Download Resistance is the opposition that a substance offers to the flow of

Resistance is the opposition that a substance offers to the flow of electric current.
It is
represented by the uppercase letter R. The standard unit of resistance is the ohm, sometimes
written out as a word, and sometimes symbolized by the uppercase Greek letter omega:
When an electric current of one ampere passes through a component across which a potential
difference (voltage) of one volt exists, then the resistance of that component is one ohm. (For
more discussion of the relationship among current, resistance and voltage, see Ohm's law.)
In general, when the applied voltage is held constant, the current in a direct-current (DC)
electrical circuit is inversely proportional to the resistance. If the resistance is doubled, the
current is cut in half; if the resistance is halved, the current is doubled. This rule also holds
true for most low-frequency alternating-current (AC) systems, such as household utility
circuits. In some AC circuits, especially at high frequencies, the situation is more complex
because some components in these systems can store and release energy, as well as
dissipating or converting it.
The electrical resistance per unit length, area, or volume of a substance is known as
resistivity. Resistivity figures are often specified for copper and aluminum wire, in ohms per
kilometer.
Opposition to AC, but not to DC, is a property known as reactance. In an AC circuit, the
resistance and reactance combine vectorially to yield impedance.
Resistance contrasts with conductance, which is a measure of the ease with which electrical
current flows through a substance.
What is transformer? Definition &
Working Principle of Transformer
Definition of Transformer
Electrical power transformer is a static device which transforms electrical energy from one
circuit to another without any direct electrical connection and with the help of mutual
induction between two windings. It transforms power from one circuit to another without
changing
its
frequency
but
may
be
in
different
voltage
level.
This is a very short and simple definition of transformer, as we will go through this portion
of tutorial related to electrical power transformer, we will understand more clearly and deeply
"what is transformer ?" and basic theory of transformer.
Working Principle of Transformer
The working principle of transformer is very simple. It depends upon Faraday's law of
electromagnetic induction. Actually, mutual induction between two or more winding is
responsible for transformation action in an electrical transformer.
Faraday's Laws of Electromagnetic Induction
According to these Faraday's laws,
"Rate of change of flux linkage with respect to time is directly proportional to the induced
EMF in a conductor or coil".
Basic Theory of Transformer
Say you have one winding which is supplied by an alternating electrical source. The
alternating current through the winding produces a continually changing flux or alternating
flux that surrounds the winding. If any other winding is brought nearer to the previous one,
obviously some portion of this flux will link with the second. As this flux is continually
changing in its amplitude and direction, there must be a change in flux linkage in the second
winding or coil. According to Faraday's law of electromagnetic induction, there must be an
EMF induced in the second. If the circuit of the later winding is closed, there must be an
current flowing through it. This is the simplest form of electrical power transformer and this
is the most basic of working principle of transformer.
For better understanding, we are trying to repeat the above explanation in a more brief way
here. Whenever we apply alternating current to an electric coil, there will be an alternating
flux surrounding that coil. Now if we bring another coil near the first one, there will be an
alternating flux linkage with that second coil. As the flux is alternating, there will be
obviously a rate of change in flux linkage with respect to time in the second coil. Naturally
emf will be induced in it as per Faraday's law of electromagnetic induction. This is the most
basic concept of the theory of transformer.
The winding which takes electrical power from the source, is generally known as primary
winding of transformer. Here in our above example it is first winding.
The winding which gives the desired
output voltage due to mutual induction in the transformer, is commonly known as secondary
winding of transformer. Here in our example it is second winding.
The above mentioned form of transformer is theoretically possible but not practically,
because in open air very tiny portion of the flux of the first winding will link with second; so
the current that flows through the closed circuit of later, will be so small in amount that it will
be difficult to measure.
The rate of change of flux linkage depends upon the amount of linked flux with the second
winding. So, it is desired to be linked to almost all flux of primary winding to the secondary
winding. This is effectively and efficiently done by placing one low reluctance path common
to both of the winding. This low reluctance path is core of transformer, through which
maximum number of flux produced by the primary is passed through and linked with the
secondary winding. This is the most basic theory of transformer.
Main Constructional Parts of Transformer
The three main parts of a transformer are,
1. Primary Winding of transformer - which produces magnetic flux when it is
connected to electrical source.
2. Magnetic Core of transformer - the magnetic flux produced by the primary
winding, that will pass through this low reluctance path linked with secondary
winding and create a closed magnetic circuit.
3. Secondary Winding of transformer - the flux, produced by primary winding, passes
through the core, will link with the secondary winding. This winding also wounds on
the same core and gives the desired output of the transformer.
Power Plants & Types of Power Plant
Under Electrical Power Generation
What is Power Plant? Types of Power Station • Thermal • Nuclear • Hydro-Electric Types of
Power Generation
What is Power Plant?
A power plant or a power generating station, is basically an industrial location that is
utilized for the generation and distribution of electric power in mass scale, usually in the
order of several 1000 Watts. These are generally located at the sub-urban regions or several
kilometers away from the cities or the load centers, because of its requisites like huge land
and water demand, along with several operating constraints like the waste disposal etc. For
this reason, a power generating station has to not only take care of efficient generation but
also the fact that the power is transmitted efficiently over the entire distance. And that’s why,
the transformer switch yard to regulate transmission voltage also becomes an integral part of
the power plant.
At the center of it, however, nearly all power generating stations has an A.C. generator or an
alternator, which is basically a rotating machine that is equipped to convert energy from the
mechanical domain (rotating turbine) into electrical domain by creating relative motion
between a magnetic field and the conductors. The energy source harnessed to turn the
generator shaft varies widely, and is chiefly dependent on the type of fuel used.
Types of Power Station
A power plant can be of several types depending mainly on the type of fuel used. Since for
the purpose of bulk power generation, only thermal, nuclear and hydro power comes handy,
therefore a power generating station can be broadly classified in the 3 above mentioned types.
Let us have a look in these types of power stations in details.
Thermal Power Station
A thermal power station or a coal fired thermal power plant is by far, the most conventional
method of generating electric power with reasonably high efficiency. It uses coal as the
primary fuel to boil the water available to superheated steam for driving the steam turbine.
The steam turbine is then mechanically coupled to an alternator rotor, the rotation of which
results in the generation of electric power. Generally in India, bituminous coal or brown coal
are used as fuel of boiler which has volatile content ranging from 8 to 33 % and ash content 5
to 16 %. To enhance the thermal efficiency of the plant, the coal is used in the boiler in its
pulverized form.
In coal fired thermal power plant, steam is obtained in very high pressure inside the steam
boiler by burning the pulverized coal. This steam is then super heated in the super heater to
extreme high temperature. This super heated steam is then allowed to enter into the turbine,
as the turbine blades are rotated by the pressure of the steam. The turbine is mechanically
coupled with alternator in a way that its rotor will rotate with the rotation of turbine blades.
After entering into the turbine, the steam pressure suddenly falls leading to corresponding
increase in the steam volume. After having imparted energy into the turbine rotors, the steam
is made to pass out of the turbine blades into the steam condenser of turbine. In the
condenser, cold water at ambient temperature is circulated with the help of pump which leads
to the condensation of the low pressure wet steam. Then this condensed water is further
supplied to low pressure water heater where the low pressure steam increases the temperature
of this feed water, it is again heated in high pressure. This outlines the basic working
methodology of a thermal power plant.
Nuclear Power Station
The nuclear power generating stations are similar to the thermal stations in more ways than
one. How ever, the exception here is that, radioactive elements like Uranium and thorium are
used as the primary fuel in place of coal. Also in a Nuclear station the furnace and the boiler
are replaced by the nuclear reactor and the heat exchanger tubes.
For the process of nuclear power generation, the radioactive fuels are made to undergo fission
reaction within the nuclear reactors. The fission reaction, propagates like a controlled chain
reaction and is accompanied by unprecedented amount of energy produced, which is
manifested in the form of heat. This heat is then transferred to the water present in the heat
exchanger tubes. As a result, super heated steam at very high temperature is produced.
Once the process of steam formation is accomplished, the remaining process is exactly
similar to a thermal power plant, as this steam will further drive the turbine blades to generate
electricity.
Hydro-Electric Power Station
In Hydro-electric plants the energy of the falling water is utilized to drive the turbine which
in turn runs the generator to produce electricity. Rain falling upon the earth’s surface has
potential energy relative to the oceans towards which it flows. This energy is converted to
shaft work where the water falls through an appreciable vertical distance. The hydraulic
power is therefore a naturally available renewable energy given by the eqn:
P =gρ QH
Where g = acceleration due to gravity = 9.81 m/sec 2
ρ = density of water = 1000 kg/m 3
H = height of fall of water.
This power is utilized for rotating the alternator shaft, to convert it to equivalent electrical
energy.
An important point to be noted is that, the hydro-electric plants are of much lower capacity
compared to their thermal or nuclear counterpart. For this reason hydro plants are generally
used in scheduling with thermal stations, to serve the load during peak hours. They in a way
assist the thermal or the nuclear plant to deliver power efficiently during periods of peak
hours.
Types of Power Generation
As mentioned above, depending on the type of fuel used, the power generating stations as
well as the types of power generation are classified. Therefore the 3 major classifications for
power production in reasonably large scale are :1) Thermal power generation.
2) Nuclear power generation.
3) Hydro-electric power generation.
Apart from these major types of power generations, we can resort to small scale generation
techniques as well, to serve the discrete demands. These are often referred to as the
alternative methods of power generation and can be classified as :1) Solar power generation. (making use of the available solar energy)
2) Geo-thermal power generation. (Energy available in the Earth’s crust)
3) Tidal power generation.
These alternative sources of generation has been given due importance in the last few decades
owing to the depleting amount of the natural fuels available to us. In the centuries to come, a
stage might be reached when several countries across the globe would run out of their entire
reserve for fossil fuels. The only way forward would then lie in the mercy of these alternative
sources of energy which might play an instrumental role in shaping the energy supplies of the
future. For this reason these might rightfully be referred as the energy of the future.
Alternator Synchronous Generator |
Definition and Types of Alternator
Under Electrical Generator
Definition of Alternator • History • Application • Types
Definition of Alternator
The definition of alternator is hidden in the name of this machine itself. An alternator is
such a machine which produces alternation electricity. It is a kind of generators which
converts mechanical energy into alternating electrical energy. It is also known as
synchronous generator.
History of Alternator
Michael Faraday and Hippolyte Pixii gave the very first concept of alternator. Michael
Faraday designed a rotating rectangular turn of conductor inside a magnetic field to produce
alternating current in the external static circuit. After that in the year of 1886 J.E.H. Gordon,
designed and produced first prototype of useful model. After that Lord Kelvin and Sebastian
Ferranti designed a model of 100 to 300 Hz synchronous generator. Nikola Tesla in 1891,
designed a commercially useful 15 KHz generator. After this year, poly phase alternators
were come into picture which can deliver currents of multiple phases.
Use of Alternator
The power for electrical system of modern vehicles produces from alternator. In previous
days, DC generators or dynamos were used for this purpose but after development of
alternator, the dc dynamos are replaced by more robust and light weight alternator. Although
the electrical system of motor vehicles generally requires direct current but still an alternator
along with diode rectifier instead of a DC generator is better choice as the complicated
commutation is absent here. This special type of generator which is used in vehicle is known
as automotive alternator.
Another use of alternator is in diesel electric locomotive. Actually the engine of this
locomotive is nothing but an alternator driven by diesel engine. The alternating current
produced by this generator is converted to DC by integrated silicon diode rectifiers to feed all
the dc traction motors. And these dc traction motors drive the wheel of the locomotive.
This machine is also used in marine similar to diesel electric locomotive. The synchronous
generator used in marine is specially designed with appropriate adaptations to the salt-water
environment. The typical output level of marine alternator is about 12 or 24 volt. In large
marine, more than one units are used to provide large power. In this marine system the power
produced by alternator is first rectified then used for charging the engine starter battery and
auxiliary supply battery of marine.
Types of Alternator
Alternators or synchronous generators can be classified in may ways depending upon their
application and design. According to application these machines are classified as1.
2.
3.
4.
5.
Automotive type - used in modern automobile.
Diesel electric locomotive type - used in diesel electric multiple unit.
Marine type - used in marine.
Brush less type - used in electrical power generation plant as main source of power.
Radio alternators - used for low brand radio frequency transmission.
These ac generators can be divided in many ways but we will discuss now two main types of
alternator categorized according to their design. These are1. Salient pole type It is used as low and medium speed alternator. It has a large number
of projecting poles having their cores bolted or dovetailed onto a heavy magnetic
wheel of cast iron or steel of good magnetic quality. Such generators are characterized
by their large diameters and short axial lengths. These generator are look like big
wheel. These are mainly used for low speed turbine such as in hydral power plant.
2. Smooth cylindrical type It is used for steam turbine driven alternator. The rotor of this
generator rotates in very high speed. The rotor consists of a smooth solid forged steel
cylinder having a number of slots milled out at intervals along the outer periphery for
accommodation of field coils. These rotors are designed mostly for 2 pole or 4 pole
turbo generator running at 36000 rpm or 1800 rpm respectively.
3.Electrical Motor | Types Classification
and History of Motor
Under Electrical Motor
Electrical Motor Classification or Types of Motor History of Motor
4. Electrical Motor
The motor or an electrical motor is a device that has brought about one of the
biggest advancements in the fields of engineering and technology ever since the
invention of electricity. A motor is nothing but an electro-mechanical device that
converts electrical energy to mechanical energy. Its because of motors, life is what it
is today in the 21st century. Without motor we had still been living in Sir Thomas
Edison’s Era where the only purpose of electricity would have been to glow bulbs.
There are different types of motor have been developed for different specific
purposes.
In simple words we can say a device that produces rotational force is a motor. The
very basic principal of functioning of an electrical motor lies on the fact that force is
experienced in the direction perpendicular to magnetic field and the current, when
field and current are made to interact with each other. Ever since the invention of
motors, a lot of advancements has taken place in this field of engineering and it has
become a subject of extreme importance for modern engineers. This particular
webpage takes into consideration, the above mentioned fact and provides a detailed
description on all major electrical motors and motoring parts being used in the present
era.
5. Classification or Types of Motor
The primary classification of motor or types of motor can be tabulated as shown,
6. History of Motor
In the year 1821 British scientist Michael Faraday explained the conversion of
electrical energy into mechanical energy by placing a current carrying conductor in a
magnetic field which resulted in the rotation of the conductor due to torque produced
by the mutual action of electrical current and field. Based on his principal the most
primitive of machines a D.C.(direct current) machine was designed by another British
scientist William Sturgeon in the year 1832. But his model was overly expensive and
wasn’t used for any practical purpose. Later in the year 1886 the first electrical motor
was invented by scientist Frank Julian Sprague. That was capable of rotating at a
constant speed under a varied range of load, and thus derived motoring action.
INDEX DC Motor Synchronous Motor 3 Phase Induction Motor 1 Phase Induction
Motor Special Types of Motor Among the four basic classification of motors
mentioned above the DC motor as the name suggests, is the only one that is driven by
direct current. It’s the most primitive version of the electric motor where rotating
torque is produced due to flow of current through the conductor inside a magnetic
field.
Rest all are A.C. electrical motors, and are driven by alternating current, for e.g. the
synchronous motor, which always runs at synchronous speed. Here the rotor is an
electro - magnet which is magnetically locked with stator rotating magnetic field and
rotates with it. The speed of these machines are varied by varying the frequency (f)
and number of poles (P), as Ns = 120 f/P.
In another type of AC motor where rotating magnetic field cuts the rotor conductors,
hence circulating current induced in these short circuited rotor conductors. Due to
interaction of the magnetic field and these circulating currents the rotor starts rotates
and continues its rotation. This is induction motor which is also known as
asynchronous motor runs at a speed lesser than synchronous speed, and the rotating
torque, and speed is governed by varying the slip which gives the difference between
synchronous speed Ns , and rotor speed speed Nr,
It runs governing the principal of EMF induction due to varying flux density, hence
the name induction machine comes. Single phase induction motor like a 3 phase, runs
by the principal of emf induction due to flux, but the only difference is, it runs on
single phase supply and its starting methods are governed by two well established
theories, namely the Double Revolving field theory and the Cross field theory.
Apart from the four basic types of motor mentioned above, there are several types Of
special electrical motors like Linear Induction motor(LIM),Stepper motor, Servo
motor etc with special features that has been developed according to the needs of the
industry or for a particular gadget like the use of hysteresis motor in hand watches
because of its compactness.