Echipamente de comutaţie de înaltă tensiune

Introducere

Echipamentele de comutatie au rolul de a modifica configuratia unei retele electrice, in mod voit sau obligat, in urma unui eveniment din reteaua electrica;

In principal sunt utilizate: intreruptoarele automate (cu posibilitatea intreruperii

curentilor electrici de defect); separatoarele (cu posibilitatea realizarii de comutatii in

lipsa curentului electric – nu au capacitatea de intrerupere a curentilor electrici de defect)

Introducere

Echipamentele de comutatie au rolul: Protectie: separarea elementelor la care au

aparut defecte prin deconectare automata; Adaptarea schemei la conditiile specifice de

functionare prin comutarea voita; Izolare (separare) pentru efectuarea unor

lucrari.

Alegere echipamente

Criterii de alegere: Generale; Specifice.

Criterii generale: Tensiunea nominala; Curentul electric nominal; Frecventa nominala; Conditiile climatice (temepratura, umiditate, poluare,

inaltimea de amplsare); Aspecte economice

Intreuptoare de inalta tensiune

Un intreruptor este definit ca fiind "un dispozitiv mecanic de comutare capabil de a face, deconectarea (ruperea) curenţilor din circuit, în condiţii normale şi, de asemenea, şi de rupere a curenţilor în condiţii specificate de circuit anormale cum ar fi un scurtcircuitele

Intreuptoare de inalta tensiune

La deschiderea contactelor, intre acestea apare un arc electric;

Este prevazut cu o camera de stingere a arcului electric.

Pentru stingerea arcului electric se folosesc medii de stingere:

Ulei; Aer comprimat; Hexaflourura de sulf SF6 ; Vid (numai in domeniul medie si joasa tensiune).

In principiu cuprinde doi electrozi: tija si tulipa, care sunt actionati cu viteza ridicata.

Intreuptoare de inalta tensiune

Caracteristici specifice: Rated Voltage Ur - maximum continuous electric

output power which a wind turbine is designed to achieve under normal operating conditions

Nominal Voltage Un - voltage by which a supply network is designated or identified and to which certain operating characteristics are referred

Rated current Ir - maximum continuous electric output current which a circuit breaker is designed to achieve under normal operating conditions

Intreuptoare de inalta tensiune

Curentul de scurtcircuit Ik

i

ip

A

Variaţia curentului de scurtcircuit

t0

Înfăsurarea superioară

Înfăsurarea inferioară

Componenta continuă atenuată"22 kI

"22

22

k

k

I

I

Ir

SF6 gas

In domeniul tensiunilor inalte, cele mai utilizate sunt intreruptoarele cu SF6 ;

Gas circuit breakers generally employ SF6 (sulfur hexaflouride) as an interrupting and sometimes as an insulating medium.

Is a synthetic gas that is colorless, odourless and noncombustible;

Un gaz stabil si cu rigiditate electrica ridicata; The dielectric strength of SF6 is approx. 2,5 times

better than atmospheric air;

SF6 gas

The SF6 gas is ussually used at a pressire of 0,30,5 MPa und than insulates approximately 10 timer than atmospheric air

Permite realizarea de echipamente cu dimensiuni reduse;

In connection with discharges, the SF6 gas partly decomposes; provides efficient cooling.

The solid decomposition products are primarily metal fluorides in the form of a powder;

The powder can easly be taken care of and does not constitute a long-term environmental hazard.

SF6 gas

Impulse voltage withstand, 10 mm gap.U [kV] 250

200

150

100

50

0 Air Oil Vacuum SF6 SF6

0,1 MPa 0,1 MPa 0,5 MPa

SF6 gas

SF6 este gaz cu bune calitati de izolare electrica: Este unul dintre cele mai grele gaze – densitatea

la 20oC si presiune 0,1 Mpa este 6,14 kg/m3 (de circa 5 ori mai greu ca aerul);

Constanta dielectrica relativa: 1,00204; Tangenta unghiului de pierderi: tan < 210-7 ; Insolubil in apa. Pure SF6 gas is non-toxic and not dangerous to

inhalte (if the oxygen content is a less 20%)

SF6 gas

Contribution to the greenhouse effect

c [%] 70

60

50

40

30

20

10

0 CO2 CH4 Others SF6

SF6 Circuit breaker

p1 > p2

p2 < p1

Moving contact

Insulatingnozzle

Arc

Fixed contact

Arc extinction in gas flow circuit-breakers.

SF6 Circuit breaker

Contact closed Contacts separate Nozzle open Arc quenches

p1 = p2 nozzle about to open flow starts breaker fully

1

234

56

7

SF6 Circuit breaker

1 – Fixed contact;

2 – Nozzle

3 – Arcing contact tip

4 – Finger contacts

5 – Puffer cylinder

6 – Fixed piston

7 – Pull conductor

SF6 Circuit breaker

Circuit breaker open

Vacuum circuit breaker

Vacuum circuit breakers use an interrupter that is a small cylinder enclosing the moving contacts under a high vacuum.

When the contacts part, an arc is formed from contact erosion.

The arc products are immediately forced to and deposited on a metallic shield surrounding the contacts.

Without anything to sustain the arc, it is quickly extinguished.

Vacuum circuit breaker

Vacuum circuit breakers are widely employed for metal-clad switchgear up to 38 kV class.

The small size of the breaker permitting significant savings in space and material.

Vacuum circuit breaker

Movable stemTwist protection

Metal bellows

Interrupter lidShield

Ceramic insulator

ShieldMoving contactFixed contact

Fixed stem

Interruptor lid

Vacuum circuit breaker

Secondary shields

Metal bellows

Mobil contact

Fixed contact

Main shield

Insulating enclosure

Secondary shield

Disconnect Switches

A disconnect switch (disconnector) is a mechanical device used to change connections within a circuit or isolate a circuit from its power source;

Is normally used to provide isolation of the substation equipment for maintenance.

Typically a disconnect switch would be installed on each side of a piece of equipment to provide a visible confirmation that the power conductors have been opened for personnel safety

Disconnect Switches

Once the switches are placed in the open position, safety grounds can be attached to the de-energized equipment for worker protection.

Switches can be equipped with grounding blades to perform the safety grounding function.

Disconnect switches are designed to continuously carry load currents and momentarily carry higher capacity for short-circuit currents for a specified duration (typically specified in seconds).

Disconnect Switches

They are designed for no load switching, opening or closing circuits where negligible currents are made or interrupted, or when there is no significant voltage across the open terminals of the switch.

They are relatively slow-speed operating devices and therefore are not designed for arc interruption.

Interlocking equipment is available to prevent inadvertent operating sequence by inhibiting operation of the disconnect switch operation until the fault and/or load currents have been interrupted by the appropriate equipment.

Disconnect Switches

Disconnect switch operation can be designed for vertical or horizontal operating of the switch blades.

Several configurations are frequently used for switch applications including:

• Vertical break• Double break switches• V switches• Center break switches• Hook stick switches• Vertical reach switches• Grounding switches

Disconnect Switches

Disconnect Switches

Disconnect Switches

Conclusions

Switching equipment is used to provide isolation, load switching, interruption of fault currents.

Electrical equipment with SF6 has been used for a long time with good results;

The contribution towards the total greehouse effect is less than one thousand.

The small size of the breaker permitting significant savings in space and material.

Conclusions

A disconnect switch used to change connections within a circuit or isolate a circuit from its power source;

Switches can be equipped with grounding blades to perform the safety grounding function.

Thank you for your attention