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13-04-2010, 10:59 AM
Post: #1
circuit breaker full report

.docx  CIRCUIT BREAKER3.docx (Size: 478.97 KB / Downloads: 1429)

Technical Seminar Synopsis On CIRCUIT BREAKERS

Presented By
- Naveen T.M
(1SI06EC069)
Siddaganga Institute of Technology
Electronics & Communication Engineering

CIRCUIT BREAKERS
Abstract:
A circuit breaker is an automatically-operated electrical switch which is designed to protect an electrical circuit from damage caused by overload or short circuit.
Used to prevent the heavy current from damaging power system components.
Unlike fuses, normal operation can be resumed with minimal turn around time.
Keywords:
Frame,Trip Unit,Arc Extinguisher,Air Break/Miniature Circuit Breaker,Oil Circuit Breaker,Air Blast Circuit Breaker,SF6 Circuit Breaker ,Vacuum Circuit Breaker.
1. Introduction:
First ever circuit breakerà SF6 type circuit breaker in the year 1938 by Germany. Researcher:Vitaly Grosse.USA developed it in the year 1951.Researchers: Lingal, Browne and Storm .First industrial application in the year 1953.
Circuit breakers requires to reduce arcing ie, Sparks jump for several inches in the highly ionized ambient atmosphere.
The Culprit: Arcing
Sparks jump for several inches in the highly ionized ambient atmosphere.
The high current can still damage the circuit.
Arcing is analogous to Flash-over in transmission lines.
2. Block diagram:
2.1 Frame:
¢ Provides space for mounting the components & holding them in place.
¢ Must withstand mechanical stresses.
¢ Provides insulation & isolation path for current.
2.2 Contacts:
¢ Provides a method for connecting the circuit with the system.
¢ Forms a part of the isolation circuit.
Basic functions:
¢ Opening
¢ Closing
2.2.1 Operation: Opening
¢ Spring is generally used for the purpose.
¢ Opening process is faster.
¢ Spring gets recoiled during Closing Operation.
2.2.2 Operation: Closing
¢ Solenoid is generally used for the
purpose.
¢ Closing process is slower.
¢ Force of attraction increases with reduction in distance.
2.3 Trip unit:
Opens the circuit during
¢ Thermal overload
¢ Short circuit
¢ Ground Fault
2.4 Arc extinguisher:
¢ Circuit Breakers differ in the type arc extinguishers used in them.
¢ Extinguishes an arc when contacts are opened.
3. Classification:
Based on operational voltage
¢ Low voltage circuit breakers
eg: air break circuit breaker.
¢ Medium voltage circuit breakers
eg: vacuum circuit breaker.
¢ High voltage circuit breakers
eg: sf6 circuit breaker.
3.1 Air break circuit breaker:
¢ Quenching medium: Air at atmospheric pressure.
¢ Suitable for high current interruption at low voltage.
¢ Principle of high resistance is used for arc interruption.
3.2 Vacuum circuit breaker:
¢ Arc Quenching medium: High Vacuum.
¢ Air at a pressure of 10-5 mm & below is called High Vacuum.
¢ An arc formed at a small separation of 1cm can also be extinguished efficiently.
¢ Contacts made of special materials.
3.3 Sf6 circuit breaker:
¢ Specialty: inert, non-toxic, non flammable heavy gas.
¢ High dielectric strength(2.5 times that of air)
¢ Disadvantage: Decomposes at high temperature.
¢ With moisture, it may spoil the parts of CB.
3.3.1 Sub categories:
¢ Double-pressure SF6 Circuit breakers
àEarly type of SF6 Circuit breaker
¢ Puffer type Circuit Breakers
àUses SF6 in a compressed form
4. Advantages:
¢ Protect an electrical circuit from overload.
¢ Protect an electrical circuit from shortcircuit.
¢ Used for high speed arc interruption
¢ Oil can be used for both insulation & arc extinguishing purpose.
5. Disadvantage:

¢ Sf6 used in circuit breakers decomposes at high temperature.
¢ With moisture, Sf6 may spoil the parts of circuit breaker.
¢ Higher the operating voltage more is the Oil required in bulk oil circuit breaker.
6. Applications of circuit breaker:
¢ UPS Equipment
¢ Power Supplies
¢ Small Generators
¢ Entertainment Systems
¢ Vending Machines
¢ Office Machines
¢ Telecom Power Distribution
¢ Railway Signaling System
¢ Automatic control systems
¢ Generator sets
¢ AC and DC Branch Circuit Protection
¢ Power conversion systems
7. Conclusion:
It prevent the heavy current from damaging power system components.
Unlike fuses, normal operation can be resumed with minimal turn around time.
8. References:
¢ Scientific american by robert.r.birge.
¢ The lock key paraldigm by michael consad.

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24-07-2010, 11:59 AM
Post: #2
RE: circuit breaker full report
many many thanks.................
16-10-2010, 03:56 PM
Post: #3
Shocked RE: circuit breaker full report

.ppt  ABCB.ppt (Size: 1.47 MB / Downloads: 540)
This article is presented by:
Shah Rishabh G
AIR BREAK CIRCUIT BREAKER


Introduction
These type of breakers employ ‘air blast’ as the quenching medium.
The contacts are opened by air blast produced by the opening of blast valve.
The air blast cools the arc and sweeps away the arcing products to the atmosphere.
This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc.
So the arc is extinguished and the flow of current is interrupted.
Types of Air blast circuit breaker
(1). Axial-blast type (2).Cross-blast type (3).Radial-blast type


Types of Air blast circuit breaker
Axial-blast type:-

In which the air-blast is
directed along the arc path as




In which the air-blast is
directed at right angles to the
arc path as shown in Fig.
22-01-2011, 03:24 PM
Post: #4
RE: circuit breaker full report



BEN McQUILLAN

WHAT TO TAKE HOME FROM THIS SEMINAR…

A MORE INTIMATE KNOWLEDGE OF THE ELECTRICAL SYSTEM OF YOUR AIRPLANE
AN OPERATIONAL UNDERSTANDING OF ELECTRICAL SYSTEM PROTECTION
FLEXIBLE DEFINITIONS OF ESSENTIAL & NON-ESSENTIAL ELECTRICAL SYSTEMS
A “CAPTAIN MINDSET” FOR THE MANAGEMENT OF YOUR AIRCRAFT SYSTEMS

WHAT IS A CIRCUIT BREAKER?
A “GATE” THROUGH WHICH ELECTRICITY TRAVELS FROM THE BATTERY TO THE COMPONENT WHICH THE CIRCUIT BREAKER PROTECTS
ABLE TO OPEN AUTOMATICALLY WHEN THE WIRING OF THE CIRCUIT GETS TOO HOT (TOO MUCH VOLTAGE AND/OR RESISTANCE) TO REMOVE ALL ELECTRICITY FROM CONTINUING BEYOND THE BREAKER TO THE COMPROMISED AREA

TYPES OF CIRCUIT BREAKERS

PULL-TYPE CIRCUIT BREAKERS
NON PULL-TYPE CIRCUIT BREAKERS
CIRCUIT BREAKER SWITCHES


WHAT DO THEY DO?
A CIRCUIT BREAKER SENSES AN OVERLOAD CONDITION WITHIN ITS ELECTRICAL CIRCUIT
GROUND FAULTS/ARCING
OVER-VOLTAGE/OVER-TEMPERATURE
IT WILL AUTOMATICALLY PREVENT ANY BATTERY POWER FROM CONTINUING BEYOND THE BREAKER TO THE FAULTY WIRING & COMPONENT

HOW DO THEY DO IT?
NORMAL LOAD VS. OVERLOAD
CIRCUITS TYPICALLY CARRY ½ THEIR RATED LOAD (NUMBER ON BREAKER LABEL)
OVERLOAD = EXCESSIVE HEAT
EXCESSIVE HEAT TRIPS BREAKER
NORMALLY FLAT LAYERED METAL STRIPS EXPAND AT DIFFERENT RATES, CURVE, AND BREAK AWAY FROM ELECTRICAL CONNECTION


more


22-01-2011, 04:24 PM
Post: #5
RE: circuit breaker full report



.ppt  ex ppt.ppt (Size: 1,008.5 KB / Downloads: 374)

presented by: M Aamir sohail khan & sufyan saleem



WHAT IS A CIRCUIT BREAKER?

A circuit breaker is an equipment that breaks a circuit either manually or automatically under all conditions at no load, full load or short circuit.

Operating Principle

Two contacts called electrode remains closed under normal operating conditions. When fault occurs on any part of the system, the trip coil of the circuit breaker get energized and contacts are separated.

Arc Phenomenon

An arc is struck when contacts are separated. The current is thus able to continue. Thus the main duty of a circuit breaker is to distinguish the arc within the shortest possible time.

The arc provides the low resistance path to the current and the current in the circuit remains uninterrupted.

The arc resistance depends upon the following factors.



Degree of ionization
Length of the arc
Cross Section of the arc

Methods of Arc Extinction




High Resistance Method

Low Resistance Method

Breaker Used I n 132KV Grid Station

Oil Circuit Breaker
Vacuum Circuit breaker
SF6 Circuit Breaker

Low Oil Circuit Breaker

Consists of two parts.
Supporting Chamber.
Circuit-Breaking chamber( consist of fixed and moving contact)

Disadvantages Of Oil Circuit Breaker
It is inflammable and there is a risk of fire.
It may form an explosive mixture with air.
It requires maintenance.
Absorbs moisture, so dielectric strength reduces.
Oil leakage problem.
Oil has to be replaced after some operations because of the carbonization of oil.

Vacuum Circuit Breaker
Vacuum is used as an arc quenching medium.
Have greatest insulating strength.
10-7 to 10-5 pressure is to be maintained.
Used in 11KV panel in control room of grid station.

Advantages
Compact, reliable and have longer life.
No fire hazards.
No generation of gas during and after operation.
Can interrupt any fault current.
No noise is produced while operating.
Require less power for control operation.

SF6 Circuit Breaker
Sulphur Hexafluoride (SF6) gas is used as an arc quenching medium.
SF6 is an electro-negative gas.
It has strong tendency to absorb electrons.
When contact are opened in a high pressure flow of SF6 gas, arc produced.
Free electron in the arc are captured by the gas.
Which build up enough insulation strength to extinguish arc.
it is much effective for high power and high voltages services,

Advantages
Simple construction, less cost.
SF6 gas is non flammable, non toxic & chemical inert gas.
Same gas is recirculated in the circuit.
Maintenance free C.B.
Ability to interrupt low and high fault current.
Excellent Arc extinction.

Advantages Of SF6 Over Oil Circuit Breakers

Short arcing time
Can interrupt much larger currents
Gives noiseless operation due to its closed gas circuit
No moisture problem
No risk of fire
No carbon deposits. So no tracking and insulation problems
Low maintenance cost



08-03-2011, 02:20 AM
Post: #6
RE: circuit breaker full report
can i get a full report on circuit breakers upto 15 to 20 pages....its really important i have to submit it on wednesday....and its mandatory to have 15-20 pages....so if u have plz mail me on my email id......deepak.bettiah23[at]gmail.com
08-03-2011, 02:24 AM
Post: #7
RE: circuit breaker full report
can i get a full report on circuit breakers upto 15 to 20 pages....its really important i have to submit it on wednesday....and its mandatory to have 15-20 pages....so if u have plz mail me on deepak.bettiah23[at]gmail.com
30-03-2011, 11:23 AM
Post: #8
RE: circuit breaker full report

.doc  tinku_Word.doc (Size: 156 KB / Downloads: 151)
Abstract.
As important as finding new renewable and environmentally friendly sources of energy is the fact of transmitting and distributing this energy in the safest and most efficient way. In this field, High Voltage Circuit Breakers (1111 CB), designed for operation of the electric network under normal conditions as well as for the interruption of faulted conditions, have played an important role in power systems over 100 years. However, research, development and improvement of the design of CBs have not stopped in our nowadays expanding grid.
The aim of this paper is to make a review of the existing different types of HV CB, comparing the most used one, SF6 CB, with the Vacuum CB, which has been developed and recently applied for HV, and could become the future environmental friendly HV CB.
Key words
Circuit Breaker (CB), Vacuum Circuit Breaker (VCB), Sulfurhexaflouride (SF6), Electric arc, Vacuum Arc.
1. Introduction
A Circuit Breaker is a switching device which can open or close a circuit in a small fraction of second. This is achieved due to its separable contacts. The closing and opening of the circuit allows to establish or to interrupt the circulation of current through the circuit under usual or unusual working conditions, such as short circuits.
The interruption process of the current in a CB, begins when the movable contacts start to separate. As a consequence, the contact area is reduced and the current density gets larger, until the energy causes the metal to begin vaporizing and an arc appears. In spite of the existence of a physical separation of the switching contacts, the established arc makes possible that the current continues flowing (Figure 1). The interruption of the circulating current will be achieved when the interrupting medium gets to turn the carrying arc plasma into an isolating medium. ([1]-[4])
In the beginning of the arc phenomena the main source of charged particles is the electrode vapour. However, as the contact separation increases the ionization degree of the arc column is also influenced by the characteristics of the surrounding medium, except for Vacuum CBs.
Attending to the medium and the method used for the interruption of the current, CBs can be grouped in the following types:
- Air Magnetic Circuit Breakers
- Air Blast Circuit Breakers
- Oil Circuit Breakers
- Sulfurhexaflouride (SF6) Circuit Breakers
- Vacuum Circuit Breakers
Oil circuit breakers were the first CB type in the grid, due to its ability to interrupt large currents. The interruption process is based on the creation of hydrogen and acetylene gas bubble, as the oil decomposes as a result of the arc established between the switching contacts. The disadvantages of using oil as quenching media in circuit breakers, as flammability and a high maintenance cost, forced to search for different mediums of quenching. Air Blast and Magnetic Air circuit breakers were developed but did not sustain in the market due to some disadvantages, as the fact that they are bulky and cumbersome. In the middle of the century, and being
considered as the new generation of CBs, SF6 and Vacuum CBs appeared.
SF6 CBs started quickly to replace oil and air CBs for HV applications, as most SF6 properties are superior to other interrupting mediums, such as its high dielectric strength or higher thermal conductivity. In contrast, Vacuum CBs started to spread in the Medium Voltage level up to rated voltages of around 36kV. ([1], [5])
Even though many CBs from the first generation, with oil or air as quenching medium, are still working, SF6 CB is undoubtedly the most common CB used nowadays for HV applications worldwide. But, it also has its limitations and disadvantages. Vacuum switching, widely used for medium voltage levels (5-38 kV), has emerged as an alternative for high voltage applications due to its environmental friendliness. Latest research on contact material composition, magnetic field application, insulation, multi-gap or long gap technology has lead to the development of various prototypes for higher voltage levels. Following, both types, SF6 and vacuum are analysed in detail.
2. SF6 CBs
In SF6 circuit-breakers, the current continues flowing after contact separation through an arc plasma of ionized SF6. The circuit breaker is designed to direct a constant gas flow to the arc that extracts heat from the arc and so allows achieving its extinction at current zero. The gas flow de-ionises also the contact gap and restablishes the required dielectric strength to prevent an arc re-strike.
The direction of the gas flow, i.e., whether it is parallel to or across the axis of the arc, has a decisive influence on the efficiency of the arc interruption process. Research has shown that an axial gas flow creates a turbulence which causes an intensive and continuous interaction between the gas and the plasma as the current approaches zero. Cross-gas-flow cooling of the arc is generally achieved, in practice, by making the arc to move in the stationary gas. However, this interruption process can lead to arc instability and resulting great fluctuations in the interrupting capability of the circuit breaker.
In order to achieve an axial gas flow, a differential pressure must be created along the arc. The first generation of SF6 CBs used the two-pressure principle of the air-blast CB. A certain quantity of gas was kept stored at high pressure and released into the arcing chamber. In later designs, the differential pressure was created by a piston attached to the moving contacts, which compresses the gas in a small cylinder as the contact opens. Some disadvantages are the relatively powerful operating mechanism required by this puffer system and the cost of this operating mechanism.
Consequently, new developments were aimed at reducing or eliminating this additional cost factor. These developments concentrated on employing the arc energy itself to create directly the differential pressure needed.
This research led to the development of the self- pressuring circuit-breaker in which the overpressure is created by using the arc energy to heat the gas under controlled conditions. During the initial stages of development, an auxiliary piston was included in the interrupting mechanism, in order to ensure the satisfactory breaking of small currents. Subsequent improvements in this technology have eliminated this requirement and in the latest designs, the operating mechanism must only provide the energy needed to move the contacts.
Parallel to the development of the self-pressuring design, the rotating arc SF6 interrupter appeared. In this design a coil sets the arc in rotation while the quenching medium remains stationary. The relative movement between the arc and the gas is no longer axial but radial, i.e., it is a cross-flow mechanism. The operating energy required by circuit breakers of this design is also minimal [1].
3. Vacuum CBs
A. General features

When the contacts separate in a VCB, the current flowing trough those electrodes initiates a metal vapour arc discharge in the contacts called the vacuum arc. The vacuum arc, once established, flows through the plasma in a self sustained way until the next current zero. The arc is then extinguished and the conductive metal vapour condenses on the metal surfaces, within a matter of micro seconds. As a result, the dielectric strength in the breaker builds up very rapidly. Figure 2 shows the internal components of a typical vacuum interrupter.
B. MV application
Medium voltage is where VCB has found its widest application field and is widely used in the range of 5 to 38kV [1].
Vacuum arcs have more than one appearance, as there are different modes of vacuum arcs. The mode of the vacuum arc depends on the current level and the size of the
contacts. At lower currents, the arc assumes the diffuse mode. The characteristics of diffuse arcs are that there are one or more cathode spots moving constantly over the contact surface. These spots repel each other and they have a fmite and variable lifetime. While some cathode spots are extinguished, some others split, creating new ones. As the current increases, the arc changes its appearance. All the plasma is focused on a small area of the electrode, about 1 cm2, so instead of multiples moving cathode spots the appearance that the arc takes is a constricted mode.
The current at which the transition from diffuse to constricted mode takes place, depends on the size of the contact and its material but it is usually between 10 and 15 kA. The constricted mode of the arc has nothing but disadvantages, as the interruption of the current is much more difficult, and it produces severe erosion on contacts. Besides, a constricted arc that remains on one spot for too long can thermically over stress the contacts to such a degree that the deionization of the contact zone at zero current can no longer be guaranteed
To overcome this problem the arc root must be moved over the contact surface and in order to achieve this, contacts are appropriately shaped so that the current flowing through them results in a radial magnetic field. This radial field, also known as transverse field, causes the arc root to rotate rapidly around the contact, resulting in a uniform heat distribution over its surface. The contacts of this type are called radial magnetic field or spiral electrodes (Figure 3).
The spiral electrodes are able to interrupt a current of 30kA with electrodes of 100mm of diameter. As it is shown in Figure 4, the electrodes size becomes too large for high current interruptions.
C. HV applicationAt high voltage, the vacuum arc adopts a constricted form, which makes more difficult the arc quenching at current zero. But the problem of switching the arc from constricted to diffuse, in HV applications, can not be achieved by subjecting the arc to a radial magnetic field, as it is solved for MV. This is so because the current would not be interrupted unless the size of the contacts were large enough. And such big electrodes would make the VCB bulky and not so competitive [1].
In contrast, for high voltage applications an axial magnetic field is applied (Figure 4). The axial magnetic field can be provided by leading the arc current through a coil, suitably arranged outside the vacuum chamber. Alternatively, the field can be provided by a suitable contact design. Such contacts are called axial magnetic field electrodes (Figure 5). With the higher magnetic field strength, the radial arc distribution is more homogenized. This way the arc energy is reduced.
Another problem in these applications, HV VCB, is related to the high-voltage capability of a single gap between electrodes. The breakdown characteristics have very high dependence of electrode area, and the dielectric strength with the contact gap. On this way, in vacuum breakdown, the breakdown voltage is proportional to the square root of the gap length
18-04-2011, 10:03 AM
Post: #9
RE: circuit breaker full report
Presented By:-
Abhishek Bhardwaj


.pptx  Seminar on Circuit Breaker.pptx (Size: 281.23 KB / Downloads: 140)
Working of the Circuit Breaker
A circuit breaker is an automatically operated electrically switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.
Principle of Circuit Breaker
As shown in fig. there are two contacts –
i. Fixed Contact
ii. Moving Contact
Under normal condition these two contacts remain in closed position . When the circuit breaker is required to isolate the faulty part, the moving contact moves to interrupt the circuit. On the separation of the contacts , the flow of current is interrupted , resulting in the formation of arc between the Contacts.
Arc interruption
An arc is struck when contacts are separated The current is thus able to continue Thus the main duty of a C.B.is distinguish the arc with in the shortest possible time.
The arc provides the low resistance path to the current and the current in the circuit remain uninterrupted.
Methods of Arc Interruption:--
1. High Resistance Interruption.
2. Current Zero Interruption.
 In high resistance its resistance is increased so as to reduce the current to a value insufficient to maintain the arc .The arc resistance can be increased by cooling, lengthening, constraning and splitting the arc. This method is not suitable for a large-current interruption, This can be employed for low power ac and dc circuit breakers.
 Current Zero Interruption is applicable only in case of ac circuit breakers . The current is not interrupted at any pt. other than the zero current instant, otherwise a high transient voltage will occur across the contact gap.
Classification of circuit breaker
There are mainly five type of Circuit Breakers:--
1. Oil Circuit Breaker.
2. Air blast Circuit Breaker.
3. SF6 Circuit Breaker.
4. Air - Break Circuit Breaker.
5. Vacuum Circuit Breaker.
Oil Circuit Breaker
Advantages :--

1. It has better insulating property then air
2. It has also good cooling property.
3. When arc is formed ,it decomposes oil into gases.
Disadvantages :--
1. It is inflammable may pose a fire hazard.
2. The possibility of forming explosive mixture with air and the production of carbon particles in the oil due to heating which reduces its dielectric strength.
Air blast circuit breaker
In air blast circuit breakers, compressed air at a pressure of 20–30 kg/cm^2 is employed as an arc quenching medium and these are suitable for operating voltages of 132KV and above.
Advantages:--
1. High speed operation.
2. Elimination of fire hazard.
3. Less maintenance.
4. Facility of high speed reclosure.
5. Cheapness and free availability of the interrupting medium, chemical stability and inertness of air.
6. Short and consistent arcing time and therefore , less burning of contacts.
7. Suitability for frequent operation.
Disadvantages :--
1. An air compressor plant has to be installed and maintained.
2. Upon arc interruption the air blast circuit breaker produces a high-level noise when air is discharged to the open atmosphere. In residential areas, silencers need to be provided to reduce the noise level to acceptable level.
3. Problem of current chopping.
4. Problem of restriking voltage.
There are types of Air blast circuit breakers :--
1. Cross-blast Circuit breakers.
2. Axial –blast Circuit breakers.
Air-break circuit breakers
 These are quite suitable for high current interruption at low voltages.
 Air at atmospheric pressure is used as an arc extinguishing medium.
 Here the principle of high resistance is employed for arc interruption. The arc resistance is increased by lengthening, splitting and cooling the arc.
 AC air –break circuit breakers are available in the voltage range 400 to 12KV. They are widely used in low and medium voltage system.
 Air –break circuit breakers are also used in dc circuits up to 12KV.
 Sf6 circuit breaker
SF6 circuit breaker are manufactured in the voltage range 3.6 kv to 765 kv. However they preferred for voltages 132kv and above.
Advantages:--
1. It has good dielectric strength and excellent arc quenching property.
2. It is an electronegative gas,i.e. it has high affinity for electrons.
3. The SF6 gas has also excellent heat transfer property.
4. Its thermal time constant is about 1000 times shorter than that of air.
5. It decomposes to SF4,SF2,S2,F2,S and F at temp. of the order of 1000 degree Celsius. After arc extinction, the products of decomposition recombine in short time, with in about 1 microsecond.
Disadvantages :--
1. It is condensate at low temperature.
2. The temperature at which SF6 changes to liquid depends on the pressure.
3. SF6 breakers are equipped with thermostatically controlled heaters wherever such low ambient temperatures are encountered.
Types of Circuit Breaker :--
1. Double-pressure SF6 circuit breakers.
2. Puffer-type Sf6 Circuit Breakers.
Vacuum circuit breakers
 The dielectric strength and arc interrupting ability of high vacuum is superior to those of porcelain, oil, air and SF6 at atmospheric pressure.
 SF6 at 7 atm. Pressure and air at 25 atm. Pressure have dielectric strengths higher than that of high vacuum.
 The pressure of 10^-5mm of mercury and below is considered to be high vacuum and it is possible to achieve pressures as low as 10^-8torr.
 Copper-bismuth, Silver-bismuth, Silver-lead and copper-lead are good materials for making contacts of the breaker.
 The rate of dielectric recovery is many times higher than that obtained in other types of Circuit Breakers. Its typical value may be as high as 20 KV/us.
It has other advantages like :-
i. Suitability for repeated operations.
ii. Least maintenance.
iii. Silent operation.
iv. Long life.
v. High speed of dielectric recovery.
vi. Less weight of moving parts
Operating mechanism
For opening and closing the circuit breaker, one of the following mechanism is employed.
1. Spring
2. Solenoid
3. Compressed Air
 The force for the opening of a circuit breakers may be applied by spring or compressed air.
 When spring is used of opening, it is precharged, i.e. compressed The precharging may be done by hand or a motor or by the closing mechanism.
 The closing mechanism may be a spring solenoid or compressed air
 For large oil C.B., Solenoid is used for closing and spring is used for opening. While for medium size breakers, spring is used for both opening and closing.
 In EHV oil circuit breakers ,compressed air is used for closing and spring is used for opening.
 In Air blast circuit breakers, compressed air is used for both closing and opening.
 In SF6 C.B., compressed air may be used for closing and a spring for opening or compressed air for both closing as well as opening.
 In Vacuum C.B., a solenoid or spring mechanism is fixed to lower end to move metallic bellows up & down inside the chamber during closing or opening the contact. The closing mechanism must be trip free.
 Spring is very good for opening as their force is large in the beginning and gradually decreases as the distance of travel of the moving contact increases, but it is not suitable for closing .
 Solenoids are very good for closing The force of attraction increases when the distance between the contacts decreases, these are not suitable for opening because they are slow in action.
 Compressed air is suitable for both closing as well as opening as its force remains almost constant even when the distance between the contacts increases or decreases.
20-04-2011, 05:44 PM
Post: #10
RE: circuit breaker full report
Hi,

Can you please send the selection of circuit Breaker PPT or any manual ,

What are all the parameters needs to consider while selecting any breaker.


Regards,
isr
indra215[at]gmail.com
16-02-2012, 11:59 AM
Post: #11
RE: circuit breaker full report
to get information about the topic circuit breakers full report ppt and related topic refer the link bellow
http://www.seminarprojects.com/Thread-ci...ull-report

http://www.seminarprojects.com/Thread-ci...ort?page=2
27-03-2012, 04:43 PM
Post: #12
RE: circuit breaker full report
circuit breaker full report


.pdf  circuit breakers.pdf (Size: 4.24 MB / Downloads: 133)


Introduction
Welcome to another course in the STEP series, Siemens
Technical Education Program, designed to prepare our
distributors to sell Siemens Energy & Automation products
more effectively. This course covers Basics of Circuit Breakers
and related products.
Upon completion of Basics of Circuit Breakers you will be able
to:
• Explain the need for circuit protection
• Identify various types of overcurrent protective devices
• Explain the basic electro-mechanical operation of a circuit
breaker
• Identify various types of Siemens circuit breakers
• Identify circuit protection ratings for various types of
Siemens circuit breakers
• Describe time-current characteristics on a time-current
curve
• Explain the benefits and function of circuit breaker
coordination



Need for Circuit Protection
Current and Temperature Current flow in a conductor always generates heat. The greater
the current flow, the hotter the conductor. Excess heat is
damaging to electrical components and conductor insulation.
For that reason, conductors have a rated continuous current
carrying capacity or ampacity. Overcurrent protection devices,
such as circuit breakers, are used to protect conductors from
excessive current flow. These protective devices are designed
to keep the flow of current in a circuit at a safe level to prevent
the circuit conductors from overheating.


Conductor Insulation

Motors, of course, are not the only devices that require circuit
protection for an overload condition. Every circuit requires some
form of protection against overcurrent. Heat is one of the major
causes of insulation failure of any electrical component. High
levels of heat can cause the insulation to breakdown and flake
off, exposing conductors.


Short Circuits

When two bare conductors touch, either phase to phase or
phase to ground, a short circuit occurs. When a short circuit
occurs, resistance drops to almost zero. Short circuit current
can be thousands of times higher than normal operating
current.



Circuit Breaker Operation

In the following illustration, an AC motor is connected through
a circuit breaker to a voltage source. When the circuit breaker is
closed, a complete path for current exists between the voltage
source and the motor allowing the motor to run. Opening the
circuit breaker breaks the path of current flow and the motor
stops. The circuit breaker will open automatically during a fault,
or can be manually opened. After the fault has been cleared, the
breaker can be closed allowing the motor to operate.


Ground Fault Sensor

An external ground fault sensor is available for the ED
frame circuit breakers. The relay functions to de-energize a
circuit within an established period of time when the current
to ground exceeds a predetermined value. This is done by
sensing the difference between two or more load conductors
passing through the sensor. A 5 mA ± 1 mA current difference
(for circuits requiring personnel protection) or a 30 mA ±
6mA current difference (for circuits requiring only equipment
protection) is the threshold for a ground fault.
Review 6
20-09-2013, 12:52 PM
Post: #13
RE: circuit breaker full report
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