विधुत सुरक्षा उपकरण

जो एसैसरीज जो विधुत परिपथ को शार्ट सर्किट, ओवर लोड तथा अर्थ लीकेज की स्थिति पर सुरक्षा प्रदान करती है वह सुरक्षात्मक एसैसरीज कहलाती है । जैसे कि M.C.B, E.L.C.B, R.C.C.B, तथा फ्यूज इत्यादि ।

M.C.B( Mini circuit breaker )- मिनी सर्किट ब्रेकर -आधुनिक समय में फ्यूज का स्थान एम.सी.बी ने ले लिया है । एम सी बी का प्रयोग काफी अधिक बढ़ गया है क्योंकि -

एम.सी.बी इसकी स्थापना अत्यधिक सरल तथा सुन्दर होती है ।एम.सी.बी अधिक भरोसेमन्द है ।एम.सी.बी शोर रहित और धुंआ रहित है ।एम.सी.बी को देखभाल की आवश्यकता नहीं होती है ।एम.सी.बी में करंट लगने का डर नहीं होता । दोष पड़ने पर संचालित करना बेहद सरल है । दोष दूर करने पर केवल स्विच की नॉब को ऊपर उठाना होता है ।तुरन्त ऑपरेट हो जाता है । ये ओवरलोड करंट के चौथे भाग पर ही परिपथ काट देता है ।एम.सी.बी की स्थिति देखकर ही दोष वाले सर्किट का पता लगाया जा सकता है ।

E.L.C.B( Earth leakage circuit breaker) - ई.एल.सी.बी. का पूरा नाम अर्थ लीकेज सर्किट ब्रेकर है

ई.एल.सी.बी अर्थ लीकेज की स्थित पर सर्किट को सप्लाई से अलग करके न केवल मनुष्य को करंट लगने से बचाता बल्कि सर्किट को सुरक्षा भी प्रदान करता है । यह अत्यंत लाभकारी है ।
R.C.C.B - Residual cutrent circuit breaker( रैजीडीयूल करंट सर्किट ब्रेकर - आर सी सी बी ) - R.C.C.B की कार्य क्षमता अत्यधिक कुशल होती है । यह 30 mA से 300 mA करंट में संचालित होने की क्षमता रखता है । यह बहुत जल्दी ऑप्रेट हो उठता है । यह महंगा भी होता है ।
Fuse in hindi - फ्यूज - फ्यूज विधुत परिपथ का वह कमजोर भाग होता है जो परिपथ में अत्यधिक करंट बहने पर पिघल जाता है जिससे कि परिपथ सप्लाई से सुरक्षित ढंग से अलग हो जाता है । वोल्टेज के आधार पर फ्यूज के 2 प्रकार होते है 1. लो वोल्टेज फ्यूज 2. हाई वोल्टेज फ्यूज । बनावट के आधार पर भी फ्यूज के दो प्रकार जोते है -1. Semi enclosed fuse - इसमें किट कैट आता है 2. Totally closed fuse जैसे कि -
एच.आर.सी कारट्रीज फ्यूज ।
कारट्रीज फ्यूज ।
लिक्विड फ्यूज ।

Electrical Laws

Electrical Laws

Ohm’s law

Ohm’s law states that the voltage v across a resistor is directly proportional to the current i flowing through the resistor.

Mathematically form

v ∝ i

Georg Simon Ohm defined the constant of proportionality for a resistor to be the resistance, R. (The resistance is a material property which can change if the internal or external conditions of the element are altered, e.g., if there are changes in the temperature.)

v =Ri

Kirchhoff’s Laws

Branch:A branch represents a single element such as a voltage source or a resistor.

Node:A node is the point of connection between two or more branches.

Loop:A loop is any closed path in a circuit.

Theorem of network topology:A network with b branches, n nodes, and l independent loops will satisfy the fundamental theorem of network topology:

b = l+n-1

Series:Two or more elements are in series if they exclusively share a single node and consequently carry the same current.

Parallel:Two or more elements are in parallel if they are connected to the same two nodes and consequently have the same voltage across them.

There are two Kirchhoff’s Laws

Kirchhoff’s current law (KCL)

Kirchhoff’s voltage law (KVL)

Kirchhoff’s current law (KCL)

Kirchhoff’s current law (KCL) states that the algebraic sum of currents entering a node (or a closed boundary) is zero.

OR

The sum of the currents entering a node is equal to the sum of the currents leaving the node.

Kirchhoff’s current law is based on the law of conservation of charge, which requires that the algebraic sum of charges within a system cannot change.

Mathematically, KCL implies that

where N is the number of branches connected to the node and is the nth current entering (or leaving) the node.

Kirchhoff’s voltage law (KVL)

Kirchhoff’s voltage law (KVL) states that the algebraic sum of all voltages around a closed path (or loop) is zero.

OR

Sum of voltages drops = Sum of voltages rise

Kirchhoff’s second law is based on the principle of conservation of energy:

Expressed mathematically, KVL states that

where M is the number of voltages in the loop (or the number of branches in the loop) and is the mth voltage.

Power,Energy Power

Power,Energy

Power

Power is the time rate of expending or absorbing energy, measured in watts (W).

We write this relationship as

where p is power in watts (W), w is energy in joules (J), and t is time in seconds (s).

And also

The power p in above equation is a time-varying quantity and is called the instantaneous power.Thus, the power absorbed or supplied by an element is the product of the voltage across the element and the current through it.

If the power has a sign, power is being delivered to or absorbed by the element. If, on the other hand, the power has a sign, power is being supplied by the element.

Passive sign convention

Passive sign convention is satisfied when the current enters through the positive terminal of an element and p = +vi . If the current enters through the negative terminal, p = -vi .

Energy

Energy is the capacity to do work, measured in joules (J).

The electric power utility companies measure energy in watt-hours (Wh), where

1 Wh = 3,600 J

Power Supplies Cell Component

Power Supplies

Cell Component

Circuit Symbol

Function of Component 

Supplies electrical energy. The larger terminal (on the left) is positive (+). A single cell is often called a battery, but strictly a battery is two or more cells joined together. 

Battery Component

Circuit Symbol

Function of Component 

, Supplies electrical energy. A battery is more than one cell. The larger terminal (on the left) is positive (+). 

DC supply Component

Circuit Symbol

Function of Component 

, Supplies electrical energy. DC = Direct Current, always flowing in one direction. 

AC supply Component

Circuit Symbol

Function of Component 

, Supplies electrical energy. AC = Alternating Current, continually changing direction. 

Fuse Component

Circuit Symbol

Function of Component 

, A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.. 

Transformer Component

Circuit Symbol

Function of Component 

, Two coils of wire linked by an iron core. Transformers are used to step up (increase) and step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is no electrical connection between the coils. 

Earth (Ground) Component

Circuit Symbol

Function of Component 

, A connection to earth. For many electronic circuits this is the 0V (zero volts) of the power supply, but for mains electricity and some radio circuits it really means the earth. It is also known as ground. 

Ideal independent source

Circuit Symbol

Function of Component 

An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit elements.

Ideal dependent (or controlled) source

Circuit Symbol

Function of Component 

An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current.

There are four type of dependent source

A voltage-controlled voltage source (VCVS).

A current-controlled voltage source (CCVS).

A voltage-controlled current source (VCCS).

A current-controlled current source (CCCS).

Charge,Current,Voltage Charge

Charge,Current,Voltage

Charge

Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C).

The following points should be noted about electric charge:

The coulomb is a large unit for charges. In 1 C of charge, there are (1/1.602×10^˗19 = 6.24×10¹⁸) electrons. Thus realistic or laboratory values of charges are on the order of pC, nC, or μC.

According to experimental observations, the only charges that occur in nature are integral multiples of the electronic charge е = ˗ 1.602×10^˗19

The law of conservation of chargestates that charge can neither be created nor destroyed, only transferred. Thus the algebraic sum of the electric charges in a system does not change.

Electric current

Electric current is the time rate of change of charge, measured in amperes (A).

Mathematically, the relationship between current i, charge q, and time t is

where current is measured in amperes (A), and (1 ampere = 1 coulomb/second )

There are two types of current

direct current(dc)

A direct current (dc) is a current that remains constant with time.

By convention the symbol I is used to represent such a constant current. Waveform of direct current is shown below

alternating current(ac)

An alternating current (ac) is a current that varies sinusoidally with time.

A time-varying current is represented by the symbol i.A common form of time-varying current is the sinusoidal current or alternating current (ac).Waveform is shown below

Voltage

Voltage (or potential difference) is the energy required to move a unit charge through an element, measured in volts (V).

The voltage V_ab between two points a and b in an electric circuit is the energy (or work) needed to move a unit charge from a to b; mathematically,

where w is energy in joules (J) and q is charge in coulombs (C). The voltage v_ab or simply v measured in Volt.

MotorElectrical

Motor

Electrical

                                                                                             

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.

Classification or Types of Motor
The primary classification of motor or types of motor can be tabulated as shown below,

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 DC (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 AC 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 N_s = 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 N_s, and rotor speed speed N_r,

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 particular gadget like the use of hysteresis motor  in hand watches because of its compactness.

Electrical Power Transformer Definition of Transformer

Electrical Power Transformer

Definition of Transformer

A transformer is a static machine used for transforming power from one circuit to another without changing frequency. This is a very basic definition of transformer. Since there is no rotating or moving part so transformer is a static device. Transformer operates on ac supply. Transformer works on the principle of mutual induction. 

History of Transformer

If we want to know the history of transformer we have go back long in the 1880s.  Around 50 years before that in 1830 property of induction which is the working principle of transformer was discovered. Later the transformer design was improved resulting in more efficiency and lesser size. Gradually the large capacity of transformers in the range of several KVA, MVA came into existence. In the year 1950, 400KV electrical power transformer was introduced in high voltage electrical power system. In the early 1970s, unit rating as large as 1100 MVA was produced and 800KV and even higher KV class transformers were manufactured in year of 1980.

Use of Power Transformer

Generation of electrical power in low voltage level is very much cost effective. Theoretically, this low voltage level power can be transmitted to the receiving end. This low voltage power if transmitted results in greater line current which indeed causes more line lossesBut if the voltage level of a power is increased, the current of the power is reduced which causes reduction in ohmic or I²R losses in the system, reduction in cross sectional area of the conductor i.e. reduction in capital cost of the system and it also improves the voltage regulation of the system. Because of these, low level power must be stepped up for efficient electrical power transmission. This is done by step up transformer at the sending side of the power system network. As this high voltage power may not be distributed to the consumers directly, this must be stepped down to the desired level at the receiving end with the help of step down transformer. Electrical power transformer thus plays a vital role in power transmission.

Two winding transformers are generally used where ratio of high voltage and low voltage is greater than 2. It is cost effective to use auto transformer where the ratio between high voltage and low voltage is less than 2. Again a single unit three phase transformer is more cost effective than a bank of three single phase transformers unit in a three phase system. But a single three phase transformer unit is a bit difficult to transport and have to be removed from service entirely if one of the phase winding breaks down. 

Types of Transformer

Transformers can be categorized in different ways, depending upon their purpose, use, construction etc. The types of transformer are as follows,

1.   Step Up Transformer & Step Down Transformer - Generally used for stepping up and down the voltage level of power in transmission and distribution power system network.

2.   Three Phase Transformer & Single Phase Transformer - Former is generally used in three phase power system as it is cost effective than later. But when size matters, it is preferable to use a bank of three single phase transformer as it is easier to transport than one single three phase transformer unit.

3.   

 Electrical Power Transformer, Distribution Transformer & Instrument Transformer - Power transformers are generally used in transmission network for stepping up or down the voltage level.  It operates mainly during high or peak loads and has maximum efficiency at or near full load. Distribution transformer steps down the voltage for distribution purpose to domestic or commercial users. It has good voltage regulation and operates 24 hrs a day with maximum efficiency at 50% of full load.  Instrument transformers include C.T & P.T which are used to reduce high voltages and current to lesser values which can be measured by conventional instruments.

4.   Two Winding Transformer & Auto Transformer - Former is generally used where ratio between high voltage and low voltage is greater than 2. It is cost effective to use later where the ratio between high voltage and low voltage is less than 2.

5.   Outdoor Transformer & Indoor Transformer - Transformers that are designed for installing at outdoor are outdoor transformers and transformers designed for installing at indoor are indoor transformers.

6.   Oil Cooled & Dry Type Transformer - In oil cooled transformer the cooling medium is transformer oil whereas the dry type transformer is air cooled.

7.   Core type, Shell type & Berry type transformer - In core type transformer it has two vertical legs or limbs with two horizontal sections named yoke. Core is rectangular in shape with a common magnetic circuit. Cylindrical coils (HV & LV) are placed on both the limbs. Shell type transformer: It has a central limb and two outer limbs. Both HV, LV coils are placed on the central limb. Double magnetic circuit is present. Berry type transformer: The core looks like spokes of wheels. Tightly fitted metal sheet tanks are used for housing this type of transformer with transformer oil filled inside.

 

 

 

Control Engineering

Control Engineering

Control system engineering is the branch of engineering which deals with the principles of control theory to design a system which gives desired behavior in a controlled manner. Hence, this is interdisciplinary. Control systemengineers analyze, design, and optimize complex systems which consist of highly integrated coordination of mechanical, electrical, chemical, metallurgical, electronic or pneumatic elements. Thus control engineering deals with diverse range of dynamic systems which include human and technological interfacing.
Control system engineering focuses on analysis and design of systems to improve the speed of response, accuracy and stability of system. The two methods of control system include classical methods and modern methods. The mathematical model of system is set up as first step followed by analysis, designing and testing. Necessary conditions for the stability are checked and finally optimization follows.

In classical method, mathematical modeling is usually done in time domain, frequency domain or complex s domain. Step response of a system is mathematically modeled in time domain differential analysis to find its settling time, % overshoot etc. Laplace transforms are most commonly used in frequency domain to find the open loop gain, phase margin, band width etc of system. Concept of transfer function, sampling of data, poles and zeros, system delays all comes under the classical control engineering stream.
Modern control engineering deals with Multiple Input Multiple Output (MIMO) systems, State space approach, Eigen values and vectors etc. Instead of transforming complex ordinary differential equations, modern approach converts higher order equations to first order differential equations and solved by vector method.
Automatic control systems are most commonly used as it does not involve manual control. The controlled variable is measured and compared with a specified value to obtain the desired result. As a result of automated systems for control purposes, the cost of energy or power as well as the cost of process will be reduced increasing its quality and productivity.

Historical Review of Control Engineering

The application of Automatic control system is believed to be in use even from the ancient civilizations. Several types of water clock were designed and implemented to measure the time accurately from the third century BC, by Greeks and Arabs. But the first automatic system is considered as the Watts Fly ball Governor in 1788, which started the industrial revolution. The mathematical modeling of Governor is analyzed by Maxwell in 1868. In 19^th century, Leonhard Euler, Pierre Simon Laplace and Joseph Fourier developed different methods for mathematical modeling. The second system is considered as Al Butz’s Damper Flapper - thermostat in 1885. He started the company now named as Honeywell.

The beginning of 20^th century is known as the golden age of control engineering. During this time classical control methods were developed at the Bell Laboratory by Hendrik Wade Bode and Harry Nyquist. Automatic controllers for steering ships were developed by Minorsky, Russian American Mathematician. He also introduced the concept of Integral and Derivative Control in 1920s. Meanwhile the concept of stability was put forward by Nyquist and followed by Evans. The transforms were applied in control system by Oliver Heaviside. Modern Control Methods were developed after 1950s by Rudolf Kalman, to overcome the limitation of classical Methods. PLC’s were introduced in 1975.

Types of Control Engineering

Control engineering has its own categorization depending on the different methodologies used, which are as follows.

1.   Classical Control Engineering : The systems are usually represented by using ordinary differential equations. In classical control engineering, these equations are transformed and analyzed in transformed domain. Laplace transform, Fourier transform and z transform are examples. This method is commonly used in Single Input Single Output systems.

2.   Modern Control Engineering : In modern control engineering higher order differential equations are converted to first order differential equations. These equations are solved very similar to vector method. By doing so, many complications dealt in solving higher order differential equations are solved. These are applied in Multiple Input Multiple Output systems where analysis in frequency domain is not possible. Nonlinearities with multiple variables are solved by modern methodology. State space vectors, Eigen values and Eigen Vectors longs to this category. State Variables describe the input, output and system variables.

3.   Robust Control Engineering : In robust control methodology, the changes in performance of system with change in parameters are measured for optimization. This aids in widening the stability and performance, also in finding alternate solutions. Hence in robust control the environment, internal in accuracies, noises and disturbances are considered to reduce the fault in system.

4.   Optimal Control Engineering : In optimal control engineering, the problem is formulated as mathematical model of process, physical constraints and performance constraints, to minimize the cost function. Thus optimal control engineering is the most feasible solution for designing a system with minimum cost.

5.   Adaptive Control Engineering : In adaptive control engineering, the controllers employed are adaptive controllers in which parameters are made adaptive by some mechanism. The block diagram given below shows an adaptive control system.

6.   

In this kind of controllers an additional loop for parameter adjustment is present in addition to the normal feedback of process.

7.   Nonlinear Control Engineering : Non linear control engineering focuses on the non linearity’s which cannot be represented by using linear ordinary differential equations. This system will exhibit multiple isolated equilibrium points, limit cycles, bifurcations with finite escape time. The main limitation is that it requires laborious mathematical analysis. In this analysis the system is divided into linear part and non linear part.

8.   Game Theory : In game theory, each system will have to reduce its cost function against the disturbances / noises. Hence it is a study of conflict and co operation. The disturbances will try to maximize the cost function. This theory is related to robust and optimal control engineering.

 

 

 

Power Plants and Types What is Power Plant?

Power Plants and Types

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 AC 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 tosuperheated 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 heatedsteam 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.

 

 

 

What is black Body?

What is black Body?

Black body is any inanimate body that always absorbs all radiation completely falling on it and radiates same amount of energy it receives at a constant temperature.
There is no real existence of black body. But approximation leads the idea to a perfect black body in practice. As per this approximation, the black body is a hollow insulated enclosure containing a small hole in one wall. 

The incident energy goes inside the black body and gets reflected again and again against the inner wall of that black body. The black body acts as a perfect absorber. Whether this cavity is heated, all energy will be emitted through this hole. 
Black body radiation curved is shown below.

Theoretically, the total energy radiated from a black body at a particular temperature is fixed but during radiation of the black body, this total energy is not of a single wavelength. Rather, the total energy radiated from this black body is of various wavelengths zero to infinity. From wavelength 780 nm to 380 nm the radiated energy is within visual sensation. Here it is to be noted that amount of radiation energy per wavelength is not same for all wavelength rather it varies with wavelength. For every temperature, there is a particular wavelength for which the radiated energy per wavelength becomes maximum.

That means at a particular temperature, peak spectral radiant exitance is at a particular wavelength. This wavelength (wavelength for peak energy radiation) depends on the temperature of this black body. Decreasing of temperature the peak of the curve shifts rightward as per the figure is given above. That implies in the graph, the peak of the each curve appears at a shorter wavelength as the temperature increases. As the energy radiation occurs at all wavelengths the curve comes very closer to the horizontal axis but never touches the axis even when the wavelength is infinitely long. The area enclosed by the curve of any temperature indicates the total energy radiated by the black body at this particular temperature. If the temperature varies, the total amount of energy radiated also varies. If we connect peak of all curves we will get a parabola as shown in the figure above. 
Above graph shows the spectral exitance versus wavelength. Spectral Exitance means power per unit area per unit wavelength. As per radiation physics, Stefan-Boltzmann law is applicable here. This law states that the total power radiated per unit surface area of a black body across all wavelengths is directly proportional to the fourth power of the black body temperature.

Here, M_e  is the radiated power per unit area and T is the temperature in Kelvin and also σ is the Stefan-Boltzmann constant. This power emits from this hole of the black body.
As per Plank’s Law

Where, P_e is the radiated power per unit area in the normal direction per unit solid angle per unit frequency by this black body at temperature T.
h is the Planck constant;
k is the Boltzmann constant;
c is the speed of light in a vacuum;
T is the absolute temperature of the body.
υ is the frequency of the electromagnetic radiation;
Following the classical theory, Wien proved that at this peak of the wavelength the absolute temperature gives a constant value, viz.,

This above expression is called Wien’s displacement Law. This Law describes the hyperbola passing through the peak points of the curves shown in the above graph.

Practical Blackbody

But the blackbodies are covering the range of temperature from about -20 to 3000 degree Celsius (253 K to 3273 K) in the practical cases. And accordingly the peak wavelengths are from 885 nm to 11500 nm. 885 nm is in the visible range whereas 11500 nm is infrared ray (IR). The temperatures of the black bodies can be determined in a freezing point black body calibration source.
Generally, a black-body appears black at room temperature. Again most of the energy it radiates is in the form of an infra-red ray. A black body’s infrared ray radiation cannot be perceived by the human eyes as the human eyes never perceive color at very low light intensities. So a black body that is viewed in the dark at the lowest visible temperature i.e. just faintly, practically it appears grey. When we make the black body a little hotter, it appears dull red accordingly. Again black body’s temperature is increased further it eventually becomes bright blue-white.
The chromaticity diagram shows the color temperature of a blackbody.


This color bar given below, shows the color temperature of a black body.