Alternator Synchronous Generator Definition of Alternator

Alternator Synchronous Generator

Definition of Alternator

The definition of alternator is hidden in the name of this machine itself. An alternator is such a machine which converts mechanical energy from a prime mover to AC electric power at specific voltage and current. 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 came 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 as-

1.   Automotive type - used in modern automobile.

2.   Diesel electric locomotive type - used in diesel electric multiple unit.

3.   Marine type - used in marine.

4.   Brush less type - used in electrical power generation plant as main source of power.

5.   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 are-

1.   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 hydel 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.

 

 

 

Induction Motor

 

Induction Motor

One of the most common electrical motor used in most applications which is known as induction motor. This motor is also called as asynchronous motor because it runs at a speed less than its synchronous speed. Here we need to define what is synchronous speed. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it depends upon the frequency and number poles of the machine. An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with fluxcurrent in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed. There are basically two types of induction motor that depend upon the input supply - single phase induction motor andthree phase induction motor. Single phase induction motor is not a self starting motor which we will discuss later and three phase induction motoris a self-starting motor.

Working Principle of Induction Motor

We need to give double excitation to make a machine to rotate. For example if we consider a DC motor, we will give one supply to the stator and another to the rotor through brush arrangement. But in induction motor we give only one supply, so it is really interesting to know that how it works. It is very simple, from the name itself we can understand that induction process is involved. Actually when we are giving the supply to the stator winding, flux will generate in the coil due to flow of  current in the coil. Now the rotor winding is arranged in such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut the coil in the rotor and since the rotor coils are short circuited, according to Faraday's law of electromagnetic induction, current will start flowing in the coil of the rotor. When the current will flow, another flux will get generated in the rotor. Now there will be two flux, one is stator flux and another is rotor flux and the rotor flux will be lagging w.r.t to the stator flux. Due to this, the rotor will feel a torque which will make the rotor to rotate in the direction of rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and the speed can be controlled by varying the input supply. This is the working principle of an induction motor of either type – single and three phase. .

Types Induction Motor

1.   Single Phase Induction Motor
       

1.   Split phase induction motor

2.   Capacitor start induction motor

3.   Capacitor start capacitor run induction motor

4.   Shaded pole induction motor

2.   

 

1.   Three Phase Induction Motor

1.   Squirrel cage induction motor

2.    Slip ring induction motor

2.   We had mentioned above that single phase induction motor is not a self starting and three phase induction motor is self starting. So what is self starting? When the machine starts running automatically without any external force to the machine, then it is called as self starting. For example we see that when we put on the switch the fan starts to rotate automatically, so it is self starting. Point to be noted that fan used in home appliances is single phase induction motor which is inherently not self starting. How? Question arises How it works? We will discuss it now. 

3.   Why is Three Phase Induction Motor Self Starting?

In three phase system, there are three single phase line with 120° phase difference. So the rotating magnetic field is having the same phase difference which will make the rotor to move. If we consider three phases a, b and c, when phase a is magnetized, the rotor will move towards the phase a winding a, in the next moment phase b will get magnetized and it will attract the rotor and then phase c. So the rotor will continue to rotate.

 

 

 

Electrical Motor

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.

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

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.

 

 

 

पूर्ण चार्ज बैट्री की पहचान

पूर्ण चार्ज बैट्री की पहचान -
वोल्टेज द्वारा - जब बैट्री पूर्ण चार्ज हो जाती है तो इसकी टर्मिनल वोल्टेज 2.5 वोल्ट हो जाती है ।

प्लेटों के रंग द्वारा - जब बैट्री पूर्ण चार्ज हो जाती है तो +ve प्लेट का रंग सफ़ेद से भूरा चॉकलेटी हो जाता है तथा -ve प्लेट का रंग सफ़ेद से सलेटी हो जाता है ।

गैस के निकलने से - जब बैट्री पूर्ण चार्ज हो जाती है तो +ve प्लेट से आक्सीजन गैस निकलती है तथा -ve प्लेट से हाइड्रोजन गैस निकलती है ।

इलैक्ट्रोलाइट के विशिष्ट गुरुत्व द्वारा - जब बैट्री पूर्ण चार्ज हो जाती है तो इलेक्ट्रोलाइट का विशिष्ट गुरुत्व 1.18 से बढ़ कर 1.21 हो जाता है । बैट्री का विशिष्ट गुरुत्व हाइड्रोमीटर द्वारा नापा जाता है ।

बैट्री की चार्जिंग अवस्था ज्ञात करने के लिए प्रयोग किये जाने वले उपकरण -

1 hydrometer
2 high rate discharge cell tester

A.C के लाभ -

A.C के लाभ -

1. AC को 400 kV तक ट्रांसमिट किया जा सकता है ।2. ट्रांसफार्मर का प्रयोग करके वोल्टेज को आवश्यकता अनुसार कम या अधिक किया जा सकता है ।3. AC बहुफेज होने के कारण अत्यधिक लाभकारी है ।4. किफायती है । कम खर्च पर अधिक लाभ प्रदान करने वाली है ।5. AC बहु फेज़ मोटरें सेल्फ स्टार्ट होती है ।

A.C की हानियां -

1. AC का बैटरी चार्जिंग में इस्तेमाल नहीं जो सकता ।2. AC सिंगल फेज मोटरें सेल्फ स्टार्ट नहीं होती ।3. AC सप्लाई में लीकेज का खतरा अधिक रहता है ।4. ए.सी धरा में कम्पन्न होता है । बहुत से उपकरणों में कम्पन्न के कारण इसका इस्तेमाल नहीं हो सकता ।5. ए.सी. धरा से एलेक्ट्रोप्लेटिंग नहीं की जा सकती ।6. ए सी में मोटरों की स्पीड को आसानी से कंट्रोल नहीं किया जा सकता ।

D.C के लाभ -

1. DC में फ्रीक्वेंसी नहीं होती ।2. डी सी में मोटरों की स्पीड को आसानी से कंट्रोल किया जा सकता है ।3. DC का प्रयोग बैटरी चार्जिंग के लिए किया जा सकता है ।4. DC का प्रयोग इलेक्ट्रोप्लेटिंग के लिए किया जाता है ।

D.C की हानियां -1. डी सी सप्लाई बहुत महगी पड़ती है ।

2. DC जनरेटर की आउटपुट कम होती है ।3. DC में ट्रांसफार्मर का प्रयोग नहीं किया जा सकता है ।4. डी.सी धरा 650 वाल्ट से अधिक पैदा नहीं की जा सकती ।

सैल - सैल एक ऐसा यन्त्र है जिसे रासायनिक ऊर्जा से विधुत ऊर्जा प्राप्त होती है

सैल - सैल एक ऐसा यन्त्र है जिसे रासायनिक ऊर्जा से विधुत ऊर्जा प्राप्त होती है सेलों के समूह को बैट्री कहते है ।

सैल मुखयतः 2 प्रकारबके होते है -
1 Primary cell 
2 Secondary cell

बैट्री - दो या दो से अधिक सैलों को श्रेणी में जोड़ना बैट्री कहलाती है । इसमें emf अधिक रहती है ।

प्राइमरी सेल - इस श्रेणी में वे सेल आते है जिन्हें रासायनिक क्रिया द्वारा विधुत ऊर्जा उत्पन्न करने के लिए कुछ रासायनिक प्रदार्थ डाले जाते है तथा सेल के डिस्चार्ज होने पर सेल को दोबारा चार्ज नहीं कर सकते अर्थात सेल को डिस्चार्ज होने पर फिर इस्तेमाल नहीं कर सकते । सवल की आयु सेल में प्रयोग किये गए प्रदार्थ पर निर्भर करती है । प्राइमरी सेल के प्रकार -

1 ड्राई या शुष्क सेल 2 साधारण वोल्टाइक सेल3 मरकरी सेल4 डेनियल सेल5 लैकलांची सेल 6 सिल्वर आक्साइड सेल 

सैकेण्डरी सेल - इस श्रेणी में वे सैल आते है जिन्हें बाहरी स्त्रोत द्वारा चार्ज किया जा सकता है । यह सेल विधुत ऊर्जा को रासायनिक ऊर्जा में एकत्रित करते है और बाद में आवश्यकता पड़ने पर विधुत ऊर्जा के लिए इस्तेमाल किया जाता है । इस सेल को डिस्चार्ज होने के बाद दोबारा चार्ज करके इस्तेमाल किया जा सकता है । सैकेण्डरी सेल के प्रकार -
1 लेड एसिड सेल
2 निकिल कैडमियम सेल
3 निकिल आयरन सेल

इलेक्ट्रोलाइट

इलेक्ट्रोलाइट - इलेक्ट्रोलाइट एक तरल चालक का घोल है तथा रासायनिक प्रतिक्रियाओं से गुजरता है ।

विधुत धरा का रासायनिक प्रभाव - विधुत धारा इलेक्ट्रोलाइट से गुजारने पर जो प्रभाव इलेक्ट्रोलाइट पर पड़ता है उसे हम विधुत धरा का रासायनिक प्रभाव कहते है । इस रासायनिक प्रभाव से हम अपने दैनिक जीवन में बहुत से अत्यंत आवश्यक कार्य सिद्ध कर पाते है जैसे कि इलेक्ट्रो प्लेटिंग और इलेक्ट्रो टाइपिंग इत्यादि ।

इलैक्ट्रोलीसिस / अपघटन - अगर विधुत धारा को इलैक्ट्रोलाइट में से गुजरा जाये तो इलैक्ट्रोलाइट अपने अव्यवों में बंट जाता है । इलैक्ट्रोलाइट का इस तरह अवयवों में बंटने की क्रिया को electrolysis या अपघटन कहा जाता है ।
अपघटन के उपयोग -

1 विधुत लेपन - यह एक ऐसी प्रक्रिया है जिसमे एक धातु की परत दूसरी धातु पर चढ़ाई जाती है ।2 इलेक्ट्रो टाइपिंग - इस विधि में पेपर पर धातु की छपाई की जाती है ।3 इलेक्ट्रो मेटालर्जी - इस विधि में धातुओं को उनके योगिक में से निकल कर शुद्ध किया जाता है ।4 सकेंड्री बैटरी बनाने में ।