Vacuum circuit breakers

Transcription

1 Vacuum circuit breakers

2 Vacuum extinguishing chamber Contacting ring Insulator valve Fixed contact Moving contact Shilding valve Corrugated sheet Linear bearing Electrical input and mechanical drive of movable contact

3 Characteristics of vacuum circuits breakers: Up to switching operation without maintenance High longevity and operational safety Non-burnable Without gas and flames emission Silent operation Low wear out Low hub of contacts Very low arc voltage and extinguishing energy More at HTML/HTML/ElectricalCircuitBreakers~ htm And : s&gs_upl=2891l2891l0l5031l1l1l0l0l0l0l172l172l0.1l1l0&q=vacuum+circuit+br eakers&spell=1&sa=x&oi=image_result_group&sa=x

4 Application areas: Short circuits currents disconnecting Cables and out-door lines switching Transformer substation Transformátorová stanice Transformers switching Generators switching Motors switching Switching of arc furnaces Switching of trolley lines Arc furnace Oblouková pec Trolley line And subsstation Podružná trakční stanice

5 Principles of vacuum extinguishing chamber Extinguishing of electric arc in vacuum At contacts disconnecting arise electric arc created by metallic vapours separated from contact material. anode arc Arc in vacuum has cone shape with Magnetic pressure top on cathode. Anode contact shape of the arc is big and enable temperature good spreading without overheating of anode surface. cathode Cathode spot

6 Under nominal current diffusion type of arc is established over all shape of electric contact. When disconnecting current arises over nominal current, arc is by magnetic forces contracted on anode and cathode. Difussion arc Contaction on anode Contaction on anode and cathode Diagram of arc crossing from difussion to contractor type in vacuum chamber

7 To increase breaker disconnecting ability anode spot must be eliminated. It is possible by means: Contact material property Contacts shape arrangement By means of electro-dynamic forces rotate the arc bottom round the anode Contact dimensions increasing External magnetic field excitation Electrodynamic force Contact with rotating arc

8 Contacts with radial magnetic field for arc rotation achieving Spiral petal contacts

9 To restrict over-voltage at low inductive currents disconnecting, chopped current must be minimised. Low arc voltage, short time of arc relates to minimum arc energy and small contacts erosion => extinguishing system is maintenance free. Short circuit current Mains voltage Arc voltage Instant of current disconnection Contacts separation Restore voltage Time Transient recovery voltage Voltage and current time curve during one phase disconnection in vacuum chamber

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11 Input terminal Vacuum chamber Output terminal Electric drive Insulating rod lever Operational principle of vacuum circuit breaker driving mechanism

12 Construction of modern vacuum contactors Terminals of fix contact Drive of moving contacts Terminal of moving contacts

13 Vacuum circuit breaker Siemens 3AH 1 Type 3AH1 maintenance fre Durability: switching operations Applicaton area: from 7,2 kv up to 24 kv.

14 Typ 3AH1 with lever drive of moving contacts Legend: 1) Upper holder of extinguishing chamber 2) Upper lead, 3) External brace 4) Vacuum switching chamber 5) Movable contact of switching chamber 6) Flexible conductor 7) Down holder of vacuum switching chamber 8) Down lead 9) Disconnecting spring 10) Pushing spring of contact 11) Třmen-Stirrup 12) Upper 13) Internal brace-vnitřní vzpěra 14) Down supporting insulator - podpěrný izolátor 15) Páka lever 16) Switching rod -Spínací táhlo

15 Type 3AH3 Circuit breaker for high power applications Maintenance-free, powerful circuits breaker, ability switching operations. Type 3AH3 usable up to 63 ka of short circuit currents and voltage 36 kv. With respect to high efficiency is determined for generator switching and industrial application Nevyžaduje údržbu, je extrémně výkonný a je schopen zvládnout až spínacích operací. Typ 3AH3 se používá při velkých zkratových proudech do 63 ka a pro jmenovitá napětí do 36 kv. Vzhledem k vysoké výkonnosti je to ideální vypínač pro generátory a pro použití v průmyslu.

16 Drives of vacuum circuit breakers Switching by means of spring energy accumulator 1 Type label 2 Crank slot 3 Spring position indicator 4 Counter of switching operations 5 On OFF indicator 6 Low voltage connector 7 ON button 8 OFF button 9 Motor with gear box 10 Switching ON spring 11 Switching ON electromagnet 12 Switching OFF spring 13 Auxiliary contact 14 Switching OFF release

17 Vacuum switch ABB VD4 VD4 type switching poll creates complete fix maintenance-free switching unit Extinguishing chamber is immersed into the peroxides-resin. All system is pollution and dust resistant 1- Top terminal 2- Vacuum extinguishing chamber 3- Insulation cover 4- Moving contact pin 5- Bottom terminal 6- Flexible outlet 7- Moving contact compression spring 8- Insulating pull-rod 9- Fixing pole hole with thread 10- Connecting rod with hole for contact drive

18 Typ 3AH3 varianta pohonu 3 driving mechanism No 3 Pohyb při spínání se přenáší přes spínací tyč (16) a páku (15) na pohonný dřík. Movement tranmission to the contacts over switching rod (16) and swipe (15) on driving shaft 1) Upper holder of switching chamber 2) Upper terminal 3) External spur 4) Vacuum switching chamber 5) Driving shaft of vacuum chamber 6) Flexible conductor 7) Upper holder of switching chamber 8) Lower terminal 9) Disconnectin spring 10) Contact pressure spring 11) Lug 12) Upper insulator 13) Internal spur 14) Lower insulator 15) Swipe 16) Switching rod Legenda k obrázku: 1) Horní držák spínací komory, 2) Horní přívod, 3) Vnější vzpěra 4) Vakuová spínací komora 5) Dřík pohonu vakuové spínací komory 6) Pružný vodič 7) Dolní držák spínací komory 8) Dolní přívod 9) Vypínací pružina,příp. přítlačná pružina kontaktu 10) Přítlačná pružina kontaktu 11) Třmen 12) Horní podpěrný izolátor 13) Vnitřní vzpěra 14) Dolní podpěrný izolátor 15) Páka 16) Spínací táhlo

19 Table 1. Characteristics of the SF6 and vacuum current interrupting technologies. Operating energy requirements Arc Energy SF6 Circuit Breakers Vacuum Circuit Breakers Criteria Puffer Circuit Breaker Self-pressuring circuit-breaker Contact material-chrome- Copper Operating Energy requirements are high, because the mechanism must supply the energy needed to compress the gas. Operating Energy requirements are low, because the mechanism must move only relatively small masses at moderate speed, over short distances. The mechanism does not have to provide the energy to create the gas flow Because of the high conductivity of the arc in the SF6 gas, the arc energy is low. (arc voltage is between 150 and 200V.) Operating energy requirements are low, because the mechanism must move only relatively small masses at moderate speed, over very short distances. Because of the very low voltage across the metal vapour arc, energy is very low. (Arc voltage is between 50 and 100V.) Contact Erosion Due to the low energy the contact erosion is small. Due to the very low arc energy, the rapid movement of the arc root over the contact and to the fact that most of the metal vapour re-condenses on the contact, contact erosion is extremely small. Arc extinguishing media The gaseous medium SF6 possesses excellent dielectric and arc quenching properties. After arc extinction, the dissociated gas molecules recombine almost completely to reform SF6. This means that practically no loss/consumption of the quenching medium occurs. The gas pressure can be very simply and permanently supervised. This function is not needed where the interrupters are sealed for life. No additional extinguishing medium is required. A vacuum at a pressure of 10-7 bar or less is an almost ideal extinguishing medium. The interrupters are sealed for life so that supervision of the vacuum is not required.

20 Switching behavior in relation to current chopping The pressure build-up and therefore the flow of gas is independent of the value of the current. Large or small currents are cooled with the same intensity. Only small values of high frequency, transient currents, if any, will be interrupted. The de-ionization of the contact gap proceeds very rapidly, due to the electronegative characteristic of the SF6 gas and the arc products. The pressure build-up and therefore the flow of gas is dependent upon the value of the current to be interrupted. Large currents are cooled intensely, small currents gently. High frequency transient currents will not, in general, be interrupted. The de-ionization of the contact gap proceeds very rapidly due to the electro-negative characteristic of the SF6 gas and the products. No flow of an extinguishing medium needed to extinguish the vacuum arc. An extremely rapid de-ionization of the contact gap, ensures the interruption of all currents whether large or small. High frequency transient currents can be interrupted. The value of the chopped current is determined by the type of contact material used. The presence of chrome in the contact alloy with vacuum also. No. of short-circuit operation No. full load operation No. of mechanical operation

21 Recommended web addresses for self-study