bbc 1basic design

•BBCBROWN BOVERI

TURBINE GENERATORSEMINAR

EGATOctober 1986

•

•

1. Basic design and operation

o Basic dimensioning criteria

o Constructional design

o Losses and their origins

o General cooling considerations

o Special generator design up to 350 MVA

o Air cooled generators compared to hydrogen cooled

o Generators with powers above 350 MVA

o Special features of water cooling

o Operation under abnormal conditions

o Excitation systems

SUBJECT: TURBO-GENERATOR

DOCUMENT No.: GKW S 100 051

BBCBROWN BOVERI

EGATOctober 1986

ISHEET No.: 0- 2


BASIC DIMENSIONING CRITERIA

Fundamental Constructional Design

Power Equation

Voltage Equation

Simplified Equivalent Circuit

Characteristic Curves. I

Phasor Dlagramm

Power Chart

Sudden Short-circuit

Transient Operation, Load Change

Unbalanced Load

Reference Parameters

Thermal Insulation Class

Effects of specified Parameters

1.

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.10

1.11

1.12

1.13

•

··It

2.

2.1

2.2

2.3." 2.4

CONSTRUCTIONAL DESIGN

Rotor Body with Rotor Winding

Laminated Core and End Structure

Stator Winding"'\, ..

Stator Frame

•

3.

3.1

3.2

3.3

3.4

4 •

4.1

4.2

4.2.1

LOSSES AND THEIR ORIGINS

Constant Losses

Voltage-dependent Losses

Current-dependent Losses

Schedule of tosses

GENERAL COOLING CONSIDERATIONS

Formation of the Winding Temperature

Cooling Media and Attributes

_____.9.K~9 2%1)

BBCBROWN BOVERI

SUBJECT:


TTJREO-GENER.~TOR

EGATOctober 1986

ISHEET No.: 0 - 3 •DOCUMENT No.: GKW S 100 051

5.

5.1

5.2

5.35.4

5.4.1

5.4.2

5.4.3

SPECIAL GENERATOR DESIGN UP TO 350 MVA

Construction and Cooling of the Stator

Air Cooling up to 200 MVA

Constructional Features of H2-coolingAuxiliary Equipment for Hydrogen Cooling

Hydrogen Supply Equipment

Carbon Dioxide Equipment

Moisture Messuring Equipment, Gas Drying •6. AIR-COOLED GENERATORS COMPARED TO HYDROGEN-COOLED

GENERATORS

6.1

6.2

6.3

6.4

7.

7.1

7.27.3

Basis of Comparison

Size, Weight, and Efficiency

Losses and Temperature Distribution

Reasons for the Differences in Temperaturestator of Air and H2-coo1ed generators

GENERATORS WITH POWERS ABOVE 350 MVA

water-cooled Stator WindingsHydrogen-cooled Core

Reinforced Rotor Cooling

Limits in the

8. SPECIAL FEATURES OF WATER COOLING

8.1 Purified Water Circuit (Deionized Water)

8.2 Disturbances in the Water Circuit

8.3 Humidity Measurement, Water Temperatur Control

9. OPERATION UNDER ABNORMAL CONDITIONS

10.

10 .1

10.2

10.3

EXCITATION SYSTEMS

Excit~tion wit~ 5:att~~ary ryrister~

s~~ttcnary Dioc~: with 3-~hasc E~cife~

Rotating Diodes with 3-phase Exciter •

BBCBROWN BOVERI


EGATOctober 1986

The synchronous machine is predominantly used as agenerator for the production of electrical energy. Two

forms of design are employed according to the type ofapplication i.e. the speed at which the machine is driven,these are:

1. BASIC DIMENSIONING CRITERIA

1.1 Fundamental Constructional Design

SHEET No.: 1-0 1TURBO - GENERATOR

GKW S 100 051

SUBJECT:

DOCUMENT No.:

a) Turbo-generators driven by steam or gas turbines:speed at 50 Hz grid frequ-;n-cY-;---·3·-0oo;i~;"1,or 1500

min-l (nuclear power stations) and at 60 Hz correspondingly to 3600 min-lor 1800 min-I. The

special turbo (non salient pole) construction isdetermined by the rotor stress at high speeds.

b) Salient pole machines driven by water-powered turbinesor diesel engines, and for small steam turbines with

~_.'-'-""-'~".._~"~'.~"_.~""---""'-~' .,-"".,.

gearing. The speed covers a wide range according to theselected number of poles from ca. 60 min- l to 1500min-I. In the case of hydraulic power stations thespeed is determined by the water conditions.

Fig. 1.01 a) Salient pole generator b) Turbogenerator

GK/KO 2960

BBCBROWN BOVERI

SUBJECT:


TURBO - GENERATOR

EGATOctober 1986

ISHEEr No.: 1-02 •DOCUMENT No.: GKW S 100 051

Fig. 1.01 shows the fundamental difference between salientpole rotors and non salient pole rotors (turbo-rotor). Thestator laminated core, with slots for the three phasewinding, is in principle the same. The rotors, which gene

rate the r ota t::_i_ng.. ~ i eld i~_C:0r:t.111ns:.t;;.on w!.tht!:!_.~~c:~.. s£2E1Yto the rotor windings, are constructed differently:a) salient pole with concentrated field windingsb) non salient pole with the field windirtgs distributed in

slots to restrain the centrifugal forces. ~

In view of its greater importance, only the turbo-generatorwill be handled more closely.The field winding in the

generator rotor is fed with direct current (excitationcurrent, field current If). A magnetic field is therebycreated which passes across the air gap to the stator.

Fig. 1.02 shows the field configuration of a turbogenerator on open-circuit i.e. with a stator current I • o.

The magnetic field rotates as a consequence of the rotation

of the rotor. This produces an alternating field which ~...induces a voltage in the stator winding. ~

Owing to the alternating field the stator is built up oflaminated stampings (stator laminated core). A constructionwith a solid core would result in induced eddy currentswhich would dampen the field. In addition to this, highlosses would be caused so that the generator would be useless. The stator has a 3-phase winding, whereby the threeindividual windings are displaced 120 0 to each other. Sincethe rotating field 9asses with a ti~e dis?lacement. the~

th~ voLtages ind~ced in the wlndtngs hav~ a 120~ phaseshin. roe st~to(~i11di.ng 13 anchored in ':one ccr:: sl,ns.

GK/KO 2960

The slots themselves, and thereby the winding, are almostfree of any field as Fig. 1.02 shows. The magnetic flux

prefers the path over the core teeth owing to the smallermagnetic resistance.

BBeBROWN BOVERI

SUBJECT:

DOCUMENT No.:

Fig.

GK/KO 2960


TURBO - GENERATOR

GKW S 100 051

No-load field ccnfig~ration

EGATOctober 1986

SHEET No.: 1-0 3

-- ---------------

BBeBROWN 8OVEl'I1

SUBJECT:


TURBO - GENERATOR

EGATOctober 1986

ISHEET No.: 1-04 •DOCUMENT No.: GKW S 100 051

1.2 Power Equation

The power equation shows the criteria for determining thebasic dimensions of the generator and these are furtherexplained in more detail below.

S· k A B d2 In. c d2 1 n

S • rated apparent power

. A • electric loading in the stator (electricalutilization)

B = air gap flux density (magnetic utilization)d • rotor diameter1 • active lengthn • rotational speedc = utilization factor, Esson coefficient.f~-= winding factor

6 • air gap

for fw~0,92 and J/d ~ 0,07 is obtained k%7,a

Every individual parameter in the power equation is limitedin some way.

The electric loading of the stator is defined as the sum of

all currents in the stator divided by the circumference ofthe bore. The allowable electric loading is determined bythe cooling of the winding since the windings can only beheatec to within prescribed limits.

QK/KO 29~O

•

•

•

BBCBROWN BOVERI


EGATOctober 1986

The following values are in general applicable for the

electric loading:

~ The air gap flux density (at no-load for U = UN) is ameasure of the magnetic utilization of the machine. Owingto the saturation of the core, the usual values lie between

0,8 and 1,0 T.


ISHEET No.: 1-05

up to 135 kA/mup to 170 kA/mup to 300 kA/m

T~]RBO - GE1E:R.:;'TOR

, for air-cooled windings

hydrogen-cooled windingswater-cooled windings

SUBJECT:

)•,,. The rotor diameter is limited by the strength of the

material and the stresses on the rotor and winding. At the

present time it is possible to achieve 1280 mm at 3000 rpm.

1.3

The allowable length of the rotor depends on the rotor

diameter. In this case the smooth running of the rotor isthe defining factor and this must be considered from case

to case. Rotors with a slenderness ratio lid = 6,4 have

already been constructed.

Voltage Equation

After the generator dimensions have been estimated according to section 1.2 it is necessary to consider the stator

voltage •

•GK/KO 2960

----,--------~--

BBCBROWN BOVERI

SUBJECT:


Ti.....RBO - GENER.:\·:m~.

EGATOctober 1986


The armature phase voltage is given by the folloWingequation:

f frequency

w number of turns per phase, w is proportional tothe slot nu-mber

f w winding factor

¢/l magnetic flux per unit length of the rotor

The parameter ~/l is a characteristic dimension of therotor. Owing to the saturation of the core it is notfeasible,to raise the flux per unit length or magneticloading of the rotor to any desired value. The optimumdesign values are given for each type of rotort e.g. rotordiameter 1 m with hydrogen cooling:-

¢/l ~ 1,0 to 1,1 Vs/m.

As can be seen from the voltage formula, the machine lengthand number of turns (slot number) have a direct influenceon the stator voltage. Por a given rating or given length asmall voltage means a small slot number, and a largevoltage means a large slot number.

1.4 Simplified Equivalent Circuit

The simplified equivalent circuit will assist the understanding of the electrical operating behaviour of thegenerator.

•. 'Ift

•

•01</1<0 29:..:.:1jQ=-- _

--------~~---~- ~

BBCBROWN BOVERI


EGATOctober 1986

The generator is represented by the synchronous generated

voltage Up and its synchronous reactance X. U and I arethe stator voltage und stator current for a phase. Thestator resistance is neglected.

TURBO - GENE~~TOR

GKW S 100 051

IISHEET No.: 1-07

-I•

xI

SUBJECT:

DOCUMENT No.:

)•~ U

t-'---------------0

Fig. 1.03 Simplified equivalent circuit

The synchronous generated voltage Up is the voltage due

to flux produced only by the field-winding current. The

synchronous generated voltage is approximately pro

portional to the field current. It is only measurablewhen running in no-load conditions. The synchronous

reactance X when considered more precisely, is split up

into Xd and Xq for the direct-axis (pole axis) andquadrature-axis (winding axis). However, for a turbo

generator it is sufficiently accurate to set

Xd~Xq.X. The synchronous reactance is the reactanceof the stator (armature) winding with the field-windingcircuit open.

GK/KO 2960

BBCBROWN BOVERI

SUBJECT:


TURBO - GENERATOR

EGATOctober 1986

SHEET No.: 1-0 8 "DOCUMENT No.: GKW S 100 051

1.5 Characteristic Curves

The above simplified equivalent circuit of the genera~or

is determined by open circuit and short-circuitconditions. Open circuit means the stator winding is

~ithout current.; then 0 .. Up. up-can be adjusted bychanging the field current. The curve U .. f (If> foropen circuit is shown in Fig. 1.04 • The bend of the

curve in the region of rated voltage U .. UN and higher 41'is caused by saturation of the stator core and rotor iron.

•short circuit

( \ /

open circuit

.i

"

air gap lineVe> (f~r

u

point U .. UN under no-load, the field current

applicable. ~~~1;._QJ~_hCUrrer1t:~~.1:E!q14!r:E!<L.t:9the rated voltagein the stator.

..e- ~ _

o o

Iko - --

At the

!to iscreate~.., .

s/~~. o.-V.'."', I

Fig. 1.04 Generator characteristic curves

Ql(Jl<O 2960

If the generator is short-circuited (U = 0) and excited

with If the_~~he__~9-~~:~i~ ..~~.~_t_~current IIt_= UdX _flows. This short-circuit current is drawn together with

the field current in fig. 1.04. This curve is a straight

line since the fields of the stator and rotor oppose one

another and therefore there is no saturation of the iron.

The field current which is necessary for the rated

current IN to flow when the stator is short-circuited

is defined as I fk •

From both curves an important characteristic value for

the generator can be derived and this is termed the

Short-circuit Ratio kc .

•lieBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 1-09

)

•

open-circuit field current

for U = UNshort-circuit field

current for I k = IN

stator short-circuit current

with excitation of I foIN stator rated current

UNPh rated phase voltage

With suitable transposition I KO = UNPh/X a further

result may be derived:

It can now be seen that the short-circuit ratio is

inversely proportional to the synchronous reactance. A

g@neratoc with a large shoft-circuit ratio theraf0re has

a small $ynchroncus reac~anc~.

GKIKQ ?a<;1) - _. ---------_. -_ ...- ._._-----_._-------

BBeBROWN SOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

SHEET No.: 1-10 •DOCUMENT No.: GKW S 100 051

This is termed a ·stiff machine·. A stiff generator canbe overloaded for a short period and has the effect of

stabilizing the ~~i~?However, this advantage is nor~allyoffset by the larger structural volume of the generator,since to achieve a small reactance it is necessary tohave a large air gap. In order to maintain the magneticflux across this air gap at the same level as for a smallgap, it is necessary to have a higher excitation current.

Since this is not possible due to the heating of thewinding , the complete generator must be increased insize.

1.6 Phasor Diagram

A phasor diagram (fig. 1.05) for steady-state operationcan be drawn from' thesimplified equivalent circuitfig. 1.03.

Fig. 1.05 Phasor diagram

GK/KO 2950 ._---_...._-----.- _._---

•

•

The stator current I and voltage U form the angle ~ ;cos'P is termed the power factor. with the apparent power

S, the active power P is given by P = S cos ~ , and the

reactive power Q by Q = S sin $I. The load angle -Jt isenclosed between the synchronous generated voltage Upand the stator voltage U. The voltage drop XI is

perpendicular to the current I.

•lieBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

SI-'EET No.: 1-11

field axis

-

1.06 Field configuration under load.

GK/KO 2960

BBCBROWN BOVERI

SUBJECT:

TURBINE GENERATOR·SEMINAR

TURBO-GENERATOR

EGATOctober 1986

SHEET No.: 1-12


This load angle can be imagined as the spatial angle

between the complete field which is rotating in the

generator, and is inducing voltage cr, and the field

produced only by the rotor current. The end winding field

has been neglected in this consideration. It is then

possible to see the axis of the complete field in the

stator from the sectional field configuration Fig. 1.06.The axis of the rotor field alone is the same as the poleaxis. The load angle lies between both.

Fig. 1.06 shows the case of an over-excited load corresponding to that of the shown phasor diagram.The

direction of rotation of the rotor is easily recognised

when one imagines that with the generator in operation

the rotor pulls the field behind it.

1,0

0,5

o

Fig. 1.07 Active power related to the load angle

The active power which the generator feeds into the gridcan b@ represented ~y

cos 0I

or by u Vp . ;.,P ... 3 - ..- .a 1 n 1.1

X •GK/KO 2960

-. ------------

BBCBROWN BOVERI


EGATOctober 1986

The second form shows that the active power rises

sinusoidally with constant excitation (Up = const.) and

reaches a maximum value at ~ = 90°. With a furtherincrease in the angle the active power becomes smalleragain. This means that stable steady-state operation isonly possible up to ~= 90°.

SUBJECT:

DOCUMENT No.:

TtJRBO-GS~ERATOR

GKW S 100 051

ISHEET No.: 1-13

1.7 Power Chart

When the voltages in the phasor diagram are divided by Xthen a current phasor diagram is produced for the

armature current I. At constant voltage the currents areproportional to the load •

..Qill. = I stator current .... apparent powerX =

--- .- u = 10 stator current with -

XU = UN and If = a

or nominal, a??ar~nt po~er. At constant voltage, current

The current I f * referred te the stator winding has the

same effect as the current If in the field winding

(If*_I f )·

excitation current referred

to the stator winding= I *f

After the values have been converted then the diagram isrotated 90°. Since, in this case, no special generatorhas been considered with a defined output, it is betterto show the power chart fig. 1.08 referred to the rated,

•GK/KO 2960

----- - -~~------------

BBeBROWN BOVERI


TURBO-GENERATOR

EGATOctober 1986

SHEET No.: 1-14 •OOCUMENTN~: GKW S 100 051

•aSN

E

0,80,6

( Tf '"'/",

0,4

0,6

C"/ p~ ie:,. D () Pe r:4 "t"D'\j )0,8 " ' ,I .-

....-...;.---=-+---------:ilIl. ( j) e YI'7f'/<:' D vAG" (_' )

oF

o//~ ccI

Fig. 1.08 Power chart

The path OA is determined by stator current I o without

excitation, which corresponds with the field current at

no-load I fo • The path AC is defined by the stator

current and the power angle9. The side OC corresponds to

the excitation component and is proportional to the field

current. The load angle 1ft is found at point O. The

theoretical stability limit is at ~= 90°. In practice a

safety margin is maintained at this point.

The circular arc through the points DC from the centre A,

is the limit imposed by t~e al1o~able a=~atu=e cu:rent.

~~e c:rcul~r a:c EC ~i:h c~ncre 0, give3 the li~i:

•GK/KO 2960

which is determined by the allowable field current. Point

C defines rated operation for which the generator is

designed. The path FC is the active power limit

determined by the turbine¥

The generator is operating as over-excited to the right

side of the P/SN axis. With respect to the reactive

power, the generator acts on the grid as a capacitor. On

the left hand side the generator is under-excited. The

generator acts on the grid as an inductance.

EGATOctober 1986

rSHEET No.: 1-15TURBO-GENERATOR



SUBJECT:

lieBROWN BOVERI

•

-All the main data for steady-state operation of the

synchronous machine can be taken from the diagram. It is

to be observed, however, that the diagram shown is only

valid for an unsaturated machine.

1.8

In pratice, at higher excitation currents additional

limitations are imposed by saturation of the core, so

that the proportional relationships shown are not

entirely valid. The reactive power represented by AE is a

little smaller and the line CE is no longer an exactly

circular arc.

Sudden Short-Circuit

If a generator is suddenly short circuited at the

terminals then very high currents will flow during a

transient period until steady short-circuit current

conditions are reached. The generator winding, and also

the generator terminals and busbars, are designed to

withstand the stresses from trese high currents without

•da~~Je. The E0rces resulting Dat~e~n the power ca:ry:ng

~- conducto~s c~n b8 vety high. TnS3a currants are also used

as the basis for designing the generator main circuit

breaker.

CK/KO 2S6O_ .._---_.__.-- ---

BBeBROWN BOVERI

SUBJECT:


TURBO-GENER..'\TOR

EGATOctober 1986

ISHEET No.: 1-16 •OOCUMENTN~: GKW S 100 051

J

•• ,', ••••••••••••• " •••••• "." •••• ", ••• ,., ... "'.4 044

I I It.O. 0,5..

•

Pig. 1.09 Sudden short-circuit current

Fig. 1.09 shows the oscillogram of the currents. i u 'iv, i w are the armature currents, if is the rotorfield current.

When a sudden load change occurs then the flux linkagesof the individual generator windings remain constant.Step-type changes in the currents are not possible since

infinitely high voltages would be induced according to

o == L di/dt.

The generator therefore does not behave according to thesiMplified steady-st~te equival~nt ci,c~it when sudden

cnang,=s o::cu::.

GK/KO 2960

•

•

BBCBROWN BOVERI


EGATOctober 1986

The alternating current component resulting from theshort-circuit is shown in Fig. 1.10 for interpretation.

ISHEET No.: 1-17TURBO-GENER.~TOR

subtransient current

steady-state:"'\, / current

~L ~ If" f\ f\ 11N '~++++H-+++++++J-+H+-+H-H++J-+I-H-H-+l~~-.v-wU1TT1WL.UlL..J,j\\ IwfTl--

"

GKW S 100 051

~ / transient current~r--.

..,....--~-.lI. I'. _

........ ~ ....IIDrn-rlrr1-J~

: ...-

SUBJECT:

DOCUMENT No.:

Fig. 1.10 Alternating component of the short-circuit

current

The subtransient state of operation occurs immediatelyafter the change and is characterized by the flux

linkages of the damping winding and excitation winding

remaining constant.

•QK/KO 2960

BICBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

ISHEET No.: 1-1 8 •DOCUMENT No.: GKW S 100 051

The transient operating state occurs somewhat later whenthe effect of the damping winding with its very small

! ' ~... --' .. :)\ )/.>vtime constant has decayed. The flux in the field windingnow remains almost the same owing to this winding's muchlonger time constant.

The two states can therefore only be differentiated fromone another because the time constants for the flux

changes are so different. ~

During subtransient operation, that is shortly after theinstant of change, the generator can be represented byits subtransient reactance X~ and the driving voltageou. During transient operation, the transienc reactance

pXd and the transient synchronous generated voltage u~

are the defining parameters. o~ and u~ are dependenton the operating condition before change. For a sudden

short-circuit from the open circuit mode, o~ • o~ = 0(0: phase voltage). ~ ;-:::>"J\t>Ck'i\ )

GK/KO 2960

The maximum effective value of the alternating currentthat occurs is I: = U/X~ The transient componentI~ = U/X~ decays with the time constant T~ (around100 ms). The difference I; - I~ decays with the time

"constant Td = 10 to 30 ms.

II

u/,'+(:. 1\' , II,' I

Iii /i 2I"~" \,/ IIl I' ,,'i i. ......_'\

J / I. \ i__~ I __..~ __ ..t. ",;.."-r:.~:! _

i I zero i ine for OililX. d.c.-cc'!1ponent

Fig. 1.11 Influence of the instant of connection

•

•

IBCBROWN BOVERI


EGATOctober 1986

Considering that a decay has already taken place at thepoint of the first current peak, the maximum possible

peak current which can occur is given by:

The alternating current component is superimposeddifferently on the decaying d.c. component (Fig. 1.11)

depending on the instant of connection. This is becausethe current cannot make an istantaneous jump.

.,~ UN/1"3i max = 1,8,2 X"

d

ISHEET No.: 1-19

UN= rated voltage(terminal voltage)

TURBO-GENERATOR

GKW S 100 051

SUBJECT:

DOCUMENT No.:

From the previous discussion it becomes evident that thesubtransient reactance should be as large as possible inorder to minimise the peak short-circuit current. The

subtransient reactance is mainly made up of the leakage-

reactance of the armature winding XIS and the leakage

reactance of the damping winding XIO (referred to the

armature)

Transient Operation, Load Change

The predominant component is the armature leakage

reactance.

qiv.;n

+

at :.::~

Transient behaviour and transient reactance are important

during load changes and with regard to stability. A

simple example will be made for a load change duringi:1d'l;;':i.'l~ o?era':ion {ccsep: 'J).:::~ ~lcl':~;e crar:g~ .a u

1.9

~ U =

~ I is the change of the stator current.

- ._--------_.__ ..... ----_..__._...----

BBeBROWN BOVERI

SUBJECT:


7URBO-GENEP-AI'CR

EGATOctober 1986

ISHEET No.: 1-20


,The smaller Xd the smaller the feedback effect on thestator winding and the easier it is for the controller to

take action.

X~ is the effective generator reactance pertaining tocontroller action. Its size is determined by the sum ofthe armature leakage reactance XlS and the leakagereactance of the field winding X1f (referred to the

armature). •x'

d +

In general, the armature leakage reactance is thepredominant component.

1.10 Unbalanced Load

During asymmetric loading of the 3 phases the armaturecurrents and the phase angles of the currents are of

different sizes. This is called unbalanced load.

The armature current system then contains a component

which rotates with the rotor and a component which

rotates in the opposite direction against the rotorrotation. The latter induces currents in the rotor ofdouble grid frequency. The system operating with therotor is desired, that in opposition is not. The opposing

field can induce heavy currents in the outer surface ofthe rotor causing losses and heating. The better thecamping winding design, the more the generator can

withstand unbalanced load.

GK/KO 2960

•lieBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

SHEET No.: 1- 21

In order to give an idea of the size of an unbalancedload, fig. 1.12 has been drawn in which one line iswithout current and the other two carry the full rated

current. The unbalanced load is 58 %.

The unbalanced load is given as a percentage ratio of thereverse current component to that of the rated current.

The normal continuous asymmetrical load values lie

between 6 % and 15 %, whereby the smaller value appliesto larger generators. Bigger values are possible for

short term unbalanced loads.


u

!u

Iv

!u~up !un

+ -!wp lwn

!vp Ivnlv

Fig. 1.12 Maximum unbalanced load•GKIKO 2950

BSCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENEPATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 1-22 •1.11 Reference Parameters

Synchonous machines vary widely in size from small unitsup to the largest ratings. Reactances and resistance inthe dimension [2], as well as voltages in [V], andcurrents in [Al, vary considerably according to the powerof the machine. However,. if these parameters are referredto a ·per unit· base then they are relativelyindependent of generator rated values. ·Per unit· 4Itparameters are defined with a small letter.

U = L.u 'N

Rr =-.Z 'N

X = L.z '

N

These parameters are dimensionless and may be referred toas ·per unit· (p.u.) or as a percentage.

1.12 Thermal Insulation Class

At the present time all large generators designed byBrown, Boveri & Cie are in accordance with therequirements of insulation material class F. Theinsulation material groups are stipulated in thefollowing regulations:

VDE 0530 Part 1, Appendix IIIEC Publication 85, Section IIANSI C 50.13, Selection 5

GKIKO 2960

•

VDE 0530 Part 1, Main Section 5

IEC Publication 34-1, Section 5

ANSI C 50.13, Section 5

The temperature limit (hot spot temperature) for class Bis 130°C, and for class F 155 GC. The allowable

measurable temperatures and heating are lower, and aredefined according to the type of machine and cooling in

accordance with:

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 1-23

1 .. 13

It has become established amongst the power utilities tospecify generators with insulation class F but at the

same time only to concede temperatures according toclass B, in the hope of prolonged life expectancy of thegenerators.

The design thermal loading of a winding is dependent on

the temperature difference between prescribed winding

temperature and temperature of available cooling medium.

Raising the former from class B to class F permits

generator power to be increased by about 10 %.

Effects of specified Parameters

The previous sections have explained the important

parameters and characteristics which describe thebehaviour of a generator, its capacity and size.

In the enquiry specification, regulatory or limit values

are collected together which are to be maintained by the

her~,

lieBROWN BOYERI

SUBJECT:

DOCUMENT No.:


TURBO-GENE?.."\TOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 1- 24

Rated Power:The rating, or nominal apparent power, of a generator canvary over a very wide range. For a given type of cooling

air, hydrogen or water - the size (volume) and weight areproportional to the rating. In some rating ranges it ispossible to choose between two types of cooling e.g. air orhydrogen. All the implications for the plant should beconsidered when making this choice - hydrogen cooling forexample will require a hydrogen gas control unit.

Rated Power Factor:As can be seen from the power chart of section 1.7, thepower angle ~ determines the magnitude o~ the rotorcurrent at a given apparent or real power. In many casesthe heating of the rotor determines the design limit, which

means _that when cos, = 0,8 is increased to COS" "" 0,9 thena reduction in size of at least 5 , results.

•

x "" reactance in ~

Short Circuit Ratio:The definition of the short circuit ratio given in section

1.5 can be converted to ~

UN2 /SNX

It is easily seen that for a given generator with powerSNl that kc is larger then when the power isSN2 < SNI' The reverse is the case i.e. a generatormust be increased in volume when a larger kc is demanded •

•- -- ._- ._--~-- - ------ .-_._-_...._---..---_.__ . -~---_._._..--.-...-...-...-----.,..--

BBCBROWN BOVERI


EGATOctober 1986

g0~~:a~ors which are hig~~y u~iliz~d (e.g.~a:er-~ooled

,.: .. J; \'1 ,) ") "'I'~ '1itjl>-.··· ,., -ro' ._ and x'/' .';'.' ,l '..) '. t n ,.1 ,> ,. . 11 .; :. -" .;:. '- '- -' •• - " '" , d . d •

The higher the short-circuit ratio then the larger the

reserve stability during the end of the decay of

transient faults, and also later during steady-state

operation. A large kc is more expensive and it remainsto be considered whether or not a cheaper solution with

smaller kc but good voltage and stability control ispreferable.

Transient and Subtransient Reactances:

As already explained in section 1.8 and 1.9, x~ limitsthe maximum short-circuit current and should therefore be

selected large; x~ should be selected as small aspossible to confer good stability. In this respect the

generator manufacturers do not have much freedom.

Machines which utilize a low current density (e.g.air-cooled generators) tend to hav~ low r~actances, and

!ISHEET No.: 1-25TURBO-GE~,rERi~.TOR

GKW S 100 051

Cooling Water Temperature:

The cooling water temperature influences the size of the

generator. Since the upper heating limit of the windingis fixed, for example the average rotor winding

temperature is 105 °C for insulation class a, then it isof importance for the manufacturer to know whether a

temperature rise of 80 K with 25 °C cooling water isavailable or 70 K with 35 °C. It should also be checked

whether or not for the few days in the year when the

cooling water temperature has a higher value, it is

possible to concede winding temperatures according toinsulation class F and thereby utilize the reserve

capacity of the generator. During the remaining time the

thermal requirements could be in accordance with class B.

DOCUMENT No.:

SUBJECT:

•

BBCBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

ISHEET No.: 1-26


This situation cannot be significantly influenced. To thesame effect, both values contain a large common term the armature leakage reactance. Only this leakagereactance can be varied in the design, and it affectsboth values in the same direction. The rotor contributionis not variable since every manufacturer usesstandardized rotors.

The range for x~ is from 0,12 p.u. for small generators ~

of about 100 MVA to 0,25 p.u. for large generators (1000MVA). The corresponding range for x~ is 0,20 p.u. to0,35 p.u •• The saturated value (short-circuit from

no-load with U a UN) is given for x~, and for x~

the unsaturated value.

ClK/KO 2960--------

•

BBCBROWN BOVERI


EGATOctober 1985

casing, stator laminated core, stator winding, rotor bodywith excitation windings, bearings, ventilator and cooler.

The general design of the turbo generator is defined byits function as a producer of current and voltage. The

major components are:

CONSTRUCTIONAL DESIGN

ISHEET No.: 2-01TURBO-GENERATOR

GKW S 100 051DOCUMENT No.:

SUSJECT:

2.

The detailed design concerns mechanical stresses during

continuous operation e.g. end bells, ribbing in the

frame, and side effects of electrical' and magneticfields, e.g. insulation and shielding, and especially the

cooling system and the cooling techniques employed.

2.1 Rotor Body with Rotor Winding

•

•

The main body of the rotor is of solid steel forged inone piece. It carries the excitation winding whichproduces the magnetic field. The rotor core also servesas a good magnetic conductor for the flux in the rotor

(c.f. Fig. 1.02) • The rotor winding is laid in axiallymilled slots and is retained with external wedges, which

prevent it from flying out under centrifugal force. Theend windings are safeguarded from such effect by the

rotor end bells (retaining rings) which are shrunk onto

the body ends.

Due to axially milled slots in the rotor iron the secondmoments of area of the rotor cross-section about the

and the quadrature ~~is 3 PQ not eq~al. In

GK/KO 2960

BBCBROWN BOYERI

SUBJECT:

COCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

SHEET No.: 2-02

in unsmooth running of larger rotors with ca. 1 mdiameter.

To compensate for this, the part of the outer surface ofthe rotor having no deep axial slots, i.e. the poleregion, is provided with transverse slots.

Fig. 2.01 Section through the rotor body

When the grid load is unbalanced the generators must be

able to take the resulting inverse field. In practice,

the outer surface of the rotor is normally capable ofcarrying any currents induced by the reverse running

field component caused by the asymmetrical load. However,the high demands set by standards and specifications

(unbalanced load of 6 % for large generators, 15 % for

small generators), make it necessary to have damperwindings.

T~e damper winding is a closed-~Lrc~i~ cage. The cage is

formed by flat COpp~~ conduccor5 :~ tn~ ~ct:,~ s~cticn,

whiCh 1 i.e 0t-::t','/~::,}n tlH:: ,-ledges .:lnd che- rcco!" wL:ding. :'heyare laid under the retaining ring at the ends and are

•

•

•

thereby shorted together at speed. Instead of having

separate conductors under the wedges the wedges themselves

can be used as damping conductors as long as they are ofgood conducting material, e.g. aluminium, and also

continous over the entire length of the rotor. A further

requirement is also their adequate mechanical strength.

•IBeBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TUR30-GE~ERA'!'OR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 2-03

•

Various systems are employed by manufacturers for coolingthe rotor winding, e.g.:

a) Cooling through radial cooling slots in the winding,whereby the coolant is fed through a special recess

(sub-slot) in the base of the slot.

b) Radial cooling with entry and exit of the coolant fromthe air gap (air gap pick-up cooling).

c) Axial cooling through hollow conductors.

Brown Boveri design all rotor windings with axially cooled

hollow conductors. This has the following advantages:

easily calculable flow and heating, large coolingholes, insensitive to dust and deposits, cleaning

possibilities.

Fig. 2.02 shows the section through a rotor slot and thegas exit in the middle of the rotor •

Gi</KO 29'50

BBCBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986


Fig. 2.02 Section through a rotor slot

The coolant is air or hydrogen. Water-cooled rotors areonly adopted for very high loads (1300 MVA).

•

The necessary pressure to drive the gas through the hollow 4Itconductors is generated in two ways:

a) On rotors of lower power machines the pressure generatedin the gas by the centrifugal force of rotation issufficient.

The gas entry is at a small radius under the end bell, theexit at a larger radius on the outer surface of the rotor.The rotor itself then operates as a radial fan.

Gi<JI<O 2960

j) w~th lnr9~:' 9ane~atocs ~~~ ~9u~~e~ ~ m~ce inte~siv~

cooling and the fan which is provided anyway for coolingthe stator is also used for the rotor. In this caseradial fans are used to their higher pressure. •

BBCBROWN BOVERI


EGATOctober 1986

In all cases the cooling gas enters beneath the rotor endbells at both ends of the rotor. A part flows through the

hollow conductors of the active portion and leaves in the

middle of the rotor. The other part cools the end windingsand leaves at the end of the rotor body.

SUBJECT:

DOCUMENT No.:

TURBO-GENER.;'TOR

GKW S 100 051

SHEET No.: 2-05

-.

•

Fig. 2.03 Sectional view of rotor coolant flow

When rotating diodes are not provided, the direct current

supply to the rotor winding is through carbon brushes and

slip rings. The conductors from slip rings to windings liein the hollow shaft. A radial fan is arranged between theslip rings for ventilation •

GK/KO 2960

BBeBROWN BOVERI

SU8JECT:


TURBO-GENERATOR

EGATOctober 1986

SHEET No.: 2-06

DOCUMENTN~: GKW S 100 051

2.2 Laminated Core and End Structure

The stator laminated core guides the magnetic flux thro~gh

the stator winding and forms the magnetic closure in thestator yoke (c.f. fig. 1.02). Eddy currents are avoided bymaking the core out of laminations instead of one solidpiece. A solid core would result in large eddy currentswhich in turn would dampen the magnetic flux and causeintollerable losses and heating. ~

The laminated core consists of individual stampings ofcircular arc form laid on top of each other.

Fig. 2.04 Stamping

The individual stampings have slots for the stator windingat the inside and dovetail grooves in the outer edges sothat they may be fixed to long wedges which are in turnsecured to carriers in the frame. The laminated core in theframe is therefore held against the reaction from the rotor

GKlKO 2960

tor~~.!e•

•

~~~~~~~~~~~~~~~~~~~~~~~~~-~~~~~----------

The stampings are held together in the axial direction bypress-plates (end plates). These must be so designed that

in fulfilling their duty of holding the stampings together,they cause the lowest possible losses in the end winding

fields of the stator and rotor. The design is thereby also

influenced by the electrical utilization of the generator.Brown Boveri use three designs.


•BIC

• BROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

ISHEET No.: 2-07

•

Low power generators have steel fingers laid on the endstampings and teeth. These are held in place by an outer

aluminium ring. The aluminium ring is fixed externally onto the core wedges.

Fore more highly utilized generators the press-plates aremade of a single spheroidal graphite casting having low

magnetic permeability (similar to air) to reduce the losses.

In order to avoid concentrations of fields and heating in

the end stampings of the core, the air gap at the end is

increased in steps, i.e. the teeth of the end stampings areshorter than the middle part. In addition the end stampings

are slit.

At further increased utilization, the leakage flux in thewinding end space becomes even higher. The losses would

also be larger so that alternative measures are necessary.

Brown Boveri's large generators are equipped with laminatedpress-plates.

The laminated press-plate is a ring, formed by stator3t1~?ings bondet together. ~~ h~s a coni~al fo~m en t~~

cutslde and is prassed against the core by lon;i:~dinal

bJlt~ whick p~ss thtough :n6 C0:~ itsa:f •

GK/KO 2560

BBeBROWN BOVERI

SUeJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

SHEET No.: 2-08 •As fig. 2.05 shows the end region flux enters thepress-plate in the same fashion as the flux in the active

region enters the stator core. The exposed end face is

laminated so no eddy current can flow in the surface. Lossdensity and heating ar~comparable to the activ region.

../~.'\.

/ •

Fig. 2.05 Field configuration with laminated end plate

The advantage of the laminated end plate is that, inaddition to the low total losses, there is no power

limitation imposed even for the largest generators when thegenerator is operated under-excited as an inductance.

The sum of the end winding fields of the stator and rotoris largest during under-excited ogeration at full turbi~e

•

The stator winding is fixed in the slots of the statorlaminated core. Large generators have two winding bars in

each slot (double-layer windings) which together with bars

from other slots form the windings. The number of windings

and slots are defined by the stator voltage and the

possible utilization of the magnetic flux (c.f. section

1. 3) •

2.3 Stator Winding

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


'TURBO-GENER.u.'TOR

GKW S 100 051

EGATOctober 1986

SHEET No.: 2-09

•

(1§5ii!ii5l!§~- protective stripe

t::::::t::l:HIf-- solid conductor

~~~~!~-Micadu~insulation

t:::::lI=:Hflf-- intermediate partition

I.~~&-- spacer

filling

anti -corona varnish

fill ingslot wedge

Fig. 2.06 Slot section with winding bars

BBCBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

ISHEET No.: 2-10.-

OOCUMENT No.: GKW S 100 051

Owing to the alternating field, eddy current losses would

be produced in thick copper bars. The bars are thereforebuilt up of strands which are twisted together over thelength of the machine. The principle is to guide each

individual strand or sub-conductor over every part of the

bar cross section so that the magnetic influences are the

same on each strand and the same current flows in each

strand. Such bars are termed Roebel Bars (Brown Boveripatent of 1912).

Fig. 2.07 Principle of the Roebel Bar with 360 0 twist

The individual sub-conductors are insulated from one

another. The bars themselves are wrapped in the main

insulation whose thickness is determined by the terminal

voltage or test voltage. Brown Boveri uses the Micadur

system of insulation. The bars are wound automatically on a

winding machine and are wrapped uniformly with a glass

fibre and mica band that is covered in a corona resisting

compound. This is impregnated under vacuum with a special

according to !~C, ANSI and VDS. •

The two bars in the slot are separated by a spacer and

fixed in the slot by slot wedges. The windings in the

slots and the end windings are continually exposed to

electromagnetic forces of double grid frequency. It is

therefore important that the bars cannot shake loose.

To prevent such loosening a -hot pre-wedging- technique is

used to achieve an artificial aging by applying pressure

and heat to the bars in the slot during manufacture. Before

the final wedging the complete winding is heated for an

extend period under uniform high pressure. In this way oneachieves good wedging which remains tight over a prolonged

period in service.

BBCBROWN BOYERJ

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

SHEET No.: 2-11

Outside the slot area the bars are bent outwards in a

radial direction around the circumference and are bolted

and brazed together at the ends to form windings.

8

,I I '

7 1

J

8 4 5

2

1 Support rings2 Blocks and spacers3 End winding4 Spring-loaded wedges5 Flexible plates6 Radial supports7 Press-plate8 Stator cor9

•GK/KO 2960

Fig. 2.08 End winding support

BBeBROWN BOYER!

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 2-12

Under fault conditions e.g. short-circuit, large forcesoccur between the individual bars in the end windings.These must not cause any damage. Special attention musttherefore be given to the fixing of the end windings.

The end winding supports consist of strong glass-epoxyrings or supports as well as conforming pads soaked in

resin which rest on seats. The design of the fixing depends

on the degree of electrical utilization. In every case the ~

end windings are designed to withstand a short circuit atthe terminals without damage. fig. 2.08 shows an example of

the end winding support.

2.4 Stator Frame

The stator frame surrounds the core and stator winding and

transfers the torque, Which is a reaction to the-rotor, to

the foundations.

The detailed design of the frame depends on conditionsWhich are defined by the cooling and utilization.

One must differentiate between air cooling (open frame) andhydrogen cooling (pressure tight frame). The coolers are

integrated in the case of pressure tight housings. In theopen construction the coolers may be outside of the frame

and situated in the foundation.

Transport problems with large generators necessitate the

housing being constructed in several parts.

•

•

The important point is that the frame is so stiff and

detuned that no resonances occur in the frame itself causedby the 100 Hz frequency of the core. The 100 HZ vibrationof the core is a rotating deformation caused by the forcesmagnetic attraction in the air gap between the stator androtor •

EGATOctober 1986

•

•

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERJ...TOR 1SHEET No.: 2-13

GK/~O 29~J.---- --------------------- --_.----- --_.- ---_ .._----

Cooling systems and the methods of cooling are determinedby the intensity of losses and the temperatures

encountered at the point where the heat losses occur. The

losses are divided into two classes - those which areindependent of load (constant losses) and those which areload-dependent, for example, those related to loadcurrent or generator voltage.

LOSSES AND THEIR ORIGINS

•3.

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENER.?,.TOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 3-01

3.1 Constant Losses

The constant losses are those which are present in the

generator when neither the stator nor the rotor is under

voltage. The losses belonging to this class are friction

losses in the bearings, windage losses in the gas,·

ventilation losses, and losses in the seals in caseswhere hydrogen cooling is necessary.

Bearing losses depend on the type of bearing, the bearing

diameter, and the weight of the rotor. The losses

themselves are dissipated in the lube oil system and are

therefore independent of the generator cooling.

3A 'v~

Pw without fan

Windage losses without the fan occur in the generator asa result of the rotation of the rotor; these losses aremainly in the air gap between rotor and stator.Parameters influencing such losses are: roughness,

surface areas of rotor and stator bore, peripheral speed,

•----_ ..• __ .•._._----

BBeBROWN BOVERI

SUBJECT:

COCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 3-02

j · gas density·y : kinematic viscosity

A · outer surface area of the rotor·v : peripheral speed

In the case of air at 50°C and 1 bar pressure the gasvalues are: J= 1,077 kg/m3 ; y:lO 18,1 10-6 m2/s;Which gives ( j yO.2) = 0,121

Typical operating values for hydrogen at 50°C, 96 %

purity, and 5 bar pressure, are: J= 0,576 kg/m3;y= 16 8 10-6 m2/s; and hence the product value( f ~O , 2) :10 0, 0 6 3 9 •

This comparison shows that identical rotors have abouthalf the loss in hydrogen at 5 bar pressure, that they

would have in air. This is one of the reasons why oneprefers hydrogen as the cooling medium.

The ventilation loss (windage loss due to the fan) is the 41'product of coolant flow and fan pressure, divided by the

fan efficiency. The fan pressure depends on the design of

the fan and the density of the gas. This permits thefollowing equation to be written:

Pw due to fan N g Q /1. f

volume rate of flow of the cooling mediumfan efficiency

•

BBeBROWN BOVERI


EGATOctober 1986

The iron loss of the stator laminated core is

approximately proportional to the square of the flux

density, and hence also to the square of the internally

induced voltage of the stator winding. Although this

induced voltage is in fact dependent on load, we may use

the generator terminal voltage U as a first

approximation. We then obtain the following approximate

equation for constant frequency:

3.2 Voltage-dependent Losses

Here again there is an advantage of hydrogen over air

(owing to the different f -values), and hydrogen at 5

pressure has approximately half the loss.

3-03

bar

ISHEET No.:'T.'URBO-GENERATO~

GKW S 100 051

SUBJECT:

DOCUMENT No.:

Piron"'" u2

3.3 Current-dependent Losses

Current dependent losses are those arising from the

currents in the stator and rotor windings. These include

losses caused by the leakage flux of the stator winding

e.g. eddy current losses in the core end regions and in

the housing, and losses in the end bells and outer rotor

surface due to the flux ripple caused by the stator

slots. The sum of these current-dependent-losses is

subdivided into:

•armature winding losses

fi~~d winding losses

st,~y load loases

P = 3 Ra r 2

':) ?.=_1

: - ..p = f(r~)

BBeBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHE5T No.: 3-04 •

[\

I armature current, Ra armature winding resistance

If rotor field current,Rf field winding resistance

It must be observed that the resistances of the windings

are dependent on the temperature and therefore the losses

rise correspondingly, even at constant current.

The field current If is supplied by excitation

equipment e.g. a thyristor bridge or exciter. Losses in

the excitation equipment are external to the generator,

however, they are included when calculating theefficiency of the generator.

3.4 Schedule of Losses

When the total losses of a 300 MVA generator, power

factor 0,85, are considered as 100 %, then the followingtable can be established:

a) armature circuit losses ( 3 R I 2 ) 10 %ab) armature current-dependent stray load losses 20 %

c) iron losses 17 %

d) field winding losses R r 225 %f

e) losses in excitation equipment 1 %

f) windage losses 15 %

g) shaft sealing losses (H2-air) .2 %

h) bearing losses (without turbine) 10 %

100 %

In the case of air-cooled ;~~e:~~~:s ?~a~~ion g) :3

and d) are smaller.

.'

•

Generators of higher utilization factor have more intensivecooling (e.g. with water) and therefore Pos. a), b) and d)take higher values.

•

I •

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: • 3-0 5

•GKIKO 2900

BBCBROWN BOVERI


EGATOctober 1986

The output of a generator is usually limited by the

temperature of either the stator or rotor winding. Other

temperatures are normally less important. Windings are

classified according to two systems of cooling.

4. Gf.l\lER~L. COOLING CONSIDERATIONS

~.l Formation of the Winding Temperature

!SHEET No.: 4-01TURBO-GE:\lERATOR

GKW S 100 051

SUBJECT:

DOCUMENT No.:

In the case of indirect cooling, the copper windings have

no direct contact with the coolant. Either the insulation

outer surface or the surrounding laminated core is

cooled. The available temperature rise between theallowable winding temperature and the cold coolant inlet

temperature is spread over:

a) the heating of the coolant

b) the heat transfer between the coolant and

the cooled surface

c) the heat passage through the iron and the

insulation; thermal conductivity

Indirect cooling is a constructively simple and low cost

solution as long as it is adequate for the needs.

In the case of direct cooling the coolant is brought into

direct contact with the winding copper e.g. by hollow

conductors. The available temperature rise is now

divided amongst only two components:

al the heating cE the ccclent

b) the heat transE=c between the coolant and cc~pec

BBeBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1985

ISHEET No.: 4-0 2 •The insulation component is not present. The utilization

and loss density may now be larger. In the case of direct

cooling the coolant can be air, HZ' or water, which is

fed through the hollow conductor windings. For the stator

winding Brown Boveri only use water.

4.2 Cooling Media and Attributes

Generators are mainly cooled by air, hydrogen, and water.

From the cost point of view air is the cheapest and water

the most expensive, not because of the cost of the

cooling medium, but because of the special precautions

and auxiliary equipment. Air is in general insufficient

above a generator power of 200 MVA (50 Hz), and is

therefore replaced by hydrogen. As this also becomes

inadequate for higher" powers then the stator ,Winding is

water cooled.

•

In evaluating the individual cooling media their

properties must be known. Some typical sets of values are

listed below. ecooling

medium ~ 'IJ c1 Akgi'ffiJ mils Ws/m 3 K w/mI<

air, 50 °c,1 bar 1,077 18,15 10-6 1080 0,028

hydrogen, 50 °c,96 % purity

1 bar pressUre 0,115 92,9 10-6 1080 0,178

4 bar: 0,460 23,2 L6 -6 4320 o ,17a8 bar 0/920 11,6 10-6 8640 0,178 •water 50 °C 988 0,57 10-6 4130 10 3 0,640

~'til/~'" .,~;: -_.._--_._- -- ---_.

IICBROWN BOVERI


EGATOctober 1986

One can see that: ~ and c j are proportional to thepressure. y is inversely proportional to the pressure,

and ~ independent of pressure. All parameters aredependent on temperature and hydrogen purity.

~ · density·y : kinematic viscocity

Cj : specific heat capacity x density

~ · heat conductivity·

SUBJECT:

DOCUMENT No.:

TUP.BO-GENERP.TO?_

GKW S 100 051

I"'H-ET!'\' .. i:l :1: , .0•. 4-03

4.2.1 Heating of the Cooling Medium

When the power loss P is removed by a cooling mediumvolume rate of flow Q then a temperature rise of~t occurs

A t (c~) = --p-Cj Q

Since the density is proportional to the pressure, then

the temperature rise of the coolant can be reduced byincreasing the pressure.

P is the heat loss removed {rom the surface area S.

Temperature Difference by Convection

When a cooling medium cools a surface of area 5, then amean temperature t is developed between the cooling

medium and the surface. This is dependent on the

coefficient of heat transfer h.

--p= h· Sat (h)

4.2.2

•

BBeBROWN BOVERI

SUBJECT:


TURBO-GENER.~TOR

EGATOctober 1986


Equations have been developed experimentally for the heattransfer coefficient, which is dependent on the type of

flow and properties of the cooling medium. An example isgiven here for the convection coefficient -h- of a pipethrough which the gas flows.

Characteristic numbers have been adopted:

Reynolds number, characteristic of

the flow; Re < 2320 laminar flow;

Re > 2320 turbulent flow

Nusselt Number, characteristic ofthe heat transfer; approximated here

for Re >5000

w • velocity of the cooling mediumdh • hydraulic diameter; for a circular-section pipe

d • dh

The above equation allows an estimate to be made of thebehaviour of the temperature rise 41 t (h) when var ious

cooling media are used. With the same cooling arrangement

and the same velocity of the cooling medium the followingrelationship is valid for two different coolants.

GK/KO 2960

•

•

BBCBROWN BOVERI


EGATOctober 1986

Taking the numbers given in section 4.2 the following

results are achieved:

TURBO-GEN2RA'!'OR

8 bar

11 %

13 %

ISHEET No.: 4-0 5

19 %

25 %

4 bar

54 %

100 %

hydrogen

50°C; 1 bar

96 % purity

100 %

100 %

air

50 °c;1 bar

SUBJECT:

DOCUMENT No.:

It can now be clearly seen how the cooling effect is

improved in going over from air to hydrogen, and also how

the cooling is increased when the gas pressure is

increased. However, it should not be overlooked that the

windage losses rise with increasing pressure.

•

Generators of up to 350 MVA can be designed with indirectcooling of the stator winding. However, it is also possiblethat the limit falls below 300 MVA under certain conditions

e.g. a power factor of below 0.8, or a short-circuit ratioabove 0.5, or high voltage (e.g. 21 kV), or high coolingwater temperature. Generator rotor windings are alwaysdirectly cooled.

SPECIAL GENERATOR DESIGN UP TO 350 MVA

•BBeBROWN BOVERI

SUBJECT:

DOCUMENT No.:

5.


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 5 -01

•

5.1 Construction and Cooling of the stator

The stator cooling removes windage losses, iron losses, and

losses in the windings. The copper windings do not come

into contact with the cooling medium itself. The heat ispartly removed directly through the insulation to thecoolant (e.g. end winding), and partly in addition through

the stator laminated core. The.surface of the core must

therefore transport not only its own losses but also thoseof the copper. The designer therefore provides the corewith a suitably large surface area.

The laminated stator core is subdivided into individual

bundles of about 50 mm wide which are separated from each

other by spacers. Radial cooling ducts of approximately 6

to 10 mm wide are then formed which create a large outer

surface in the core.

Fig. 5.01 shows the basic principle of cooling using the

indirect method. The cooling gas from the fan divides into

one branch leading to the roto~, and two branches leading

GK/KO 2960

BBeBROWN BOVERI

SUBJECT:


TUREO-GE~ERATOR

EGATOctober 1986

SHEEi No.: 5-0 2 •DOCUMENT No.: GKW S 100 051

Fig. 5.01 principle of indirect cooling

One cooling flow branch of the stator passes between therotor end bell and stator end windings then into the airgap. The cooling gas is then split up into flows through

the individual radial cooling slots and from there axially

to the cooler. This cooling section is compartment 1.

The other cooling flow branch flows through the end

windings over the back of compartment 1 and intocompartment 2. The cooling gas in compartment 2 then flowsradially inward through cooling ducts in the stator

laminated core. The flow in the air gap is led into th~

middle of the machine and mixes partly with the gas leaving

the rotor. This then cools the middle part of the stator(compartment 3) leaving in a radial direction.

•

otherwise the cooling gas would be preheated too much bywindage losses (especially with air) before it reached thepoint where it is required for cooling.

~ - ""': ~ ~ ; .. -.... ... ~ •.,;~ f • :;;

•----~_.- _._._-_._------_._-----

The construction of the core, the inside of the casing,and the end windings, therefore have a distinctivecooling design, namely, radial cooling ducts, axial gasducts along the yoke of the laminated core, and end

windings which allow the cooling gas to pass through.

The selection of the cooling medium, whether air or

hydrogen, now determines the differences in theconstructional design of the casings.

EGATOctober 1986

5-03ISHEET No.:TURBO-GENERATOR


GKW S 100 051

SUBJECT:

DOCUMENT No.:

BICBROWN BOIIERI

•

5.2 Air Cooling up to 200 MVA

The first generators to be designed in the history of

electrotechnology were air cooled. As the unit power

increased, air cooling was insufficient. Hydrogen wasintroduced as a new cooling medium which meant thathigher powered generators could be built within the

same external dimensions.

•

After the introduction of H2-cooling, development ofair-cooled generators was neglected.

About 10 years ago the development of air-cooledgenerators was started again, mainly because of the

considerable advantages for operation and maintenance.

The capabilities of air-cooled generators are limited bythe allowable heating of the windings and by air friction

and windage losses. There are no limitations on themechanical side, since there are already hydrogen-cooled

BBeBROWN BOVERI

SUBJECT:


TURBO-GENER.ATOR

EGATOctober 1986

ISHE..=T No.: 5-0 4 •DOCUMENT No.: GKW S 100 051

Brown 30veri have increased the possible unit rating upto 200 MVA (50 Hz) by intensifying the air cooling.

The common features of air-cooled and hydrogen-coole~

generators have already been described under section

5.01. The constructional difference to the H2-cooled

machine is only determined by having to adopt anexplosion-proof casing.

In the case of air cooling it is unimportant where thecoolers are situated, whether on the foundations or in

the casing. The latter does not have to be air-tight. Infact, there is a small continual escape of air at the

glands where there is an overpressure relative to outside.

At points where there is fan suction, e.g. near to thebearing, air enters from the outside. Special openingswith air filters are therefore provided to clean this air.

•

5.3 Constructional Features of H2-cooling

With hydrogen cooling one requires an air-tight casing

since hydrogen and air must not mix. As already shownabove, cooling is improved by raising the hydrogen

pressure. An air-H2 mixture is explosive when the

hydrogen content lies between 5 \ to 85 \. The generatoris,however, operated with a gas purity of between ca. 96 %

to 98 %.

•

The hydrogen is cooled by water coolers. The water

pressure is adjusted so that it lies about 0.5 bar below

that of the hydrogen. This ensures that water cannot

enter the generator if there is a leak in the coolers.

Since the casing is a closed pressure-vessel, the

hydrogen coolers cannot be placed outside to the

generator. They must be integral with the casing and are

normally arranged vertically at the four corners near the

bearings, or longitudinally above the stator core.

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERAT'JR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 5 -0 5

•

The generators are provided with oil shaft seals to avoida mixture of air and hydrogen at the bearings where the

shaft leaves the casing.

The principle of the shaft sealing is to force oil intothe gap between the casing and rotating shaft. The oil

flows towards the hydrogen side and air side. No hydrogen

can escape against the direction of flow of the oil. The

oil can, however, absorb hydrogen on the HZ side, and

air on the air side. The oil must therefore be de-gassed

so that the hydrogen and air are removed. There is

consequently a continual small loss of HZ from the

generator and this must be replaced.

The HZ consumption of large generators is held to a

minimum by using a seal oil system with three circuits.

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATO?

GKW S 100 051

EGATOctober 1986

SHEET No.: 5 -06 •

o Pump

(5) Fan

i Non-return valve

, Differential pressure regulator

I c:J Oil, containing hydrogen

~ Oegas5ac oil

Jt P1 Oii. :cf"'C3i-;:H; Jir

2

3

4

Bearing

Sealring

Oil tank

Vacuum-oil tank

Fig. 5.02 Principle of the triple circuit seal oil system ~

GK/I<IJ 29"0

g!.

DE

Gas tight sealingof the generatorrotor shaft

Air_Sid~--

e:: :; ~ .;

End-Shield

1/H2-Side

•/

Sealing-oil plantwith associatedpiping, control andinstrumentationsystems

•

End-Housing

.. I

Gas-tight seali~gof the generatorrotor shaft

". J i.

/ ·Air-Side

•

'. Floating Ring - Type Shaft-Sealing

Air saturated lube oil is fed to the shaft sealing ring at

about 0.5 bar above the hydrogen pressure in the generator.In addition to the air-seal oil supply, evacuated

(degassed) oil is fed to the H2 side at a slightly higherpressure, which also partly flows into the air side. Air

saturated oil is thereby separated from the H2 side. Apart of the evacuated oil flows, of course, also to the

hydrogen side. But this flow is maintained very small by

means of an auxiliary oil circuit with H2 saturated oil.The pressure of the H2 oil circuit is controlled so that

only small quantities need be taken from the degassedsupply. The degassed oil required is taken from the vacuum

oil tank which is fed from the lube oil tank.

•BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENEPJ'.,.TOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 5 -0 7

5.4

5.4.1

The air seal oil circuit is the most important. It can

maintain the sealing function alone, even though there are

higher gas losses. Sealing is guaranteed by back up pumpsin the air-oil circuit in case the main pumps should fail.

The shaft sealing system is a source of losses, which

amont to around 50 kW to 100 kW.

Auxiliary Equipment for Hydrogen Cooling

Hydrogen Supply Equipment

It is insufficient to fill and pressurize the generatoronly once with hydrogen and then leave it to itself. The

shaft seals and small leaks in the casing require a certain

amount of hydrogen which is supplied by a permanentlyt: -u~""ly !"'l-"n".- 2 .;)' t'" i:' e".....'~ •

_____GI<~KO 296o __. - --------_.--------

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

1SHEET No.: 5-08 •5.4.2 Carbon dioxide Equipment

Since hydrogen and air must never mix, it is necessaryduring the filling and emptying the generator to have anintermediate gas. Carbon dioxide, CO2 , is used for this

purpose.

Before the generator is filled with hydrogen the air isfirst displaced using CO2 gas. CO2 is heavier than airand is introduced into the generator housing from below.

The H2-connections at the top allow the air to be vented

to atmosphere.

After a 90 , CO2 purity is achieved the 82 is

introduced from above displacing the CO2 out below.

If and when the generator must be opened, the reverseprocedure is carried out in order to replace the hydrogen

by air.

5.4.3 Moisture Measuring EqUipment, Gas Drying

Even though the generator is operated as a closed system it

can happen that the hydrogen becomes gradually moistthrough water leaking from a hydrogen cooler. The moisturecan condense at colder parts and result in damage (arcing,

ground faults).

It is therefore recommended to install moisture detectorsand gas drying equipment. This monitoring equipment

QK/KO 2960

•

----"~

6.1 Basis of Comparison

6. AIR-COOLED GENERATORS COMPARED TO HYDROGEN-COOLED

GENERATORS

In setting out to compare hydrogen-cooled generators withair-cooled it is necessary to set down a clear basis of

comparison. The comparison relates primarily to theefficiency, since it is often on this point that the

major advantage is to be found for the hydrogen-cooled

generator.

EGATOctober 1986

ISHEET No.: 6-01TURBO-GENERATOR


GKW S 100 051

SUBJECT:

DOCUMENT No.:

BBCBROWN BOVERI

•

Air- Hydrogen-cooled cooledgenerator generator

The rated figures of the air-cooled generator are taken

machine in the middle range and ~ith the usual degree ofutilization.

188 MVA 188 MVA160MW 160MW0.85 0.8550 Hz 50 Hz15kV 15kV± 5% ± 5%50 s-\ 50 S-1

40 "C 40 "CF FInsulation Insulationclass B class B~ 1000m anyo 300kPa> 14% > 14%<30% <30%0.54 0.54IEC IEC

Comparison of generator ratings for the air

and the hydrogen-cooled machine

Apparent powerActive powerPower factorFrequencyVoRageVoRage variationSpeedCold gas inlet temperatureInsulation classHeating of stator and rotorwinding limned byInstallation elevationGauge pressure in the generatorSubtransient reactanceTransient reactanceShort-circuit ratioRecommendations

Table 6.01

•GK/KO 2960

BBCBROWN BOVERI

SUSJECT:


TURBO-GENERATOR

EGATOctober 1986

1SHEET No.: 6-02 •DOCUMENT No.: GKW S 100 051

6.2 Size, Weight, and Efficieny

The comparable values for length, diameter, weight, andrated efficiency are given in Table 6.02. Fig. 6.01 showsthe efficiency against load.

Air· Hydrogen-cooled cooledgenerator generator

Core lengthRotor diameterActive length I rotor diameterEsson coefficientweight of coreCopper weight of statorCopper weight of rotorHeaviest weight to be liftedlor assemblyEfficiency at rated power output

100%100%436100%100%100"'100%

100"'98.64

92%87%4.63144%n%72%70%

108%98.63

Table 6.02 Dimensional comparisons

A 13 , smaller rotor diameter was chosen for the

hydrogen-cooled generator so that the slenderness ratio oflength to diameter approximately remained the same. Owingto the greater utilization of the material the loaddependent losses are higher, whereas losses independent ofload are smaller, therefore the sum of the losses at ratedload is the same. The efficiency of the hydrogen-cooledmachine at part load remains at a higher value. Theadvantage of hydrogen with its lower density now becomesapparant i.e. the windage losses are clearly lower.

•

100

%

98

/r~~ -

I 98 V7I'17

/,

96 J

I

9S0 25 so 75 100 % 125

Pel centage d I'IIt8d load

•BICBROWN BOVERI

SU8JECT:

DOCUMENT No.:


TtJR3i)-GE~EPATOR

GK'N S 100 051

EGATOctober 1986

, SHEET No.: 6-03

•

Fig. 6.03 Efficiency comparison between air-cooled and

hydrogen-cooled generators

Summarizing, it may be said that with respect to

efficiency, the air-cooled and H2-cooled generators are

about equal, as long as the part-load range is not

considered.

The following constructional features of the air-cooled

generator are the reason why the efficiency of the two

methods of cooling are the same:

a) approx.30 % larger active volume i.e. lower utilization,

b) a well designed fan with low flow losses and high

efficiency

BBCBROWN BOVERI

SU8JECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

ISHEET No.: 6-04 •c) well formed air guidance at the fan and in the cooling

ducts

d) low-loss design of the end winding space. i.e. smallpreheating of the cooling air.

6.3 Losses and Temperature Distribution

As the efficiency characteristic shows, the individuallosses have varying significance in the total loss

account. These losses at rated load are split up as

follows:

•

iron losses

stator I 2 Rand

stray load losses

rotor losses If R

windage and

frictional losses

bearing losses

air-cooledgenerator

18 %

18 %

19 %

37 %

8 %

100 %

hydrogen-cooledgenerator

13 %

34 %

37 %

8 %

8 %

100 %

•

GK/KO 2geo

The iron losses for the H2-cooled generator are smaller

fo~ a9?Co~imat91y the same fl~x 1~nsity o~ing ~o ~he

current density) cC2ults in the l~ad dependent lossesbeing much moce significant. With hydrogen, the windagelosses are considerably lower.

---------------------------- ---------

•

BBCBROWN BOVERI


EGATOctober 1986

air-cooled H2 cooledgas heating by

windage 30 K 15 K

temperature contribution forheat transfer 20 K 5 K

temperature contribution forheat conduction through

the insulation of the bars 15 K 30 K

mean stator windingtemperature rise 65 K 50 K

The mean stator winding temperaturesgenerator types may be compared from

break-down of components:

SUBJECT:

DOCUMENT No.:

TURBO-GENERATOR

GKW S 100 051

ISH:E'T No.:

for the twothe following

5-05

The temperature components quoted are the computed mean

values over the length of the laminated core. They areintended to illustrate where the main differences lie in

the two forms of cooling i.e. air and hydrogen. The maintemperature component with air cooling is due to the air

density, whereas with hydrogen cooling is mainly found inthe bar insulation. That is practically the temperature

difference between the laminated core and copper. Thedifference between the two temperature totals is due tothe standards e.g. lEe. It is explained in section 6.4.

---_._---------------

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GE~E.RATOR

GKW S 100 051

EGATOctober 1986

.rSHEET No.: 6-0 6

6.4 Reasons for the Differences in Temperature Limits in theStator of Air and H2-cooled generators

The insulation class for both air and hydrogen-cooledgenerators is the same (class F). The generators aredesigned for class a, that means for heating limits (hotspots) of 130 ~c, or 90 K, at 40°C cold gas temperature.These temperatures cannot, however, be verified bymeasurement. The temperatures which in practice are

measured are those of temperature detectors installedbetween the upper and lower bar which indicate the mean

winding temperature in this range. The allowable

temperatures quoted here are defined in IEC standards asvoltage related and cooling medium related values.Voltage related means, in effect, dependent on the

insulation thickness. Cooling medium related is

effectively utilization dependent, or, current density

dependent.

The reason is that with thick insulation or high currentdensity (e.g. with H2-cooling), the difference between

hot spot temperature and measured temperature tends to belarger. Since the temperature limit is stipulated as

130°C, the allowable measured temperatures are set at

different levels.

In the example given, at 15 kV, the allowable temperature

for air cooling is 40°C + 76 K = 116°C, and for H2cooling is 40°C + 61 K = 101°C measured by embeddedtemperature detector (ETD).

GK/I<O 2'160 ------_. __._._- .

At the present time, the limit of indirect cooling forstator windings lies at about 350 MVA. The reasons for

this are the transfer to higher voltage (21 kV) and the

consequent use of thicker insulation. Since all copper

losses must be carried over the insulation, thetemperature difference between core and copper rises, and

therefore the relative expansions between the bars andlaminations become too excessive. It is then better to goto water-cooled stator windings.

GENERATORS WITH POWERS ABOVE 350 MVA

•BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:

7.


TUREO-GENErtATOR

GKW S 100 051

EGATOctober 1985

ISHEET No.: 7 - 0 1

•

7.1 Water-cooled Stator Windings

The winding is directly cooled when water cooling is

used. The copper losses are not carried over the

insulation. Solid sub-conductors in the winding bars areinterspersed by hollow sub-conductors through which waterflows. The insulation of the sub-conductors is only

0.2 mm thick, so that the temperature difference between

a hollow and the most remote solid sub-conductors within.a bar is only about 10 K. Owing to the good heat transfer

from water to hollow conductor, the hollow conductor

itself assumes the same temperature as the water (about

1 K difference). In general, the winding has the same

level as the water. It will normally not exceed 80 °c .

BBCBROWN BOVERI

SUBJECT:


TT.."RBO-GEm:R.~.TOR

EGATOctober 1986

SHEET No.: i -0 2 •DOCUMENT No.: GKW S 100 051

The limit of cooling is not determined by the coppertemperature, but rather by the heating of the water.

Water velocities of up to 2 mls are usual in the hollowconductors.

=c= . -- hollow conductor

•

•

.~ .Mlcadur Insulation

filling

antl- corona varnish

fillingspacer

~~~~=.-protective striP

= g

]~iii~= filling* slot wedge

Fig. 7.01 Slot section for water cooling

•

IBCBROWN BOVERI


EGATOctober 1985

.;

Water inlets and outlets are situated at the ends of the

stator. The water flows from the inlet manifold through

insulating teflon hoses in to the individual winding ends

where it is distributed to the individual hollow

conductors.

SHEET No.: 7 -0 3

---- _. ;--

TURBO-GE:NERA70R

GKW S 100 051

SUBJECT:

DOCUMENT No.:

•7.2

Fig. 7.02 Schematic of water cooling

At the other end of the machine the water leaves by a

similar system of teflon hoses and a manifold ring.

Hydrogen-cooled Core

The core ls not included in the Yat~~ ~~~1~~g ~n~

therefor8 be ~epa~acely cealed ~ith hydrogen, which is

also used for cooling the rotor winding.

GK/KO 29€0 -------- ----------

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GSNE?..ATOR

GKW S 100 051

EGATOctober 1986

, SHE-=T No.: 7-04

Radial slots are no longer useful and also take up toomuch space in the axial direction which, at increasing

power represents a loss of valuable active length of thecore. For this reason the hydrogen is guided through

axial cooling holes in th~ laminated core. The gas entersat the end plates and leaves through a radial slot in themid sec~ion at the back of the yoke.

\ \" '\ \'~

Fig. 7.03 Schematic of the core and rotor cooling

•

Since the ampere-turns (mmf) in the stator also appear inthe rotor then the rotor too sees a higher loading as the

electric loading increases (c.f. Section 1.2). This leadsto excessive heating if no additional measures are taken.

The H2-cooling of the rotor winding is therefore

boosted by adding the fan pressure to the pressurealready produced by the rotor itself.

7.3 Reinforced Rotor Cooling

EGATOctober 1986

, SHEET No.: 7 -J 5


GKW S 100 051

SUBJECT:

DOCUMENT No.:

IICBROWN BOVERI

•

In order to make the fan pressure effectively act on therotor conductor one must prevent a gas short-circuit over

the air gap between rotor inlet and outlet. To this end,

the air gap entry at both ends is blocked at the endbells by means of a gas baffle, which allows just

sufficient passage for cooling the air gap space. Radial

fans are used owing to their higher pressure •

•

BBCBROWN BOVERI


EGATOctober 1986

The winding cooling water must be strictly controlled for

purity to ensure safe operation at high stator voltages

of ca. 20 kV. A distinction is made between this circuit

and other water circuits that do not have to fulfil theserequirements, and therefore this water is termed PrimaryWater, or Purified Water (sometimes also referred to as

,deonized water also).


8. SPECIAL FEATURES OF WATER COOLING

ISHEET No.: 8-01TURBO-GENERATORSUBJECT:

8.1 Purified Water Circuit (Deionized Water)

The purified water flows in a closed circuit and cools

the stator winding and terminals. The water flows through

coolers external to the generator and is cooled by asecondary water circuit which also serves the hydrogen

coolers.

The conductivity of the water in normal operation mustbelow 0.5 uS/em. Measurements on many turbo-generatorshave shown that in practice this level can be held to0.2 uS/cm.

Two pumps are provided connected to separate supplies

(one is a spare). The pump in operation circulates the

water in the circuit. The cooling water flows throughcoolers, a filter, a tapping point for measuring the

conductivity and then to the winding.

•

IICBROWN BOVERJ

SUBJECT:


TUR30-GENE~ATOR

EGATOctober 1986


'. '.~_:

0 Pump e Filter

X Make-up lIallie e Deionizer

1 Non-return lIallie e::l Orifice

~ Pressure relief lIallie Water tank

O€) Conductivity 2 Cooler

Fig. 8.01 Purified water circuit of the stator winding •

Part of the water is cantinously taken over a

regenerating bypass where an ion exchanger brings it down

to the required conductivity.

The inlet pressure of the purified water should always be

below the hydrogen pressure in the generator so that,

water cannot leak into the generator. However, this means

that hydrogen can slowly leak into the water system via

for example the flexible pipes. The hydrogen contained in

the water can then separate out in the water tank and be

vented to atmosphere through a non-return valve. The

water tank has a continuous small flow during operation.

It also serves as a reservoir for water leakage losses of

the pumps.


EGATOctober 1986

ISHEET No.: 8-03TU'RBO-GENERATOR.


SUBJECT:

BBCBROWN BOVERI

•

8.2 Disturbances in the Water Circuit

•

Hydrogen entering the water system is in principle

harmless. However, no air must be allowed to enter the

circuit.

A very thin layer of stable oxide covers the inner

surface of the hollow sub-conductors so long as the

circuit remains tight and is chemically balanced. No

technically significant corrosion of the copper will take

place.

But if air should now enter the circuit e.g. due to aleakage, then the carbon dioxide in the air will acidify

the water so that the oxygen in the air can attack and

indicator on toe filter itself.

BBCBROWN BOVERI

SUBJECT:


TURBO-GENER..;'1'C?.

EGATOctober 1986

. ISHEET No.: 8-04 •DOCUMENT No.: GKW S 100 051

A further rise in the concentration of 02 causes the

formation of CuO which builds up on the inner surface ofthe hollow conductors attached to the cu20 layer. Theresulting deposits can be heavy an can becom detached,

causing restriction of the sub-conductors.

However, long before the first hollow conductor becomesblocked, the deposits become evident from the pressure

drop across the filter. Also, reduced stator cooling ~water flows caused by widespread deposits areannunciated. After the alarm there is still adequate timefor diagnoses and remedial action by flushing.

It is important to recognize changes in the behaviourpattern of the pressures in the purified water circuit.

8.3 Humidity Measurement, Water Temperature Control

It is even more important to monitor the humidity in this

type of generator than that of a purely H2-cooled

machine. A water-cooled generator caries an additionalrisk owing to the purified water circuit. Condensationcan form on the cold outer surface of the flexible hoses

to the windings when the moisture content is high with acorrespondingly high dew point. A flashover on a hose can

result.

They are blown off and carried with the gas flow and canbe deposited under the end bells which leads to

corrosion, and possibly even cracks.

As with the cold hydrogen gas temperature, which is held

at 40 °c, the purified water circuit also has the inlet

temperature regulated to a constant value. In the event

that there is no humidity measurement unit and drying

equipment installed, then the inlet of the purified water

should be about 3 K above the cold gas temperature to

prevent moisture from condensing out.


•

~ "": ":; :: J)

;

•

BICBROWN BOYER!

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986

ISHEET No.: 8-05

------------------

a) Isolating a damaged cooler

Abnormal conditions can occur when there is a partial

failure of equipment in the plant. The generator may be

required to continue operation.

Since the cooling power with a cooler out of service

is reduced the temperature of the coolant will rise.

With unity power factor, or with reduced power, the

generator may still continue in operation with higher

cold gas temperatures provided the limits of the

machine are respected.

EGATOctober 1985

ISHEt'l No.: 9-01'I'U?,SO-GE~mRAT:JR


GKW S 100 051

OPERATION UNDER ABNORMAL CONDITIONS

SUBJECT:

DOCUMENT No.:

BBeBROWN BOVERI

9 .

•

b) Partial failure of the shaft sealing leakage of

the casing

It is sensible to reduce the hydrogen pressure when

the shaft sealing has malfunctioned, or there is a

serious leak in the casing. The hydrogen loss is

thereby reduced. The load must then be adjusted to the

new conditions. In the most instances, even here, it

is possible that the turbine load can remain constant

if the power factor is adjusted to unity. At this

operating point there are considerably lower losses

than at the rated value, so that even at lower

pressure, i.e. reduced cooling, operation can continue

without exceeding the rated design temperatures •

•

At present three types of excitation systems are in use:

The original method of excitation of turbo-generators was

with a d.c. exciter directly coupled to the generator.

Such exciters could supply units of up to 100 to 150 MW

maximum.

10. EXCITATION SYSTEMS

EGATOctober 1985

ISH:ET No.: 10-01TU;:{BO-GENE.'Q.ATGR


GK",.l S 100 051

SUBJECT:

DOCUMENT No.:

BBCBROWN BOYERI

•

- excitation with stationary thyristors

- stationary diodes with a 3-phase exciter

- rotating diodes with a stationary field, rotatingarmature 3-phase exciter

10.1 Excitation with Stationary Thyristors

When the excitation is provided by stationary thyristors

(Fig. 11.01) then the excitation power is taken from the

main generator itself. No special exciter machine is

necessary.

A transformer lowers the generator voltage to level

corresponding to the highest excitation voltage required.

In the thyristor converter the alternating current is

rectified and fed to the oppropriate field windings via

the generator slip rings.

A field breaker is situated between the excitation

recifier and the slip rings. When a fault occurs in the

generator the field breaker disconnects the field winding

r~ducej in the shortest posaiola time which minimizes

effects of damage.

- --- .----- --- --------- -----------

BBCBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986


4

3

w---J--•

5

1 turbine

2 generator

3 unit transformer

4 unit generator main

circuit breaker

5 excitation transformer

6 thyristor converter

7 field breaker

8 field dumping resistance

9 voltage regulator

:ig. lQ.Ol Excit~tion equip~~nt with stationary

excitation equipment can be serviced during operation. Thestatic arrangement, as well as the multi-channel design,

permits simple repair or replacement of all components.

The field voltage of the generator can be changed almostinstantaneously and also reversed, by virtue of the

thyristors. Fast changes in the field current and optimum

control of the generator can therefore be provided.

•BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKTtl S 100 051

EGATOctober 1986

ISHEET No.: 10-03

10.2

In the arrangement described, an exciter is not required,so that the end of the shaft only carries the slip rings.

This leads to a shorter shaft row and in turn a smaller

foundation and possibly even a smaller machine hall. Ashorter shaft also contributes towards smoother running of

the machine.

Stationary Diodes with 3-phase Exciter

In this case (Fig. 10.02), the excitation power is supplied

by an exciter which is coupled to the generator shaft

(inner-pole synchronous machine).

The 3-phase current is rectified by stationary diodes and

then supplied to the field windings via slip rings.

The excitation of the 3-phase exciter machine is provided

by a permanent magnet pilot exciter.

Adjustments to the generator field voltage are made bychanges in the field of the exciter. A change in the

occ~r as fast as with thyristor conceol.

BBCBROWN BOVERI

SUBJECT:


TURBO-GENE&"\TOR

EGATOctober 1986


5

•

~ig. 10.02 Excitation equipmen: with stationa:y diodesand 3-phase exciter

1 turbine2 generator

3 unit transformer4 unit generator main

circuit breaker

5 permanent magnet generator6 thyristor converter7 field breaker for the

3-phase exciter

8 dumping resistance for~r.e 3-?hasa ~xciter

9 3-phase exciter forthe main generator

10 diode rectifier

11 field breaker formain generator

12 dumpingresistance for themain generator

13 voltage regulator

•

10.3 Rotating Diodes with 3-phase Exciter

As in the case of excitation through stationary

thyristors (c.f. 11.1), there is also an excitation

breaker and resistance, since the field winding is

directly accessible through the slip rings.

•lieBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENE.QATOR

GKW S 100 051

EGATOctober 1986

TSHEET No.: 10-05

•

•

•

When the excitation is from rotating diodes, (Fig. 10.03)

the power is supplied by a rotating armature a.c. exciter

directly coupled to the generator shaft. This is similar

to the case with stationary diodes (c.f. 10.02). A pilot

exciter provides the field energy required for the

external poles. The main generator field voltage is

regulated by controlling the field voltage of the

exciter. The dynamic control characteristics correspond

to these of an excitation with stationary diodes i.e. the

speed of control of the generator field voltage is again

limited by the time constant of the exciter •

The exciter is a 3-phase external pole synchronous machinewith rotating armature, i.e. the field winding is in the

stator and the a.c. voltage is induced in the rotating

part. Rotating diodes rectify the current which is directly

fed to the main generator field winding. This system

requires no generator slip rings. Maintenance-free

operation is therefore possible over a prolonged period •

BBeBROWN BOVERI

SUBJECT:


TURBO-GENERATOR

EGATOctober 1986


•

•591

J---}

1 turbine

2 generator

3 unit transformer

4 unit generator main

circuit breaker

5 permanent magnet generator

8 dumping

resistance for the

3-phase exciter

9- 3-phase exciter for

the main generator

10 rotating diodes

•Fig. 10.03 Excitation equipwent with rotating diodes and3-phase excitet'

CW'/KO ~o _

With this arrangement the diode rectifier is not directly

accessible. Redundancy is provided to avoid an interruption

in operation when a diode failure occurs. Defect components

are automatically indicated isolated by rotating safety

devices. The individual diodes with associated circuits are

designed as plug-in modules. This enables easy replacement

during a planned shut down and is requires only a shortinterruption of the turning gear operation. Complete cooldown of the turbine is therefore not necessary when

exchanging the modules.

•

•

BBCBROWN BOVERI

SUBJECT:

DOCUMENT No.:


TURBO-GENERATOR

GKW S 100 051

EGATOctober 1986

!SHEET No.: 10-07

•

A field breaker for the field winding of the main generator !

is not possible with this type of excitation system. Only

the exciter machine can be deenergized by a breaker and

resistor. Correspondingly longer deenergizing times of themain generator are the result •

bbc 1basic design

Documents