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6 HV circuit-breaker technology

arc

moveable contact

fixed contact

SF6 flow

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Circuit-breaker technology• LV: (< 1000 V, industry, utility, domestic)

- atmospheric air, elevated arc voltage forcescurrent zero

• MV (1 - 72 kV, distribution)- vacuum (majority)- SF6- air (dc, magnet blast, airblast)- oil

• HV (>72 kV, transmission)- SF6- oil, airblast

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HV circuit-breakers

• from approx. 1900 oil circuit-breakers: bulk oil breakers

• development focussed to reduction of oil content:low-oil volume ("minimum oil") circuit-breakers

• parallel there was a development of compressed air ("airblast"), the pneumatic technology of which is used for:

• from 1970 SF6 is the HV circuit-breaker medium- double pressure technology (all voltages, outdated)- puffer technology (all voltages)- selfblast technology (<= 245 kV)- rotating arc technology (<= 145 kV)

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Application of quenching mediaat HV Circuit-Breakers

Germany (data RWE)

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increase of capacity per break

electra 2003

GVA / break

550 kV 63 kA

ABB

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(Bulk) Oil circuit-breakers

life tank dead tank

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Early years

CIGRE

CIGRE

Oil CB by Kelman (1901)

Water expansion CB

CIGRE

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Oil-breakers

photo NUON

Essent

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Bulk oil breaker under test

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oil volume

arcing chamber

Minimum oil circuit-breaker

H2 gas

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Circuit-breaker

compressed air (air-blast)

Advantage:• cheap

• non flammable

• chemical little active

• good isolating

• (large) breaking capacity

Disadvantage:• constant high pressure

• pressure control required

• current chopping

• noise

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Principle double-pressure breaker

• derived from air blast technology

• disadvantage: high pressure must always be available

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Air blast technology

photo Alliander

150 kV 40 kA 4 chambers

150 kV 40 kA 2 chambers

"Freistrahlschalter"

Phase to phase

photo Alliander

150 kV 40 kA 2 / 4 chambers

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1 phase of air blast 300 kV / 31,5kA CB(re)tested KEMA 2006

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SF6 gas: HV workhorse

• high ionisation energy (19.3 eV vs 15.5 eV N2)

catches free electrons so thatthese cannot initiate avalanchetype breakdown

• very good heat conductor at low temperatures (by dissociation F- atoms releases)F- atoms take away the heat

• high breaking capacity (10 larger than air)

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SF6 breakdown

voltage

Solvay

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Reason for excellentarc extinction properties

SF6 heat conductivity

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SF6 gas• very high electrical

conductivity at elevated temperatures (low arc voltage) S-atom ionizes easily

• SF6 gas is colorless, odorless, inert and not poisonous

• technical disadvantage: relative easy to reignite by very steep, relative low TRV values (short-line fault)

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SF6 gas, cautions• in presence of arc (or any electrical discharge) very

toxic dissociation products can arise, like: metal fluorides, metal sulphites and metal oxides

• liquefies at low temperatures, permanent heating of switchgear is necessary (Canada, Scandinavia)

• expensive (approx. 30 Euro / kg)

• in the presence of moisture, the decomposition products hydrolyse and form very aggressivecorrosive HF

• greenhouse gas (24000 x CO2)

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Circuit-breakers SF6

1e generation: double pressure SF6, derived fromcompressed air

Disadvantage:• high pressure (f.e. 16 bar) must always be there• compressor required• pressure control required• condensation

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Blast valveHigh pressure intermediate receiver

Moving contact

Interrupter unit

Grading capacitor

Tripping spring

Insulating rod

High pressureSF6 high pressure storage tank

Compressor

Air receiver

Drive

Al2O3 filter

Off

Areva

SF6 double-pressure breaker1e generation

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2e generation: single-pressure SF6, puffer principle

Disadvantage:• heavy mechanism required

Features:• only one (low) pressure required• extinction pressure by means of movable cylinder• (exhaust) nozzle• very large breaking capacity

Circuit-breakers SF6

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closed position

arc has been drawnSF6 is compressed

high pressure in cylinder arc heavily blasted

clears at current zero

Principal single pressure breaker(puffer breaker)

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Puffer principlePlansee

fixed main contact

fixed arcing contact

isolator

moving main contact

moving arcing contact

nozzle

arc

compression volume

cross section

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Puffer principle

VATech / Siemens

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Puffer principle

Siemens

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Contact system (puffer breaker)

VAtech

main contact

arcing contact

nozzle

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Blast technologies

axial blast (most common) radial blast (double nozzle)

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3e generation: “self-blast” principle

Disadvantage:• less pressure at low (short-circuit) currents• in transition area: critical current (?)

Features:• arc energy supports pressure build up in arc

chamber, result:• less heavy mechanism required (10-20% from

puffer)• smaller puffer required

Circuit-breakers SF6

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Selfblast outdoor type CB

ABB

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Self-blast breaker principle

s[m

m]

I[kA

]

t [ms]10 20 30 40

p[M

Pa]

Contact separation

Open position

Closed position

Areva

Pressure course

Current

Travel curve

Arc extinction

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Guide element

Moving contact

Fixed contact

Pressure chamber

ArcNozzle

Simulation of Gas Flow

Areva

Self-blast breaker principle

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Auto puffer CB

ABB

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Self-blast technology�Motivation: reduction of drive energy and therefore more simplerdrives and a significant cost reduction The puffer cb generates a quenching pressure during the opening-operation, which is sufficient for the interruption of a short-cirucit current (= high drive energy)

�The selfblast cb uses the energy of the arc to generate the quenching pressure necessary for the interruption of a short-circuit current, less energy from the drive is needed

�The selfblast principle is well known since decades. Basis of the success was the target not to interrupt all currents, but to interrupt short-circuit currents only

�The result is a « load »-breaker, which interrupts normal currents with a small puffer. The quenching pressure for the interruption of short-circuit currents is partly generated by the energy of the arc

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Rotating arc technology

Arc rotates electro dynamically in cool background gas

1. Connection 2. Coil 3. Fixed contact 4. Arcing contact

5. Moving contact 7. Connection 8. Sliding contact 9. Arc

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Rotating arc principle 145 kV

VAtech

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• Motivation: additional reduction of drive energy• The basic design is the same as for « normal »

selfblast circuit-breakers, but the two contact areas are moving with half speed in the opposite directions

• The total speed is still 100% for the interruption, but both contact parts (breaking-chamber and upper contact) are moving with 50% of the speed, therefore no change of the interrupting capability

• But the drive energy is reduced down to appr. 33% due to the lower speed of the breaking-chamber

• Mechanically more complicated

Double motion technology

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1

2

3

a b c d

VD

VH

1 Fixed contact system

2 Break with pressure chamber

3 Fixed piston

VD Volume of pressure chamber

VH Volume of auxiliary puffer

a Closed positionb Interruption of short-circuit currents c Interruption of small currentsd Open position

Areva

Double motion technology

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Double speed (single motion) technology

EnergoInvest

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Contact system of modern CB

new typeold type

ABB

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Development: reducing drive energy

• drives are very important, simplification is highly wanted

ABBmost failures in circuit breakersare due to mechanism (43 %)

• use the thermal energy of the arcto build up the necessarypressure• self blast / auto expansion /

self compression type breaker• attach new functions to drives (motion adapted to

fault)

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Realized reduction of drive energy

Areva

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Examples of spring drives

19981934

1984

Areva

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Principle of spring drive mechanism

Siemens

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Modern spring drive

Siemens

CIGRE WG A3.06 2007

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Modern (hydrau) spring drive

ABB

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(Hydraulic) spring operated400 kV - 63 kA breaker

Tennet

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550 kV single break CB

Mitsubishi

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Gas Insulated Substation (GIS)

• all conductors completely enclosed• three phases in single enclosure (up to 245 kV)• very little environmental influence• low maintenance• very compact• more expensive• high volume SF6• very fast switching transients VFTO (GIS

enclosure acts as a transmission line)

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SF6 reduction in GIS results

Areva

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Space reduction by GIS application

IEEE Switchgear Committee

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Vatech/ Siemens

Three-phase enclosed, double busbar

Three-phase GIS

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UHV kV - GIS

single-phase enclosed, double busbar

Toshiba