing a hydroturbomachine. In this manner the design is made more repeata-

ble.

10.7.2. General goals

The immediate aim is to reduce costs by increasing the designer's productivity. Nearly as important

the reduction of the design period. The designer can examine numerous permutations of the design

the screen. This coupled with the computer's ability to quickly execute complex calculations

an improvement of a typical design's quality.

The user no longer is forced to carry out monotonous tasks, such as dimensioning and hatching.

~hus the quality of the workplace can be bettered.

Some

CAD

programs can produce (eliminating the conventional drawing) a punched tape for the

~lumerical control of machine tools. Ultimately, they could lead to the automated factory.

10.7.3. Hardware for a

CAD

system

The object which is to be designed is represented on a screen instead of on paper. As the screen is

smaller than most paper formats, the user can usually define a window and move and magnify

it.

Suitable terminals are manufactured in numerous different varieties and sizes, with and without

colour

[10.191].

Commands are keyed in using a typewriter keyboard. Graphic information (i.e., the drawing) is

usually entered with a light-pen or graphics tablets. Sometimes a workstation is equipped with

printer to produce lists.

To reduce costs and to enable the exchange of information, several stations are served

a single

computer. Most systems have their own

n~inicomputer and are not connected to a firm's main-frame

computer. Experience has shown that in the latter case response times are excessive. In the near

future low cost microcomputers should be utilized, as their power is starting to rival that of the minis.

The

computer requires at least one relatively fast mass memory device to permanently store data (i.e.

drawings). Disk storage units are mainly used.

slower, but more reliable storage medium should

used to safeguard the data, tape units are popular for this application.

Drawings are made on paper by a plotter, which can operate on a mechanical or electrostatic basis.

10.7.4.

Software for the

CAD

system

Without programs every computer is useless. Software can be divided into three major categories:

Vstem software, applications software written by outside suppliers and application software written

the user.

Systems software usually is written by the computer manufacturer and enables the machine. to

Perform tasks on a very basic level, i.e., input and display data. Applications software permits the

machine to perform complex tasks, which are immediately useful.

the

CAD

field applications software written by outsiders usually can

classified as so-called

drafting systems. These enable the designer to draw general mechanical designs. It is not important

bearing or

hydrcpowcr plant is bcing dcsigncd. Somc softwarc

suppliers

combine hardware

and softwarc to

makc

a turnkcy

CAD

systcm.

Obviously thc user buys thc softwarc hc nccds whcrl

is rcactily ;~vailablc, as thc pt~rchase

price

bclnw the cost of wriiing the programs.

thc other hand, softwarc suitable for narrow fields

(

hydroturbincs) simply is not available. Thc user will usually combinc

commercially

available

drafting sofiwarc with spcci;~lizcd software of his own. Rcf. [10.192] offcrs soggcstions

011

obtaining

further information on

CAD

hardware and software.

10.7.5.

Profile

commercial computer

aided

design program

for

Francis turbines

For several years the Voith company has been developing the Franzl system of programs.

The stated goal was to automate the most often repeated parts of the mechanical design.

Franzl should not be confused with CAD-programs that serve solely as drafting sy:

:ms.

The Voith system combines calculation, selection and drafting procedures. Thus Voith

officials prefer calling the program a computer design system.

Franzl is utilized as a tool in the proposal and preliminary design stages of a project.

These stages are often repeated and are relatively expensive and time consnming.

Using

design handbook the program attempts to offer a solution based upon one of

model

turbines. The number and scope of the model turbines are continually increasing.

Typically the program asks the user to

key

major parameters, e.g., guide var?e pitch

diameter, specific speed and so on. Five modules successively treat the hydraulic outline,

the shaft and coupling flange, the runner, the stay rings and the turbine covers.

The program then prints the input data and calculated parameters such as physical

di~nensions, stresses, weights, pressures, bearing forces, resonance frequencies etc. If satis-

fied, the designer may have a section drawn on a graphics screen. The section can also

be drawn by a plotter.

The

end result is

basic hydraulic outline, which the designer uses as a starting point for

iurther design work. In this manner the problem of the blank sheet is avoided.

If dissatisfied with the output, the

desizner can actively intervene and change parameters

in the various modules. Several program modules are either existent or in planning stages

usc the data produced by Franzi. These include draft tube design, automatic cost

calculation and an interface to a pure drafting system. Thus a Francis turbine could be

designed from start to finish on

computer. The Franzl system is described in further

detail in

[10.36].

hlatsuda and Nagafuji [10.139] dcscribe the use of an automatic design program, developed in Japan

in conjunction with a numerical control machining process which allows for

fast and economic

manufacture of rotor models. This enables the design and performance development of turbines and

pump-turbines to

carried out within a short period with little manual work. In this program a

rotor is automatically designed by putting in all the necessary design parameters. It is also possible

to check the effect of any of the input data on the performance

charactcristics by changing selected

elemcnts and comparing the experimental results of the rotor with the standard ones.

The output of this design provides full information of the rotor

blade surface coordinates.

program

has been developed for automatic

generation

of the data required for a numerically controlled

machining of a model rotor. To represent in detail the three-dimensional shape of the rotor, the

drawings are plotted in radial and pattern making sections.

There are two methods of making a model runner. The one is

nlaching the blades from a solid disk.

The

othcr is finishing the runner from

piece which has been cast to form the rough blade shape.

fie

total system of n.c. machining, according to

[10.139]

is implemented on

levels. On level

both

front and back surfaces of the blade are divided into a fine mesh and the coordinate values on the

lIlesh

are typed out on a list or punched out on thc cards and also are plotted out on cards tjr

checking whenever required. Level

consists of a n.c. system developed for machinin the runner

milling machine w~th

degrees of freedom.

requires a complicated part programming.

rovided

with

a library in whlch a number of routi~es corresponding to the various shapes of

i0rtpieces are prepared. The cards, lists and plots are turned out by this system and they are used

check in advance the interference between tool and work-piece which are likely to occur during

cutting. All the data from lcvel

are processed in level

and converted to the sequential instructions

ofthe n.c. machine. The control tape finally obtained on level

is fed into the machining control unit

and the n.c. process is carried out.

10.7.6.

Conclusions

Because of the high cost of program development and hardware engineering managers should

weigh the advantages of a computer aided design system. Perhaps instead of introducing

acomplete system, which treats all stages of the design, a partial automation would be more suitable.

Only those stages that are oftcn repeated, and contain many monotonous tasks or those that could

stand the introduction of com~lex calculations would be computerized.

On the other hand in times of increasing competition, there may be no choice left. The ability to

designs quickly of the highest quality may become a major advantage.

11.-Regulation

hydro power

sets,

the

generator

1.1.

Introduction

The constant speed requirement of the usual hydro turbo set si~pplying an

grid

means of a synchronous generator (the alternator) needs speed regulation, sometinle~

connection with load distribution

and

load regglation.

011

the one hand thc control loop

used for this purpose irlcludes the governor with

device for metering the speed deviation

and

soriietimes also for metering the

acceleration,

and its servomotor for the load adjust-

n~ent of the turbine.

On the other hand, the control

lo~p includes slsc? the p!ant or the controlled system.

This

cor~sists of the hydro turbo set with the turbine and the alternator, its piping and the

electric grid connec:cd with it.

The

different meci~anical, hydraulic and electronic designs for metering the deviation of

speed

and

their features merit some considerations. The rather large controlling forces of

gates and

runncr vanes require oil-operated servomotors.

Their-

vnlvcs are actuated from

the

speedometer via relays by sleeve valves .x.ith their special linkage including feedback,

and

~nter-llnkii~g devices for different control loops at doublc

regulated

lnachines.

Tile

governor nceds devices to adjust the speed droop as

characteristic of the set, to limit

rl~e

gate opening. to set the damping of possible oscilli~tions in the control loop, and to

synchronize the set.

In this context

the condition; fur dynamic stabiiity

thz control loop have to be

considered. They

iticlude the incrtia of the set mainly due to its alternator and the

characterisiics due to certain loads of the supplied grid. Also the characteristics of the

turbine and of the pipe system with respect to water hammer and its boundary conditions

have to be accounted for.

For a proper

operiition, the individual time constailts for start

and shut down of the

structural

members of the plant such as penstock and set, have to be tuned to each other,

and also with respect to limit overspeed by fly-wheel effect.

The references

1.1 to

11.51

zive a matcrial survey of control due to hydro power, [I 1.61 brings

historical survey. The control of hydro power plants

general is treatcd in [11.7; 11.81, its stabilizing

p~oblems

1.9

11,

131.

classilication of the governors is rnade

i11

1.141,

the

load control, also

nith electronic devices, in

[11.15

to 11.191. the related power swing

1.201.

Water level control

treated in [11.21; 11.221, self regulation in [11.23], the control of speed and

voltage

[1I.Z1].

The

dynarnic behaviour of the controlled system is generally investigated in

1.251,

by means of frequency rcsponse curves

1.26; 11.271, by stochastic signals in

1.281. The

~latural frequencies of thc controlled systen~ are considered

j11.29;

11.301,

with

respect to the

boundary

conditiolls of

penstocks

1.31;

11.32). and

with

respect to rock-bored penstocks in

1.331.

Governing under transient load is reported in

1.341,

the relevant damping factors are introduced

[I 1.351, non-linear solutions in [I 1.361, the simulation of a hydro power system in

1.371. Gover-

oars

for small plants are described in [I 1.381, optinlization of control

electronic governing is

in [11.39], electric equipment of the turbine governor in [11.40]. motor and generator of

,he

speedometer

in [11.41], control by means of positive displacement pumps in

1.421. electro

governors in [I 1.431, an electronic governor head in [I 1.441,

computerized

governor

[11.45], use of micro computers in [I 1.461, use of module techniques in [11.47] and that of

,+oprocessors in [I 1.481.

fie locking spring is introduced as a safety device in [I 1.491, recording instruments are presented

(11.501, the determination of the runner vanelgate vane interrelation in

1.511, the emergency

dosing device in [11.52],

runaway speed limiter for Kaplan turbines in

1.531. the regulating work

(11.541, the prediction of fly-wheel mass in

1.551, the optimization of Pelton turbine governors

[11.56], the water column effect in speed control in [11.57]. the safe control of a by-pass outlet in

(11.581, and the starting up of a set in [11.59].

[

the field of control the technical terms in the follow text following mainly from the

English equivalents of the German Standards for automatic speed control technology

DIN

19229

621

-53.

Traditional denotations of some terms (if any at all) are occasion-

ally

added in brackets for the orientation of the "old fellows".

The following text has been kindly revised by my colleague Professor Dr.

Schmidt

with

respect to the proper use of control conceptions.

The

common treatment of regulation and generator in one chapter was made to keep

consecutive chapters in balance with respect to their length.

One joint fact between both members is the need for frequency control, when the genera-

tor feeds an

grid as usual, another can be seen in the circumstance that, at excitation

unaltered, the alternator output increases linearly with frequency, and thus may change

regulation.

Usually the electric machine of the set is a generator of

AC,

an alternator. In pumped

storage and tidal power plants with special pumping, the alternator is also used as motor.

The alternator requires a special consideration. Contrary to the turbo generators of

thermal

szts, its number of pole pairs has to be adapted to the relatively small and widely

varying head.

This requires a salient pole design instead of the usual drum rotor, standardized for the

usual

therrnal turbo set.

Moreover the construction of the electric machine has to match the strongly varying

features

the hydraulic set, e.g., withstanding runaway, forming a structural unit togeth-

with turbine and generator especially in the case

a rim generator shrunk onto the

runner, and a critical operation

with respect to shaft vibration. Thus the design

shaft

and adjacent bearings is

concentra:ed on the effort to shift the lov~est critical speed to a

margin above runaway.

higher heads, the relative heavy electric rotor poses problems of low critical speed and

sufficient cooling.

primped

storage plants and tidal power plants with double effect, and equipped with

pump-turbine, the generator, then also used as motor, has to reverse its rotation

between the different modes of operation. Pole changing between pumping and turbining,

itarting up the filled or emptied machine into pumping either by synchronous operation

(back-to-back connections of neighbouring sets or thyristor-coxitrolled frequency),

asynchronous operation, or by

pony motor, pose problems of fatigue and heating ir, the

conductor.

Concerning the ref~rcnccs on the

set's

clcctric ni;~chinc.

survey is prcqcntcd

.hO;

11.611. l<cccll,

1.1rgc dc(ig11s

Hra,lll;in pl:~nts ;ire treated

111

1.62],

and

iarzc s;lli~nt pole 1n;l~hin~s in

1.631.

I~idividuiil constructions of altcrn;ltors ;~nd gcncrators ;ire co~~sidcrcd

111

.h1

1.661, i~ldu~~i~~

gcncrntors in

1.671. motor gcncrators of pumped storage plants in [I

1.68

to 11.70j. qtochnstic loads

on the rotor in

1.711. rcsonancc of torsion and

bending

v~brations

[I 1.721, currcnl-induccd

forces

[I 1.731, and resulting strcsscs in [I 1.741.

Cooling is trcntcd in

[I 1.75; 11.761, diflercnt c.xciting systclns in

1.77; 11.781, the insulation problem

1.791, the upruting of old macllincs

[I 1.801, rccent Japanese tcchrlology

1.811, and recent

Wcsi German technology in [I 1.821.

The

f;llowing text has been kindly revised with respect to the proper use of electric

conceptions by

1Mr.

Wil1y;deputy director at Siemens Erlangen, West Germany.

11.2.

Regulation of hydro power sets, governors, accessories

11.2.1.

The

governor, its purposes, its design

11.2.1

.I.

Survey of control, different kinds,

why

specd control

water

power

plants the alternator output us~ially has to

adapted to the power

demand of the grid.

For

this purpose the output or such other values, which depend on

it,

e.g.,

the

speed, have to be measured continuously and to be adjusted to the demand.

The direct measurement

output exists in load control, which is usually combined with

specd control (Fig.

11.2.1

(11.16;

11.17;

11.191.

Fig.

11.2.1.

Speed control in connection with that of other quantities. a) Combined power and speed

control

Wattmeter;

pilot servomotor;

combination lever;

speedometer;

main servomotor;

7 feedback.

Combined speed and head control. 8 float on the head water pond;

speedometer;

combination lever;

servomotor; 12 valve;

feedback.

542

The load control by speed is possible since both the values are assisned to each other by

the proportional band necessary for load distribution

individual plants and sets.

speed control is also useful for the checking of voltage and proper operation of

multitude

of machines supplied from the grid the set is connected with. The stability of

frequency in the usual

grid supports the control of load factor by reactance. In favour

of the speed control, the fact exists that even the isolated set, disconnected from the

grid,

e.g., by short circuit, may be controlled preliminarily by its speed rise,

p1.3; 11.41.

smaller sets

MW)

connected with an

grid an increasing tendency exists, to

ornit the speed control. There in the case of emergency, e.g. short circuit, an overspeed

limiter has to shut down the set after disconnection from the grid. During

normal

operation of such sets its speed is retained by the electromagnetic forces between alter-

nator rotor and the rotating magnetic field of the stator and the rotor damper

windins.

In rare cases of smaller plants in remote areas, fed from reservoirs with varying headwater

level, also the head may control the flow (Fig. 11.2.1 b) by follower control

[I 1-22].

11.2.1.2.

Control loop, governor, controlled system

The speed control is effected by a closed control loop, in which a governor is connected

in series .with the controlled system. This consists of the turbine, its water ways, the

generator and its electric grid. The latter is subjected to disturbances by continously

varying demand of load.

The input of the governor is the speed of the set, its output the position of a servomotor

for the adjustment of a turbine's distributor (gate, needle valve, jet deflector). The

govsr-

nor consists of a speed measuring device, that actuates

sleeve valve (Fig.

11.2.2a),

which

in turn controls the oil flow for the servomotor, that adjusts the opening of the turbine.

In the case of a proportional (speed) governor the 'deviation of actual speed from a rated

value is measured by a tachometer, which thereby operates the sleeve valve

via amplifiers.

In the case of a proportional-integral governor with acceleration feedback (acceleration

governor), an accelerometer simultaneously measures the derivative of speed, which then

together with the speed deviation actuates the sleeve valve (Fig.

11.2.2b).

The load vs speed characteristic of the governor and its set is represented by the propor-

tional band (permanent speed droop). It is realized by certain devices in the feedback

linkage of servomotor (see Cap.

11.2.1.4). Moreover the governor contains also devices

for speed

adjustmen; and synchronization of the set, for limiting the load and for stabiliz-

ing governor oscillations (dash pot, accelerometer).

The steady state gain as the

outp~lt/input ratio of the governor at steady state is expressed

now by the ratio of servomotor opening to speed deviation. In the usual case of a large

grid with nearly coilstant frequency this ratio tends to become rather large. Only

when the set supplies a grid by itself or during synchronization, the steady state gain is

smaller.

11.2.1.3.

Working together of turbine

and

grid,

self

control

Under settled speed the equilibrium on the shaft of a set requires that the torque of the

turbine is balanced by the grid-conditioned torque of the generator. Hence the settled

speed of a set adapts itself to the point

at which the torque vs speed characteristic of

the turbine intersects the corresponding grid-conditioned torque vs speed characteristic

of the generator (Fig. 11.2.3), provided this point of intersection is dynamically stable.

Fig.

11.2.2. Schematic diagrams of a speed governor on mechanical basis: a) Proportional integral

governor with elastic feed back. 1 gate regulating ring; 2 servomotor;

sleeve valve;

combination

!c\.er;

speedometer (tachometer);

isostatic device (springs that return the point

of the dash pot

pisron always to the same station);

dash pot with adjustable throttle in short circuit; 8 speed-

adjustment for the rated

spced. b) Proportional integral governor with an acceleration feedback:

sate regulating ring; 2 servomotor;

sleeve valve;

combination lever;

speedometer (tacho-

mew);

accelcrometer (detail see c)). c) Conibined hydraulic tachometer and accelerometer (Design

Vevey-Charmilles Engineering Works):

spring-suspcnded fly-weight with a baffle platc;

speed

mctcring nozzle;

flywheel with a bame plate;

acce!eration-metering nozzle.

Fig.

11.2.3.

Speed self control of

set with generator

supplying

grid by itsclf under various kinds of load

torque vs speed:

load by machine tools; change of

the load from the

torqu::

1M,

IM,

shifts the

point of stable operation from

load

turbomachines (blowers, compressors, impeller

pumps);

pure resistor load (electric bulbs, electric

heating, electrolytic cells);

turbine torque vs speed

speed

under different openings

and