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HYDROGEN / WATER - COOLED TURBOGENERATORS:

A MATURE TECHNOLOGY ON THE MOVE

R. JOHO* Y. SABATER H. FERRETTO D. ABRAHAM W. FERENS

ALSTOM

Switzerland France France Germany Poland

SUMMARY

The decades from 1960 to 1980 brought a tremendous growth of hydrogen/water-cooled

turbogenerators, resulting in some 1200 MVA for full-speed two-pole units and 1600 MVA for half-

speed four-pole units. This development was mainly driven by the nuclear power generation programs.

With the merger of two European manufacturers in 1999, it was decided to continue with the large

two-pole line of the one partner and the nuclear four-pole line of the other partner. Possible synergies

of the two generator lines were thoroughly examined with the primary goal of increasing reliability

and availability. In addition, both series have always been submitted to continuous improvement.

Selected examples of related technology improvements will be described. Using the synergies and the

continuous improvement the availability of the fleet of large units could be brought up to exceptional

high numbers.

Both generator lines are currently in uprating of output for power plants beginning operation around

2011-2012. Coal power plants with low-emission technologies are making use of large full-speed

turbines, requiring generators up to the 1400 MVA range. Nuclear reactors of the third generation will

use half-speed turbine sets requiring generators up to the 2000 MVA range. It is shown how this will

be achieved by increase in utilization and by moderate increase in dimensions. Efficiency in power

generation has become of utmost importance for caring of the primary energy resources. For the newly

developed 2000 MVA generator it will be demonstrated how highest efficiencies can be achieved.

The technologies available will also in future allow a potential for uprating. Both generator lines might

get further aligned by components, in order to bring their ratings up. Four-pole units will be structured

into generator families around different kind of nuclear reactors, for both 50 Hz and 60 Hz, and

involving the experienced static excitation, as an option to the well-referenced brushless exciters. By

the modular build-up around experienced components the manufacturer will be able to satisfy future

customer requirements with a premium performance of the generator.

KEYWORDS

Turbogenerator, Hydrogen-cooling, Water-cooling, Two-pole generator, Four-pole generator, Design,

Development

* reinhard.joho@power.alstom.com

1. INTRODUCTION

The years 1960 to 1980 brought a tremendous growth of hydrogen/water-cooled turbogenerators up to

1200 MVA full-speed (two-pole) and 1600 MVA half-speed (four-pole). The main driver was the fast

developing nuclear power generation technology. In the mid 80'ies a complete new series of two-pole

generators was introduced by a Swiss manufacturer [1]. In parallel an unsurpassed construction boom

of nuclear power plants in France was served with four-pole generator solutions by a French

manufacturer [2]. The two manufacturers were joining their turbomachinery program in a 1999 joint

venture and a subsequent takeover in 2000. The company now cares for a fleet of more than 600 two-

pole generators and more than 80 four-pole generators. Soon after the merger, the generator program

was clearly allocated in the new organisation. Design responsibility is in Switzerland for two-pole and

in France for four-pole generators. The manufacturing lead center is in Poland for two-pole generators,

in France for four-pole generators, and in Switzerland for rotors. The paper deals with the generator

designs from 1985 up, which basically represent the actual main design features.

2. THE HYDROGEN/WATER-COOLED GENERATOR FLEET

Hydrogen/water-cooled generators are driven by steam turbines (Fig. 1,2). They are designed for table

mounting. Today, the applied power range is from 600 MW up to the highest ratings. Table 1 shows

the MW-classes built for two-pole units, as far as they originate of the new series, started in mid

80'ies. A total of 18 units are in operation for 50 Hz and 60 Hz. They total an EOH (Equivalent

Operating Hours) of more than 1 million and an excellent FOR (Forced Outage Rate) of 0.05%.

Table 1: Two-pole generators (Class 600 MW up, commissioning since 1985)

Plant class MW-class Units 50 Hz 60 Hz Plant references

Nuclear 1200 1 x Leibstadt

Coal 900 2 x Lippendorf

Coal 800 1 x Zimmer

Coal 700 5 x Manjung,Amer 9,Hemweg 8

Coal 600 9

6

x

x

x Shidongkou,Staudinger,Rutenberg,..

China (Commiss. 2008/9)

Steam data of modern PWR reactors make it advantageous for turbine performance to run at the next

lower synchronous speed, which is at 1500 rpm for 50 Hz, using a four-pole generator. The four-pole

generator fleet is listed from 1985 up in Table 2. It consists mainly of second series of P4 types and

N4 types of the French nuclear program. The 28 units in operation have accumulated an EOH of more

than 1.5 million and have an excellent availability. The present references are mainly 50 Hz, but there

is 60 Hz experience from units commissioned before 1985.

Fig. 2: 1722 MVA four-pole generator of the N4

series of the French nuclear power program Fig. 1: 950 MVA two-pole generator in thermal

power station Manjung, MY

1

Table 2: Four-pole generators (Class 1000 MW up, commissioning since 1985)

Plant class MW-class Units 50 Hz 60 Hz Plant references

Nuclear 1500 5 x N4, Oskarshamn 3

Nuclear 1300 18 x Continuation of P4/P'4

Nuclear 1200 2

4

x

x

Ling Ao II (Commiss. 2010/11)

Hong Yan He (Commiss. 2012/14)

Nuclear 1000 6 x x Ulchin,Koeberg,Chinon

3. DESIGN FEATURES OF HYDROGEN/WATER-COOLED GENERATORS

Hydrogen/water-cooled generators have highest utilization number. The definition is given by

C Esson = Sn / (Dr2 ∗ lfe ∗ n)

where Sn: Apparent power, Dr: Rotor diameter, lfe: Core length, n: Rotational speed

Both 2-pole and 4-pole generator types are achieving numbers of close to 40 kVAmin/m3. It is evident

that such high utilization goes along with high specific loss densities in the generator components, be

it in the windings, in the core and in the end regions. The hydrogen serves primarily for heat removal

from the rotor winding and the stator core, but is also indispensable for removal of stray field losses in

end regions. The water cooling of the stator winding bars is a prerequisite for achieving the high

utilization inside the given housing dimensions, which themselves are subject to limits of

transportation, especially the Schnabel car railway transportation (Fig. 3).

Fig. 3: A two-pole generator stator being unloaded from Schnabel car to ship

Two-pole generators are characterized by (Fig. 4):

- Modular housing, center-flanged vertical coolers (Fig. 1)

- Range covered by three standardized rotor diameters and stepped core length

- Pedestal bearings for isolating shaft from frame vibrations

- Rotor winding two-path axial cooling, supported by a high-efficient radial fan on NDE

allowing rotor withdrawal without fan removal

- Static excitation: Simple technology, fast reacting

2

Fig. 4: Two-pole hydrogen/water-cooled generator

The proven key technologies applied:

- Stator end winding: Clamped between rings, axial movable, support re-tightenable

- Stainless steel stator bar water tubes

- Laminated conical core press plate

- Single- and triple-circuit shaft seal system

he water tubing in the stator bars in stainless steel technology is in operation for over 30 years [3]. It

since more than 20 years the standard solution, with an excellent operation record worldwide.

ustomers recognize the robustness of the system, which is characterized by a functional separation of

lectrical connection and water box (Fig. 5).

m ed successfully for over 35 years in more than 100

works with a supply of air-saturated oil and a supply of

an injection of vacuum oil (Fig. 6). A leakage rate of less than

bar(g) and a high hydrogen purity inside the generator, which

far outweigh the higher investment. The system is

ystem auxiliary. It is applied depending on generator

pressure.

T

is

C

e

Fig. 5: Stainless steel water tubing and functional

separation of bar connection and water box Fig. 6: Triple-circuit shaft seal: Floating

rings (FR), separating the oil flows

The triple-circuit shaft seal is a unique syste

hydrogen/water-cooled generators. It

hydrogen-saturated oil, separated by

5 Nm3/day at highest unit pressures of 6

reduces the gas friction loss in the generator, by

fully modularized, including the shaft seal oil s

type, shaft diameter and rated hydrogen

, us

3

Typical data of a large two-pole generator are shown in Table 3.

able 3: Typical data of a large two-pole

enerator [4]

T

g

Model GIGATOP 2-pole

Class 934 MW

MVA 1167 MVA

pf 0.8

UN 27 kV

Speed 3000 rpm

SCR 0.51

pH2 (gauge) 5 bar

Efficiency 98.88 %

Excitation Static Fig. 7: Housing structure of a four-pole generator

Four-pole generators are characterized by (Fig. 8):

- Modular housing, flanged channels for hydrogen ducting, vertical coolers in end covers (Fig. 7)

NDE and DE

r diameters (each frequency) and stepped core length

arings

gle-circuit sh riple circuit)

tor radial-tra w also multi-path axial), axial fans on both ends

- Terminal box on NDE, if needed on

- Range covered by two standardized roto

- End shield be

- Sin

o

aft seal (now also t

oling (no- R nsversal co

Fig. 8: Four-pole hydrogen/water-cooled generator

The proven key technologies applied:

- A cantilevered brushless exciter (Fig. 9). The armature

and the diode arrangement of this unique type of exciter

are housed in a steel ring of bell shape, which is flanged

to the rotor end. The dc field is inserted coaxially in the

armature bore. The short design eliminates the usual

third bearing. This results in a short overall length and

an excellent shaft dynamic behaviour.

4

Fig. 9: Cantilevered brushless exciter

Fig. 10: Stator end winding support

- A reinforced stator end winding support (Fig. 10), that has pr

generators. It is characterized by a solid outer glass-fiber ring and th

outer ring. This gives excellent radial and circum

allows the axial thermal cycling of the end winding.

oven its sustainability in many

e winding ends bolted to the

ferential stiffness. A flexible support system

Table 4: Typical data of a large 4-pole generator

Model GIGATOP 4-pole

Class 1550 MW

MVA 1722 MVA

pf 0.9

UN 20 kV

Speed 1500 rpm

SCR 0.38

pH2 (gauge) 3.8 bar

Efficiency 98.93 %

Excitation Brushless, cantilevered

Terminal Double terminal box

Typical data of a large four-pole generator are

shown in Table 4.

Running tests for:

-Confirmation, -Verification, -Extrapolation

The verification of the performance of

hydrogen/water-cooled generators is done in the

acknowledged way of factory running tests

(Fig. 11). As an established practice, these are

routinely done on first units of a generator type,

and are in accordance to the relevant international

standards. The challenge for largest units is to

provide the driving motor up to 15 MW, for both

frequencies, for the electrical test runs according to

the segregated loss method, and the rigid mounting

on the factory hall floor. The culmination is the

routinely performed sudden short-circuit test from

up to 70 % rated voltage. In addition to

performance confirmation for the customer, by

additional special tests, the manufacturer gets

valuable information to verify the design tools,

which is also essential as a base for designing

higher ratings.

As part of the manufacturing process, all rotors are

routinely passing test runs in the overspin test bed,

such as excited heat runs, balancing runs, and an

overspeed test at 120 % rated speed. Fig. 11: Factory running tests on a

800 MVA two-pole generator

5

4. EXAMPLES OF CONTINUOUS IMPROVEMENT

The continuous product improvement system involves component improvements, learnings from

operation experience, technology alignments. The continuous product improvement system is strictly

subject to the same stringent product development quality rules as applied for new developments. In

the following, the scope is explained by way of examples.

4.1 Laminated conical press plate

A critical issue of the largest two-pole generators is the core end heating in underexcited operation. As

a longstanding practice, large two-pole generators with hydrogen/water cooling are equipped with

laminated press plates on the ends of the core. They consist of stacked laminations, which are

compacted to a ring by vacuum pressure resin impregnation. By its one-side conical shape such a press

art of the magnetic stray flux of the end winding at lowest losses.

two-pole generators, a special investigation was done in a

performance enhancement of the press plate. Supported by electro-magnetic and thermal numerical

nts.

in large generators having water-cooled winding

Roebel bars in the end

solution is the concept of

us field neutralization inside

such bars end in one

lification in the stator bar end

Fig. 13: Twin Roebel bar

plate receives and internally guides p

Facing a continuous uprating of

calculations a couple of design improvements were found. The main improvement consists in an

enlargement of the lateral clearance of adjacent laminations, and the insertion of radial slits extending

from the slot bottom into the yoke (Fig. 12). Both measures serve to sustainably reduce eddy currents

produced by axial flux components. The improvements were integrated into the manufacturing process

f press plates. The solution is also available for replacemeo

4.2 Cross-transposed four-stack Roebel bars

The use of twin Roebel bars is an established solution

bars (Fig. 13). However they need an individual coi

winding, and an additional cross-change per coil. An

a cross-transposed four-stack Roebel bar (Fig. 14), w

each bar while keeping a simple manufacturing of th

large solid lug on both sides, this contributes to a

connections.

Fig. 12: Laminated conical press

plate with enlarged

clearances and radial slits

l connection of the two

alternative, much easier

hich gives a continuo

e Roebel bar [5]. Since all

considerable simp

Fig. 14: Principle of cross-transposed Roebel bar

6

4.3 Rotor cooling of four-pole generators

As a long-standing practice, four-pole generators are equipped with a radial-transversal cooling of the

al direction with a highly efficient use of

ooling gas, and was found an optimum solution for highest ratings (Fig. 15). Because the conductors

wn gas flow applies to one half cooling of the copper stack. The

nding

(2 slot half indicated by gas outlets)

.4 Technology alignments of four-pole generators

rom a manufacturer's standpoint, after merger with another manufacturer, it is obvious to compare

e two existing technology lines, and to check for alignment. A detailed analysis has led to the

llowing technology alignments of four-pole with two-pole technology:

- The stainless steel tubing for the cooling water in the stator bars. This unique and robust

technology is widely approved and, with the stainless steel water box gives highest availability.

m Pressure Impregnation) system, used for the stator bar main

This results in a unique insulation system up to the experienced

epares for the 30 kV range.

- The triple-circuit shaft seal will be applied for the new EPR generator series, which has a

hydrogen pressure equal to experienced levels of two-pole units. The hydrogen loss thus can be

kept at a low 5 Nm3/day.

enerators with ratings up to 2000 MVA (Table 5).

Model GIGATOP 4-pole

rotor winding [2]. Although a proven solution it is rather complex and not suited for supporting a

further increase in unit output. Facing this situation, a cooling concept of a small air-cooled type was

checked and found to have potential for largest sizes. This multi-path forward flow cooling system

gives uniform temperature distribution in axial and radi

c

have two parallel gas ducts: The sho

second half cooling (symbolized by gas outlets) is arranged with a half-pitch shift, and thus contributes

to an even more uniform temperature distribution.

Fig. 15: Principle of multi-path forward flow cooling in rotor wind

4

F

th

fo

- The Micadur® VPI (Vacuu

insulation, is generally applied.

27 kV of two-pole units, and pr

5. TRENDS TOWARDS HIGHER OUTPUTS

A new area of large power plants brings along a need for larger steam turbines and thus for generators.

There is a revival of coal plants using low-emission technologies. This goes along with a need for two-

pole generators beyond 1000 MW. Current projects in Germany require generator ratings up to

1400 MVA. For the new nuclear power plants of the third generation, projects require four-pole

g

Class 1750 MW

MVA 1944 MVA

pf 0.9

Table 5: Typical data of a large four-pole

generator for EPR (Project Flamanville 3)

UN 23 kV* / 27 kV

Speed 1500 rpm

SCR 0.42

pH2 (gauge) 6.0 bar

Efficiency 99.00 %

Excitation Brushless, cantilevered

* requiring terminal box

on NDE and DE

7

8

enerator manufacturer for the current and future uprate The following shows the approach of the g

requirements of the market.

Manufacturer's approach Achieved by

lti-path forward flow cooling

• Increase rated voltage • Based on existing insulation system, limits current

loading in stator bars and bushings

• Uprate brushless exciter • Refine cooling in cantilevered exciter

This means that also the future requirements can be accomplished by using hydrogen cooling

technology for the rotor winding and water cooling technology for the stator winding. These

technologies and all related designs are based on mature and highly reliable solutions and allow a

predictable availability and a reliable maintenance scheduling [6].

enerator families around the

60 Hz, and taking into account differing electrical

bining static excitation with four-

generator line were clearly allocated. Despite the maturity of the

roduct there is always room for continuous improvement of the components and technologies, for

sing synergies, and for further alignment of the technologies.

utputs. The investigations show that even these

gns, hence

enerators”, ABB Review 1/1989

] J.M. Guillard, R. Damiron, J.C. Marino, “1710MVA Generators for the French N4 Nuclear

6

[3] ho, N. Krick, A. Huber, “Ge ding Design –

E Tran s on Energy Conversion, Vol.16, No.1,

March 2001

[4] L. Busse, K.-H. Soyk, “World's Highest Cap Steam Turbos nite-fired

Lippendorf Power Plant”, ABB Review 6/1997

[5] J. Haldemann, “Transpositions in Stator Bars of Large Turbogenerators”, IEEE Transactions on

Energy Con ptember 200

[6] M. Verrier, y, G. Martinet, “N ent in

for Nuclear Power Plants with Reliability Target”, CIGRE Session 200

• Increase hydrogen pressure • Enabled by triple-circuit shaft seal

• Moderate increase in length • Checked by shaft dynamic calculation

• Moderate increase in rotor diameter • Mechanical optimization by finite element analysis

• Reduced temperatures in end zone • Low-loss laminated conical press plate (two-pole)

• Improved cooling of copper shield (four-pole)

• High-efficient rotor cooling • Mu

Future work of the manufacturer will also involve structuring of g

ifferent kinds of plant types, for 50 Hz andd

performance requirements. A flexible modularization will allow com

pole generators. Although short circuit ratios of 0.4...0.5 in this large power range are widely accepted,

special SCR requirements may be considered by an optional air gap (by increasing the stator bore

diameter), while keeping all other dimensions. Of course such a special option will result in a derating

on other generator performances. A plant layout option for the large sizes will be the single terminal

box on NDE for a high rated voltage, and a double terminal box for a low rated voltage.

6. CONCLUSIONS

A large hydrogen/water-cooled generator fleet and the shared experience of the two merged generator

engineering communities results in a broad design and operational know how. The responsibilities for

the two-pole and the four-pole

p

u

The market will require considerable higher generator o

rger units will be based on robust, proven and accepted generator technologies and desila

remain in fields of known high performance reliability.

BIBLIOGRAPHY

[1] K. Weigelt, “Design Features of Large Turbog

[2

Stage”, CIGRE Session 1988, Paper 11-0

J. Oliver, J. Michalec, B. Zimmerli, R. Jo

Amos 3 with 25 Years Experience”, IEE

nerator Win

saction

acity ets for the Lig

version, Vol.19, No.3, Se

M. Thiery, P. Cha

4

pmew Develo the Design of Generators

4, Paper A1-105