Junction Breakdown

In reverse-biasing, a very small current flows due to the minority charge carriers. The current is termed leakage saturation current (Is).
If reverse voltage is further increased, a large current flows suddenly at a certain reverse-bias voltage. This mechanism of producing a large reverse current is called breakdown.
There are two breakdown mechanisms:
i. Zener breakdown
ii. Avalanche breakdown.
The main difference between the Zener breakdown and Avalanche breakdown are as follows:

1. Zener breakdown occurs due to a high electric field intensity across the junction.

          Avalanche breakdown occurs due to a collision of charge carriers with other atoms.

    

    2.   Zener breakdown occurs normally at a low-reverse voltage.

          Avalanche breakdown occurs at a high-reverse voltage.

    3.   Zener breakdown occurs in a heavily-doped diode.

          Avalanche breakdown occurs at a high-reverse voltage.

   4.    Zener breakdown voltage decrease with a rise of temperature.

         Avalanche breakdown voltage increase with an increase of temperature.

Principle of work of synchronous moto

Synchronous motor works on the principle of the magnetic locking. When two unlike poles are brought near each other, if the magnets are strong, there exists a tremendous force of attraction between those two poles. In such condition the two magnets are said to be magnetically locked.

       If now one of the two magnets is rotated, the other also rotates in the same direction, with the same speed due to the force of attraction i.e. due to magnetic locking condition. The principle is shown schematically in the Fig.1.

Fig.  1  Principle of magnetic locking

       So to have the magnetic locking condition, there must exist two unlike poles and magnetic axes of two must be brought very close to each other. Let us see the application of this principle in case of synchronous motor.

       Consider a three phase synchronous motor, whose stator is wound for 2 poles. The two magnetic fields are produced in the synchronous motor by exciting both the winding, stator and rotor with three phase a.c. supply and d.c. supply respectively. When three phase winding is excited by a three phase a.c. supply the the flux produced by the three phase winding is always of rotating type, which is already discussed in the previous post. Such a magnetic flux rotates in space at a speed called synchronous speed. This magnetic field is called rotating magnetic field. The rotating magnetic field creates the effect similar to the physical rotation of magnets in space with a synchronous speed. So stator of the synchronous motor produces one magnet which is as good as rotating in space with the synchronous speed. The synchronous speed of a stator rotating magnetic field depends on the supply frequency and the number of poles for which stator winding is wound. if the frequency of the a.c. supply is f Hz and stator is wound for P number of poles, then the speed of the rotating magnetic field is synchronous given by,

                            N_s  = 120f/P r.p.m.

       In this case, as stator is wound for say 2 poles, with 50 Hz supply, the speed of the rotating magnetic field will be 3000 r.p.m. This effect is similar to the physical rotation of two poles with a speed of N_s  r.p.m. For simplicity of understanding let us assume that the stator poles are N₁ and S₁ which are rotating at a speed of N_s. The direction of rotation of rotating magnetic field is say clockwise.

       When the field winding on rotor is excited by a d.c. supply, it also produces two poles, assuming rotor construction to be two pole, salient type. Let these poles be N₂and S₂. 

       Now one magnet is rotating at N_s having poles N₁ and S₁ while at start rotor is stationary i.e. second magnet is stationary having poles N₂ and S₂. If somehow the unlike poles N₁ and S₂ or S₁ and N₂ are brought near each other, the magnetic locking may get established between stator and rotor poles. As stator poles are rotating due to magnetic locking rotor will also rotate in the same direction as that of stator poles i.e. in the direction of rotating magnetic field, with the same speed i.e N_s. Hence synchronous motor rotates at one and only one speed i.e. synchronous speed. But this all depends on existence of magnetic locking between stator and rotor poles. Practically it is not possible for stator poles to pull the rotor poles from their stationary position into magnetic locking condition. hence synchronous motors are not self starting.

Power system protection

This portion of our website covers almost everything related to protection system in power system including standard lead and device numbers, mode of connections at terminal strips, color codes in multi-core cables, Dos and Don’ts in execution. It also covers principles of various power system protection relays and schemes including special power system protection schemes like differential relays, restricted earth fault protection, directional relays and distance relays etc. The details of transformer protection, generator protection, transmission line protection & protection of capacitor banks are also given. It covers almost everything about power system protection.

The switch gear testing, instrument transformers like current transformer testing voltage or potential transformer testing and associated protection relay are explained in detail. The close and trip, indication and alarm circuits different of Circuit breakers are also included and explain.

Objective of power system protection

The objective of power system protection is to isolate a faulty section of electrical power system from rest of the live system so that the rest portion can function satisfactorily without any severer damage due to fault current.

Actually circuit breaker isolates the faulty system from rest of the healthy system and this circuit breakers automatically open during fault condition due to its trip signal comes from protection relay. The main philosophy about protection is that no protection of power system can prevent the flow of fault current through the system, it only can prevent the continuation of flowing of fault current by quickly disconnect the short circuit path from the system. For satisfying this quick disconnection the protection relays should have following functional requirements.

ABCD Parameters of Transmission

A major section of power system engineering deals in the transmission of electrical power from one particular place (e g. Generating station) to another like substations or distribution units with maximum efficiency. So its of substantial importance for power system engineers to be thorough with its mathematical modeling. Thus the entire transmission system can be simplified to a two port network for the sake of easier calculations.

The circuit of a 2 port network is shown in the diagram below. As the name suggests, a 2 port network consists of an input port PQ and an output port RS. Each port has 2 terminals to connect itself to the external circuit. Thus it is essentially a 2 port or a 4 terminal circuit, having

Supply end voltage = VS

and Supply end current = IS

Given to the input port P Q.

And there is the Receiving end Voltage = VR

and Receiving end current = IR

Given to the output port R S.

As shown in the diagram below.

Now the ABCD parameters or the transmission line parameters provide the link between the supply and receiving end voltages and currents, considering the circuit elements to be linear in nature.
Thus the relation between the sending and receiving end specifications are given using ABCD parameters by the equations below.


VS = A VR + B IR ———————-(1)

IS = C VR + D IR ———————-(2)

Career for electrical and electronics engineers

Electrical and electronics engineering has a great scope in the world. As we know without electricity we can even imagine our life. Each and every steps of our life electricity play the important role.Some of the best job that the electrical and electronics engineers are:

• Aerospace Engineers
• Electronics Engineers
• Engineering Manager
• Marine Architect
• Mathematician
• Mechanical Engineer
• Mining and Geological Engineer
• Naval Architect-er

The useful skills that the electrical and electronics engineers :

• Accept the responsibility and face it and done it 
• Communicate orally 
• Identify, analyze, and solve the problems 
• Work without supervision 
• Interest in computing/technical design
• Practicality and creativity of electical system
• Work as a team member with coordination
•  Careful work and accuracy
• Diagnostic ability in field 
• Analytical skills of project
• Communication skills 
• Interest in electromagnetism equipment
• Interest in electronics, machines,
• Investigating, identifying skills
• Logical thinking
• Problem solving skills
• Work independently and in teams

Scope of electrical and electronics engineers

Scope

Electrical and Electronics engineers conduct mainly on research and
design, develop, test of the development of
electronic systems and the manufacture of electrical and
electronic equipment and devices. They are responsible for a
wide range of technologies. They design, develop, test,
and supervise the manufacture of electrical and electronic
equipment. Some of this equipment includes broadcast and communications systems; electric
motors, machinery controls, lighting, and wiring in buildings, automobiles, aircraft, and radar
and navigation systems; and power generating, controlling, and transmission devices used by
electric utilities. Many electrical and electronics engineers also work in areas closely related to
computers.

Preparation  

If your goal is to achieve a fulfilling career, building the groundwork will take some care. While
in school, keep your options as wide as possible -- the further you go, the narrower your focus
must become. While the decision to major and minor is an important step, your decision should
not be limited to an engineering curriculum or even to the classroom.

strip-chart recorder

Strip-chart Recorder

Strip-chart recorder is the graphic recorder which display and store a pen and ink record of the history of some physical event which records one or more variables with respect to time.Its is an X-t recorder.

It can perform the measurement as follows steps:

1. A long roll of graph paper moving vertically.
2. A system for driving the paper at some selected speed. A speed selector switch is generally provided chart speed of 1-100 mm/s are usually used.
3. A stylus for making marks on the moving graph paper. the stylus moves horizontally in proportional to the quantity being recorded.
4. A stylus driving system which moves the stylus in a nearly exact replica or analog of the quantity being recorded

A range selector s/w is used so that i/p to the recorder drive system is within the acceptable level.

X-Y Recorder

Best device t0 plot Relati0n of tw0 vAriaBle 

X-Y recorder is the best device to plot relation of two variable.It is an  instrument which gives a graphic record of the relationship between two variables. In strip chart recorder, self balancing potentiometer is used and these self balancing potentiometer is used and these self balancing potentiameter plot the emf as a function of time. In X-Y recorder, an emf is plotted as a function of another emf. This is done by having one self balancing potentiometer control the position of the roll while another self balancing potentiometer controls the position of recording pens. 

The marking mechanism in X-Y plotter may be

1.     Marking with ink filled stylus 
2.     Marking with heated stylus 
3.     Chopper bar 
4.     Electric stylus 
5.     Optical marking method

A signal enters each of the two channels. The signals are attenuated to the inherent full scale range of the recorder. The signal then passes to a balance circuit where it is compared with an internal reference voltage. The error signal (i.e the difference between the input signal voltage and the reference voltage ) is fed to a chopper which converts dc signal to an ac signal. The signal is then amplified in order to actuate a servo meter which is used to balance the system and hold it in balance as the value of quantity being recorded changes.

The action described above takes place in both axes simultaneously. And hence, we get record of two variable in same graph.

Factors affecting Corona

                               Factors Affecting Corona 

The phenomenon of corona is affected by the physical state of the atmosphere as well as by the conditions  of the line. The corona depends on the following factors:

1. Atmosphere:  As corona is formed due to ionization of air surrounding the conductors,therefore, it is affected by the physical state of atmosphere. In the stormy weather, the number of ions is more than normal and as such corona occurs at much less voltage as compared with fair weather.
2. Conductor size.  The corona effect depends upon the shape and conditions of the conductors. The rough and irregular surface will give rise to more corona because unevenness of the surface decrease the value of breakdown voltage. Thus a stranded conductor has irregular surface and hence gives rise to more corona that a solid conductor.  
3. Spacing between conductors. If the spacing between the conductors is made very large as compared to their diameters, there may not be any corona effect. It is because larger distance between conductors reduces the electrostatic stresses at the conductor surface, thus avoiding corona formation.
4. Line voltage. The line voltage greatly affects corona. If it is low, there is no change in the condition of air surrounding the conductors and hence no corona is formed. However, if the line voltage has such a value that electrostatic stresses developed at the conductor surface make the air around the conductor conducting, then corona is formed.

Report on solar power water pumping

           Report on solar power water pumping

                                                           

 The system consists of a photo-voltaic (PV) array, a permanent magnet (PM) DC motor and a helical rotor pump. The operation of the PV array is analyzed using PSPICE. The efficiency of the system is improved with a maximum power point tracker (MPPT) and a sun-tracker. Simulation and field test results are presented.

The main advantage is that the sunlight is intense, when the demand for irrigation is high. In addition to the solar energy available at the time of use so that the independent farmers or fuel supply of electrical cables. Solar pumps have the potential to revolutionize small-scale irrigation in developing countries in the near future. The technical feasibility of solar energy (photo-voltaic) established. The pumps were important limiting factor is the high cost and lack of familiarity with the technology they require a concerted effort in the training of technicians and large-scale introduction in a region with already adequate technical assistance . However, incentives and initiatives, the payments to be made by multinational companies / authorities of the scheme in rural areas for small-scale irrigation systems in remote rural areas where electrification is an expensive affair spread.  The system model is the introduction of solar water pumps and irrigation systems to help provide sustainable development for farmers in the United Nations or in rural areas electrified. Various agencies and financial institutions are to assist in the development of credit-control to target rural area without electricity.

In conclusion, photo-voltaic power for irrigation is cost competitive with traditional energy sources for small ,remote applications, if the total system design and utilization timing is carefully considered and organized to use the solar energy as efficiently as possible. In future, when the prices of fossil fuels rise and the economic advantages of mass production reduce the peak watt cost of the photo-voltaic cell, Pumping Water for Irrigation Using Solar Energy.

Electromagnetic current-meter

   Electromagnetic (e/m) current-meter is an electrical induction-measurement instrument, with no moving parts, mounted in a totally enclosed streamlined probe. The probe can be mounted on rods and held at various depths or suspended on a cable.

The e/m meter has the advantages of being smaller and having a wider measurement range than the propeller meters. It is particularly useful at very low velocities when propeller meters become erratic. Its sensitivity and lower vulnerability to fouling from weeds and debris make it attractive for use in heavily polluted or weedy streams.Each unit is provided with a surface control box with a digital display and dry-cell batteries. A set of stainless steel wading rods is also standard equipment. Latest models have built-in battery-charger circuits.It will be appreciated that since each river is unique, a careful assessment of its width, depth, likely flood velocities, cable-support facilities, availability of bridges, boats, etc. needs to be made before a discharge measurement programme can begin.The discharge at the chosen measuring point is best obtained by plotting each velocity observation on a cross section of the gauging site with an exaggerated vertical scale. Isovels (velocity profiles – contours of equal velocity) are then drawn and the included areas measured by a planimeter. Alternatively, the river may be subdivided vertically into sections and the mean velocity of each section applied to its area. In this method the cross-sectional area of any one section, where measurements, are taken should not exceed 10 per cent of the total cross-sectional area.

Power line communication

Power line communication (PLC) presents an interesting and economical solution for Automatic Meter Reading (AMR). If an AMR system via PLC is set in a power delivery system, a detection system for illegal electricity usage may be easily added in the existing PLC network. In the detection system, the second digitally energy meter chip is used and the value of energy is stored. The recorded energy is compared with the value at the main kilo Watt-hour meter. In the case of the difference between two recorded energy data, an error signal is generated and transmitted via PLC network. The detector and control system is proposed. The architecture of the system and their critical components are given. The measurement results are given.

The Pico-hydro power

                                     tHe PiCo HyDrO PoWeR

The Pico hydro is hydro power with a maximum electricaloutput of five kilowatts (5kW). Hydro power systems ofthis size benefit in terms of cost and simplicity from differentapproaches in the design, planning and installation than thosewhich are applied to larger hydro power. Recent innovationsin pico-hydro technology have made it an economic source ofpower even in some of the world’s poorest and mostinaccessible places. It is also a versatile power source. ACelectricity can be produced enabling standard electricalappliances to be used. Common examples of devices whichcan be powered by pico-hydro are light bulbs, radio andtelevision.

Wireless power transfer objective

Wireless Power transfer objective:

The objective of this paper is to give an idea of  wireless power transfer objective which is in developing stage and it can be a future existence. Due to the extinguishing energy resources, there is a serious search of alternative energy resources which are endless and Eco-friendly. The answer for this is wireless power transfer which came in 17^th century . It consists of microwaves for transmission of electromagnetic radiation, and for vibrating the objects resonance concept is used and solar cells for sun’s radiation in outer space. Research has been going in various countries to bring W P T into a practical environment.