CHAPTER-1

INTRODUCTION

1.1 General

With the advancement of power system, the lines and other equipment operate at very high voltages and carry large currents. High-voltage circuit breakers play an important role in transmission and distribution systems. A circuit breaker can make or break a circuit, either manually or automatically under all conditions viz. no-load, full-load and short-circuit conditions. The American National Standard Institute (ANSI) defines circuit breaker as: "A mechanical switching device capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time, and breaking currents under specified abnormal circuit conditions such as those of short circuit". A circuit breaker is usually intended to operate infrequently, although some types are suitable for frequent operation.

A high-voltage power breaker in the Siemens switchgear manufacturing plant in Berlin is shown in fig 1.1

Fig.1.1-A high-voltage power breaker in the Siemens switchgear manufacturing plant

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CHAPTER-2

CIRCUIT BREAKER

A circuit breaker is an automatically operated electrical 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 interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

An early form of circuit breaker was described by Thomas Edison in an 1879 patent application, although his commercial power distribution system used fuses. Its purpose was to protect lighting circuit wiring from accidental short-circuits and overloads. A modern miniature circuit breaker similar to the ones now in use was patented by Brown, Boveri & Cie  in 1924. Hugo Stotz, an engineer who had sold his company, to BBC, was credited as the inventor on DRP (Deutsches Reichspatent) 458329. Stotz's invention was the forerunner of the modern thermal-magnetic breaker commonly used in household load centers to this day.

With the introduction of alternating current (AC) electrical energy as a versatile power source for every conceivable application by the end of the 19th Century, the problem of transporting and distributing this energy arose /a/. In the case of changing the topology of a power system and protecting against (total) failure, the Circuit Breaker (CB) is an irreplaceable element. Although it is commonly said that: "the circuit breaker opens the circuit", it is in fact the electric-arc (arc for short) formed inside the circuit breaker, which interrupts the circuit current.

How the arc is able to interrupt a (short-circuit) current is known through many years of practical experience and from the science of plasma physics e.g. /b, c, d ,e, f, g, h, i, j, k/.

However, since many energy exchange processes play a role in the extinguishing process of the arc, we are still unable to predict, with a near to 100% probability, whether a (newly built) circuit breaker will interrupt a certain current in a specific circuit. It is for this reason that circuit breakers are put to the test during the design and proving stages.

These tests are carried out in so called 'High Power Laboratories' /l/. High Power Laboratories test especially High-Voltage Circuit-Breakers in a separate test circuit, since in-grid-testing would jeopardize normal operations of the power system. Test circuits try to simulate the most conceivable network or circuit conditions /m/. This is quite difficult since the electrical phenomena which occur when a circuit is interrupted are rather complicated and depend on numerous network (and arc) conditions.

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The most harsh conditions occur when a circuit breaker has to interrupt a short circuit current.

At first the breaker is subjected to a high current which heats it up considerably (or the arc for that matter) and by means of the accompanying Lorentz forces parts are put under great mechanical stress. When the breaker interrupts the current (at a natural current zero) the subsequent Transient Recovery Voltage (TRV) subjects the breaker (or former arc channel) to a high dielectric stress. Both phenomena, i.e. the high current and the high (transient) voltage, have to be withstood by the breaker and cannot be avoided in any way

Fig. 2.1-Cutaway View of Molded Case Circuit Breaker

A  circuit  can  be  connected  or  disconnected  using  a  circuit  breaker  by manually  moving  the operating handle to the ON or OFF position.  All breakers, with the exception of very small ones, have a linkage between the operating handle and contacts that allows a quick make (quick break contact action) regardless of how fast the operating handle is moved.  The handle is also designed so that it cannot be held shut on a short circuit or overload condition.  If the circuit breaker opens under one of these conditions, the handle will go to the trip-free position.  The trip-free position is midway between the ON and OFF positions and cannot be re-shut until the handle is pushed to the OFF position and reset. A circuit breaker will automatically trip when the current through it exceeds a pre-determined value.  In lower current ratings, automatic tripping of the circuit breaker is accomplished by use of thermal tripping devices.   Thermal trip elements consist of a bimetallic element that can be calibrated  so  that  the  heat  from normal  current  through  it  does  not  cause  it  to  deflect.    An abnormally  high current,  which  could  be  caused  by  a  short  circuit  or  overload  condition,  will cause the element to deflect and trip the linkage that holds the circuit breaker shut.   The circuit

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breaker will then be opened by spring action.   This bimetallic element, which is responsive to the  heat  produced  by  current  flowing  through  it,  has  an  inverse-time characteristic. If  an extremely high current is developed, the circuit breaker will be tripped very rapidly.

2.1 High voltage circuit breaker

Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5 kV or higher, according to a recent definition by the International Electro technical Commission (IEC). High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays  operated through current transformers . In substations the protective relay scheme can be complex, protecting equipment and buses from various types of overload or ground/earth fault.

2.2 Essential qualities of hv circuit breaker

•In closed position they are good conductors.•In open position they are excellent insulators.•They can close a shorted circuit quickly and safely without unacceptable contact erosion.•They can interrupt a rated short-circuit current or lower current quickly without generating an abnormal voltage.2.3 Types of hv ckt breaker

High-voltage breakers are broadly classified by the medium used to extinguish the arc.*Bulk oil*Minimum oil*Air blast*Vacuum*SF6

Some of the manufacturers are ABB, GE (General Electric), Tavrida Electric, Alstom, Mitsubishi Electric, Pennsylvania Breaker, Siemens, Toshiba, Koncar HVS, BHEL, CGL, Square D (Schneider Electric), Becker/SMC (SMC Electrical Products).Due to environmental and cost concerns over insulating oil spills, most new breakers use SF6 gas to quench the arc. Circuit breakers can be classified as live tank, where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. High-voltage AC circuit breakers are routinely available with ratings up to 765 kV. 1200kV breakers were launched by Siemens in November 2011, followed by ABB in April the following year. High-voltage circuit breakers used on transmission systems may be arranged to allow a

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single pole of a three-phase line to trip, instead of tripping all three poles; for some classes of faults this improves the system stability and availability.

2.3.1 Bulk Oil Circuit Breaker or BOCB

Fig. 2.2-conceptual view of bulk oil circuit breaker

Bulk Oil Circuit Breaker or BOCB is such types of circuit breakers where oil is used as arc quenching media as well as insulating media between current carrying contacts and earthed parts of the breaker. The oil used here is same as transformer insulating oil.

2.3.2 Minimum Oil Circuit Breaker or MOCB

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Fig. 2.3-MOCB

These types of circuit breakers utilize oil as the interrupting media. However, unlike bulk oil circuit breaker, a minimum oil circuit breaker places the interrupting unit in insulating chamber at live potential. The insulating oil is available only in interrupting chamber. The features of designing MOCB is to reduce requirement of oil, and hence these breaker are called minimum oil circuit breaker.

2.3.3 Air Blast Circuit Breaker

Fig. 2.4-air blast circuit breaker

These types of air circuit breaker were used for the system voltage of 245KV, 420KV and even more, especially where faster breaker operation was required. Air Blast Circuit Breaker has some specific advantages over oil circuit breaker which are listed as follows,

1) There is no chance of fire hazard caused by oil.2) The breaking speed of circuit breaker is much higher during operation of air blast circuit breaker.3) Arc quenching is much faster during operation of air blast circuit breaker.4) The duration of arc is same for all values of small as well as high currents interruptions.5) As the duration of arc is smaller, so lesser amount of heat realized from arc to current carrying contacts hence the service life of the contacts becomes longer.6) The stability of the system can be well maintained as it depends on the speed of operation of circuit breaker.7) Requires much less maintenance compared to oil circuit breaker.

There are also some disadvantages of air blast circuit breakers1) In order to have frequent operations, it is necessary to have sufficiently high capacity air compressor.2) Frequent maintenance of compressor, associated air pipes and automatic control equipments is also required.

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3) Due to high speed current interruption there is always a chance of high rate of rise of re-striking voltage and current chopping.4) There also a chance of air pressure leakage from air pipes junctions.

As we said earlier that there are mainly two types of ACB, plain air circuit breaker and air blast circuit breaker. But the later can be sub divided further into three different categories.

Axial Blast ACB.Axial Blast ACB with side moving contact.Cross Blast ACB.

2.3.4 Vacuum Circuit Breaker or VCB and Vacuum Interrupter

Fig.2.5-vacuum circuit breaker

A vacuum circuit breaker is such kind of circuit breaker where the arc quenching takes place in vacuum. The technology is suitable for mainly medium voltage application. For higher voltage Vacuum technology has been developed but not commercially viable. The operation of opening and closing of current carrying contacts and associated arc interruption take place in a vacuum chamber in the breaker which is called vacuum interrupter. The vacuum interrupter consists of a steel arc chamber in the centre symmetrically arranged ceramic insulators. The vacuum pressure inside a vacuum interrupter is normally maintained at 10 – 6 bar.

The material used for current carrying contacts plays an important role in the performance of the vacuum circuit breaker. CuCr is the most ideal material to make VCB

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contacts. Vacuum interrupter technology was first introduced in the year of 1960. But still it is a developing technology. As time goes on, the size of the vacuum interrupter is being reducing from its early 1960’s size due to different technical developments in this field of engineering. The contact geometry is also improving with time, from butt contact of early days it gradually changes to spiral shape, cup shape and axial magnetic field contact. The vacuum circuit breaker is today recognized as most reliable current interruption technology for medium voltage system. It requires minimum maintenance compared to other circuit breaker technologies.

2.3.5 SF6 Circuit Breaker:-

Fig.2.6-sf6 circuit breaker

A circuit breaker in which the current carrying contacts operate in Sulphur Hexafluoride or SF6 gas is known as an SF6 Circuit Breaker.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 tow different ways,

1) SF6 + e = SF6 – 

2) SF6 + e = SF5 – + F

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.

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Hence, for heavier and less mobile charged particles in SF6 gas, it acquires very high dielectric strength. Not only the gas has a good dielectric strength but also it has the unique property of fast recombination after the source energizing the spark is removed. The gas has also very good heat transfer property. Due to its low gaseous viscosity (because of less molecular mobility) SF6 gas can efficiently transfer heat by convection. So due to its high dielectric strength and high cooling effect SF6 gas is approximately 100 times more effective arc quenching media than air. Due to these unique properties of this gas SF6 Circuit Breaker is used in complete range of medium voltage and high voltage electrical power system. These circuit breakers are available for the voltage ranges from 33KV to 800KV and even more.

CHAPTER-3

Past and Present of Circuit Breakers and their Testing

Circuit breakers have been used since the beginning of electric energy distribution. The first ‘circuit breakers’ were very simple open air, hand-operated ‘knives’ but soon they were put in some kind of containment and means were found to ‘quench’ the arc as well as possible. Early circuit breakers used oil (or oil/water mixtures) to quench the arc but were of the plain break type. An example of this is given in /k/ where a circuit breaker for 200 – 300A at 40kV, made by a J.N. Kelman in 1901, is shown. In the 1920s circuit breakers hindered further development of electric power systems and a worldwide search for their improvement was started /h/. The oil plain break type was replaced by all kinds of oil circuit breakers with improved quenching by means of, for instance, an explosion pot, cross flow pump or a combination of these ideas /h/. In as early as 1902 a circuit breaker design using compressed air was introduced /h/ because it had comparable quenching characteristics but was much less dangerous to operate than the types using oil. This type of circuit breaker, like the oil type, was improved over and over again by such means as open air arcs, contained arcs, cross blow types, axially blown types, etc.

They were used together with oil circuit breakers depending on whichever type served the specific situation best. Also as early as in the 1920s vacuum (thought to be applicable already by the end of the 19th century /n/) was investigated as a ‘quenching’ medium /o/, but in those days industrial processes were incapable of producing a bottle that could maintain a vacuum over an extended period of time and for a number of switching operations /p/. The major problems were solved in the 1950s /p/ and since then this type of breaker has conquered the medium voltage range of applications.

In the 1950s SF6 was tested for its quenching properties /q/, as this gas had been known for its excellent dielectric properties since the 1940s. It was found to be superior over oil and air and therefore SF6 has now virtually taken over the entire High Voltage range of applications and for the Extra High Voltage and Ultra High Voltage range it is the only medium in use.

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CHAPTER-4

Digital Testing of High voltage Circuit Breakers:-

A circuit breaker is a switching device that the American National Standards Institute (ANSI) defines as: "A mechanical switching device, capable of making, carrying, and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking current under specified abnormal circuit conditions such as those of short circuit.” ANSI adds, as a note “a circuit breaker usually intended to operate infrequently although some types are suitable for frequent operation." High-voltage circuit breakers play an important role in transmission and distribution systems. They must clear faults and isolate faulted sections rapidly and reliably. In short, they must possess the following qualities:

1. In closed position, they are good conductors.2. In open position, they are excellent insulators.3. They can close a shorted circuit quickly and safely without unacceptable contact erosion.4. They can interrupt a rated short-circuit current, or lower current, quickly without generating an abnormal voltage.5. The only physical mechanism that can change in a short period of time from a conducting to an insulating state at a certain voltage is the arc. It is this principle on which all circuit breakers are based.

The first circuit breaker was developed by J.N. Kelman in 1901. It was the predecessor of the oil circuit breaker and capable of interrupting a short-circuit current of 200 to 300 A in a 40 kV system. The circuit breaker was made up of two wooden barrels containing a mixture of nil and water, in which the contacts were immersed. Since then, circuit breaker design has undergone a remarkable development. Now a days. one pole of a circuit breaker is capable of interrupting ti3 kA in a 550 kV network, with SF,, gas as the arc quenching medium.

Still, the design of a circuit breaker is not only a science but also an art. Because of the complex phenomena involved, circuit breaker prototypes have to be verified by practical tests in the laboratory. In high-power laboratories, the ability of circuit breakers to interrupt short circuit currents is verified in test circuits, which are in fact lumped element representations of the power system These test circuits must produce the correct waveforms for the(short-circuit) current as well as for the voltage that strikes the circuit breaker immediately after the breaker has interrupted the test current. The waveforms of current and voltage to which the test object is subjected are laid down in ANSI and International Electro Technical Commission (KC) standards. These standardized waveforms represent 9OX of the possible fault conditions in the real system.

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4.1 Circuit Breaker Switching and Arc Modeling

The switching action, the basic function of the circuit breaker, refers to the change from conductor to insulator at a certain voltage. Before interruption, the (short circuit) current flows through the arc channel of the circuit breaker. Because of the nonzero resistance of the arc channel, this short - circuit current causes a voltage across the contacts of the circuit breaker: the arc voltage. The arc behaves as a nonlinear resistance. Thus, both arc voltage and arc current cross the zero-value at the same time instant. If the arc is coded sufficiently at the time the current goes through zero, the circuit breaker interrupts the current, because the electrical power input is zero. During current interruption, the arc resistance increases from practically zero to almost infinite in microseconds. Immediately after current interruption, the transient recovery voltage builds up across the circuit breaker.

Fig. 4.1-switching and arc modeling

As the gas mixture in the inter electrode space does not change to a completely insulating state instantaneously, the arc resistance is finite at that time, and a small current can flow: the post-arc current, Black-box arc models are mathematical descriptions of the electrical properties of the arc. This type of model does not simulate the complicated physical processes inside the circuit breaker but describes the electrical properties of the circuit breaker. Measured voltage and current traces are used to extract the parameters for the differential equations describing the nonlinear resistance of the electrical arc for that specific measurement.

4.2 Digital Testing

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The functionality of high-voltage circuit breakers is tested in high-power laboratories, Due to the necessary power and the physical size of the equipment, testing is rather expensive and time consuming. In order to obtain as much information as possible about the degradation and operating limits of the circuit breaker from the cost intensive tests, a project started with the following partners: KEMA High-Power Laboratory, The Netherlands.Delft University of Technology, The Netherlands.Siemens RG, Germany; RWE Energie, Germany. andLaborelec cv, Belgium.

This project is sponsored by the Directorate GeIieral XII of the European Commission in Standards, Measurements, and Testing Program under contract number SMt'4-CT96-212 1. The project is aimed at developing digital testing of high-voltage circuit breakers, i.e., a software product for testing of ;I model of such a device, once its characteristic fingerprints are obtained from refined measurements during standard tests. Digital testing offers a wide range of new possibilities for users, manufacturers, standardizing bodies, and test laboratories for fine tuning circuit breaker abilities in relation with standards and real power systems. Some developments are:

*Evaluation of the relevance of future standards with respect to real power systems * Evaluation of the relevance of future standards for different circuit breaker technologies and extinguishing media*Estimation of the circuit breaker's interrupting limit* Reduction of full-scale testing in high-power laboratories Identification of network topologies that can pose special difficulties lo a circuit breaker* Acceleration of development of new circuit breaker designs

Monitoring the aging processes fit circuit breakers in service Expansion OF services for high-power laboratories.

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CHAPTER-5

MEASUREMENT AND DATA ANALYSIS

High-resolution measurements of current and voltage in the critical period around short-circuit current zero must supply the necessary parameters, characterizing the breakers' behavior. A tailor-made high-frequency measuring system was realized for this purpose. This system consists of a number of battery-powered, single channel, 40 MHz, 12 bit AD converters, each storing the data temporarily in on-board local RAM (2Stik samples each). The concept of on-site data storage is necessary for reaching a maximum overall system bandwidth, Cables to the current and voltage sensors thus be kept very short, and the system can operate 011 floating potential. The arc voltage is measured with standard broad-band RCR-type voltage dividers; current is measured with a special Rogowski coil. After the remote RAM is filled, data is transmitted serially through optical fibers to the processing unit in the command center. The greatest challenge with respect to developing the equipment in this application design lies in the electromagnetic compatibility, since the microelectronics has to function in an extremely hostile environment of intense EM fields of various origin.

The system relies heavily on digital signal processing methods for reconstructing the actual voltage and current signals from the raw sensor output. On the one hand, this has to dc) with the specific frequency response of the sensors and on the other hand , with corrections needed for the (reproducible) induced voltages and capacitive current that distort the measured signals. 'rests in various laboratorics have proven that the system can measure post-arc current as small as so mA, microseconds after the interruption of many tens of kA. Data analysis software has been produced to carry out the signal reconstruction practically on line during the tests (Figure l), and to evaluate the performance OF the test object. Even the newest professional multipurpose mathematical or laboratory software is not competitive to this custom-made software considering. Flexibility and speed in visualizing and data processing of practically unlimited amount of measured data in a user-friendly way. After an extensive series of the most critical fault interruption duty for circuit breakers (the so-called “short-line fault,” see the section on “Applications of Digital Testing”), a test database from various types of commercially available circuit breakers was set up. With this experimental material, an empirical arc model based on classical arc models was validated that gave very good coverage of the observed processes. From the total number a! ( > E O ) interruption attempts, the result of the attempt (failure/success) was predicted correctly in more than 90% of the cases by evaluating the characteristics of the arc behavior with the model.

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Fig. 5.1-current time characteristics

The model has a set of (three) parameters, which are extracted automatically during the evaluation of each test (Figure 5.1). Automated analysis of the collection of all the parameter sets (in other words, the breakers’ “fingerprints“) obtained from a whole series of tests makes it possible to evaluate various physical quantities as a function of test conditions. The aim of using this method is to quantify the breaker performance (the margin M of interruption), indicating how successful the breaker passed the test (M > 0) or how far off it is from passing it (M An example is given in Figure 3, where the degradation of the three breaker poles (A, B, and C) is presented during a sequence of successive tests. It can be seen clearly that the margin of the breaker decreases with every test. The rate of margin decay (among others) is a measure of the endurance of the breaker with respect to this type of tests.

5.1Arc-Circuit Interaction Software

At the final stage of the realization of digital testing, measured arc model parameters will be used as input for the arc model. Of course, this arc model behaves as a nonlinear element in the electrical circuit and must therefore be analyzed with a dedicated computer program. The analysis of arc-circuit interaction involving nonlinear elements in relation to stiff differential equations makes it necessary to perform the calculations with a variable step size and adjustable accuracy of the computed currents, voltages, and conductances. Because they have fixed step-size solvers, EMTP and comparable programs are less suitable for this purpose and therefore a new approach, the integration of differential algebraic equations (DAE) by means of the backward differentiation formulas @DO method, has been chosen in developing a new software package for electrical transients computation. This new transient program, XTrans, has been developed at the Delft University of Technology especially for arc circuit interaction studies. The program runs on a PC with the MS-Windows operating system and works fully graphical, as shown in Figure 4. The program is in use at several high-

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power and high-voltage laboratories in the world. The program makes use of libraries that contain information about the behavior of element models. The program structure is depicted in Figure5.2.

Fig. 5.2-behaviour of element model

This structure has been realized with object-oriented programming. The compiled code of the element models is placed in dynamic link libraries @Us). The models are, therefore, separate from the main program, which makes it easy to create new models and use them in the main program

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CHAPTER-6

APPLICATION OF DIGITAL TESTING 6.1 Influence of Parallel Capacitance

Powerful possibilities with digital testing are created when the arc model, validated as described in the section on Measurements and Data Analysis, is coupled with a circuit analysis package. Then, the performance of a circuit breaker, the fingerprints of which were obtained from real tests, can be estimated in circuits other than the test circuit. For example, the influence of various standard substation components on the breakers' capabilities can be estimated through digital testing. Here the influence of a parallel capacitance is calculated (for example, the parasitic capacitance at a current transformer, CT,) in the substation. The performance of a short-line fault interruption is compared in the presence of two types OE CTs: CT 1, having 200 pF of parasitic capacitance, and C1' 2, having 400 pP. These CTs can be located near the circuit breaker and remote (the latter implying an additional 50 pH of bus bar between CT and breaker).

As a reference, the case without CT has a performance o f 1 .O. Table 1 shows that the difference between the two types of CTs is rather small when compared to the gain obtained by the CT that was installed to the breaker as closely as possible.

6.2Critical Line Length Determination

One of the most severe currents for a circuit breaker to interrupt is the short-line fault (SLF). In the case of a short-line fault, the short-circuit point is on a high-voltage transmission line a few kilometers away from the breaker terminals. After current interruption, a very steep, triangular-shaped waveform (with a rate of rise of 5-10 kV/microsecond) stresses the extinguishing medium between the contacts. The percentage SLF indicates to what extent the short-circuit current is reduced by thetransmission line, e.g., a short-circuit current of 40 kA is reduced to 36 kA in case of a 90% SLF. In the IEC standard, 75% and 90% SLF tests are prescribed. As an example of digital testing, the critical line length, the short-line fault percentage that stresses the circuit breaker most, will be determined for a 145 kV, 31.5 kA, SF, circuit breaker. A direct SLF test circuit is shown in Figure.

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Fig. 6.1-SLF test circuit

Three different indicators, active at different time intervals (before current zero, at current zero, and after current zero) are used to quantify the stress on the circuit breaker model. Before current zero: the time before current zero where the arc resistance equals the surge impedance of the transmission line (H = 3, The closer the value is to current zero, the more severe the breaker is stressed by the test circuit. At current zero: the arc resistance XO. The lower the arc resistance value at the current zero crossing, the stronger the breaker is stressed by the test circuit. After current zero: the post-arc energy Epa. This value is the integral of the multiplication of the small post-arc current and the recovery voltage. It is clear that only for successful interruptions an Epa value can be calculated. The higher the Epa value is, the more severe the breaker is stressed by the test circuit. The actual computation is based on 75 current zero recordings of the circuit breaker of which the circuit breaker model parameters have been determined. For each set of parameters, the stress at the various short line fault percentages is computed. At last, the overall stress is visualized, which is shown in Figure6.2.

Fig.6.2-strees relation

All indicators show that the circuit breaker model is stressed most severely at a 93% SI, F, whereas a 90% SLF is prescribed in the IEC standard. This shows that digital testing can he applied to use the information obtained from laboratory tests for the development of future standards.

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6.3 Advantages

•Evaluation of the relevance of future standards for different circuit breaker technologies and extinguishing media.•Estimation of circuit breaker’s interrupting limit.•Reduction of full scale testing in high-power laboratories.•Identification of network topologies that can pose special difficulties to a circuit breaker.•Acceleration at development of new circuit breaker design.•Monitoring the aging process of circuit breaker in service.

6.4 Disadvantages

•Testing in costlier•Testing is time consuming•A tough procedure

CHAPTER-7

CONCLUSION

Digital testing gives precise information about the breaker, as obtained from laboratory tests. This is useful for the development of future standards. Powerful possibilities with digital testing are created when arc model and data analysis is coupled with a circuit analysis package. The performance of a circuit breaker whose finger prints are obtained from real tests can be estimated in other circuits also.

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