NETWORK THEOREMS SHORT QUESTIONS AND ANSWERS

1) Explain the applications of current sources

These are the following applications of current sources:

1) For regulating current related power supplies current sources can be used

2) Definite network study procedures can be used

3) Transistors that shows a stable current behavior uses current sources.

2) Explain the ideal voltage source and the ideal current source

Irrespective of the amount of current drawn one that maintains a steady voltage source is called the ideal voltage source. Some terminals with resistance will be provided with a similar current without any change and this is called as ideal current source.

3) Reason for network theorems and methods to solve electrical circuits.

The reason is:

1) The logical solution becomes very easy during their use

2) A difficult circuit can be reduced to an easy circuit during their use.

4) Explain the correct use of the term circuit and network

An arbitrary arrangement of passive works is called the term team network and the presence of active sources and current flow implies the circuit.

5) Explain the behavior of circuit under highest power transfer conditions

At the load terminals, the load voltage is one-half of the open circuited voltage

One of the total power leaks in the internal resistance of the source and therefore the effectiveness is only 50%.

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6) Explain bilateral circuit element

Current passing through the bilateral circuit element will pass through both the ends of the circuit.

7) Difference between a mesh and a loop

A closed path of a network is called a loop. A majority elementary outline of a loop that cannot be divided into other loops is called a mesh.

8) On what basis reference node is chosen in nodal analysis

It is a random choice to make the reference node in nodal analysis, but the frequent choice of reference node is easier as majority of components are linked to it.

9) Define linear circuit elementary

When the circuit follows ohm’s law, the circuit elements are linear, so the repetition of voltage doubles the current flowing through them.

10) Calculate mesh currents

Branch currents are easy for calculation as they flow in branches. Mesh currents are very imaginary and cannot be calculated.

11) Where do we use star/delta and delta/star transformation

A neither series nor parallel kind of resistances are found in some networks for instance a three terminal network, delta network/ star network. Through there are series and parallel circuit, it is not easy to make simpler network series.

12) Basis of nodal analysis

Nodal analysis is based on Kirchoff’s current law but mesh analysis is based on Kirchoff’s voltage law.

13) Why not to operate power system under maximum power conditions

There is a great voltage fall in lines because the effectiveness is low(50%) under the conditions of maximum power transfer. Because of maximum power the goal has elevated efficiency. Therefore extreme power conditions are not suitable.

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ALSO READ : MAGNETIC CIRCUITS-QUESTION-ANSWERS

Importance of Grounding Electric Current

There are some amazing discoveries in the electric field, and there has been an important lesson behind the significance of grounding electric currents. There are various benefits of electricity to the people and it is still required in our everyday life. But you need to ground your electrical system

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or else it will be risky.

The supply of power in an electrical circuit is called an active wire. Whereas, a neutral wire carries that current back. An extra ‘grounding wire’ can be connected to the outlet and other electric devices and also safely linked to the ground at the breaker box. For safety during short circuit, the ground wire is used for returning the current safely to the ground. Thereby preventing fatal accidents.

THE IMPORTANCE OF GROUNDING ELECTRICITY

Here are 5 the reason why grounding electric currents is essential

1. PROTECTION AGAINST ELECTRIC CURRENT

One of the most essential factors for grounding electric currents is that it defends your equipment, your home and everyone from fatal accidents. Due to lightning strike or power discharge or some other reasons, dangerous high voltage electricity is produced in your system. This extra electricity goes to the ground if the system is grounded or else it blow out everything connected to the system.

2. ALLOWS DIRECT CURRENT

You will be benefited because of the direct power flow wherever you need through the electric system if your system is grounded properly.

3. STABILISES VOLTAGE LEVELS

For easier and right amount of power distribution you need to ground your electric system therefore preventing circuits from getting overloaded.

4. EARTH IS THE BEST CONDUCTOR

Earth is a great conductor of electricity and extra electricity will carry the path of least resistance. You are just channelizing the extra power to be earthed rather than passing into you.

5. AVOID FATAL INJURIES

Without proper earthing you are risking yourself and the entire system thereby leading to huge loss.

It’s clear that grounding electric perform is a smart move, but how does it work?

Most of the homes have their electrical system grounded through a metallic rod inserted into the ground or a metallic tube into the house from an underground water-supply program. A copper conductor is connected to the rod or pipe to a set of devices for earthing. Using electrical cable covered in metal makes it as a ground conductor between wall outlets and service panel.

In electric devices that use plastic-sheathed wire, an extra wire is used for earthing. As electricity is always looking for the quickest direction returning to the ground, if there is a problem where the neutral wire is damaged or split, the grounding wire provides an immediate direction to the floor. Through this immediate actual connection, the earthing provides a direction of least level of resistance, avoiding a person from becoming the quickest medium, and suffering a serious electric shock.

HOW CAN YOU TELL IF YOUR CURRENT IS GROUNDED?

You can usually tell whether your electric device is grounded by checking your power plugs. If they are compatible with plugs of three prongs, your system should posses three cables, one of which is a grounding wire.

Similarly, an equipment designed to be earthed is wired and has a three-wire cable and a three-pronged plug. The third cable and prong provide the earthing link between the metallic structure of the equipment and the grounding of the cabling system.

When dealing with equipment, ensure that you:

  1. Do not touch a device if its cord’s insulating material has started to erode away where it enters into the metal covering. In this situation, contact between the metal conductor and the frame could make the whole equipment live with electricity, and touching the device will make you as a conductor of the current.
  2. Inspect, maintain, and arrange maintenance of wires where they get into a steel pipe, a covering, or where in-wall wires get into an electrical box.

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MAGNETIC CIRCUITS-QUESTION-ANSWERS

1) Does a magnetic circuit consume energy?

In order for setting up a magnetic flux, energy is required but no energy is required to continue it. The magnetic field holds the supplied energy and this energy is returned to the circuit when the magnetic field collapses, but finally the energy is consumed in the electric circuit.

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2) What is the reason for the leakage in magnetic circuit?

A large amount of flux is confined to the intended path in a practical magnetic circuit unfortunately there is a small amount of flux leak in the surrounding air. Leakage flux or stray flux is harmful to the electric machine.

3) There are lots of electric insulators but no magnetic insulators, Explain

As flux can be set up in the air, there is no need for magnetic insulators. There are lots of electric insulators such as air ( no current can pass through it).

4) What is the material to be selected for making electromagnets?

Energy required for demagnetizing a material of 1 m cube, varies for different materials:

1) For Soft iron: energy: 10 J/m cube

2) For Alnico, energy: 50,000 J/m cube

Electromagnets have the characteristic material to initiate small amount of energy for demagnetization.

5) Give Reason, air flux is termed as useful flux.

Air gaps are required for the rotation of rotor in case of an electric machine and for the usage in moving-coil instruments. It is a link between stationary and moving parts therefore it is a useful flux.

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6) Permeability of a material.

It is a measure of how well magnetic lines focus inside its boundaries under the magnetizing force influence. Large permeability and flux density is available in ferromagnetic material and it is greater than in a non magnetic material with similar magnetic force.

7) Difference between magnetic and electric circuit.

There is no leakage of energy in magnetic circuit and for the creation of flux, energy is required. The energy consumption is done as long as the current flows in the electric circuit and the leaked energy is given out as heat.

In a magnetic circuit, reluctance of a magnetic circuit is not stable and it depends on the flux density (B). In an electric circuit, the resistance is almost constant and its because of resistivity varies with temperature.

8) Cause of Hysteresis

1) Power loss and increase in temperature of the machine.

2) Reduces the machine competency

9) Curie Temperature

Magnetic material’s temperature increased above a certain value, curie temperature. There is a loss of magnetism in the material above this temperature and becomes paramagnetic until its temperature is lowered below this point. Curie temperature for iron: 700 degree c.

10) Hysteresis means?

It is used to describe the behavior of uncertain values with respect to the temperature changes. There are many physical phenomena associated with Hysteresis. If exact values of H are known still we cannot guess the value of B unless we know the increasing and decreasing value of both B and H.

11) Importance of magnetic circuit

It is used by transformers, generators and motors.

Loud speakers, telephone receivers, watt-hour meters, telephone ciruit also depend on magnetic flux.

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Electrical Power transformer, definitions and its types

A transformer, a static machine used in converting power from one circuit to another without any need to change in frequency. This defines the work of a transformer. It is a static device where there is no rotation or moving part. Transformer works on ac supply. The basic principle of a transformer is mutual induction.

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History of Transformer

If you are interested in knowing about the history of transformer we have to rewind back to 1880s. In 1830 property of induction, the working principle of transformer was found. Later the transformer design was enhanced leading to more performance and smaller size. Progressively the huge capacity of transformers with several KVA range, MVA was introduced. During 1950, 400KV electric power transformer was found in high voltage electrical power system. At the start of 1970s, a 1100 MVA unit rating was generated followed by 800KV and even higher KV class transformers were built during the year of 1980.

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Applications of Power Transformer

Electrical energy generation at lower voltage level is very much affordable. Actually the receiving end receives the transmitted low voltage power. But if this is transmitted then it will lead to greater line current that will lead to more losses. And if you increase the voltage power, there is a reduction in the power of the current which causes reduction in ohmic or I2R losses in the system, decrease in capital cost due to reduction of the cross sectional area of the conductor and it also enhances the voltage regulation the system.

Therefore low-level power must be stepped up for effective electric power transmission. Step up transformer completed this work at the receiving end of the electrical power system. And now the Step down transformer comes into the picture because the high power voltage cannot be directly distributed to the customers. This shows the importance of transformer in electrical power transmission.

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The reason behind the usage of the two winding transformers are usually where the ratio of high voltage and low voltage is greater than 2. In such cases one can use an auto transformer where the ratio between the higher and the lower voltage is less than 2.

Comparatively, a single unit three phase transformer is affordable when compared to a bank of three single phase transformers. The only draw back is a single three phase transformer is difficult to maintain because even if one of the phases breaks down then you need to discard the entire device.

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Types of Transformer

Transformers can be classified in different ways, based upon upon their objective, use, construction

etc. The types of transformer are as follows,

1) Step Up Transformer and Step Down Transformer – This is actually used for stepping up and down the voltage levels of power in transmission and distribution power system network.

2) Three Phase Transformer and Single Phase Transformer – Three phase is mostly used in three phase power system as it is affordable than later. But when size comes into the picture, it is more suitable to use a bank of three single phase transformer as it is convenient to transport than one single phase transformer unit.

3) Electrical Power Transformer, Distribution Transformer and Instrument Transformer – For stepping up or down the voltage levels in the transmission network, power transformers are used. It works mainly during high or peak loads and has the highest possible performance at or near full load. Distribution transformer steps down the voltage for distribution to domestic or commercial customers. It has good voltage reputation and works all the day with the highest possible performance at 50% of full load. Instrument transformers include C.T and P.T are mainly for reducing high voltages and current to lesser values which can be read by conventional instruments.

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4)Two Winding Transformer and Auto Transformer –

When the ratio between high voltage and low voltage is greater than 2 then you can use two winding transformer. Auto transformer is used when the ratio is lesser than 2 and it is easily affordable.

5) Outdoor Transformer and Indoor Transformer – Transformers used for setting up at the outdoors is called Outdoor Transformer and the one used for indoor purpose is called indoor transformer.

6) Oil Cooled and Dry Type Transformer – Oil is used as a medium for cooling in the oil cooled transformer and air is the medium used for cooling in the dry cooled transformer.

7) Core type, Shell type and Berry type transformer – Core type transformer consists of two vertical legs or divisions with two horizontal sections known as yoke. Core is rectangle-shaped common magnetic circuit. The limb contains cylindrical coils (HV and LV).

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Shell type transformer: It contains a central limb and two external limbs. The central limb contains both HV, LV coils. It contains a double magnetic circuit.

Berry type transformer: It contains wheel like spokes at its core. Metal sheet tanks are welded and are used for sheltering this type of transformer with transformer oil filled inside.

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Electrical Engineering interview questions: part 1

1. Why star delta beginner is recommended with induction motor?

An induction motor is referred with star delta starter for the following reason:

• The power is saved because of voltage drops as the starting current is reduced 3-4 times.

• The motor is saved because of the star delta circuit comes along with circuit during start of motor and thus voltage is reduced by three units.

• Damage of motor winding is prevented because of the increase in starting torque.

2. Comparison between generator and alternator

Generator and alternator are two devices, which converts mechanical power into electrical power. The basic principle followed by both of them is electro-magnetic induction, the only distinction is their construction. A fixed magnetic field and a rotating conductor is available on the generator that comes on the armature connected with slip rings and brushes colliding against each other, hence it transforms the emf induced into the dc current for external load whereas an alternator has a fixed armature and a rotating magnetic field for higher voltages but for reduced voltage outcome both rotating armature and stationary magnetic field is used.

3. Benefits of AC systems over DC systems

Due to the following factors, AC systems are recommended over DC systems:

a. Maintenance is easy and can change the voltage of AC power for transmission and distribution.

b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission

c. AC is produced from the power stations so AC is better for usage than DC instead of converting it.

d. If a big fault occurs in a network, it is simpler to get rid of in an AC system, as the sine wave current will automatically become zero at some point making the current interruption easier.

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4. How can you compare power power engineering with electrical engineering?

Power engineering is a sub department of electrical engineering. It deals with generation, transmission and distribution of power in electric form. Design of all power accessories also comes under power engineering. Power engineers focus on maintenance and design of the power grid i.e. called on grid systems and they might perform on off grid systems that are disconnected to the program.

5. What are the various kind of wires used for transmission?

Cables, which are used for power transmission, can be classified in three forms:

• Low-tension wires, which can transfer voltage up to 1000 v.

• High-tension wires can transmit voltage up to 23000 v.

• Super tension wires can transmit voltage 66 kV to 132 kV.

6. Why back emf used for a dc motor? emphasize its importance.

The emf which is induced developed when the rotating conductors of the armature between the magnetic poles, in a DC motor, cut the magnetic flux, is a contradiction to the current flowing through the conductor, when the armature is rotating, is known as back emf. Its value depends upon the rotational speed of the armature conductors. The initial value of back emf is zero.

7. What is slip in an induction motor?

Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually indicated as a percentage of synchronous speed (Ns) and showed by the symbol ‘S’.

8. Explain the application of storage battery power.

Storage batteries power are used for various purposes, some of the uses are mentioned below:

• For the working of protective devices and for emergency lighting at power generating stations and substations.

• For ignition and automobile lighting, airplanes etc.

• For steam lighting and diesel engines.

• As a supply source of power in telephone exchange, labs and broad casting channels.

• Many medical centers, banks, non-urban areas where power supplies are not available, emergency lighting can be the solution.

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Electrical Engineering: Understanding It’s Scope, Salary and Other Aspects

Let’s begin by seeing what is electrical engineering. Later on, we will take a look at the various aspects related to this field.

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What is electrical engineering?

Electrical engineering is the branch that is related to the technology of electricity. Electrical engineers work on a wide variety of components, systems and devices. Ranging from tiny microchips to large scale power station generators.

Guess what?

Electrical engineering happens to be one of the oldest and core branches of engineering. A number of relatively newer engineering branches have emerged from this very branch. E.g. Power engineering, Electronics and communication engineering, Control engineering etc.

Simply speaking, Electrical Engineering happens to be a branch of Engineering that deals with ideas identified with electricity and electric hardware e.g. generation, transmission and utilization of electricity, electromagnetism, machinery like generator, transformers, motors, AC Current, DC Current, circuit systems, control systems and so forth.

Scope of electrical engineering:

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Electrical engineering is a standout amongst the most popular engineering branch in India and has been one of the main driving thrusts of high innovation in the course of recent decades. Electrical engineering is quickly growing not just inside core zones like wireless communications and mobile technologies additionally in different areas, e.g. biotechnology, nanotechnology and biomedical engineering.

Taking into consideration how popular this branch is, getting admission into prestigious institutions like the IITs and NITs is enormously competitive. The same applies in case of job hunting as well.

Electrical Engineering is a core branch of Engineering. An evergreen branch. Qualified Electrical Engineers are dependably sought after, since most Industries utilize electricity and electric machines. Engineers are needed by industries for operational, support and manufacturing purposes.

Considering how popular and differing electrical engineering is, regardless of the possibility that recession influences one segment, electrical engineers can look for jobs in other sectors. Renewable resources, energy, environmental conservation, power conservation and sustainability areas will see a considerable measure of jobs in the coming couple of years for electrical engineers because of issues, e.g. climate change and global warming. Likewise, with mobile technologies and communications as yet going solid, ECE students have a steady future right now.

Job opportunities in this sector:

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In case of graduates, job openings are available in the Government sector and in addition private sector. Discussing Government sector jobs the major recruiters happen to be – Indian Railways, BHEL, Indian Armed Forces, Thermal Power Plants, ONGC, Power Stations, State Electricity Boards, PWD Department and so on. In the previously mentioned Government organizations and divisions, one might discover job posts like-

  • Assistant electrical engineers.

  • Electrical engineers.

Most of the private assembling units and industries makes utilization of electric power and machines. Consequently, it is safe to mention that indirectly or in a direct way, an extensive extent of ventures recruit Electrical Engineers!

Graduates may discover below mentioned job posts in different industries, apart from the two mentioned above:

  • Automation engineer

  • Plant designing and planning officer

  • Purchase and Quality Control Executive

Graduates may likewise take up a job as a teacher in the wake of finishing the M.Tech. program. They may likewise go for PhD program and venture into the Research and Development division.

Salary prospects:

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Starting salary relies on various factors, like, nature of college, marks secured in exams and so forth and may fluctuate between 2-5 lakh rupees each year.

Electrical engineering offers a promising career ahead for skilled professionals with loads of job opportunities and good remuneration. As seen above, even recession wise, this is a safer field to pursue.

So, if you hold a liking towards this core branch of engineering, then this ones definitely for you!