CIRCUIT BREAKERS

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220KV SF6 Circuit Breaker Operation and Its Testing:

220KV SF6 Circuit Breaker Operation and Its Testing Submitted By R.VISHNU

Circuit Breaker Definition:

A circuit breaker is a piece of equipment which can i. Make or break a circuit either manually or by remote control under normal conditions. ii. Break a circuit automatically under fault conditions. iii.Make a circuit either manually or by remote control after fault cleared. Circuit Breaker Definition

Basic Operation Of CB:

A circuit breaker essentially consists of fixed and moving contacts, called electrodes. Under normal operating conditions, these contacts remain closed and will not open automatically until and unless the system becomes faulty. The contacts can be opened manually or by remote control whenever desired. When a fault occurs on any part of the system, the trip coils of the circuit breaker get energized and moving contacts are pulled apart by some mechanism, thus opening the circuit. Basic Operation Of CB

Types Of CB:

Classification by voltage Classification by location Classification by interrupting media Types Of CB

Classification By Voltage:

Low voltage breaker - less than 1KV Medium voltage breakers - lKV to 52 KV High voltage breakers - 52KVto765KV Ultra HV breakers - >765KV Classification By Voltage

Classification By Location:

Classification By Location Outdoor type (AIS) Indoor Type (GIS)

Classification By Interruption:

Oil Circuit Breaker Air Blast Circuit Breaker Vacuum Circuit Breakers SF6 gas circuit breaker Classification By Interruption

SF6 Circuit Breakers:

SF6 gas circuit breaker shall be designed such that the gas leakages are minimum during their service period and utilities shall let out least am`ount of SF6 gas into atmosphere during maintenance. First major overhaul of the SF6 gas breakers installed in 1980s is the major task for some of the utilities SF6 gas has excellent insulating strength because of its affinity for electrons It is non-toxic and non-flammable and is characterized by super cooling characteristic. Its dielectric strength is greater than that of traditional dielectric gases. It also has exceptional arc quenching properties. The properties of SF6 gas are dielectric strength. SF6 Circuit Breakers

Operation Of SF6 CB:

A circuit breaker essentially consists of fixed and moving contacts, under normal condition these contacts remains closed and will not open automatically until unless the system become faulty. In the closed position of the breaker, the contacts remain surrounded by SF6 gas at a pressure of about 7.5 bars. When a fault occurs on any part of the system, the trip coils of the circuit breaker get energized and the moving contacts are pulled apart by bell-crank mechanism, thus opening of the circuit breaker. When the breaker operates, the moving contact is pulled away and an arc is struck between the contacts. Operation Of SF6 CB

First Generation SF6 CB:

The first generation of SF6 gas circuit breakers uses the dual pressure principle of air blast breakers. The SF6 gas is compressed and stored in a stationary high-pressure receiver, .much as in the earlier air blast circuit breakers and to interrupt the current, gas is blown into the breaking chamber, from there it is collected in a low-pressure receiver and subsequently pumped back to the high- pressure receiver. The major disadvantage of this approach is liquefaction of SF6 gas at the storage pressures at low temperatures First Generation SF6 CB

Second generation SF6 CB:

Second-Generation SF6 circuit breakers work on the single – pressure principle, i.e. the breaker is filled with SF6, gas at rated pressure and the differential quenching pressure required for extinguishing the arc is generated during the opening movement of contact System It explains the process of current interruption. The compression cylinder moves along with contact system against a fixed piston, during the breaking operation, thus generating the required quenching pressure inside the compression cylinder. As the contacts separate, an arc established between them, is extinguished for a few mille-seconds at the current zero. At the same instant, the quenching gas flowing out of the nozzle at high speed, de-ionizes the contact gap and thus prevents the regeneration of the arc. In open condition the breaker contact gap with SF6 gas forms the insulation to withstand the recovery voltage of the system. Second generation SF6 CB

Properties Of SF6:

SF6 gas has good dielectric strength because of the electron attachment property of SF6 molecules. It is non-toxic It is non-flammable and is characterized by super cooling characteristics It also has exceptional arc quenching properties. Corona inception voltage for SF6, gas in a non-uniform electric field is also considerably higher than that for air Properties Of SF6

Advantages Of SF6 CB:

Since the dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers can interrupt much larger currents. Due to the superior arc quenching property of SF6, such circuit breakers have very short arcing time. The SF6 circuit breaker gives noiseless operation due to its closed gas circuit and no exhaust to atmosphere unlike the air blast circuit breaker. The closed gas enclose keeps the interior dry so that there is no moisture problem. There is no risk of fire in such breakers because SF6 gas is non-inflammable. There are no carbon deposits so that tracking and insulation problems are eliminated. Advantages Of SF6 CB

Constructional Details Of SF6:

The main parts of the SF6 circuit breaker are as follows, i. Interrupt assembly ii. Bell-crank mechanism iii. Supporting insulator iv. Hydraulic mechanism v. Control cabinet. Constructional Details Of SF6

PowerPoint Presentation:

220 KV SF6 Circuit Breaker

Interrupt Assembly:

Interrupt assembly is the heart of the circuit breaker. The gas tight interrupter unit consists of a porcelain insulator, the contact tube. Graphite nozzle, the moving contact tube, the blast cylinder and the blast piston. The current flows from the terminal plate through contact support, the contact tube and fingers, the guide tube and the flange. The flanges are of two interrupter units connected by conductors in order to bridge the housing. Contact tube and the guide tube are fitted with arc quenching nozzles made up of arc resistant material, graphite Interrupt Assembly

PowerPoint Presentation:

Interrupt Assembly Diagram

Bell-crank mechanism:

The main purpose of the Bell-crank mechanism is to convert the vertical motion of the supporting rod into the horizontal motion of the contacts. It is placed between the two brakes of the circuit breaker and moving contacts of the two brakes are connected to this Bell-crank mechanism. It consists of the two vertical jaws which are used to convert the vertical motion into horizontal motion. The supporting rod is connected at the bottom of vertical jaw and another end is connected to two moving contacts. During the closing operation the vertical rod is moves upwards then this vertical motion is converted into the horizontal motion of the moving contact which closes the two contacts and continuity of power takes place. During the open operation the supporting rod moves downwards which opens thecircuitbreaker. Bell-crank mechanism

PowerPoint Presentation:

Bell-crank mechanism Diagram

Supporting Insulator:

The supporting insulator is placed between the hydraulic mechanism and the bell crank mechanism. The size of the insulator depends upon the rating of the circuit breaker. In the supporting insulator a steel iron rod is placed, which connects the bell crank mechanism and the hydraulic mechanism. Depending on the operation this steel rod moves up and down When the circuit breaker is placed on the transmission line, under normal condition the breaker contacts are to be closed manually or automatically i.e. the rod moves in the upward direction, then the fixed and moving contacts are closed which closes the circuit and the continuity of power takes places. During abnormal condition, large amount of current flows through the contact terminals, in a short time the contact opens and the rod moves in down ward direction, due to the hydraulic pressure Supporting Insulator

PowerPoint Presentation:

Supporting Insulator Diagram

Hydraulic Mechanism:

It mainly works on the differential pressure principle. The operating force is produced by a differential piston. The opening side (smaller surface area) of the differential piston is under constant pressure. The closing side (large surface area) of the piston is pressurized for closing and de-pressurized for opening The breaker is arrested in the ON and OFF positions by hydraulic force. Hydraulic Mechanism

PowerPoint Presentation:

Closing operation of hydraulic mechanism

PowerPoint Presentation:

Opening operation of hydraulic mechanism

Control Cabinet:

All the operations can be performed from the control cabinet The control units accommodates all the equipment for control and monitoring of oil pressure in the hydraulic system and monitoring the SF6 gas filled in the circuit breaker. \ The Parts Of Control Cabinet : Control cubicle Hydraulic Pump Set Contactor Plate Hydraulic pressure monitoring unit Terminal block assembly Oil filters Control Cabinet

PowerPoint Presentation:

The front and rear view of the control cabinet

TESTING OF SF6 CIRCUIT BREAKER :

Lightning Impulse withstand Voltage test Switching Impulse withstand Voltage test Power Frequency Voltage withstand test. Radio interference voltage (R.I.V) test Corona Inception & Extinction voltage test Temperature rise test TESTING OF SF6 CIRCUIT BREAKER

  CASE STUDY:

Circuit breaker is a device which can break or make the circuit automatically or by manually under fault condition. The speed of contact during the closing and opening operation is also analyzed by this system. The closing speed and opening speed according to IEC standard are shown in below. Closing —— 3 to 4 msec Opening —— 6 to 8 msec These timings are also analyzed by AUTOSCAN BRK 4.0 AUTOMATED SYSTEM CASE STUDY

PowerPoint Presentation:

Close operation of circuit breaker

PowerPoint Presentation:

Open operation of circuit breaker

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