Circuit Breakers : Principles & Operation

Fig 1 : A 2-pole miniature circuit breaker

All electric circuits needs a switching device and also a protective device. Switchgear is the general term covering a wide range of equipment connected with switching and protection. A circuit breaker is a switching and circuit interrupting device. A circuit breaker serves two purposes:

(i) Switching on and off during normal operation for maintenance etc.
(ii) Switching during abnormal conditions- short circuits, earthing etc. to protect the associated equipment.

What is a Circuit Breaker ?
A circuit breaker is an apparatus in electrical systems that has the capability to, in the shortest possible time, switch from being an ideal conductor to an ideal insulator and vice-versa.

Furthermore, the circuit breaker should be able to fulfill the following requirements:

1.  In the stationary closed position, conduct its rated current without producing impermissible heat rise in any of its components.

2.  In its stationary positions, open as well as closed, the circuit breaker must be able to withstand any type of overvoltages within its rating. 

3. The circuit breaker shall, at its rated voltage, be able to make and break any possible current within its rating, without becoming unsuitable for further operation.

In earlier times, oil and compressed air were typical insulating and extinguishing medium. Nowadays they are almost entirely replaced by SF6 gas for economical and practical reasons, and also due to increased demands for higher ratings.

The circuit breaker is a crucial component in the substation, where it is used for coupling of busbars, transformers, transmission lines, etc. The most important task of a circuit breaker is to interrupt fault currents and thus protect electric and electronic equipment. The interruption and the subsequent reconnection should be carried out in such a way that normal operation of the network is quickly restored, in order to maintain system stability. In addition to the protective function, the circuit breakers are also applied for intentional switching such as energizing and de-energizing of shunt reactors and capacitor banks. For maintenance or repair of electrical equipment and transmission lines, the circuit breakers, together with the disconnectors, earthing switches or disconnecting circuit breakers with built-in disconnecting function, will ensure personnel safety. So 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, by interrupting continuity, to immediately discontinue electrical 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.

In short, a circuit breaker is a sort of automatic switch which can interrupt the fault currents. Two important parts of a circuit breaker that need consideration are:

(i) Arc extinction system and (ii) Relay for operation

Principles of arc extinction :

The current interruption process in a high-voltage circuit breaker is a complex matter due to simultaneous interaction of several phenomena. When the circuit breaker contacts separate, an electric arc will be established, and current will continue to flow through the arc. Interruption will take place at an instant when the alternating current reaches zero. When a circuit breaker is tripped in order to interrupt a short-circuit current, the contact parting can start anywhere in the current loop. After the contacts have parted mechanically, the current will flow between the contacts through an electric arc, which consists of a core of extremely hot gas with a temperature of 5,000 to 20,000 K. This column of gas is fully ionized (plasma) and has an electrical conductivity comparable to that of carbon. When the current approaches zero, the arc diameter will decrease, with the cross-section approximately proportional to the current. In the vicinity of zero passage of current, the gas has been cooled down to around 2,000 K and will no longer be ionized plasma, nor will it be electrically conducting.

 Two physical requirements (regimes) are involved:

Thermal regime : The hot arc channel has to be cooled down to a temperature low enough that it ceases to be electrically conducting.

Dielectric regime : After the arc extinction, the insulating medium between the contacts must withstand the rapidly-increasing recovery voltage. This recovery voltage has a transient component (transient recovery voltage, TRV) caused by the system when current is interrupted. If either of these two requirements is not met, the current will continue to flow for another half cycle, until the next current zero is reached. It is quite normal for a circuit breaker to interrupt the short-circuit current at the second or even third current zero after contact separation.

Arc Extinction Process :

Whenever a circuit carrying current is interrupted by a circuit breaker an arc is inevitably formed between the contacts which prolongs the current interrupting process for a duration ranging from 10 to 100 or more milliseconds. Since arc is produced in every circuit breakers, therefore suitable energy dissipating device must be incorporated in the design of circuit breaker. Unless carefully controlled, arc can lead to danger of fire or explosion. The arc consists of a column of ionized gas i.e. gas in which the molecules have lost one or more of their negative electrons, leaving positive ions. The negative electrons are attracted towards the positive contact and being light, more towards it very rapidly. The positive ions attracted towards the negative contact. Due to electron movement the current flows. The ionization process is accompanied by the emission of light and heat. Also some portion of power is dissipated as heat. The temperature of arc may be as high as 6000⁰ C. Two methods commonly used are:

(i) High resistance interruption :

In this the arc is controlled in such a way that its resistance is caused to increase rapidly, thereby reducing the current until it falls to a value that is insufficient to maintain the ionization process. The arc resistance may be increased by

(a) Arc lengthening
(b) Arc cooling
(c) Arc splitting

(ii) Low resistance interruption :

In this the arc resistance is kept low, in order to keep the arc energy to a minimum and use is made of a natural or artificial current zero when the arc extinguishes itself and is then prevented from re striking.

Protection of contacts :

During arcing mechanical as well as electrical erosion of contacts occurs. Therefore the resistance to erosion by arching is the important property of contact materials. In case of dc circuits the process of erosion is represented by loss of material from one contact and the deposition of part of this material on to the other contact. However, in case of ac circuits there is no marked direction of transfer, as either contact becomes successively positive and negative.

There are two distinct forms of protections which may be employed with the object of reducing the rate of erosion of contacts by arcing thereby prolonging their useful life.

(a) Arc dispersion :

In this the destructive effects of the arc are minimized, using one of the following methods:
1. Oil immersion of contacts
2. Multiple break contacts
3. De ionization of arc path
4. Magnetic blow out of arc
5. Blast principle using air, oil, gas or water.

(b) Arc prevention :

In this the occurrence or arc is prevented by reducing the current and voltage below the minimum arcing values or reducing its destructive effects as far as possible. The principle devices used to quench circuits of this kind are :
 
(i) Discharge resistance (ii) Rectifiers (iii) Condensers

Circuit Breakers : Selection Criteria

There are a few different criteria to consider when selecting a circuit breaker including voltage, frequency, interrupting capacity, continuous current rating, unusual operating conditions and product testing. This article will give a step by step overview on selecting an appropriate circuit breaker for your specific application.

a) Voltage Rating : The overall voltage rating is calculated by the highest voltage that can be applied across all end ports, the distribution type and how the circuit breaker is directly integrated into the system. It is important to select a circuit breaker with enough voltage capacity to meet the end application.

b) Frequency : Circuit breakers up to 600 amps can be applied to frequencies of 50-120 Hz. Higher than 120 Hz frequencies will end up with the breaker having to derate. During higher frequency projects, the eddy currents and iron losses causes greater heating within the thermal trip components thus requiring the breaker to be derated or specifically calibrated. The total quantity of deration depends on the ampere rating, frame size as well as the current frequency. A general rule of thumb is the higher the ampere rating in a specific frame size the greater the derating needed. All higher rated breakers over 600 amps contain a transformer-heated bimetal and are suitable for 60 Hz AC maximum. For 50 Hz AC minimum applications special calibration is generally available. Solid state trip breakers are pre-calibrated for 50 Hz or 60 Hz applications. If doing a diesel generator project the frequency will either be 50 Hz or 60 Hz. It is best to check ahead of time with an electrical contractor to make sure calibration measures are in place before moving forward with a 50 Hz project.

c) Maximum Interrupting Capacity : The interrupting rating is generally accepted as the highest amount of fault current the breaker can interrupt without causing system failure to itself. Determining the maximum amount of fault current supplied by a system can be calculated at any given time. The one infallible rule that must be followed when applying the correct circuit breaker is that the interrupting capacity of the breaker must be equal or greater than the amount of fault current that can be delivered at the point in the system where the breaker is applied. Failure to apply the correct amount of interrupting capacity will result in damage to the breaker.

d) Continuous Current Rating : In regards to continuous current rating, molded case circuit breakers are rated in amperes at a specific ambient temperature. This ampere rating is the continuous current the breaker will carry in the ambient temperature where it was calibrated. A general rule of thumb for circuit breaker manufactures is to calibrate their standard breakers at 104° F. Ampere rating for any standard application depends solely on the type of load and duty cycle. Ampere rating is governed by the National Electrical Code (NEC) and is the primary source for information about load cycles in the electrical contracting industry. For example lighting and feeder circuits usually require a circuit breaker rated in accordance with the conductor current carrying capacity. To find various standard breaker current ratings for different size conductors and the permissible loads consult NEC table 210.24.

e) Atypical Operating Conditions : When selecting a circuit breaker it is crucial to have in mind the end user location. Each breaker is different and some are better suited for more unforgiving environments. Below are a few scenarios to keep in mind when determining what circuit breaker to use:

• High Ambient Temperature: If standard thermal magnetic breakers are applied in temperatures exceeding 104° F, the breaker must be derated or recalibrated to the environment. For many years, all breakers were calibrated for 77° F which meant that all breakers above this temperature had to be derated. Realistically, most enclosures were around 104° F; a common special breaker was used for these types of situations. In the mid 1960s industry standards were changed to make all standard breakers be calibrated with 104° F temperature in mind.

• Corrosion and Moisture: In environments where moisture is constant a special moisture treatment is recommended for breakers. This treatment helps resist mold and/or fungus that can corrode the unit. In atmospheres where high humidity is prevalent the best solution is the usage of space heaters in the enclosure. If possible, breakers should be removed from corrosive areas. If this is not practical, specifically manufactured breakers that are resistant to corrosion are available.

• High Shock Probability: If a circuit breaker is going to be installed in an area where there is a high probability of mechanical shock a special anti-shock device should be installed. Anti-shock devices consist of an inertia counterweight over the center pole that holds the trip bar latched under normal shock conditions. This weight should be installed so that it does not prevent thermal or magnetic trip units from functioning on overload or short circuit scenarios. The United States Navy is the largest end user of high shock resistant breakers which are required on all combat vessels.

• Altitude: In areas where the altitude is over 6,000 feet, circuit breakers must be derated for current carrying ability, voltage and interrupting capacity. At altitude, the thinner air does not conduct heat away from the current carrying components as well as denser air found in lower altitudes. In addition to overheating, the thinner air also prevents the of building a dielectric charge fast enough to withstand the same voltage levels that occur at normal atmospheric pressure. Altitude issues can also derate most used generators and other power generation equipment. It is best to speak with a power generation professional before purchasing.

• Resting Position: For the most part, breakers can be mounted in any position, horizontally or vertically, without affecting the tripping mechanisms or interrupting capacity. In areas of high wind it is imperative to have the breaker in an enclosure (most units comes enclosed) on a surface that sways a bit with the wind. When a circuit breaker is attached to an inflexible surface there is a possibility of disrupting the circuit when exposed to high winds.

Instrument Transformers: CT and PT

 

Fig :1: (A) The current transformer is designed to connect in series with the line to transform the line current to the standard 5 amperes suitable for the meter or relay. The voltage transformer is designed to connect in parallel with the line to transform the line voltage to 115 or 120 volts suitable for the meter or relay. To keep the voltage at the meters and relays at a safe value, the secondary circuit must be grounded. (B) The polarity markers indicate the relative instantaneous directions of current in the windings. The polarity, or instantaneous direction of current, is of no significant difference for current-operated or voltage-operated devices. Correct operation of current-current, voltage-voltage, or current-voltage devices usually depends on the relative instantaneous directions.

Instrument Transformer :

The name instrument transformer (IT) is a general classification applied to current and voltage devices used to change currents and voltages from one magnitude to another or to perform an isolating function, that is, to isolate the utilization current or voltage from the supply voltage for safety to both the operator and the end device in use. Instrument transformers are designed specifically for use with electrical equipment falling into the broad category of devices commonly called instruments such as voltmeters, ammeters, wattmeters, watt-hour meters, protection relays, etc. Instrument transformers (ITs) are designed to transform voltage or current from the high values in the transmission and distribution systems to the low values that can be utilized by low voltage metering devices. There are three primary applications for which ITs are used: metering (for energy billing and transaction purposes); protection control (for system protection and protective relaying purposes); and load survey (for economic management of industrial loads).

Depending on the requirements for those applications, the IT design and construction can be quite different. Generally, the metering ITs require high accuracy in the range of normal operating voltage and current. Protection ITs require linearity in a wide range of voltages and currents. During a disturbance, such as system fault or overvoltage transients, the output of the IT is used by a protective relay to initiate an appropriate action (open or close a breaker, reconfigure the system, etc.) to mitigate the disturbance and protect the rest of the power system. Instrument transformers are the most common and economic way to detect a disturbance. Typical output levels of instrument transformers are 1-5 amperes and 115-120 volts for CTs and VTs, respectively. There are several classes of accuracy for instrument transformers defined by the IEEE, CSA, IEC, and ANSI standards. Figure 1 shows how the polarity markers are used to keep the direction of current flow in the meters exactly the same, as if the primary circuit was carried through the meters. Grounding of the secondary circuit is most important, but in complicated three-phase connections, the best point to ground is not always easily determined.




Current Transformer (CT) :

These can be used to supply information for measuring power flows and the electrical inputs for the operation of protective relays associated with the transmission and distribution circuits or for power transformers. These current transformers have the primary winding connected in series with the conductor carrying the current to be measured or controlled. The secondary winding is thus insulated from the high voltage and can then be connected to low-voltage metering circuits. Current transformers are also used for street lighting circuits. Street lighting requires a constant current to prevent flickering lights and a current transformer is used to provide that constant current. In this case the current transformer utilizes a moving secondary coil to vary the output so that a constant current is obtained.



Potential Transformer (PT) :

Potential transformers, are also known as voltage transformers, are instrument transformers. They have a large number of secondary turns and a fewer number of primary turns. Potential transformers are used to increase the range of voltmeters in electrical substations and generating stations. The potential transformer converts voltages from high to low. It will take the thousands of volts behind power transmission systems and step the voltage down to something that meters can handle. These transformers work for single and three phase systems, and are attached at a point where it is convenient to measure the voltage. These transformers are required to provide accurate voltages for meters used for billing industrial customers or utility companies.

Frequently Asked Questions : Part 1

Author : Engr. Yousuf Ibrahim Khan (BSc. EEE, AIUB)

1. What is Electrical Safety ?

Ans : Electricity is a wonderful utility, but can be dangerous if not approached carefully. There are three basic hazards that cause injury or death – shock, arc-flash, and arc-blast. It is important to remember that even a small amount of current passing through the chest can cause death. Most deaths occurring for circuits of less than 600 volts happen when people are working on “hot,” energized equipment. So you need electrical safety.

2. What is a Shock ?

Ans : An electrical shock is a current that passes through the human body. Any electrical current flows through the path of least resistance towards ground; if an external voltage contacts a human body, e.g. by touching a live wire with the hand, the voltage will try to find a ground, and a current will develop that flows through the body’s nervous system or vascular system, and exit through the closest part of the body to ground (e.g., the other hand which may be touching a metal pipe.) Nerve shock disrupts the body’s normal electrical functions, and can stop the heart or the lungs, or both, causing severe injury or death.

3. Can you define Arc-Flash and Arc-Blast ?

Ans :   

Arc-Flash : An arc-flash is an extremely high temperature conductive mixture of plasma and gases, which causes very serious burns when it comes into contact with the body, and can ignite flammable clothing. Arc temperatures reach up to 35,000°F – which is 4X the temperature of the sun’s surface! 



Arc-Blast :  Arc-blast is a pressure wave resulting from arcing, which can carry molten metal fragments and plasma gasses at very high speeds and distances. This can not only carry very hot shrapnel to injure a person, but can actually be strong enough to destroy structures or knock workers off ladders.


4. What is Electric Arcing ?

Ans : An  electric  arc  takes  place  when  current  flows  through  the  air  or  through  insulation  between  two conductors at different potentials. Injury from arcs may be as a direct result of burning from the arc, in which case it is not unusual for the severity of the burn to be increased because molten metallic conductor particles may enter the burn. Arc burns are usually very severe and are often fatal.

5. How to avoid being shocked ?

Ans :  Preventing  yourself  from  receiving  an  electric shock  can  be  summed  up  in  three  words:  isolate, insulate and ground.

Isolate: Isolate yourself from the source of electric shock. Secure the power to equipment before you attempt  to work on  it. Be  sure  to  keep all electrical equipment covers, doors, and enclosures in  place   when   you   are   not   actually working on the equipment. If you must leave circuitry exposed, rope  off  the  area,  post appropriate signs, and warn your fellow workers of the danger. 

Insulate:  Make sure that the electrical tools and equipment you use are properly insulated. Use  only  approved  insulated  hand  and portable  electric  power  tools.  Check  power  and  extension  cords frequently for deterioration, cracks, or breaks. Breaks in the insulation cause many electrical accidents.

Ground:  Electric current always follows the path of least resistance. To  prevent  yourself  from being  the unintentional   path    to   ground, make sure that your equipment is well grounded. Well-grounded equipment will direct any stray electric current  to  ground,  thereby protecting  you  from  electric shock.  A good ground can also help protect your equipment from excessive voltage spikes or lightning. 

6. What is Earthing ?

Ans : The electric shock received by touching the metal parts of an appliance which might become live due to detective  insulation  is  because  of  the  current  flowing  through  the  human  body  caused  by  the  voltage between  the metal parts and earth. Effective earthing will keep  zero potential  in between such points and thus the accidents will be prevented. 

7. What is Fusing ?

Ans :  Fusing of electrical circuits is used to protect the wiring and equipment (NOT YOU). If you connect between active and neutral or active and ground you will get shocked. The fuse will happily deliver its rated current (1 - 50 A). More than enough to stop your heart or make you crispy. Fuses are also very important in preventing fires if a fault occurs.

8. Can you explain Mains Power ?

Ans :  Single phase power is delivered on an active and neutral pair of conductors. The neutral conductor is tied to ground at certain locations. A separate ground wire is used to keep appliances at ground potential.
The neutral wire cannot do this as currents through it can cause a voltage drop, thus raising the voltage above ground.

9. What is an Earth Leakage ?

Ans : Current that flows to ground is called earth leakage and might be produced by water in an electrical appliance or someone standing on the ground touching something that is live.

10. What is a Power Surge ?

Ans : A power surge, also called a spike or transient, is a short-duration electrical disturbance with high levels of voltage and current. Depending on their source and magnitude, surges can cause immediate, catastrophic damage or the continuous degradation (latent damage) of electronic systems and components. Surges can come from sources inside and outside a building. Even under normal power conditions, surges are generated within a facility by the on/off cycling of electrical loads, such as air conditioners and compressors. These types of surges continuously assault electronic components causing them to malfunction or fail. Surges can be created when a disconnected electrical load is reconnected. For example, when the utility recovers from an outage and power is reintroduced to a building, a very fast high-voltage pulse is induced. This high-voltage pulse is due to the sudden change  in current flow in the electrical distribution system. As a result, these changes in the system (disconnecting and reconnecting of loads) can create surges. Power surges assault circuit boards, control logic power boards and other components in electrical and electronic devices, causing them to malfunction or fail.

11. What is a Blackout ?

Ans : When an electric utility company is unable to  provide enough power to meet its customer's demands, it will methodically turn off power to blocks of customers for a period of time. This power allocation helps ensure customers have electrical service, even if it is interrupted for a little while, rather than no power at all for extended periods of time. These power allocation events are known as "blackouts" or planned outages. Power Surges are caused from Blackouts.

12. What are Surge Protection Devices ?

Ans :  SPDs or Surge Protection Devices are designed to "catch" a surge, then conduct the harmful levels of current away from the devices it is protecting. When building loads are re-energized and the utility reapplies power to the distribution system, spikes will be generated. SPDs sense the spikes as they enter the building electrical system and shunt them away before the surge can damage the building loads. In this way, loads are protected from the excessive voltage and current from a surge, so they are not damaged by them. So, the device that is used to safeguard against surges is called a surge protection device or SPD. SPDs reduce voltage surges to an acceptable level that can be tolerated by sensitive loads connected to the system.

13. Can you please tell me about Circuit Breakers ?

Ans : While a fuse protects a circuit, it is destroyed in the process of opening the circuit. Once the problem
that caused the increased current or heat is corrected, a new fuse must be placed in the circuit. A circuit
protection device that can be used more than once solves the problems of replacement fuses. Such a
device is safe, reliable, and tamper proof. It is also resettable, so it can be reused without replacing any
parts. This device is called a CIRCUIT BREAKER because it breaks (opens) the circuit.

14. What are Fuse Holders ?

Ans : For a fuse to be useful, it must be connected to the circuit it will protect. Some fuses are "wired in"
or soldered to the wiring of circuits, but most circuits make use of FUSE HOLDERS. A fuseholder is a
device that is wired into the circuit and allows easy replacement of the fuse.

15. What is a Surge Protector ?

Ans : A TRANSIENT VOLTAGE is a temporary, unwanted voltage in an electrical circuit. Transient Voltages are normally erratic, large voltages or spikes that have a short duration and a shout rise time. Devices like Computers, Electronic Circuits (TVs – Microwave Ovens – Sound Systems etc) require protection against Transient Voltages. Protection methods usually include proper wiring to National Electrical Code Requirements, to include grounding, shielding of the power lines, and use of Surge Protectors.

A Surge Protector is an electrical device that provides protection from high-level transient voltages by limiting the level of voltage allowed downstream from the Surge Protector/Suppressor (more commonly called a Surge Suppressor). Surge Protector/Suppressors can be installed at service entrance panels and individual loads.

Topics Covered

Black body radiation and the Planck law. Stimulated and spontaneous emission, atomic and spectral line width, 3-level atomic, systems. Laser operation under steady state condition, laser output coupling and power . Q-switching and mode locking. Line broadening mechanisms: homogeneous and inhomogeneous broadening. Open resonator and Gaussion beam, stability criterion for optical resonators. Principles of operation of gas, solid state and semiconductor lasers.

Topics Covered

Introduction to Thin Film Technology. Vacuum systems. Kinetic theory of gases. The physics and chemistry of evaporation/deposition mechanism. Physical vapor deposition and related techniques. Theories of epitaxy and nucleation, molecular beam epitaxy. Chemical vapor deposition techniques: reaction types, growth kinetics. Liquid phase epitaxy and related techniques. Theories of plasma and discharges. Sputtering  (DC, RF and ECR). Solution based deposition techniques (Sol-gel), spray pyrolysis.

Topics Covered

Definition and measure of information, information capacity. Fundamentals of error control coding: forward error correction (FEC) and automatic repeat request. . Binary coding: and automatic repeat request. Binary Coding: properties of codes, construction of binary compact codes. Convolutional coding: Viterbi and sequential decoding; algebra of linear block codes; error correction and detection using block codes; transmission line codes.

Topics Covered

Biological nervous system : the bran and neurons . Artificial neural networks. Historical backgrounds. Hebbian associator . Perceptions : learning rule, illustration ,proof, failing Adaptive linear ( ADALINE) and Multiple Adaptive linear (MADALINE) networks . Multilayer perceptions: generating internal representation Back propagation, cascade correlation and counter propagation networks. Higher order and bidirectional associated memory .Hopfield networks: Lyapunov energy function. attraction basin. Probabilistic updates: simulated annealing, Boltzman machine. Adaptive Resonance Theory (ART) network ART1, ART2, Fuzzy ART mapping ( ARTMAP) networks. Kohonen's feature map, learning vector Quantization ( LVQ) networks. Applications of neural nets.

Topics Covered

Numerical methods. Graphical methods. Equations with known exact solution. Analysis of singular points. Analytical methods. Forced oscillation systems. Systems described by differtial difference equations. Linear differential equation with varying coefficient. Stability of nonlinear systems.

Topics Covered

Wavelet transform. Chaos and bifurcation theorems. Walsh function. Green's function. Finite element techniques. Fuzzy logic. Genetic algorithms.

Topics Covered

Numerical techniques using computer solution of differentiation and integration  problems, transcendental equations, linear and non-linear differential equations and partial differential equations.

Topics Covered

Wiring system design, drafting, estimation. Design for illumination and lighting. Electrical installations system design: substation, BBT and protection, air-conditioning, heating and lifts. Design for intercom, public address systems, telephone system and LAN. Design of security systems including CCTV, fire alarm, smoke detector, burglar alarm, and sprinkler system. A design problem on a multi-storied building.

Topics Covered

Practical study of electronic equipment: radio receivers, television receivers, Audio Cassette and CD player, VCR, VCP, DVD player, satellite TV receiver system.

Topics Covered

Human body: Cells and physiological systems. Bioelectricity: genesis  and characteristics. Measurement of bio-signals: Ethical issues, transducers, amplifiers and filters. Electrocardiogram: electrocardiography, phono cardiograph, vector cardiograph, analysis and interpretation of cardiac signals, cardiac pacemakers and defibrillator. Blood pressure: systolic, diastolic mean pressure, electronic manometer, detector circuits and practical problems in pressure monitoring. Blood flow measurement: Plethymography and electromagnetic flow meter. Measurement and interpretation: electroencephalogram, cerebral angiograph and cronical X-ray. Brain scans. Electromayogram (EMG). Tomograph: Positron emission tomography and computer tomography. Magnetic resonance imaging. Ultrasonogram. Patient monitoring system and medical telemetry. Effect of electromagnetic fields on human body.

Topics Covered

Introduction: Applications, functional elements of a measurement system and classification of instruments. Measurement of electrical quantities: Current and voltage, power and energy measurement. Current and potential transformer. Transducers: mechanical, electrical and optical. Measurement of non-electrical quantities: Temperature, pressure, flow, level, strain, force and torque. Basic elements of DC and AC signal  conditioning: Instrumentation amplifier, noise and source of noise, noise elimination compensation, function generation and linearization, A/D and D/A converters, sample and hold circuits. Data Transmission and Telemetry: Methods of data transmission, DC/AC telemetry system and digital data transmission. Recording and display devices. Data acquisition system and microprocessor applications in instrumentation.

Topics Covered

Nanosystems and Devices:  Introduction-  nanomaterials, nanodevices, nanostructures. Nanoscale Lithography: X-ray, Electron-Beam and Ion-Beam; Soft Lithography; Scanning Probe Lithography. Advances in Device Technology: nanoscale silicon devices, process technology, present challenges. Self Assembled Nanocrystals: self assembly, surface defects and passivation, structures, energy levels, transitions, luminescence and lasing. Nano Electro Mechanical Systems (NEMS): stress in thin films, mechanical to electrical transduction, surface  engineering techniques, process flow, NEMS actuators, high aspect ratio system technology. Nano Biotechnology: scope and dimensions; detection of biological species on electrical, mechanical and optical criteria; Bio functionality on silicon; Biochip sensors and systems- structures, process technology.

Topics Covered

Nanomaterials and nanostructures: graphene, carbon nanotubes, fullerenes, molecules and organic nanostructures. Synthesis methods of nanostructures: electric arc, pulsed laser deposition, chemical vapor deposition (CVD); thermal CVD, catalytic CVD, micro wave CVD (MWCVD), plasma enhanced CVD (PECVD), spray pyrolysis. Physical and opto-electronic properties; characterization techniques. Applications: carbon nanotube and graphene based devices, bio-sensors, bio-inspired nanostructures, molecular motors, fuel cells and solar cells.

Topics Covered

Fundamentals of quantum mechanics: effective-mass Schrodinger Equation, matrix representation, Greenis function: Fundamentals of nonequilibrium statistical mechanics: scattering and relaxation. Carrier transport: density of states, current, tunneling and transmission probabilities, introduction to transport in the collective picture. Basic principles of a few effective devices: resonant tunnel diode, super lattice, quantum wire and dot.

Topics Covered

Introduction to N port network for lossless Junctions . Resonant circuits and different types of resonators. Modern microwave transmission lines and microwave integrated circuits (MICs); TEM, quasi TEM and non TEM type MIC lines, microstrip lines. Microwave passive devices: directional couplers, hybrid junction / magic T, Wilkinson power divider, microstrip line filters, isolators, phase shifters, attenuators. Microwave amplifiers and oscillators.

Topics Covered

Generalized approach to field theory: introduction to reaction concept, wave propagation through isotropic, anisotropic and gyrotropic media. Scattering of EM Waves. Microwave antennas-theory and design. Advanced topics in EM theory.