alstom-IPBD

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ENERBUS

Isolated Phase Bus



The global solution

for quality and performance up to 52,000 A

Low range :Typical 1

Insulator mounting with

tubular conductor

High range :Typical 3

Insulator mounting and enclosure collar

bracket with octagonal conduit

Safety of personnel

Continuous operation

Reduced maintenance

Simplified civil engineering

Losses are non existent in

the adjacent steel structures

and reinforcement

Live equipment is inaccessible

Direct phase-to-phaseshort-circuit cannot occur

Insulators are protected frompollution and inclement weather

Reduced electromagnetic forcesand self supporting enclosuresallow simple support structures tobe used

The magnetic field outside theenclosures is practically nil duringcontinuous operation



The higher unit capacities ofgenerating sets installed in thermal,hydro and nuclear power stationshas led to increased ratings(voltage, nominal current andshort-circuit current)on the main circuit connections

between generators and main,auxiliary, or voltage transformers.

These connections require a specialdesign to limit short-circuit forcesand temperature rises in adjacentsteel work.

ALSTOM Power has been buildingmore than 700 connections with itscontinuous enclosure type isolatedphase buses for more than 40 years.

An isolated phase bus is an assemblyof rigid conductors, complete withconnections, joints and insulatingsupports, each contained in earthedmetal enclosures.

In the case of continuous enclosuretype isolated phase buses, theenclosures are electrically continuousand short-circuited at each end of the connection.

For 1,450 MW generating sets,ALSTOM Power has supplied isolatedphase buses with a rated current of 52,000 A at 20 kV, and capable of withstanding a short-circuit currentof 1,200,000 A (peak).



Performance

Under normal conditions

The phase conductors and thebonded enclosures are comparableto the primary and secondary turnsof a short-circuited transformer.

The magnetic field produced by thecurrent in the primary conductorinduces an equal and oppositecurrent in the enclosures, and theresulting magnetic field outside theenclosures is almost nil duringnormal operation.

Losses in the adjacent steel structuresand in the concrete reinforcementare virtually non-existent, as arethe corresponding temperature rises.

There is no need to open any loopwhich may be formed by the steelreinforcement and structures.

It is not necessary to insulate theenclosures from their supportingstructures.

Any current in these structures isnegligible since the transformer effectprevents any significant current flowin the supports.

Under short-circuit conditions

When a polyphase short-circuitoccurs in circuits connected to theisolated phase bus, the alternatingcurrent components in the conductorsand in the enclosures are very close

in value due to the transformer effect.

However the direct-currentcomponents of these currents havedifferent values at a given time ofthe short-circuit.

These components, initially identical,are reduced by different timeconstants in the case of the conductor(time constant of circuit connected tothe conductor) and in that of the

enclosure (time constant of circuitformed by the enclosures).

The magnetic field outside theenclosures is therefore essentiallydue to the difference between thedirect-current components of thecurrents in both the conductors andthe enclosures.

The corresponding electromagneticforces on the conductors aretherefore much lower than those

which would be observed withoutcontinuous enclosures.

The electromagnetic forces,exerted on the enclosures, are of thesame order of magnitude as thoseon the conductors they enclose butof opposite direction.

The resultant stresses on the adjacentsteel structures and civil works aretherefore much reduced leaving

only electromagnetic forces due toelbows, tap connections andterminations.



1 - Connection to main transformer

2 - Isolated phase bus system

3 - Main transformer

4 - Tap connection to voltagetransformer cubicle

5 - Generator

6 - Isolated phase bus support

7 - Current transformers mounting

8 - Connection to generator

9 - Excitation transformer cubicle

10 - Auxiliary transformer cubicle

11 - Tap connection to auxiliaryand excitation transformers

12 - Voltage transformer cubicle

13 - Neutral earthing cubicle

CAD - General layout

1 2 3 4 5

6 7 8 9 10 11 12 13



Standard technology

Conductor

For the main connections, theconductor consists of :- for high current ratings, an

octagonal duct made up of two99.5 % pure aluminium sections

welded together at regular intervalsby spacers, thus maintaining aconstant clearance.

This clearance permits a reductionin the temperature rises in theconductor for self cooled systems,and a reduction in the loss of airpressure for forced-air cooledsystems.

- for lower current ratings, a tubularduct made of a 6101 aluminiumalloy, designed according to the

short-circuit current.

Enclosure

The enclosure is made of a 99,5 %pure aluminium circular duct.

Painting

For more effective cooling theconductors and enclosures are, incertain cases, painted with a matt

paint.

Supporting structures

The welded enclosures are by theirvery design self supporting, thusenabling the supporting structures,usually of galvanised steel, to bespaced at maximum intervals.Each enclosure is secured to thesestructures by clamped or slidingsupports to allow for expansion.Enclosure supports are made ofaluminium-alloy collar bracketswhich can easily be moved alongthe enclosure as required by the civilworks tolerances.

Supporting insulators

The coaxial conductor inside theenclosure is supported by symmetricalshed porcelain insulators with a longcreepage distance.

These insulators provide insulation

for the connections without requiringspecial arrangements such aspressurisation.

Several types of insulator mountingare used :- for the high range, a 3-insulator

mounting is mostly used :. one lower insulator carrying the

weight of the conductor,. two lateral insulators withstanding

phase-to-phase forces in case of

short-circuit. The three insulators are only stressedin compression, thus ensuring ahigh safety factor.

- for the low range, a single ora 2-insulator mounting is used :

. bearing the conductor weight,

. ensuring free conductorexpansion,

. bearing any stress caused by apossible short-circuit.

For inspection, maintenance

or replacement, each insulator iseasily accessible through a sealedinspection door.

Expansion joints

Expansion joints on the conductorand the enclosure allow the isolatedphase buses to expand freely andrestrict any expansion forces imposedon the civil works to those of friction.

Connections

Connections to the generator, themain and auxiliary transformers, theV.T. cubicles and the disconnectingdevice if required, are made usingcopper or aluminium braids,

which provide the best short-circuitwithstand level and maximumflexibility.

Consequently, neither the expansionforces of the isolated phase buses,nor the vibrations of the power unitsare transmitted.

Terminations

At each end, the enclosures

are short-circuited by means ofaluminium plates.

At the generator and switchgearcubicles, the isolated phase bus issealed by means of epoxy resin orporcelain through-bushings.

At the main and auxiliary transformers,sealing is provided by the transformerterminals, the bus enclosure beingconnected to a pipe section integrated

into the transformer through insulatingsynthetic rubber bellows.



Wall entrances

Where the isolated phase buspasses through the power stationwall, the space between theenclosures and the wall is blockedwith an aluminium plate and

insulating flanges allowing isolatedphase bus expansion.

Current transformers

Current transformers, mostly ofthe bushing type, are fitted aroundthe terminals of the generator andof the main and auxiliarytransformers.

When this type of mounting is not

feasible, the current transformersmay be installed inside theenclosures, close to a bolted joint foreasy and fast removal.

A sealed terminal box, completewith sealing glands and securedto the enclosure, permits the exit of the secondary leads of thesetransformers.

Cooling system

ALSTOM Power manufacturesisolated phase buses cooled by twodifferent systems :- for ratings above 25,000 A,

forced-air cooling is always used,- for ratings under 25,000 A,

both self cooling and forced-aircooling systems may be used.

Compared with self cooling,forced-air cooling allows anappreciable reduction in isolatedphase bus size and in the lossestransferred to the ambient air, but onthe other hand, it entails an increasein the total losses.

When no technical consideration(limitation of losses transferred to theambient air, size limitations, etc)makes it necessary to use forced-aircooling, an economic solution isselected on the basis of the cost of the isolated phase bus and that ofthe losses.

Forced-air cooling unit

Forced-air cooling is by circulationof air in a closed circuit with cleanand dry make-up air supplied by apressurising system.

Generally the forced-air cooling unitconsists of an air-water heatexchanger and two fans, one of which is on standby.

The air blown into two phases isdrawn into the third, cooled whenpassing through the heat exchangerand returned to the circuit.



Pressurisation

In the case of forced-air coolingthe bus is slightly over pressurisedto prevent entry of humid orpolluted air.

In the case of self cooling,pressurisation is not necessary, owingto the use of porcelain insulators witha long creepage distance ; so theenclosures are provided with filterspermitting circulation of a slight airflow and breathing of the bus.

Pressurisation may however benecessary in the case of aparticularly aggressive environment.

The standard pressurisationequipment consists of a relief valve,including filters and a dryer ifnecessary, safety valves and controldevices.

A dry-air flushing-out system mayalso be provided for use beforestarting.

Generator terminal casing

Where necessary, the isolated phasebus connections between theconductors and the generatorterminals are protected by aperforated aluminium sheet casing

for self cooling.

Solid aluminium barriers providephase-to-phase and phase-to-neutralprotection.

For ratings above 20,000 A,a forced-air cooled solid casing maybe provided to ensure suitablecooling of the connections and thecurrent transformers placed aroundthe terminals.

This is because the generatorterminals are generally too closefor self cooling.

Earthing of generator neutral

The generator is usually earthedthrough a resistance and a currenttransformer.

This equipment is enclosed in asheet steel cubicle.

Earthing for maintenance

Each conductor may be earthedby means of a rod or an isolatingswitch.

The isolating switch is mountedeither directly on the isolated phasebus or in a cubicle.

Voltage transformer cubicle

An isolated phase bus can feedvoltage transformers, for meteringor protection.

These transformers may be installed

in aluminium boxes welded onthe isolated phase bus enclosuresor in cubicles.

The cubicles are standardisedand can be of withdrawable orfixed types.

The active elements in the cubiclesare phase segregated.

Other switchgear can also be

housed in the cubicles such as surgearresters, earthing switches andcapacitors.

The low-voltage wiring is brought toa box common to the three phases.

Cubicle for withdrawable

voltage transformersStandard pressurising unit

Associated equipment





The isolated phase bus size isdetermined for each project by itsspecific data through a computerprogramme.

The results of the programme aresubsequently used by the design

office, working on standarddocuments.

The design of the ENERBUSproducts is enhanced by the useof a CAD system.

Each isolated phase bus is dividedinto fully assembled prefabricatedsections in the factory.

This especially applies to the elbowsand the tap connections, allowingthe correct positioning of the element

sections.

Where necessary, additional lengthsor connecting sleeves are provided tomake up for any variation in thedimensions of the civil works.

On-site erection is greatly simplifiedby the use of fully factory-assembledsections.

Both factory assembly personneland on-site erection teams includespecialised aluminium welders and

qualified electricians.

Typical overall dimensionsof ALSTOM Power ENERBUSunder the followingconditions :

. Self cooling

. Ambient temperature : 40°C

. Conductor temperature rise : 65°C

. Enclosure temperature rise : 40°C

U (BIL)

in (mm)

3500 A

4000 A

5000 A

6000 A

7500 A

10000 A

15000 A

25000 A

25000 A

60 kV

D x L

300 x 1200

350 x 1250

400 x 1400

75 kV

D x L

400 x 1400

450 x 1550

110 kV

D x L

500 x 1700

560 x 1830

750 x 2850

850 x 3150

1050 x 3750

1300 x 4500

1450 x 4950

125 kV

D x L

500 x 1880

600 x 2000

800 x 3000

900 x 3300

1100 x 3900

1350 x 4650

1500 x 5100

150 kV

D x L

850 x 3150

1000 x 3600

1150 x 4050

1450 x 4950

1550 x 5250

170 kV

D x L

950 x 3450

1000 x 3600

1200 x 4200

1500 x 5100

1550 x 5250

Forced-air cooling is proposed for largest currents or for reducing IPB sizes.

In these cases, IPB dimensions are customised by ALSTOM Power according to the project requirements.

Design and construction

Quality assurance and associated services



- substantial local content,from 30 to 80 %, if required by theterms of the project.

Regardless of the place of manufacture,ALSTOM Power (France) remains fullyresponsible for the products.

Some of the countries where ENERBUSis being manufactured are :France, China, Croatia, Greece,Korea, India, Brazil, Republic of South Africa...

Erection

With a worldwide network ofoperations or agents in over fiftycountries, ALSTOM Power can

maintain close contact with customers,relying on local reputation andexperience.

With thorough knowledge of localeconomics and business conditions,ALSTOM Power supplies its ENERBUSisolated phase buses and can deployappropriately skilled personnel at shortnotice virtually anywhere in the world.

Amongst the 600 specialists ofthe ALSTOM Power’s FieldEngineering Services Division,some 20 high skilled andexperienced people are dedicatedto erection, welding and supervisionof erection on-site of the ENERBUS

isolated phase buses.

Maintenanceand After Sales Services

Our customers can fully rely onour quick and thorough responsesfor :- supplies of additional spare parts

when required,- routine checking and cleaning,- inspections during periodic

maintenance of the generatorunits,

- prompt action when ourproducts are damaged by externalfactors.

A quality assurance programmeensures that the required qualitystandard for the various types of equipment is always met.

Quality is controlled by the applicationof procedures and checks included in

the programme covering design,procurement, fabrication and erection.

The special features of the ENERBUSrange allows ALSTOM Power toadapt its role to any project structure,providing :- the design only to licensees,- the design and the supply of

insulators, moulded parts andother specific items while themanufacturing is sub-contractedto fully proven and tested localcompanies,

- the design, the manufacturing, thedelivery up to site and the on-siteassembly.

Local manufacturing

The ENERBUS products, with theirstraight forward technology, arecommonly manufactured in severalcountries worldwide.

The localisation of manufacturing

brings 2 major advantages :- savings on the cost of packing &

freight, which results in a reductionof around 8 to 15 % of the totalprice,

CertifiedISO 9001



ALSTOM Power - Electrical & Control Systems - 4, avenue André Malraux - 92309 Levallois-Perret Cedex France

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