ČESKÉ VYSOKÉ UČENÍ TECHNICKÉ V PRAZE Fakulta elektrotechnická Katedra elektrických pohonů a trakce K13114 SF 6 Circuit Breakers 2015

Property of SF6 Colourless Odourless Non-toxic Non-flammable Chemically-resistant Stabile up to high temperatures

Property of SF6 SF6 has excellent insulating property. SF6 has high electro-negativity. That means it has high affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion. The attachment of electron with SF6 gas molecules may occur in two different ways, These negative ions obviously much heavier than a free electron and therefore over all mobility of the charged particle in the SF6 gas is much less as compared other common gases. We know that mobility of charged particle is majorly responsible for conducting current through a gas.

Property of SF6 Disadvantages of SF6 CB The SF6 gas is identified as a greenhouse gas, safety regulation are being introduced in many countries in order to prevent its release into atmosphere. Puffer type design of SF6 CB needs a high mechanical energy which is almost five times greater than that of oil circuit breaker.

Arc-extinguishing in SF6 medium Simple contacts separation Arc-extinguishing in liquid SF6 medium Arc-extinguishing using energy of electric arc Rotation of electric arc Double-pressure extinguishing chamber Single-pressure extinguishing chamber (impulse „puffer“ system)

SF 6 properties - dielectric strengths Testing electrodes arrangement a.) comparative curves of the dielectric strengths of SF6 , nitrogen and insulating oil at 50 Hz and various gas presures.

SF 6 properties - dielectric strengths Testing voltage Testing electrodes arrangement b.) breakdown and initial corona voltages in SF6 at various gas presures for a point – to – plate gap having a length of 2,54 cm.

SF 6 properties - dielectric strengs Relative scale in % (c) Breakdown voltages for SF6 and air at 50 Hz at various gas pressure between specially designed contacts having gap length of 5 cm Ud breakdown voltage of SF6 at 50 Hz Ud1L breakdown voltage of air at 50 Hz

SF 6 properties - dielectric strengs (d) Breakdown voltages for SF6 and air with 1/50 ms impulse waves at various gas pressure between specially designed contacts having gap length of 5 cm __________ positive impulse polarity of stationary contact - - - - - - - - - negative impulse polarity of stationary contact Ud breakdown voltage of SF6 with 1/50 ms impulse waves Ud1L breakdown voltage of air with 1/50 ms impulse wave

Construction of the SF6 circuit breakers

Types of SF6 Circuit Breaker There are mainly three types of SF6 CB depending upon the voltage level of application - Single interrupter SF6 CB applied for up to 245 KV(220 KV) system. -Two interrupter SF6 CB applied for up to 420 KV(400 KV) system. -Four interrupter SF6 CB applied for up to 800 KV(715 KV) system.

Double-pressure systems Jet Fix contact lamella Sparking contact Moving contact Lamellas of moving contact Main closing valve - ventil Drive lever Páka pohonu Compressed SF6

Single-pressure systems Fix contact (rod-shape) Moving contact (tulip - shape) Kluzné kontakty – slippery contacts Válcová komora – moving tube chamber Fix piston Driving rod

Single-pressure HV systems Svorka - Terminal Izolační pouzdro- Insulation box Zhášecí tryska – extinguishing jet Pohyblivý opalovací kontakt – moving arcing contact Pohyblivý kontakt- movable contact Pevný opalovací kontakt - fixed arcing contact Pevný kontakt – fixed contact Izolační táhlo – insulating pull rod Ventil zabraňující explozi- anti-explosion valve

Single-pressure EHV systems Horní vodič proudu – upper terminal Nepohyblivý opalovací kontakt fixed arcing contact Pohyblivý opalovací kontakt -movable arcing contact „Puffer“ prostor „Puffer“ volume Dolní vodič proudu- lower current conductor Tryska - Jet Nepohyblivý hlavní kontakt- fixed main contact Pohyblivý hlavní kontakt- movable main contact „Puffer“ válec – „puffer“ cylindr Plnící ventil – charging valve Nepohyblivý píst – fixed piston

Construction of puffer system CB Design of the Interrupter Unit The interrupter is enclosed in the porcelain insulator and is the core unit of the circuit breaker. It includes insulator, fixed main contact, fixed arcing contact, nozzle, cylinder, moving arcing contact, moving main contact, moving contact support, push rod etc. (see figure 4) Absorbent is mounted in the upper part of the fixed contact. The push rod links to the insulating rod in the bushing then to the drive shaft of crankarm case. Interrupter bushing is made from high-strength porcelain which has high strength and good gas-tightness. http://www.multi-link.com.my/lw36.html

Braking phases of puffer system CB

Principle of arc extinguishing When the circuit breaker receives the opening signal, the moving contact assembly - cylinder, moving main and arcing contact, pull rod and other moving parts are moved downward by the opening spring forces. Firstly, the main contacts part and the current transfers to the inner arcing contacts are still closed. Then the arcing contacts separate leading to an arc between them. On short-circuit interruption due to the high fault current, the arc zone gets a high energy. The thermal energy of the arc zone is transferred into the thermal expansion chamber creating a low-temperature high gas pressure in the chamber. As the pressure in the thermal expansion chamber gets higher than the pressure in the compression chamber the control valve closes. When the arc current approaches current zero, high pressure gas will flow through the nozzle and extinguish the arc. The gas in the compression chamber will be compressed during the circuit breaker opening operation. However, at a certain pressure, the overpressure relief valve will open and allowing the gas to escape. Therefore the operating mechanism does not have to counteract higher gas pressure and less mechanical energy and force is needed. When breaking low current (normally below several kilo amps), due to the low arcing energy, not sufficient gas pressure is generated in the thermal expansion chamber. In this case, the gas pressure of the compression chamber is higher than the pressure of expansion chamber, the control valve is open and the compressed gas will blow through the contacts. When the arc current reaches zero, the pressurized gas flows through the nozzle and extinguish the arc.

Single-pressure EHV systems (Extra High Voltage) Jednotlakové systémy Jednotlakový vypínač 550 kV Single-pressure circuit breaker 550 kV Jednotlakový vypínač 170 kV Single-pressure circuit breaker 170 kV

Single-pressure MV systems (Middle Voltage) Jednotlakové systémy http://www.youtube.com/watch?v=5JoIN_2-1EY Jednotlakový vypínač 40,5 kV Single-pressure circuit breaker 40,5 kV Jednotlakový vypínač 36 kV Single-pressure circuit breaker 36 kV

Encapsulated distribution substations Voltage from 50 up to 800 kV Vypínač -Circuit breaker Přípojnicový odpojovač- bus bar disconnecting switch Odpojovač od země- grounding disconnecting switch Transformátor proudu – current transformer Transformátor napětí- voltage transformer Izolátorová průchodka SF6 – vzduch- insulating bushing SF6-air Hydraulický pohon- hydraulic drive Ovládání odpojovačů- disconnecting switch control boxes Ovládací skříň – control cabinet

Encapsulated distribution substations Needs small area for instalation Possibility to install distribution substations in the city centre Operational High safety level Quick installation Low cost maintenance High operational reliability More expensive

Encapsulated distribution substations Porovnání zastavěné plochy Comparison of area needs

Encapsulated distribution substations

The End Some interesting presentations http://www.multi-link.com.my/lw36.html https://www.youtube.com/watch?v=15yBfEQyBVY The End