Utilization of Electrical Energy List of contents

1 Illumination: 1.1 Nature of light, visibility spectrum curve of relative sensitivity of human eye and wave length of light 1.2 Definition: Luminous flux, solid angle, luminous intensity, illumination, luminous efficiency,

depreciation factor, coefficient of utilization, space to height ratio, reflection factor, glare, shadow, lux. 1.3 Laws of illumination – simple numericals 1.4 Different type of lamps, construction and working of incandescent and discharge lamps – their characteristics, fittings required for filament lamp, mercury vapour sodium lamp, fluorescent lamp, halogen lamp, neon lamp, compact filament lamp(CFL), LED Lamp, comparison of incandescent, fluorescent, CFL & LED 1.5 Calculation of number of light points for interior illumination, calculation ofillumination at different points, considerations involved in simple design problems. Illumination schemes; indoor and outdoor illumination levels 1.6 Main requirements of proper lighting; absence of glare, contrast and shadow 1.7 Awareness about time switches, street lighting, flood lighting, monument lighting and

decorative lighting, light characteristics etc. Multiple choice Questions

2 Electric Heating

• Advantages of electrical heating

• Heating methods:

• Resistance heating – direct and indirect resistance heating, electric ovens, their temperature range, properties of resistance heating elements, domestic water heaters and other heating appliances, thermostat control circuit

• Induction heating; principle of core type and coreless induction furnace, their construction and applications

• Electric arc heating; direct and indirect arc heating, construction, working and applications of arc furnace

• Dielectric heating, applications in various industrial fields

• Infra-red heating and its applications (construction and working of two appliances) Solar Heating

3 Electric Welding:

3.1 Advantages of electric welding

3.2 Welding methods

3.4 Principles of resistance welding, types – spot, projection, seam and butt welding, welding equipment

3.5 Principle of arc production, electric arc welding, characteristics of arc; carbon arc, metal arc, hydrogen

arc welding method

4 Electrolytic Processes:

4.1 Need of electro-deposition

4.2 Laws of electrolysis, process of electro-deposition - clearing, operation, deposition of metals,

polishing and buffing

4.3. Equipment and accessories for electroplating

4.5. Principle of galvanizing and its applications

5 Electrical Circuits used in Refrigeration, Air Conditioning and Water Coolers:

6 Electric Drives:

7 Electric traction

1 Illumination

1.1 Visibility spectrum curve of relative sensitivity of human eye and wave length of light Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light which is the visible spectrum that is visible to the human eye having

wavelengths are between 4 x 10-7 m(4,000 Å or 0.4 m m) to 7 x 10-7 m(7,000 Å or 0.7 m m). ( Å stands for 'angstrom' and is equal to 10-10 m.)

1.2 Various Terminology • Luminous flux (in lumens) is a measure of the total amount of light a lamp puts out. The

luminous intensity (in candelas) is a measure of how bright the beam in a particular direction

• The illumination (or illuminance) E of a surface is the luminous flux per unit area that reaches the surface:

• Solid angle: Plane angle is subtended at a point in a plane by two converging straight lines and its magnitude is given by Solid angle = 2

• Luminous efficiency : It is the ratio of luminous flux to power, measured in lumens per watt • Depreciation factor: It is reverse of the maintenance factor and is defined as the ratio of

the initial meter-candles to the ultimate maintained metre-candles on the working plane. • Coefficient of utilization It is defined as the ratio of total lumens reaching the working plane

to total lumens given out by the lamp • Space to height ratio Spacing Height Ratio is defined as the ratio of the distance between

adjacent luminaires (centre to centre), to their height above the working plane. • Reflection factor the ratio of reflected light to the incident light is called the reflection factor.

It‟s value always less than unity • Glare It is a visual sensation caused by excessive and uncontrolled brightness. Glare is

difficulty of seeing in the presence of bright light caused by a significant ratio of luminance • A shadow is a dark area where light from a light source is blocked by an opaque object. It

occupies all of the three-dimensional volume behind an object with light in front of it. • A shadow is a dark area where light from a light source is blocked by an opaque object. It

occupies all of the three-dimensional volume behind an object with light in front of it. • The lux (symbol: lx) is the SI derived unit of illuminance and luminous emittance,

measuring luminous flux per unit area. It is equal to one lumen per square metre.

(a) Law of inverse squares (b) lamberts cosine law

Law of inverse squares: Illuminance (E) at any point on a plane perpendicular to the line joining the point and source is inversely proportional to the square of the distance between the source

and plane. E = I / d2

Where, I is the luminous intensity in a given direction. the light source the

surface appears dimmer

Cosine Law of Illuminance: Illuminance at a point on a plane is proportional to the cosine of the

angle of light incident E= cosθ , Iθ is the luminous intensity of the source, Ɵ is the angle

2

between the normal to the plane, d is the distance to the illuminated point

1.4 Incandescent and discharge lamps

Incandescent lamp technology uses electric current to

• Heat a coiled tungsten filament to incandescence. • The glass envelope contains a mixture of nitrogen and a small amount of other inert gases

such as argon Discharge lamps produce light by passing an electric current through a gas that emits light when ionized by the current

• Discharge lamps: (a) Sodium vapour lamp (b) Mercury Vapour lamps

Fig. Incandescent lamp

1.5 Sodium vapour lamp • The lamp consists of a discharge tube having special composition of glass to withstand the

high temperature of the electric discharge • The lamp consists of a discharge tube having special composition of glass to withstand

the high temperature of the electric discharge

• The temperature inside the discharge tube rises and vaporizes sodium. • Sodium vapour has the highest theoretical luminous efficiency and

gives monochromatic orange-yellow light.

1.6 Mercury Vapour lamps

• It is similar to construction of the sodium vapour lamp. • The electric discharge first takes place through argon and this vaporizes

• The mercury drops inside the discharge tube. • The space between two bulbs is filled with an inert gas. • Mercury vapour lamps are used for lighting of secondary roads, car parking areas, parks

and gardens, factory sheds, etc.

1.7 Fluorescent lamp • A fluorescent lamp is a low weight mercury vapour lamp that uses fluorescence to deliver

visible light • An electric current in the gas energizes mercury vapor which delivers ultraviolet radiation

through discharge process and the ultraviolet radiation causes the phosphor coating of the lamp inner to radiate visible light

1.8 Halogen Lamps & Neon Lamps Unlike incandescent lamps, halogen lamps use a halogen gas fill (typically iodine or bromine), to

produced what is called a “halogen cycle” inside the lamp. In the halogen cycle, halogen gas combines with the tungsten that evaporates from the lamp.

• Halogen lamps are sometimes called “quartz” lamps because their higher temperature requires quartz envelopes instead of the softer glass used other incandescent lamps. A halogen lamp comes with a few modifications to eliminate this blackening problem of incandescent lamp

Neon Lamps is cold cathode lamp and consists of a gas bulb filled with a neon gas with a

small percentage of helium. It gives orange pink colored light. • The efficiency of neon lamp lies between 15-40 lumens/watt

• The power consumption is of the order of 5watts. Compact Filament Lamp (CFL) & LED Lamp

• CFLs produce light in the same manner as linear fluorescent lamps. Their tube diameter is usually 5/8 inch (T5) or smaller.

• CFL power ranges from 5 to 55 watts. • LEDs are solid-state semiconductor devices that convert electrical energy directly into

light • LEDs can be extremely small and durable; some LEDs can provide much longer lamp

life than other sources.

1.9 Comparisons

Tungsten Filament Lamp and LED

Tungsten Filament Lamp

• Voltage fluctuation has comparatively more effect on the light output.

• Luminous efficiency increases with the increase in the voltage of the lamp

• It gives light close to natural light. Therefore objects are properly seen

• high working temperature and heat radiations

• brightness is more

• initial cost per lamp is quite low.

LED

• Light Emitting Diode bulbs

• High Efficiency

• Life 50000 hours

• High cost

• 6-8 watts normally

• Small in size

Fluorescent Tubes

• Voltage fluctuation has comparatively low effect on light output

• Luminous efficiency increases with the increase in wattage and increase in length of tube.

• It does not give light close to natural light • low working temperature heat radiation is low. • Brightness is less. • initial cost per tube is more

1.10 Calculation of number of light points for interior illumination

The number of lamps required in a particular place can be designed by following three methods: 1 Watt per square meter: This is a rough method. Watts per square meter are calculated on the

basis of efficiency of lamp (lm/watt). 2. Inverse square law: This method is used in street light calculations. In this method law of illumination is used for this candle power of the 0lamps should be known. 3. Lumen per square meter method: This method is used for design of general lighting. In this method, lamp efficiency, Depreciation factor, utilization factor etc. are used.

1.11 Illumination schemes The interior lighting schemes may be classified as (i) direct lighting (ii) semi direct lighting (iii) semi-indirect lighting (iv) indirect lighting (i) Direct lighting: It is most commonly used type of lighting scheme. In this lighting scheme more than 90 % of total light flux Is made to fall directly on the working plane with the help of deep reflectors. it is most efficient but causes hard shadows and glare. It is mainly used for industrial and general outdoor lighting. (ii) Semi-direct lighting:

• In this lighting scheme 60-90 % if the total light flux is made to fall downwards directly with the help of semi-direct reflectors, remaining light is used to illuminate the ceiling and

walls. • Such a lighting system is best suited to rooms with high ceiling where a high level of

uniformly distributed illumination is desirable (iii) Semi-indirect lighting:

• In the lighting scheme 60-90 % of total light flux is thrown upwards to the ceiling for defuse reflection and the rest reaches the working plane directly except for some absorption.

• It is mainly used for indoor light decoration purposes. (iv) Indirect lighting:

• In this light scheme more than 90% if total light flux is thrown upwards to the ceiling for diffuse reflection by using inverted or bowl reflectors.

• In such a system the ceiling acts as the light source, and the glare it reduced to minimum

Main requirements of proper lighting: • Proper Illumination Level • Uniformity of illumination • Colour of light • Shadows: • Glare

1.12 Street lighting The main objectives of street lighting are

(i) To make the traffic and obstructions on the road clearly visible in order to promote

safety and convenience. (ii) To make the street more attractive.

(iii) To increase the community value of the street. • The principle employed for street lighting is different from that of interior lighting. There are

no walls and ceiling which reflect or diffuse light, hence only direct lighting scheme can be employed and hard shadows and high contrast cannot be avoided.

• Mercury vapour and sodium discharge lamps have been found to have certain particular advantages for street lighting purposes. The most important of these low power consumption for a given amount of light.

Flood lighting

• Flood light means flooding of large surfaces with light from powerful projectors.

• It is employed to serve one or more of the following purposes.

• Flood lighting it is necessary to concentrate the light from the light source into a narrow beam. The particular type of reflector and its housing used for concentrating the light into narrow beam is known as flood light projection.

Multiple Choice Questions

Q1 Carbon arc lamps are commonly used in (A) domestic lighting (B) street lighting (C) cinema projectors (D) photography.

Q2 Light waves travel with a velocity of (A) 3 x 10

10cm/s

(B) 3 x 1012

cm/s (C) 3 x 10

15 cm/s

(D) 3 x 1018

cm/s Q3 Candela is the unit of (A) Luminous flux

(B) Luminous intensity (C) Wavelength

(D) None of the above.

Q4 The unit of luminous flux is (A) steradian (B) candela (C) lumen (D) lux.

Q5 Illumination level required for precision work is around (A) 50 lm/m

2

(B) 100 lm/m2

(C) 200 lm/m2

(D) 500 lm/m2.

Q6 Which of the following lamp gives nearly monochromatic light ? (A) Sodium vapor lamp (B) GLS lamp (C) Tube light

(D) Mercury vapor lamp.

Q7 The illumination level in houses is in the range (A) 10-20 lumen/m

2

(B) 30 - 50 lumen/m2

(C) 40-75 lumen/m2

(D) 100-140 lumen/m2

Q8 One lumen per square meter is the same as (A) One lux (B) One candela (C) One foot candle (D) One lumen meter.

Short/long Answer types questions Q1 Define luminous intensity, reflection factor, coefficient of utilization. Q2 Explain working principle Incandescent and discharge lamps

2 ELECTRICAL HEATING

Electric heating is any process in which ELECTRICAL ENERGY is converted to “HEAT ENERGY”.

Electrical heating is based on the principle of that when electric current passes through a medium heat is

produced. Let us take the case of solid material which as resistance „R‟ ohms and current flowing

through it is I amps for „t‟ seconds than heat produced in the material will be H=I²Rt Joules.

1.1 Advantages of Electrical Heating over other Methods of Heating

• Clean and atmosphere / Free from dirt.

• No pollution / No flue gas is produced

• Response quickly

• Accurate Controlled temperature can made easily • Comparatively safe • Localized application

• Overall efficiency is much higher

• Uniform heating

• Highest efficiency of utilization

Transfer of Heat Conduction: This phenomenon takes place in solid, liquid and gas. Heat transfer is proportional to the difference of temperatures between two faces. No actual motion of molecules.

Convection: This phenomenon takes place in liquid and gas. Heat is transferred due to actual motion of molecules

Convection: This phenomenon takes place in liquid and gas. Heat is transferred due to actual motion of molecules

Classification of Electrical Heating

1 Power Frequency heating/ ohmic heating

a) Resistance Heating

b) Arc Heating both are of direct and indirect types 2

High Frequency heating

a) Induction Heating

b) Di-electrical Heating

c) Infrared Heating

2 Microwave Heating

1.2 RESISTANCE HEATING This method is based upon the I²R loss. Whenever current is passed through a resistor material heat is produced

because of I²R losses. The generation of heat is done by electric resistor carrying current.

There are two methods of resistance heating. They are:

2.2.1.1 Direct Resistance heating and

2.2.1.2 Indirect Resistance Heating

Direct Resistance heating

Electric current is passed through the body (charge) to be heated Mode of heat transfer is Conduction.

Example - Resistance Welding

Indirect Heating

Electric current is passed through highly resistive material (heating element) placed inside an oven. Heat produced due to I²R loss in the element is transmitted to the body

Mode of heat transfer is Conduction &/or Convection &/or Radiation Example –

Room Heater

CAUSES OF FAILURE OF HEATING ELEMENTS

Formation of hot spots.

Oxidation

Corrosion

Mechanical failure

Fig. Resistance Indirect Heating

Electric ovens It essentially consists of a high resistive material through which an electric current is passed placed in a chamber made of heat insulating material.

The element may be in the form of strip or wire and is placed on the top, bottom of the oven depending

upon circumstances.

Resistance ovens are used for various purposes such as heat treatment of metals, drying, backing of

pottery materials, cooking of food etc.

The temperature of oven can be controlled by controlling (i) voltage or current (ii) time and (iii)

resistance.

The automatic control of temperature can be obtained by providing thermostat which will operate a

switch to OFF or ON the circuit as soon as the temperature exceeds or fall below the adjusted value.

Domestic water heaters

Most of electric water heating is done by immersion heaters which consists of resistance coils placed

in slotted cylinders of ceramic material. The material used for resistance coil is nichrome wire coated

with magnesium oxide for preventing oxidation of the element which heat up the water due to 𝐼2R

loss in it.

Properties of resistance heating elements

Low temperature coefficient

High melting point

Free from oxidation

1.3.1 Induction heating

• Induction heating is based on the principle of transformers.

• There is a primary winding through which an a.c current is passed.

• The coil is magnetically coupled with the metal to be heated which acts as secondary.

• An electric current is induced in this metal when the a.c current is passes through the primary

coil.

The following are different types of induction furnaces:

1. Core type (low frequency) induction furnaces.

2. Coreless type (high frequency) induction furnaces

Coreless type induction furnace

• In this furnace, heat developed in the charge due to eddy currents flowing through it.

• When primary coils are excited by an alternating source, the flux set up by these coils induce

the eddy currents in the charge. The direction of the resultant eddy current is in a direction opposite to

the current in the primary coil. These currents heat the charge to melting point and they also set up

electromagnetism forces that produce a stirring action to the charge.

1.3.2 Electric arc heating

• The heating of matter by an electric arc. The matter may be solid, liquid, or gaseous. When the

heating is direct, material to be heated is one electrode; for indirect heating, the heat is transferred from

the arc by convection, or radiation.

Electrodes used in arc furnaces:

• 1. Carbon electrodes

• 2. Graphite electrodes

• 3. Self-baking electrodes

Types of arc heating furnaces:

• 1. Direct arc furnaces

• 2. Indirect arc furnaces

Direct arc furnaces

• When supply is given to the electrodes, two arcs are established and current passes through

the charge, as shown in Fig. As the arc is in direct contact with the charge and heat is also

produced by current flowing through the charge itself, it is known as direct arc furnace.

In indirect arc furnace, the arc strikes between two electrodes by bringing momentarily in contact charge

in this furnace is heated not only by radiation from the arc between electrode tips but also by conduction

from the heated refractory during rocking action; so, the efficiency of such furnace is high.

1.3.3 Dielectric Heating

• Dielectric heating, also known as electronic heating, RF (radio frequency) heating, and high-

frequency heating, is the process in which a radio frequency alternating electric field, or radio

wave or microwave electromagnetic radiation heats a dielectric material.

We understand dielectric heating as the generation of thermal energy (heat) in a non- conducting

material by the application of an electromagnetic force or field it. This is the way microwave oven

heats things placed in it.

1.3.4 Infra-red heating & Solar Heating

• In this method of heating, heating elements consist of tungsten filament lamps together with

reflectors to direct the whole of heat emitted on to charge (material to be heated).

• The lamps are operated at 2300 degree celcius there by giving a large amount of infrared

radiations and the reflectors are plated with rhodium which prevents the leakage of heat through the

chamber. The lamps used are rated between 250-11,000 watts as 250V.

1.3.5 Solar Heating:

In solar water heating collectors capture and retain heat from the sun. This heat is then transferred to a

liquid. Heating of the sun trapped using the greenhouse effect. Solar radiation is energy in the form of

electromagnetic radiations from the infrared to the ultraviolet example – solar cooker, solar water

heater etc.

3 .Electric Welding

Welding is a joining process in which metals, or sometimes plastics, are heated, melted and mixed

to produce a joint with properties similar to those of the materials being joined.

There are three main components needed to create a weld. These are:

A heat source such as an electric arc, a flame, pressure, or friction. The most common heat

source is an electric arc. An arc is the physical gap between the end of the electrode and the

base metal. The physical gap causes heat due to resistance of current flow and arc rays. The

arc melts the metals to create the joint.

Shielding, which is the use of gas, or another substance to protect the weld from air as the

weld is being formed. Oxygen from the air makes welds brittle and porous.

Filler material, which is the material used to join to the two pieces together.

Other processes that join metals together include:

Brazing is the joining of metals with a filler metal having a melting point above 450°C

(842°F), but below the melting point of base metals. The joined metals can be different

metals. The joint is not as strong as a welded joint.

Soldering is the joining of metals using a filler metal with a melting point below 450°C

(842°F). The joined metals can be different metals. The "filler “metals commonly used are

lead-tin alloys. The joint is not as strong as a welded joint or a brazed joint.

There are over 70 different welding processes. The type of welding process used is related to

the specific application. The most common processes are:

Shielded Metal Arc Welding (SMAW), also known as Manual Metal Arc Welding, MMAW.

Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas (TIG) Welding.

Flux Cored Arc Welding (FCAW).

Gas Metal Arc Welding (GMAW), also known as Metal Inert Gas (MIG) Welding or hard

wire welding.

Plasma Arc Welding (PAW), Plasma Arc Cutting (PAC) and Gouging

Submerged Arc Welding (SAW)

Resistance Spot Welding (RSW) or spot welding.

Air Carbon Arc Cutting (CAC-A) and Air Carbon Arc Gouging (CAG)

Oxyfuel Gas Welding (OFG), Cutting and Heating (oxygen-acetylene [oxyacetylene]

(OAW) or oxygen-propane [oxy-propane] mixtures are the most common fuel mixtures

used).

Resistance welding processes

Depending on the shape of the work pieces and the form of the electrodes, resistance welding

processes can be classified into several variants among which the most commonly used are spot

welding, projection welding, seam welding and butt welding. More details are described below:

Resistance Spot Welding

Spot welding is a resistance welding process for joining metal sheets by directly applying opposing

forces with electrodes with pointed tips. The current and the heat generation are localized by the

form of the electrodes. The weld nugget size is usually defined by the electrode tip contact area.

Spot welding is the predominant joining process in automotive industry for assembling the

automobile bodies and large components. It is also widely used for manufacturing of furniture and

domestic equipment etc.

Resistance Projection Welding

Projection welding is a resistance welding process for joining metal components or sheets with

embossments by directly applying opposing forces with electrodes specially designed to fit the

shapes of the workpieces. The current and the heat generation are localized by the shape of the

workpieces either with their natural shape or with specially designed projection. Large deformation

or collapse will occur in the projection part of the workpieces implying high process/machine

dynamics.

Projection welding is widely used in electrical, electronics, automotive and construction industries,

and manufacturing of sensors, valves and pumps etc.

Resistance Seam Welding

Seam welding is a resistance welding process for joining metal sheets in continuous, often leak

tight, seam joints by directly applying opposing forces with electrodes consisting of rotary wheels.

The current and the heat generation are localized by the peripheral shapes of the electrode wheels.

Seam welding is mostly applied in manufacturing of containers, radiators and heat exchangers etc.

Resistance Butt Welding

Butt welding is a resistance welding process for joining thick metal plates or bars at the ends by

directly applying opposing forces with electrodes clamping the workpieces. A forging operation is

applied after the work pieces are heated up. Often no melt occurs, thus a solid state weld can be

obtained.

Butt welding is applied in manufacturing of wheel rims, wire joints and railway track joints etc.

Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at

the joint between two parts is melted and caused to intermix - directly, or more commonly, with an

intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created.

Since the joining is an intermixture of metals, the final weldment potentially has the same strength

properties as the metal of the parts. This is in sharp contrast to non-fusion processes of joining (i.e.

soldering, brazing etc.) in which the mechanical and physical properties of the base materials cannot

be duplicated at the joint.

Fig. 1 The basic arc-welding circuit

In arc welding, the intense heat needed to melt metal is produced by an electric arc. The arc is

formed between the actual work and an electrode (stick or wire) that is manually or mechanically

guided along the joint. The electrode can either be a rod with the purpose of simply carrying the

current between the tip and the work. Or, it may be a specially prepared rod or wire that not only

conducts the current but also melts and supplies filler metal to the joint. Most welding in the

manufacture of steel products uses the second type of electrode.

Basic Welding Circuit

The basic arc-welding circuit is illustrated in Fig. 1. An AC or DC power source, fitted with

whatever controls may be needed, is connected by a work cable to the workpiece and by a "hot"

cable to an electrode holder of some type, which makes an electrical contact with the welding

electrode.

An arc is created across the gap when the energized circuit and the electrode tip touches the work

piece and is withdrawn, yet still with in close contact.

The arc produces a temperature of about 6500ºF at the tip. This heat melts both the base metal and

the electrode, producing a pool of molten metal sometimes called a "crater." The crater solidifies

behind the electrode as it is moved along the joint. The result is a fusion bond.

Arc Shielding

However, joining metals requires more than moving an electrode along a joint. Metals at high

temperatures tend to react chemically with elements in the air - oxygen and nitrogen. When metal in

the molten pool comes into contact with air, oxides and nitrides form which destroy the strength and

toughness of the weld joint. Therefore, many arc-welding processes provide some means of

covering the arc and the molten pool with a protective shield of gas, vapor, or slag. This is called arc

shielding. This shielding prevents or minimizes contact of the molten metal with air. Shielding also

may improve the weld. An example is a granular flux, which actually adds deoxidizers to the weld.

Fig. coating on electrod

Figure 2 illustrates the shielding of the welding arc and molten pool with a Stick electrode. The

extruded covering on the filler metal rod, provides a shielding gas at the point of contact while the

slag protects the fresh weld from the air.

The arc itself is a very complex phenomenon. In-depth understanding of the physics of the arc is of

little value to the welder, but some knowledge of its general characteristics can be useful.

Nature of the Arc An arc is an electric current flowing between two electrodes through an ionized column of gas. A

negatively charged cathode and a positively charged anode create the intense heat of the welding

arc. Negative and positive ions are bounced off of each other in the plasma column at an accelerated

rate.

In welding, the arc not only provides the heat needed to melt the electrode and the base metal, but

under certain conditions must also supply the means to transport the molten metal from the tip of the

electrode to the work. Several mechanisms for metal transfer exist. Two (of many) examples

include:

1. Surface Tension Transfer® - a drop of molten metal touches the molten metal pool and is

drawn into it by surface tension

2. Spray Arc - the drop is ejected from the molten metal at the electrode tip by an electric pinch

propelling it to the molten pool (great for overhead welding)

If an electrode is consumable, the tip melts under the heat of the arc and molten droplets are

detached and transported to the work through the arc column. Any arc welding system in which the

electrode is melted off to become part of the weld is described as metal-arc. In carbon or tungsten

(TIG) welding there are no molten droplets to be forced across the gap and onto the work. Filler

metal is melted into the joint from a separate rod or wire.

More of the heat developed by the arc is transferred to the weld pool with consumable electrodes.

This produces higher thermal efficiencies and narrower heat-affected zones.

Since there must be an ionized path to conduct electricity across a gap, the mere switching on of the

welding current with an electrically cold electrode posed over it will not start the arc. The arc must

be ignited. This is caused by either supplying an initial voltage high enough to cause a discharge or

by touching the electrode to the work and then withdrawing it as the contact area becomes heated

4 Electrolytic Process

Electrolytic process is the use of electrolysis industrially to refine metals or compounds at a

high purity and low cost. Some examples are the Hall-Héroult process used for aluminium, or the

production of hydrogen from water. Electrolysis is usually done in bulk using hundreds of sheets

of metal connected to an electric power source. In the production of copper, these pure sheets of

copper are used as starter material for the cathodes, and are then lowered into a solution such as

copper sulphate with the large anodes that are cast from impure (97% pure) copper. The copper

from the anodes are electroplated on to the cathodes, while any impurities settle to the bottom of

the tank. This forms cathodes of 99.999% pure copper.

What is an Electrolytic Cell?

As for an electrolytic cell, we can say that in many respects, it is much the same as a galvanic cell as

it requires a salt bridge, two electrodes and the flow of electrons from the anode to the cathode.

However, the two still manage to be different from each other in many respects. For one, an

electrolytic cell converts electrical energy into chemical energy and not the other way round.

The ensuing redox reaction in the process is not a spontaneous one and for the reaction to start,

electric energy has to be introduced in the apparatus. Unlike a galvanic cell, an electrolytic cell

requires both metals to be placed in the same container. The positive electrode, in this case, is called

the anode and the negative electrode is called the cathode. For the supply of electrons, an external

battery is used.

Faraday’s Law of Electrolysis

As stated in the law of Faraday, when one mole of electric charge is made to pass through an

electrolytic cell, it will discharge half a mole of a divalent metal ion. Based on this theory, Faraday

devised his two laws of electrolysis which states that the respective weight of a substance formed at

an electrode during the process of electrolysis is directly proportional to the quantum of electricity

that can pass through that electrolyte and the weight of a variety of substances that will be formed

by passing the same quantity of electricity shall be proportional to the respective weight of the given

substances.

The Outcome of an Electrolysis Reaction When an electrolysis takes place, there are some primary factors that are the determining factors

about whether or not complete electrolysis will take place. Sometimes, an excess of voltage is

needed to overcome the surface interaction at the electrodes. This phenomenon is more prevalent in

the case of gases. Sometimes, more than one-half reactions could be taking place during the

electrolysis.

This means that there are more than two possibilities for cell reaction. A given inert electrode‟s

ability to undergo electrolysis reaction will depend on the present reactants in the electrolyte

solution while at the same time, an active electrode is capable of running on its own to perform the

oxidation or reduction half-reaction in the solution. These theories can help in predicting the

outcome or the expected result of an electrolysis reaction conveniently.

Solved Examples for You

Question: How does aluminium react to the process of electrolysis?

Solution: Aluminium can be most easily found in most rocks. It is one of the most abundantly found

in the crust of the earth. However, isolation of the metal from impurities and other metals proves to

be a very costly affair. This is the reason why separation of aluminium through electrolysis is very

difficult to achieve. This is because, in the stated reaction, it would be water which would get

electrolyzed in preference to aluminium itself.

Reducing Aluminium from its Fluoride Salts by Electrolysis

However, in the year 1886, scientists Charles Hall and Paul Herault developed a practical way.

Their method was aimed at achieving electrolysis of the metal in an economic manner. The

apparatus includes a carbon cathode and a carbon anode and a crust of frozen electrolyte. Carbon

anode is a device that could lower the anode as it gets consumed

Galvanizing is the process which employs an electrochemical action for providing a coating of

highly corrosion resistant material on the surface of another metal. The galvanizing process is

widely used for providing a coating of zinc on iron and steel.

It is very much low cost process and widely used for corrosion resistant coating on sheet

metal, household items for daily used made from iron and steel e.g. buckets, tubs and other containers. Galvanized is also done on machine parts, tools, ships tanks and wires etc.

Applications of Galvanizing:

1. To galvanized sheet metal.

2. To galvanized house-hold items such as buckets, tubs and other containers.

3. To galvanized machine parts, tools, ships, tanks and wires.

4. Metal pipes and wires are most popular galvanized items which find application in industrial

use as well as in articles made for domestic use.

Meaning and Purpose of Anodizing:

It is the process in which a film of oxide is provided on metal surface is known as anodising.

(i) The give a protective coating on the metal surface like aluminium, zinc, copper and bronze.

(ii) To provide a decorative appearance on the surface.

(iii) To provide a bright and smooth surface on aluminium articles prior to electroplating.

(iv) To provide specific colour base for subsequent painting on the surface.

(v) To improve the corrosion resistance of aluminium and aluminium products.

The anodized is achieved by using different electrolytes varying current and temperature of

solution etc.

Anodising process is neither a purely electrical process nor purely chemical process; it is a

combination of both hence called electrochemical processes.

Applications of anodising:

1. To provide a protective coating on the metal surface.

2. To anodising on steel for producing a black film on various steel parts used a decorative

article.

3. Several galvanized iron and steel articles and machine parts are anodised to improve the

resistance of galvanised coating to rusting, abrasion, wear and increase its life.

4. To anodising zinc to give distinct colour coatings.

5. Anodising is done on silver jewellery and show pieces made of silver

Short/Long Answer type questions

Q1 Define Heating with its advantages.

Q2 Explain resistance heating with its types

Q3 Explain Dielectric heating in detail.

5 Refrigeration

Refrigeration is a process of removing heat from a low-temperature reservoir and transferring it to a

high-temperature reservoir. The work of heat transfer is traditionally driven by mechanical means, but

can also be driven by heat, magnetism, electricity, laser, or other means. Refrigeration has many

applications, including, but not limited to: household refrigerators, industrial freezers, cryogenics,

and air conditioning. Heat pumps may use the heat output of the refrigeration process, and also may be

designed to be reversible, but are otherwise similar to air conditioning units.

Methods of refrigeration can be classified as non-cyclic, cyclic, thermoelectric and magnetic.

Non-cyclic refrigeration

This refrigeration method cools a contained area by melting ice, or by sublimating dry ice. Perhaps the

simplest example of this is a portable cooler, where items are put in it, then ice is poured over the top.

Regular ice can maintain temperatures near, but not below the freezing point, unless salt is used to cool

the ice down further (as in a traditional ice-cream maker). Dry ice can reliably bring the temperature

well below freezing.

Cyclic refrigeration This consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and

rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic

power cycle. In the power cycle, heat is supplied from a high-temperature source to the engine, part of

the heat being used to produce work and the rest being rejected to a low-temperature sink. This satisfies

the second law of thermodynamics.

A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and

rejects heat as it circulates through a refrigerator. It is also applied to heating, ventilation, and air

conditioning HVACR work, when describing the "process" of refrigerant flow through an HVACR unit,

whether it is a packaged or split system.

Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by

pumping heat from a lower temperature heat source into a higher temperature heat sink. Insulation is

used to reduce the work and energy needed to achieve and maintain a lower temperature in the cooled

space. The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in

1824 as a heat engine.

Cyclic refrigeration can be classified as:

Vapor cycle, and

Gas cycle

Vapor cycle refrigeration can further be classified as:

Vapor-compression refrigeration

Vapor-absorption refrigeration

The Vapor Compression Refrigeration Cycle involves four components: compressor,

condenser, expansion valve/throttle valve and evaporator.

STEP 1: COMPRESSION The refrigerant (for example R-717) enters the compressor at low temperature and low pressure. It is in a

gaseous state. Here, compression takes place to raise the temperature and refrigerant

pressure. The refrigerant leaves the compressor and enters to the condenser. Since this process requires

work, an electric motor may be used. Compressors themselves can be scroll, screw, centrifugal or

reciprocating types.

STEP 2: CONDENSATION

The condenser is essentially a heat exchanger. Heat is transferred from the refrigerant to a

flow of water. This water goes to a cooling tower for cooling in the case of water-cooled

condensation. Note that seawater and air-cooling methods may also play this role. As the

refrigerant flows through the condenser, it is in a constant pressure.

One cannot afford to ignore condenser safety and performance. Specifically, pressure control is

paramount for safety and efficiency reasons. There are several pressure-controlling devices to

take care of this requirement

STEP 3: THROTTLING AND EXPANSION

When the refrigerant enters the throttling valve, it expands and releases pressure. Consequently,

the temperature drops at this stage. Because of these changes, the refrigerant leaves the

throttle valve as a liquid vapor mixture, typically in proportions of around 75 % and 25 %

respectively.

Throttling valves play two crucial roles in the vapor compression cycle. First, they maintain a

pressure differential between low- and high-pressure sides. Second, they control the amount of

liquid refrigerant entering the evaporator.

STEP 4: EVAPORATION

At this stage of the Vapor Compression Refrigeration Cycle, the refrigerant is at a lower

temperature than its surroundings. Therefore, it evaporates and absorbs latent heat of

vaporization. Heat extraction from the refrigerant happens at low pressure and temperature.

Compressor suction effect helps maintain the low pressure.

There are different evaporator versions in the market, but the major classifications are liquid

cooling and air cooling, depending whether they cool liquid or air respectively.

6 Electrical Drives

Definition: The system which is used for controlling the motion of an electrical machine, such

type of system is called an electrical drive. In other words, the drive which uses the electric

motor is called electrical drive. The electrical drive uses any of the prime movers like diesel or a

petrol engine, gas or steam turbines, steam engines, hydraulic motors and electrical motors as a

primary source of energy. This prime mover supplies the mechanical energy to the drive for

motion control.

Parts of Electrical Drive The main parts of the electrical drives are power modulator, motor, controlling unit and sensing

units. Their parts are explained below in details.

Power Modulator – The power modulator regulates the output power of the source. It controls

the power from the source to the motor in such a manner that motor transmits the speed-torque

characteristic required by the load. During the transient operations like starting, braking and

speed reversing the excessive current drawn from the source. This excessive current drawn from

the source may overload it or may cause a voltage drop. Hence the power modulator restricts the

source and motor current.

The power modulator converts the energy according to the requirement of the motor e.g. if the

source is DC and an induction motor is used then power modulator convert DC into AC. It also

selects the mode of operation of the motor, i.e., motoring or braking.

Control Unit – The control unit controls the power modulator which operates at small voltage

and power levels. The control unit also operates the power modulator as desired. It also generates

the commands for the protection of power modulator and motor.

Sensing Unit – It senses the certain drive parameter like motor current and speed. It mainly

required either for protection or for closed loop operation.

Advantages of Electrical Drive

The electric drive has very large range of torque, speed and power.

Their working is independent of the environmental condition.

The electric drives are free from pollution.

The electric drives operate on all the quadrants of speed torque plane.

The drive can easily be started and it does not require any refueling.

The efficiency of the drives is high because fewer losses occur on it.

The electric drives have many advantages shown above.

The only disadvantage of the drive is that sometimes the mechanical energy produced by the

prime mover is first converted into electrical energy and then into a mechanical work by the help

of the motor. This can be done by the help of the electrical link which is associated with the

prime mover and the load.

Because of the following advantages, the mechanical energy already available from a non-

electrical prime mover is sometimes first converted into electrical energy by a generator and

back to a mechanical energy of an electrical motor. Electrical link thus provides between the

non-electrical prime mover and the load impact to the drive flexible control characteristic.

For example – The diesel locomotive produces the diesel energy by the help of the diesel

engine. The mechanical energy is converted into an electrical energy by the help of the

generator. This electrical energy is used for driving the other locomotive.

Disadvantages of Electrical Drive

The power failure completely disabled the whole of the system.

The application of the drive is limited because

it cannot use in a place where the power supply is not available.

It can cause noise pollution.

The initial cost of the system is high.

It has a poor dynamic response.

The output power obtained from the drive is low.

During the breakdown of conductors or short circuit, the system may get damaged due to which

several problems occur.

Application of Electric Drive

It is used in a large number of industrial and domestic applications like transportation systems,

rolling mills, paper machines, textile mills, machine tools, fans, pumps, robots and washing, etc.

Motors are of various types. The DC motors can be divided in four types – shunt wound DC

motor, series wound DC motor, compound wound DC motor and permanent magnet DC motor.

AC motors are of two types – induction motors and synchronous motors. Now synchronous

motors are of two types – round field and permanent magnet. Induction motors are also of two

types – squirrel cage and wound motor. Besides all of these, stepper motors and switched

reluctance motors are also considered as the parts of drive system.

So there are various types of electric motors, and they are used according to their specifications

and uses. When the electrical drives were not so popular, induction and synchronous motors

were usually implemented only where fixed or constant speed was the only requirement. For

variable speed drive applications, DC motors were used. But as we know that, induction motors

of same rating as a DC motors have various advantages like they have lighter weight, lower cost,

lower volume and there is less restriction on maximum voltage, speed and power ratings. For

these reasons, the induction motors are rapidly replaced the DC motors.

Belt drive, gears, chain drives

Belt drive

A belt is a looped strip of flexible material used to mechanically link two or more rotating shafts.

A belt drive offers smooth transmission of power between shafts at a considerable distance. Belt

drives are used as the source of motion to transfer to efficiently transmit power or to track

relative movement. Types of Belt Drives:

In a two pulley system, depending upon the direction the belt drives the pulley, the belt drives

are divided into two types. They are open belt drive and crossed belt drive. The two types of belt

drives are discussed below in brief.

Open belt drives:

An open belt drive is used to rotate the driven pulley in the same direction of driving pulley. In

the motion of belt drive, power transmission results make one side of pulley more tightened

compared to the other side. In horizontal drives, tightened side is always kept on the lower side

of two pulleys because the sag of the upper side slightly increases the angle of folding of the belt

on the two pulleys.

Crossed belt drives:

A crossed belt drive is used to rotate driven pulley in the opposite direction of driving pulley.

Higher the value of wrap enables more power can be transmitted than an open belt drive.

However, bending and wear of the belt are important concerns.

A chain drive can be defined as a series of links connected by pin joints.

Now we can move on to chain drive.

A chain drive consists of an endless chain wrapped around two sprockets.

Advantages of chain drive

Here are some advantages of chain drives compared with gear and belt drives

They can be used for both long and short distances

A number of shafts and be driven from a single chain

They are compact and have small overall dimensions

They do not present fire hazard

Temperature and environmental conditions do not affect their working

They do not require initial tension

They have very high efficiency (up to 96%)

They do not slip

Gear drive has become the most important and popular means of motion and power transmission

system. A gear drive is a pair of meshing gears as shown below

Gears are components of machines for the transmission of power and motion from one shaft to

other separated by small distance. It is a toothed wheel, i.e., wheel with a number of teeth. It

provides with projections known as teeth and in between two teeth, there is a vacant space,

which is called tooth space, to accommodate the incoming tooth in rotation.

As it appears, toothed wheels avoid the problem of slippage which is quite prominent in belt

drive. Hence, these wheels produce positive drive and no slip. When one gear wheel rotates,

other wheel also rotates in the opposite direction as has been shown above. The power is

transferred effectively and no loss is observed. The velocity ratio remains same throughout the

operation.

7 Electric Traction

Introduction:

By electric traction is meant locomotion in which the driving (or tractive) force is obtained from

electric motors. It is used in electric trains, tramcars, trolley buses and diesel-electric vehicles

etc. Electric traction has many advantages as compared to other non-electrical systems of traction

including steam traction.

Traction Systems

Broadly speaking, all traction systems may be classified into two categories:

(a) Non-electric traction systems

They do not involve the use of electrical energy at any stage. Examples are: steam engine drive

used in railways and internal-combustion-engine drive used for road transport.

(b) Electric traction systems

They involve the use of electric energy at some stage or the other. They may be further

subdivided into two groups:

First group consists of self-contained vehicles or locomotives. Examples are: battery-electric

drive and diesel-electric drive etc.

Second group consists of vehicles which receive electric power from a distribution network fed

at suitable points from either central power stations or suitably-spaced sub-stations.

Examples are: railway electric locomotive fed from overhead ac supply and tramways and trolley

buses supplied with dc supply.

Direct Steam Engine Drive

Though losing ground gradually due to various reasons, steam locomotive is still the most widely

adopted means of propulsion for railway work. Invariably, the reciprocating engine is employed

because

It is inherently simple. Connection between its cylinders and the driving wheels is simple. Its

speed can be controlled very easily..

Diesel-electric Drive

It is a self-contained motive power unit which employs a diesel engine for direct drive of a dc

generator. This generator supplies current to traction motors which are geared to the driving

axles. In India, diesel locomotives were introduced in 1945 for shunting service on broad guage

(BG) sections and in 1956 for high-speed main-line operations on metre-guage (MG) sections. It

was only in 1958 that Indian Railways went in for extensive main-line dieselization. Diesel-

electric traction has the following

Advantages:

No modification of existing tracks is required while converting from steam to diesel-electric

traction.

It provides greater tractive effort as compared to steam engine which results in higher starting

acceleration.

It is available for hauling for about 90% of its working days.

Diesel-electric locomotive is more efficient than a steam locomotive (though less efficient than

an electric locomotive).

Disadvantages

For same power, diesel-electric locomotive is costlier than either the steam or electric

locomotive.

Overload capacity is limited because diesel engine is a constant-kW output prime move

Life of a diesel engine is comparatively shorter.

Diesel-electric locomotive is heavier than plain electric locomotive because it carries the main

engine, generator and traction motors etc.

Regenerative braking cannot be employed though rheostat braking can be.

Electric Traction Systems

The system which uses electrical power for traction system i.e. for railways, trams, trolleys, etc.

is called electrical traction. The track electrification refers to the type of source supply system

that is used while powering the electric locomotive systems. It can be AC or DC or a composite

supply.

Selecting the type of electrification depends on several factors like availability of supply, type of

an application area, or on the services like urban, suburban and main line services, etc.

The three main types of electric traction systems that exist are as follows:

Direct Current (DC) electrification system

Alternating Current (AC) electrification system

Composite system.

1- DC Electrification System

The choice of selecting DC electrification system encompasses many advantages, such as space

and weight considerations, rapid acceleration and braking of DC electric motors, less cost

compared to AC systems, less energy consumption and so on.

In this type of system, three-phase power received from the power grids is de-escalated to low

voltage and converted into DC by the rectifiers and power-electronic converters.

This type of DC supply is supplied to the vehicle through two different ways:

3rd and 4 the rail system operate at low voltages (600-1200V)

Overhead rail systems use high voltages (1500-3000V)

The supply systems of DC electrification include;

300-500V supply for the special systems like battery systems.

600-1200V for urban railways like tramways and light metro trains.

1500-3000V for suburban and mainline services like light metros and heavy metro trains.

Due to high starting torque and moderate speed control, the DC series motors are extensively

employed in the DC traction systems. They provide high torque at low speeds and low torque at

high speeds.

AC Electrification System

An AC traction system has become very popular nowadays, and it is more often used in most of

the traction systems due to several advantages, such as quick availability and generation of AC

that can be easily stepped up or down, easy controlling of AC motors, less number of substations

requirement, and the presence of light overhead catenaries that transfer low currents at high

voltages, and so on.

The supply systems of AC electrification include single, three phase, and composite systems.

The Single phase systems consist of 11 to 15 KV supply at 16.7Hz, and 25Hz to facilitate

variable speed to AC commutation motors. It uses step down transformer and frequency

converters to convert from the high voltages and fixed industrial frequency.

The Single phase 25KV at 50Hz is the most commonly used configuration for AC electrification.

It is used for heavy haul systems and main line services since it doesn‟t require frequency

conversion. This is one of the widely used types of composite systems wherein the supply is

converted to DC to drive DC traction motors.

Three phase system uses three phase induction motor to drive the locomotive, and it is rated at

3.3.KV, 16.7Hz. The high-voltage distribution system at 50 Hz supply is converted to this

electric motor rating by transformers and frequency converters. This system employs two

overhead lines, and the track rail forms another phase, but this raises many problems at crossings

and junctions.

Advantages;

Fewer substations are required.

Lighter overhead current supply wire can be used.

Reduced weight of support structure.

Reduced capital cost of electrification.

Electric Braking

The electric braking of a DC motor is of three types, (i) Rheostatic or dynamic braking, (ii)

Plugging or reverse current braking and (iii) Regenerative beaking.

(i) Rheostatic or dynamic braking:

In case of DC shunt motors, armature is disconnected from the supply and a rheostat (variable

resistor) is connected across it. The field winding is left connected across the supply. Obviously,

now armature is driven by the inertia and hence machine starts acting as a generator. Thus the

machine will now feed the current to the connected rheostat and heat will dissipate at the rate of

I2R. Braking effect is controlled by varying the resistance connected across the armature.

In case of DC series motor, motor is disconnected from the supply and field connections are

reversed and a rheostat is connected in series. The field connections are reversed to make sure

that the current through field winding will flow in the same direction as before.

(ii) Plugging or Reverse current braking:

In this method, armature connections are reversed and hence motor tends to run in opposite

direction. Due to reversal of the armature terminals, applied voltage V and back emf Eb starts

acting in the same direction and hence the total armature current exceeds. To limit this armature

current a variable resistor is connected across the armature. This is similar for both series and

shunt wound methods.

Plugging gives greater braking torque as compared to rheostatic braking. This method is

generally used in controlling elevators, machine tools, printing presses etc.

(iii) Regenerative braking:

Regenerative braking is used where, load on the motor has very high inertia (e.g in electric

trains). When applied voltage to the motor is reduced to less than back emf Eb, obviously

armature current Ia will get reversed, and hence armature torque is reversed. Thus speed falls. As

generated emf is greater than applied voltage (machine is acting as a DC generator), power will

be returned to the line, this action is called as regeneration. Speed keeps falling, back emf Eb

also falls until it becomes lower than applied voltage and direction of armature current again

becomes opposite to Eb.

Electrical Multiple Unit popularly called EMU is a very popular train configuration for sub-

urban travel. EMU services are running presently in Mumbai (popularly called Local), Delhi

(EMU), Kolkata (EMU), Chennai (EMU), Hyderabad etc. These services are very

popular among daily Commutator for

In-time services

Reliability in services with very rare failure

Very low fare

Vendor compartment to carry daily market products such as milk, vegetables, Tiffen supply in

offices

It is called Electrical Multiple Unit as it consists of multiple motored vehicle built-in the train

composition.

Question 1. Name Some Of The Various Methods Of Traction Motor Control?

Answer : o Rheostatic control

o Thyristor control

o Metaldyne control

o Buck and boost method

o Series parallel control

o Field control

Question 2. What Are The Basic Requirements Of A Braking System?

Answer : o The basic requirements of a braking system are given below.

o Easy to use for driver to operate.

o It should be inexhaustible.

o The maintenance should be a minimum.

o It should be simple, quick, robust and reliable in action.

o Kinetic energy of the train be storage during braking which could be used

subsequently during acceleration of the train.

Question 3. What Are The Various Methods Of Applying Electric Traction?

Answer :

There are three methods of applying electric braking.

They are: o Plugging or reverse current braking

o Rheostatic braking

o Regenerative braking

Question 4. Give Some Of Advanced Methods Of Speed Control Of Traction Motors?

Answer : o Tap changer control

o Thyristor control

o Chopper control

o Microprocessor control

Question 5. What Are The Advantages Of Microprocessor Based Control Of Traction

Motors?

Answer : o High speed of response

o High accuracy

o Over voltage and over speed protection

o Electronic interlocking

o Less sensitive to temperature variations and drift

o Numbers of components used are less

Question 6. Define Dead Weight And Adhesive Weight?

Answer :

Dead weight: The total weight of locomotive and train to be pulled by the locomotive is known as dead

weight

Adhesive weight:

The total weight to be carried on the driving wheels is known as the adhesive weight.

Question 7. What Is Tractive Effort?

Answer : The effective force necessary to propel the train at the wheels of the locomotive to which the

motor is geared is called the tractive effort. It is measured in newtons and is tangential to the

driving wheels.

Total tractive effort required to run a train on tract = Tractive effort to produce acceleration +

Tractive effort to overcome effort of gravity + Tractive effort to overcome train resistance.

Question 8. Define Electric Drives?

Answer : Systems employed for motion control are called as drives and drives employ any of the prime

movers such as diesel or petrol engines, gas or steam turbines, hydraulic motors and electric

motors for supplying mathematical energy for motion control. Drives employing electric

motion are called as electrical drives.

Question 9. What Are The Various Parts Of Electrical Drives?

Answer : o Electrical motors and load

o Power Modulator

o Sources

o Control Unit

o Sensing unit

Question 10. What Are Various Advantages Of Electrical Drives?

Answer : 1. They are having flexible control characteristics. The study state and dynamic

characteristics of electrical drives can be shaped to satisfy load requirements.

2. Drives can be provided with automatic fault detection systems. PLCs and computers

can be employed to automatically control the drive operations in a desired sequence.

3. Drives are available in wide range of speed, power and torque.

4. Control gear required for speed control, starting and braking is usually simple and easy

to operate.

5. It can operate in all the four quadrants of speed - torque plane. Electric braking gives

smooth deceleration and increases life of the equipment compared to other forms of

braking.