Technical interfaces of turbo- generator-sets to be ... · Vervielfältigungen, Verwendung und...

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Sept. 2004Sept. 2004

Technical interfaces of turbo-generator-sets to be considered for an optimum component selection

Oliver DrubelElectrical Calculation, Turbogenerator development



Overview

! Motivation! Interfaces of a turbo generator! Coupling to the turbine - necessary shaft line calculations! Coupling to foundation and suspension philosophies! Electrical interfaces to the bus-system! Control and protection! Excitation system! Starting up of the generator! Shaft grounding! Cooler philosophy! Examples ! Conclusion



Motivation

! Liberalization of the electricity market increases the need for optimized solutions - optimized means an economical optimization fulfilling all technical constraints

! Strong cost differences for the plant up to 2mio€ between advanced and conventional generator technologies are possible

! General system simplifications allow for an increase in reliability and reduction in maintenance

! Interfaces of the generator have to be defined clearly to allow for an adequate integration in the plant layout

! A proper risk evaluation needs the knowledge of technical key areas



Development to solutions with low need of auxiliaries and interfaces

Future development focus for large 2-pole turbogeneratorsAir cooled

H2 / H2cooled

H2O / H2cooled

State of the art

Technology leadership

<330MVA

330MVA -500MVA

400MVA -500MVA

500MVA -660MVA

500MVA -1300MVA

>1300MVA

Simplification in operation and maintenance



Generator Interfaces

Coupling to steam turbine

Generator ac terminals to busducts

Outer cover

Axial fan for closed air circulation

Leakage air filter

Elastic suspension of core

Stator core: stacked laminations

Rotor winding: solid conductors

Retaining ring

Housing upper part

Housing lower part w. coolers

Ribs / separation walls

Rotor body: slotted forging

Endwindingsuspension

TurbogeneratorTOPAIR 23

Pedestal bearing

Stator winding: Roebelbars

Air filter for brushgear

Core suspension rings

Sliprings and brushgearfor dc excitation

Shaft grounding NDE

Shaft grounding DE

Control+Protection



Coupling to the turbine

! Axis height, coupling sizes, bearing arrangement (single or double bearing)!Adjustments to either generator or turbine coupling are

necessary or intermediate shaft!Flexibility in bearing concepts

! Shaft line rotor dynamics (critical speeds, unbalance response, torsional natural frequencies, fault cases, transformer selection, xd", ...), restricted speed ranges, start up procedure



Shaft line rotor dynamics -shaft line calculations

! Torsional torques and eigenfrequencies



Coupling to the turbine necessary shaft line calculations

! Philosophies for mechanical torque determination:! The shaft line responsible determines the philosophy, but the

generator supplier must be capable to support adequate

! Lateral shaft oscillations! Simply mechanical, no electrical involvement! Mechanical generator model with bearing stiffnesses required



Interface data for brushless exciteror static excitation and AVR

Current limiter

P/Q Limiter

Rotor earth fault protection



Arrangement during gas turbine starting-starting up of gas turbines

Startup-Trans-former

CableTransformer -SFC300m

SFC

GeneratorCable andSwitchgearSFC-Generator

positive d.c.link voltage,trafo. sideMP 4455

positive d.c.link voltage,geno. sideMP 4454

negative d.c.link voltage,MP 4453

phase U,MP 4449

phase V,MP 4451

phase W,MP 4447

phase U,MP 4450

phase V+W,MP 4444

phase U,MP 4445

MP 4442 MP 4452

phase U,MP 4436

MP 4440

Grid

rectifiermain inductor commutator



Arrangement during gas turbine starting-starting up of gas turbines

Start up philosophy for different gas turbine manufacturers:

With SFC With ponny motor

Generator with static excitation

Generator with brushless excitation

Only with start up brushes

Additionally the speeds for fast cooling and other special rotation modes have to be considered for lateral rotor Eigenfrequencies



Shaft grounding - Converter induced shaft voltages

DE NDE

Turbine Generator

none DE ModuleShaft Grounding Shaft Grounding

RC Module

Ins. BearingRule No.4,5

Cu Braid Cu Braid

Shaft Grounding

∫ −=⋅t

lEd

dd cϕrr

Low ohmic ground on drive end and capacity on NDE allows to avoid low frequency grounding and reduction of excitation peaks



Converter Improvement- shaft grounding

Time t (µs)

Shaf

tvol

tage

u shaf

t(V

)

0 50 100 150 200 250-60

-40

-20

0

20

40

60

80

100

120108V

-54V

30V

Before modification

Aftermodification

The converter improvement reduced the shaft voltages of a 500MVA plant from 108V to 30V peak –a reduction by a factor of 3 had been predicted by the mathematical model



Shaft grounding

! Normal operation shaft voltages are well below critical voltage limits with todays ALSTOM design

! Higher shaft voltages are strongly related to the thyristor switching within frequency converters

! The shaft voltage caused by the frequency converter is a coupled inductive capacitive phenomenon

! A solution to reduce the shaft voltages by a factor of about 3 has been predicted and successful implemented where necessary



Cooler philosophy

! Difference is based in different areas:!Amount of waterflow!Difference between cold gas –water

temperature distance!Open water or closed water circuit! Integration of cooling circuit within steam

water circuit



Cooler philosophy

! Amount of waterflow!High amount of water

!Cheaper generator coolers!Low water temperatures in the piping

(<60°C)!Low amount of water

!Expensive generator coolers!Cheaper re-coolers

•Cooling tower: Usually higher water flow

•Air recoolers: Usually low water flow



Cooler philosophy

! Open water or closed water circuit! Closed water allows for a more reliable operation of the coolers! Special attention to the cooler material choice is necessary to

allow for open water circuits

! Integration of cooling circuit within steam water circuit! An intermediate water water cooler should be used in case of

hydrogen cooled generators in order to prevent hydrogen explosions in the steam circuit.



Normal interface responsibilities

! Generator responsibilities:! Excitation specification! Cooler specification! Shaft grounding! Electrical and thermal

protection philosophy

! Turbine supplier responsibilities:! Shaft line responsibility +

shaft line protection! Starting philosophy

! Plant responsibilities:! Foundation

Most of the interfaces are normally within the scope of the generator supplier

Shaft line responsibility is normally with the turbine supplier but the generator supplier contributes with:

"Mechanical generator model with bearing stiffness

"Electrical generator torque

The interface responsibility has to be agreed on a contractual basis



Examples

!Coupling of a TOPGAS generator to a M701 single shaft



Examples

!Coupling of a TOPACK generator to a GT 6B



Conclusion

!Combination of turbine and generator of different suppliers can allow for more economic solutions

!Most critical interface are the rotor shaft dynamics ! In order to reduce the no. of interfaces it is of

advantage to include the excitation, cooler and shaft grounding in the generator responsibility

!Several success stories of generators coupled to different turbine suppliers reveal its advantages on a liberalized market

Technical interfaces of turbo- generator-sets to be ... · Vervielfältigungen, Verwendung und...

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