2 workshop 2110017

SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH CENTRE, UMRAKH

Course Contents

PART -1 (STUDY)

PART -2 (PRACTICAL EXERCISES)

SR

NO NAME OF STUDY PRACTICALS DATE SIGN

1. To Study of safety devices. / /

2. To Study type of earthing. / /

3. To Study the different type of wirings for House hold Applications. / /

4. To study the working of table fan and ceiling fan.

/ /

5. To study the working of induction type energy meter / /

6. To study multi meter and perform difference functions of it.

/ /

SR

NO NAME OF STUDY PRACTICALS DATE SIGN

1. To Study different electrical and electronics symbols.

/ /

2. Familiarization of electrical and electronics components and study of measuring devices & PCB fabrication and soldering practice.

/ /

3. study and perform the fluorescent tube light wiring. / /

4. To perform the Full wave circuit on breadboard and verify the waveform on SCR.

/ /

5. To measure power & energy in 1- AC circuit. / /

6. To performs the wiring that control (A) Two lamps by two separate switches (House Wiring)

(b) One lamp by two 2-way switches (Stair-case Wiring).

/ /

7. To determine power factor of RLC series circuit.

/ /

SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH CENTRE, UMRAKH

DOs and DONTs in Laboratory:

1. Understand the equipment to be tested and apparatus to be used.

2. Select proper type (i.e. A. c. or D. C.) and range of meters. 3. Do not touch the live terminals.

4. Use suitable wires (type and size). 5. All the connection should be tight.

1. Do not leave loose wires (i.e. wires not connected).

2. Get the connection checked before switching ON the supply.

3. Never exceed the permissible values of current, voltage, and / or speed of any machine, apparatus, wire, load, etc.

4. Switch ON or OFF the load gradually and not suddenly.

5. Strictly observe the instructions given by the teacher/Lab Instructor

SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH CENTRE, UMRAKH Page 1

General Workshop Rules

All students in the workshop are expected to adhere to the following guidelines.

The students are supposed to come in proper workshop uniform dress. Wearing shoes in

the workshop is compulsory.

Do not fool around in the lab: Take your lab work seriously and behave appropriately in the laboratory. Be aware of your classmates safety as well as your own at all times.

To successfully complete the experiments in one lab period, you must come prepared to the laboratory. You must read the experiment in advance and answer the pre-lab

questions.

Please treat the instruments with care, as they are very expensive. Return the components to the correct bins when you are finished with them.

Before leaving the lab, place the stools under the lab bench.

Before leaving the lab, turn off the main power switch to the lab bench.

Keep your work area neat and uncluttered- Have only books and other materials that are

needed to conduct the experiment in the laboratory.

Experiment: The student works with a partner and they both take the data on separate

notebooks. The lab instructor will look at the data and sign on your notebook at the end of the experiment.

Any student missing a lab (not present in the lab) with no proper or reasonable excuse will get a 0 grade on that specific lab and will have his/her final letter grade reduced. Any student missing two labs with no proper excuse will automatically get a failing grade

(F).

This laboratory can be used by students during laboratory hours only.


Electrical Safety Principles

When planning and performing work on electrical systems and equipment, keep these principles in mind:

Understand the procedure completely before starting the work.

Use good quality footwear/shoes in order to provide maximum resistance.

Never energize any circuit unless you are sure that no one is working on the circuit. Give electric supply to the wiring system only after thorough verification.

Before replacing a blown fuse always remember to put the switch off.

Do not touch switch boards, main switches, holder points etc with wet hands.

Do not use broken switches, sockets or plug.

Use non-conductive tools whenever possible.

Before putting the plug pins in socket put off the plug switch and disconnect the plug by pulling the plug pin and not by pulling cable.

Take utmost care while handling lamps, lamp holders, switches etc, because these materials are brittle.

Never drape electrical cords over heat sources

Before beginning work, tie back long hair, and roll up loose sleeves.

Know the location and how to operate shut-off switches and/or circuit breaker panels. Use these devices to shut off equipment in the event of a fire or electrocution.

Dont over bend cables when pulling them through a bend in a raceway, often a

Pressure or squeezing develops causing insulation damage.


Electrical engineering an over view

Some definitions

1. Electric current: - Rate of change of charge with respect to time. (I=dq/dt). One ampere is the current produced when a pressure of one volt is applied across a circuit having one ohm resistance.

2. EMF: - EMF is electro motive force. Potential difference between two points in a circuit is the electrical pressure difference required to drive a current between them. Potential difference may be termed as voltage.

3. Voltage of a torch battery is 1.5 V and that of automobile battery is 12V. KSEB supply voltage for domestic installation is 240 V.

4. Electric power (watt):- Electric power, P = Voltage * current * Power factor Unit of

electric power is watt (W)

5. Electric energy:-Unit of electric energy is KWh (Kilo Watt hour) 1 unit energy = 1 KWh KSEB provides one KWh meter at every Installation for measuring consumed energy.

6. Resistance is the property of a substance due to which it opposes the flow of current

through it. Unit of resistance is ohm

7. Where I is the length of material & A is the area of cross section

8. Effect of temperature on resistance:-When temperature increases resistance of pure metals and Alloys increases when temperature increases resistance of electrolyte,

insulators etc decrease.

9. Resistance in series:-Consider three resistors connected in series, and then the total resistance of the circuit will be the sum of the three resistors.

10. Ohms law:-Ohms law states that, the ratio of potential difference between any two points in a conductor to the current flowing between them is constant.

11. R = V /I Keeping temperature constant.


Study of Electric Power supply

Electricity:- Electricity is a form of energy. Electricity is the flow of electrons. We get electricity,

which is a secondary energy source, from the conversion of other sources of energy, like coal,

natural gas, oil, nuclear power, Hydel power and other natural sources, which are called primary

sources.

Electric power supply system

AC&DC: DC or direct current is steady current. It never changes its direction, and AC is

alternating in nature. AC voltage can be increased or decreased with the help of transformers. By

using high voltage AC, we can drastically reduce the transmission losses. AC can be converted

into DC easily but reverse is not so easy.

In India state electricity boards are the authorities to generate and distribute electric

energy. Power plant generates electric power at a voltage of 11 KV. This power is transmitted by

increasing the voltage at different levels as 33 KV, 66KV, 110 KV, 220KVor 400 KV from

different substations. At load centers this voltage again stepped down as 11 KV and a feeder

network is created. This feeder line energizes the 11KV/415V step down transformer, and from

these transformers electric supply can be given to consumers at 240V and 415 V as single phase

or three phases.

All domestic and commercial consumers get electric energy from the distribution network

of concerned electricity boards. Based on the power requirements of consumers Electricity

Boards may give 3-phase connection (for high power) or single phase connection (for low

power). In the three phase connections 4 wires are provided, where as in single-phase connection

one phase and a neutral connection are provided to the consumers. Phase to neutral voltage in

our country is 230 V and phase-to-phase voltage is 400 V of frequency 50 Hz. Most of the

appliances work on single-phase supply. There are some motors, which require three phase

supply.A KWh meter is provided at the consumer end for measuring the electrical energy

consumed. KSEB introduces different tariffs for different consumers, as per their connected load

and nature of connection.


PRACTICAL: 1

AIM: - STUDY OF SAFETY DEVICES. Date :- / /

Importance of safety devices

The safety features are inbuilt with electric power distribution. The current is to flow

through the path it is expected to pass and should not take another path through which it is not

expected to pass. Conductors made of copper or aluminum are provided across the path for

carrying the current and insulators like PVC, paper or rubber are provided across the path

through which the current is not expected to flow.

Under abnormal condition there can be failure of insulations and current will flow

through the undesired path which can cause damage to equipments and more important the safety

of the user. Sometimes the user may inadvertently touch a live conductor and cause electric

shock. The circuit may also carry under short circuit condition much more than normal value of

the current. The inbuilt safety features will isolate the faulty circuit from the rest of the supply.

The very high currents caused by short circuit situation can cause lots of damage to

electrical installation. Protective devices are needed to break short-circuit and overload currents.

Circuit breakers and fuses are protective devices that control the power going to a

particular route of wiring. In case of an overload or a short on that circuit, the breaker or fuse

trips and automatically shuts off power to that circuit. Fuses are the commonly used protection

devices to protect components like wires, transformers electronics circuit modules against

overload. The general idea of the fuse is that it "burns fuse link" when current gets higher than

it's rating and thus stops the current flowing.

Types of safety devices:-

Fuse Circuit breakers( MCB, MCCB & ELCB) Earthing.

Basically two types of protections are provided in the power supply system of domestic consumers.

a. Protection from over current. b. Protection from leakage current due to failure of insulation or

inadvertent contact with live conductors by the user.


Protection against electrocution

The use of exposed, substandard, badly wired, wrongly connected or damaged equipment

as well as frayed or badly repaired cables reduces the safety of an installation and increases the

risk of person receiving an electric shock.

Electrocution is a passage of current through human body, which is dangerous. The flow

of current through human body effects vital functions.

a. Breathing b. Heartbeat

A correctly chosen RCCB can detect small currents flowing to earth and reduces the risk

of electrocution. Effect of electric current through human body has been well researched and

following chart summarizes the results: Human sensitivity to electricity

500mA Immediate cardiac arrest resulting in death. 70-100mA Cardiac fibillarillation; the heart begins beats at a steady 20-30 mA Muscle contraction can cause respiratory paralysis 10mA Muscle contraction : the person remains stuck, to the conductor 1-10 mA Prickling sensations

However, electrocution should not be viewed in terms of current alone but in terms of

contact voltage. A person gets electrocuted by coming in contact with an object that has a

different potential from his/her own. The difference in potential causes the current to flow

through the body.

The human body has known limits: Under normal dry conditions, voltage limit = 50V.

In damp surroundings, voltage limit = 25V


Over current and Short circuit

One type of situation that wiring needs to be protected against is over current. The electrical

wiring is rated for certain maximum current. If you try to pull more current through it, the wiring

will heat considerably. When the wiring heats too much, it will cause the melting of cable

insulation, cause fire if there is something flammable near cable and even melt the copper

conductors in the cable. So protection is needed to guarantee that in case of something tries to

pull too much current through mains wiring, this cannot happen for any long time until the fuse

blows and stops the current.

Many people are familiar with a "short circuit", which is a type of fault that occurs when two

conductors of an electric circuit touch each other. The current flow caused by a short circuit is

usually high and rapid and is quickly detected and halted by conventional circuit protective

devices, such as fuses or circuit breakers. Ground faults are one type of problem when the

insulation fails.

Protection against over current

Every electrical circuit shall be protected against over current by suitable over current devices. These devices could be

1. Miniature Circuit Breaker (MCB) 2. Molded Case Circuit Breaker(MCCB) 3. Semi enclosed rewirable fuses 4. High Rupturing Capacity (HRC) fuses

Typical breaking capacities of protective devices are as follows:

HRC fuses - 80 kA

MCB - 16 kA

Rewirable fuses - 1 to 4 kA

1) FUSES Fuse is a wire of short length having low melting point which gives protection against excessive

current. This excessive current may be due to over load or short circuit. Under normal working

condition the current flowing through the circuit is within safe limit. But when some faults such

as short circuit occurs the current exceeds the safe limit value, the fuse wire gets heated and

melts. This will cause breaking of the circuit. After one fusing operation, fuse wire must be

rewired with the same size wire.

This basic guide will help you decide which fuse to fit to ensure the safe use of your household appliances.

Appliances up to 700 Watts = 3 Amp fuse

Appliances between 700 and 1000 Watts = 5 Amp fuse

Appliances over 1000 Watts = 13 Amp fuse


COMMON FUSE TYPES

a) Rewirable fuse b) Cartridge fuse c) HRC fuse

a) Rewirable fuse:

This is the cheapest method for protecting a circuit from short circuit. Wires of

different diameters made of lead and tin are used in the circuit. When large current flows these

wires melts and disconnects the faulty circuit from the rest of the supply.

There are different types of fuses. The usual type is the rewirable type in which the

fuse wire is carried in a removable fuse link (Fig. a). The fuse link is made of porcelain or other

suitable insulating material. The fuse carrier is push-fitted to the fuse base to make the

connection through. An advantage of this type is that the blown fuse wire can be replaced with

negligible cost. But there is a chance of selecting a wrong size of fuse wire. Another

disadvantage with rewirable fuse is that it may sometimes lead to fire hazards, when the fuse

wire blows.

Fig. (a) Re-wirable fuse

The semi enclosed rewirable fuses has the following drawbacks:

It normally melts on 50 % to 100 % excessive overload. The melting current

cannot be accurately predicted. It takes time to rewire the fuse. Standard fuse wire should be always made available.

However it is the cheapest mode of protection from short circuit.


b) Cartridge fuse

Cartridge fuse consists of a tube with metal end caps at both ends

(Fig. b). The tube is usually made of glass with no filling material.

The fuse wire is placed inside the tube, connected between the end

caps. Since the tube is made of glass, the fuse element can be easily

inspected for breakage. When the fuse is blown, the whole cartridge

has to be replaced. The advantages of cartridge fuses are, quick and

easy replacement and the fuse rating is marked on the end cap of the

cartridge itself. Cartridge fuses are mainly: used in various electrical

and electronic equipment.

(Fig. b Cartridge fuse)

c) High Rupturing Capacity Fuse (HRC)

This is a completely enclosed cartridge type of fuse. These fuses are screwed or linked in

the circuit. Generally it is used in the high power circuits. High Rupturing Capacity (HRC)

fuse consists of a porcelain tube! with metal end caps and fixing tags (Fig. c). The fuse

element is held inside the tube between the end caps and the tube is filled with silica sand or

granulated quartz. When the fuse element blows, the silica inside the tube prevent the

formation of an arc, and thus avoids the possibility of fire hazards. HRC fuse links are

available in a range of 10A to 800A.

The HRC fuse has the following advantages: It is very reliable. It has an enclosed fuse wire, therefore no chance its arc doing any damage to the surroundings. It has low temperature rise at rated load. Maintenance free

The drawbacks are: It is costly. Take time to replace the fuse.


2) CIRCUIT BREAKERS MCB and ELCB MCB is miniature circuit breaker. It is automatic in action. When excessive current passes

through the circuit, handle of MCB will moves down and thus trips the circuit. After one such an

operation we can manually reset the supply by solving the fault in that circuit. Thus rewiring

fault size fuse wire in the case of fuse can be avoided by using MCBs.

ELCB is earth leakage circuit breaker. It protects the circuit from any leakage of current. It

protects the circuit from lightning and thunder.

a) Miniature Circuit Breaker (MCB)

Miniature circuit breakers are compact devices used in distribution boards for protection

against overload and short circuit show in fig a.. The overload protection is achieved by a

thermal trip mechanism using a bimetallic strip. An electromagnetic trip mechanism is also

incorporated for instantaneous tripping in the event of a short circuit.

When there is a sudden increase in current due to a short circuit, the circuit should open

immediately, but the bimetallic strip does not respond quickly. In this case, the solenoid attracts

the plunger and thus triggers the trip mechanism. After clearing the fault, the MCB can be

switched on manual. Fig a. Fig b. Fig b. shows the current path in a typical miniature circuit breaker when it is in the 'on'

position. The current passes through a solenoid coil and a bimetallic strip. When an overload

condition persists for a few seconds, the bimetallic strip bends and triggers the trip mechanism.

Current becomes large enough. The magnetic operation is very fast and is used for braking fault

currents.

In most cases of MCBs, both types are provided so that overload currents and short circuit currents are handled with the same degree. It should however be remembered that the

mechanical operation of opening the contacts takes a definite minimum time, typically 20ms, so

that there can never be the possibility of truly instantaneous operation.

In many installations, MCBs are preferred over fuses mainly because there is no need of

rewiring the fuse wire or replacing the cartridge. MCBs are available in a range of 0.5A to 63A

normal operating current and for the entire range, the, physical dimensions are almost identical.


The principle of operation of an MCB is based on the following two principles.

i. Thermal operation ii. Magnetic operation

i. Thermal operation

In thermal operation, the extra heat produced by the high current warms the bimetal strip.

This results in bending the bimetallic strip and trips the operating contacts. The thermal

operation is slow. Hence, it is not suitable for speedy disconnection required to clear fault

currents. However, it is ideal for operation in the event of small but prolonged overload currents.

Thus, in general the thermal operation is suitable for opening the circuit in the event of excessive

current due to the overloaded machines.

ii. Magnetic operation

The magnetic operation, on the other hand is suitable for protection against high short

circuit currents. This magnetic operation is due to the magnetic field set up by a coil carrying the

current, which attracts an iron part to trip the breaker when the current becomes large enough.

The magnetic operation is very fast and is used for braking fault currents.

In most cases of MCB' s, both types are provided so that overload currents and short

circuit currents are handled with the same degree. It should however be remembered that the

mechanical operation of opening the contacts takes a definite minimum time, typically 20ms, so

that there can never be the possibility of truly instantaneous operation.

In many installations, MCBs are preferred over fuses mainly because there is no need of

rewiring the fuse wire or replacing the cartridge. MCBs are available in a range of 0.5A to 63A

normal operating current and for the entire range, the, physical dimensions are almost identical.

The major advantages of MCBs are

Instantaneous opening of the contact on short circuit faults Can be designed to operate even for very small overload currents They can be quickly reset by hand They cannot be reclosed if fault persist

In many cases they preferred over fuses as there is no need to rewire it.


b) Earth Leakage Circuit Breaker

The earth leakage circuit breaker (ELCB) is a protective device, which will automatically

trip, when there is an earth leakage within the installation. It is also known as residual

current circuit breaker (RCCB). It works on the current balance principle. The main part is

a core consisting of three windings. Here one winding carries the phase current, the other

winding carries the neutral current and the third winding to the tripping circuit. Under

normal operating conditions the net flux in the core is zero as such no emf induced in the

trip coil. However, when earth fault occurs, the phase and neutral current varies, the net

flux in the core will be different and as such, emf is induced in the trip coil and it is

energized. It then opens the circuit. The functioning of the ELCB can be checked using a

switch.

RCD - Residual Current Device. This is a generic term for the entire range of RCDs.

RCCB - Residual Current Circuit Breaker. This is basically a mechanical switch with an RCD

function added to it. Its sole function is to provide protection against earth fault currents.

RCBO- Residual Current Breaker with over current Protection. This is basically an over current

circuit breaker (such as an MCB) with an RCD function added to it. It has two functions.

Types of RCD

RCDs can be divided into two categories based on the means by which they detect and respond

to earth fault currents. The two types are Voltage Independent (VI) and Voltage Dependent

(VD). These are sometimes also referred to as electromechanical and electronic types

respectively. The VI type uses the output energy from the CT to activate a relay which in turn

activates a tripping mechanism causing the RCD to trip. The VD type uses electronic circuitry to

detect the earth fault current and to activate a tripping mechanism causing the RCD to trip. The

VI device derives its operating energy from the earth fault current whereas the VD device

derives its operating energy from the mains supply.


PRACTICAL: 2

AIM: - TO STUDY OF EARTHING. Date :- / / What is earthing /grounding?

Earthing or grounding is the term used for electrical connection to the general mass of

earth. Equipment or a system is said to be 'earthed' when it is effectively connected to the ground

with a conducting object. Earthing provides protection to personal and equipment by ensuring

operation of the protective gear and isolation of faulty circuit during:

1. Insulation failure 2. Accidental contact 3. Lightning strike

Importance of earthing

Earthing is necessary for proper functioning of certain equipments. Earthing is done also

for preventing the operating personal from hazardous shocks caused by the damage of the

heating appliances. Consider an electric heater connected to the supply using two-pin plug and

socket. If by some chance the heating element comes in contact with the metallic body of the

heater, the body of the heater being a conducting material will be at the same potential as the

heating coil. If a person comes and touches the body of the heater, current will flow through his

body, which will result in an electric shock.

To avoid unnecessary accident, it is recommended that electric heater be connected to a

3-pin socket using a 3-core cable. (Note: To see a three-core cable, open a plug of an electric

iron. There will be three wires, red, blue and green. The green wire connected to the body of the

iron is the earth wire) In this case the body of the electric heater is connected to the green wire of

the cable, which is connected to the earth through the earth terminal. Besides the body of the

electric heater, bodies of hot plates, kettles, toasters, heaters, ovens, refrigerators, air

conditioners, coolers, electric irons etc could be earthed using three pin plugs. The resistance of

the path to the earth terminal through the earth wire is very low. Hence, even if the heating

element comes in contact with the metallic body and a human being comes in contact with the

metallic body, major part of the current will flow only through the earth wire (usually the green

wire in a 3 core cable). Moreover because of the low resistance path, a large current will flow

through the phase wire and the fuse will blow off. For large current to flow, earth resistance

should be low. To achieve this proper earthing has to be done.

Earthing is classified as:

1) System earthing 2) Equipment earthing

System earthing: It is the earthing of neutrals of generating stations and substations. It is employed to limit the voltage of live conductors with respect to potential of general mass of earth. This is necessary to prevent failure of insulation.

Equipment earthing: Is earthing of noncurrent carrying metal parts of electrical equipments. As per Rules 33 and 61 of Indian Electricity Rule 1956 non-current carrying metal parts


must be earthed with two separate and distinct earth continuity conductors to an efficient

earth electrode. However equipments with double insulation need not be earthed

Some Definitions:

Earthing: A tower/ equipments connecting to the general mass of earth by means of an electrical conductor.

Earth Electrode: Connection to earth is achieved by electrically connecting a metal plate, rod or other conductors or an array of conductors to the general mass of earth. This metal plate or rod or conductor is called as "Earth electrode".

Earth lead: The conductor by which connection to earth is made.

Earth loop impedance: The total resistance of earth path including that of conductors, earth

wire, earth leads and earth electrodes at consumer end and substation end.

Factors affecting the value of earth electrode resistance

1. Electrode material. 2. Electrode size. 3. Material and size of earth wire. 4. Moisture content of soil. 5. Depth of electrode of underground. 6. Quantity of dust and charcoal in earth pit.

Earth resistance consists of following components

1. Resistance of metal electrode 2. Contact resistance between electrode and soil 3. Resistance of soil away from electrode surface.

The resistance decreases with the presence of moisture and salt in soil. To increase the

effectiveness of earth, the total earth resistance should be reduced. Efforts should be made to

reduce the resistance contributed by each of above three components.

Earth Electrodes

Earth electrodes can be following shapes

1. Driven Rods or pipes 2. Horizontal Wires 3. Four Pointed Stars 4. Conductive Plates

A. Round Vertical Plates B. Square Vertical Plates

5. Buried Radial Wires 6. Spheres made of metal 7. Water Pipes


Water pipe as earth electrode

As water pipes exist extensively and these are most of the time embedded in earth, they

can make a good earth electrode. Such earthing is not objectionable with alternating currents. But

with direct currents, the flow of fault currents in pipes produces electrolysis and results in heavy

corrosion of pipes. This electrolysis process makes the water also harmful to certain extent. If

water pipes are proposed to be used as earth electrode, then only main water supply pipe should

be used as an electrode. The water supply main pipe should have metal-to-metal joints between

its segments.

A perfect electrical connection should be made between water pipe & earth conductor.

Pipe should be cleaned thoroughly with emery paper. Earth conductor also should be cleaned

thoroughly. The cleaned conductor should be wrapped 4 to 5 times and ends clamped by nuts &

bolts. The earth resistance achieved by such an arrangement is usually a fraction of an ohm. Low

resistance of such system is due to long length of water pipe and the fact that it is mostly

embedded below earth. This method is mostly used for grounding in telephone services.

Electrodes should be made of a metal, which has a high conductivity. Normally copper is used.

The size of the electrode should be such, that it is able to conduct the expected value of stray

equipments. For example a 3 phase star wound generator must have its neutral point at earth

potential.

The salts commonly used for chemical treatment of soil are

1. Sodium Chloride 2. Calcium Chloride 3. Sodium Nitrate 4. Magnesium Sulphate

Other factors, which affect the soil resistivity, are

1. Temperature of soil: the resistivity increases when temperature falls below the freezing point. If the temperature falls from 20degrees C to O degree C, soil resistivity goes up from 7200-ohm cm to 14000-ohm cm.

2. Moisture Content of Soil: Small changes in moisture content seriously affect the resistivity. For example if the moisture content changes from 25% to 30%, soil resistivity drops from

250000-ohm cms to 6400-ohm cm. It is important that earth electrodes should be in contact

with moist soil. It should be ensured that the electrodes are deep in soil and if possible below

the permanent water level.

3. Mechanical Composition of soil: finer the grading, lower the resistance.


Methods of placing earth electrodes in soil

1. Pipe Earthing:

Pipe earthing is done by permanently placing a pipe

in wet ground. The pipe can be made of steel, galvanized

iron or cast iron. Usually GI pipes having a length of 2.5m

and an internal diameter of 38mm are used. The pipe

should not be painted or coated with any non-conducting

material.

Fig. A (1) shows an illustration of a typical pipe

electrode. The pipe should be placed atleast 1.25m below

the ground level and it should be surrounded by alternate

layers of charcoal and salt for a distance of around 15 cm.

This is to maintain the moisture level and to obtain lower

earth resistance. The earth lead of sufficient gauge should

be firmly connected to the electrode and it should be

carried in a Gl pipe at a depth of 60cm below the ground

level. A funnel with a wire mesh should be provided to

pour water into the sump. Three or four bucket of water

should be poured in a few days particularly during summer

season. This is to keep the surroundings of the electrode

permanently moist.

Fig. A (1) Cross section of pipe earthing

2. Plate earthing

A typical illustration of plate earthing is

shown in Fig. E (2). The plate electrode should

have a minimum dimension of 600x600x3.15mm

for copper plate or 600x600x6.3mm for Gl plates.

The plate electrode should be placed at least 1.5m

below the ground level. The earth conductor is to

be securely connected to the plate by means of

bolts and nuts. The bolts and nuts should be of the

same material as that of the plate. The earth

conductor should be carried in a Gl pipe buried 60

cm below the ground level. The plate electrode

should be surrounded by a layer of charcoal to

reduce the earth resistance. A separate Gl pipe with

funnel and wire mesh attached is provided to pour

water into the sump.


3. Strip earthing

For all places having a rocky soil

bed, this type of earthing is suitable. On

this system, wires or strips made of GI of

size 25 mm x 4 mm or made of copper of

size 25 mm x 1.6 mm are embedded 0.5

m, below the soil in the form of a network.

The length should not be less than 1.5 m

as per ISI specification. Detail are given in

figure below.

Effect of Soil Properties in Earthing

While it is not possible to change the fundamental nature /properties of soil at a given

location, but local variations of soil conditions do occur even in a small area. When a location for

making earthing pit has to be selected, preference should be given to location, which is likely to

give minimum electrical resistance. In the list below, soils have been arranged in ascending order

with regard to their electrical resistance.

Wet marshy lands, or lands containing ashes (Avg Resistivity 2400 ohm cms) Clay, loamy soil, arable land clay Clay & loam mixed with varying proportion of gravel & sand (Avg Resistivity

15,800 ohm cms) Damp & wet sands Dry sand Gravel & Stones


PRACTICAL: 3

AIM: To Study the different type of wirings for House hold Applications. Date :- / /

Introduction

A network of wires connecting various accessories for distribution of electrical energy from the

suppliers meter board to the numerous electrical energy consuming devices such as lamps, fans and other domestic appliances through controlling and safety devices is known as wiring system. The suppliers service cable feeding an installation terminates in what is usually called the

service fuses. In an ordinary house the service fuse is called as service cutout. Such cutouts

including service meters remain the property of the supplier and represent the furthest point of

the supplier responsibility. The point at which the consumer's wiring is connected into cutout is

known as point of commencement of supply or consumer's terminals. From consumer terminals

onwards the supply cables are entirely under the control of consumer's and so laid out as per his

selection. A typical house wiring circuit is shown in fig. a

fig (a)

Systems of distribution of electrical energy

Since as per recommendations of ISI the maximum number of points of lights, fans and socket-

outlet that can be connected in one circuit is 10 and the maximum load that can be connected in

such a circuit is 800 watts, hence in case more load or more points are required to be connected

to the supply system, then it is to be done by having more than one circuit.


In distribution board system, which is most commonly adopted for distribution of electrical

energy in a building, the fuses of various circuits are grouped together on a distribution board, sometimes simply known as fuse board.

The two copper strips, known as bus-bars, fixed in a distribution board of hard wood or metal

case are connected to the supply main through a linked switch so that the installation can be

switched off as a whole from both the poles of supply if required. A fuse is inserted in the + ve or

phase pole of each circuit so that each circuit is connected up through its own particular fuse.

In large buildings, however, if only one distribution board were used, some of the points would

be at a considerable distance from it and in such cases it is advisable to employ sub-distribution

boards either to save cable or to prevent too great voltage drop at the more distant points (lamps

or fans or other appliances). In such cases main distribution board controls the circuit to each

sub-distribution board from which the sub-circuits are taken, as shown in fig. a

The number of circuits and sub-circuits are decided as per number of points to be wired and load

to be connected to the supply system. For determination of load of an installation the following

ratings maybe assumed unless the values are known or specified.

1. Fluorescent lamps 40 watts. 2. Incandescent lamps, fans, and socket outlets 60 watts. 3. Power socket-outlets 1,000 watts. 4. Exhaust fans as per capacity of exhaust fans.


The Tree System

Another system of distribution of electrical energy in a building is the tree system. In this

system smaller branches are taken from the main branch, as shown in fig. b and the wiring

system resembles a tree. As each branch is taken off, a fuse is inserted. This system used to be

employed in early days. Now-a-days it is no more adopted due to the following draw-backs in

this system.

1. The voltage across all the lamps does not remain the same. The lamps in the

last branch will have least voltage across them on account of voltage drop in

leads.

2. A number of joints are involved in each circuit. 3. Fuses are scattered. 4. In case of occurrence of fault all the joints have to be located and if some of these

joints are concealed beneath floors or roof spaces, a lot of difficulties are to be

faced. Sometimes a number of such joints are required to be opened for testing

purposes, so damage is caused to installation, conductors and building. Methods of wiring

There are two methods of wiring known as

1. joint box system (or Tee system) and 2. Loop-in system


Joint Box or Tee System: In joint box system the connections to the lamps are made through joints made in joint boxes by

means of suitable connectors or joint cutouts. In this method though there is a saving in the

quantity of wire or cable required but the same is offset by the extra cost of joint boxes. The

other disadvantage of T-connections is that the number of T-connections made in a wiring

system results in weakness if not properly made. Now-a-days the use of this system is limited to

temporary installations only, as its cost is low. 2. Loop- in- system: This system is universally employed for connections of various lamps or other appliances in

parallel. In this system when a connection is required at a light or switch, the feed conductor is

looped-in by bringing it direct to the terminal and then carrying it forward again to the next point

to be fed, as shown in fig. d. The switch and light feeds are carried round the circuit in a series of

loops from one point to another until the last point on the circuit is reached. The phase or line conductors are looped either in switch board or box and neutral conductors are

looped either in switch board or from light or fan. Line or phase should never be looped from light or fan.


The advantages and disadvantages of loop-in system are as follows;

Advantages

1. Joint boxes are not required. 2. In loop-in system no joint is concealed beneath floor or in roof 3. spaces. As they are made only at outlets so they are accessible for inspection

and opening out merely by removing the fitments concerned. Hence fault location is easy.

Disadvantages:

1. Length of wire or cable required is more and voltage drops and copper losses are,

therefore, more.

2. Looping-in switches and lamp holders is usually difficult.

SYSTEMS OF WIRING

The types of internal wiring usually employed in our country are:

1. Cleat wiring:

In this system of internal wiring the cables used are either VIR or PVC type. The cables

are held by porcelain cleats about 6 mm above the walls or ceiling. The cleats are made in two

halves, one base and the other cap. The base is grooved to accommodate the cables and the cap is

put over it and whole of it is then screwed on wooden plugs (gutties) previously cemented into

the wall or ceiling. Thus the cables are firmly griped between the two halves of the cleats and

secured to the supporting wall or ceiling. The cleats used are of different sizes and different types

in order to accommodate cables of various sizes and different numbers of cables respectively.

The cleats are of three typesone groove, two grooves and three grooves to accommodate one,

two, and three cables respectively.


Advantages:

1. It is the cheapest system of internal wiring. 2. Its installation and dismantlement is easy and quick. 3. Material is recoverable after dismantlement. 4. Inspection, alterations and additions can be easily made. 5. Skill required is little.

Disadvantages:

1. It is not good looking. 2. It is quite temporary and perishes quickly. 3. The wires are exposed to mechanical injury.

4. The insulation catches dampness from the atmosphere and common salt like substance

appears on the insulation which lowers the insulation resistance and Causes leakage.

Hence this system of wiring cannot be used in damp places.

5. Oil and smoke are injurious to VIR insulation.

Fields of Application:

The wiring of this type is very suitable for temporary installations in dry places. This is also acceptable where appearance is not so important and cheapness is the main consideration. This system is not suitable for use in domestic premises.

2. Wooden Casing and Capping Wiring:

The cable used in this type of wiring is either VIR or PVC or any other approved

insulated cables. The cables are carried through the wooden casing enclosures. The casing

consists of V-shaped grooves (usually two to hold the cables of opposite polarity in different

groves) and is covered at the top by means of rectangular strip of wood, known as capping, of

same width as that of casing. The capping is screwed to the casing by means of wooden screws

fixed at every 15 cm on the centre fillet. To protect the casing against white ants first class

seasoned teak wood, varnished by shellac varnish is employed. Two or three cables of same

polarity (either all phases or all neutrals) may be run in one groove and in no case the cables of

opposite polarity should be run in the same groove. The casing ia usually placed 3.2 mm apart

from the wall or ceiling by means of porcelain distance pieces of thickness not less than 6.5 mm

in order to keep the casing dry at the back.


3. CTS or TRS Wiring.

In this type of wiring the cables used may be single core, twin core or three core TRS

cables with a circular oval shape. Usually single core cables are preferred. TRS cables are

sufficiently chemical proof, water proof, steam proof but are slightly affected by lubricating oils.

TRS eaoles are run on well seasoned, perfectly straight and well varnished (on all four sides)

teak wood batten of thickness 10 mm at least. The width of the batten depends upon the number

and size of cables to be carried by it. The battens are available in width of

13,19,25,31,38,44,50,56,63,69 and 75 mm. The wooden battens are secured to the walls or

ceiling by flat head wood screws to wood or other approved plugs at an interval not exceeding 75

cm. The cables are held on the wooden batten by means of tinned brass link clips already fixed

on the batten with brass pins and spaced at an interval of 10 cm in case of horizontal runs and 15

cm in case of vertical runs. The wiring after erection is neatly painted with two coats of oil-less

non-cracking paint as specified in IS 732 and so on.

Advantages

1. Its installation is easy and quick and saving in labor largely compensate for the

extra cost of the cable.

2. Its life is long. 3. Within certain limits it is fire proof. 4. It can withstand the action of most chemicals such as acids and alkalies. 5. It is cheaper than other types of wiring except cleat wiring. 6. If the job is carried out with proper attention, it gives a nice

appearance.

Disadvantages

1. Good workmanship is required to make a sound job in TRS wiring. 2. This type of wiring cannot be recommended for use in situations open to sun

or rain unless preventive steps are taken to preserve the insulation of cables.

Fields of Application

The TRS wiring is suitable for low voltage installations and is extensively used for lighting purposes everywhere i.e. in domestic, commercial or industrial buildings except workshop where it is liable to mechanical injury. This type of wiring is suitable in situations where acids and alkalies are likely to be present.

4. Lead Sheathed Wiring

This type of wiring employs conductors insulated with VIR and is covered with an outer

sheath of lead aluminum alloy containing about 95% lead. This metal sheath gives protection to

the cable from mechanical injury, dampness and atmospheric corrosion. The whole lead covering

is made electrically continuous and is connected to earth at the point of entry to protect against

electrolytic action due to leaking current and to provide safety against the sheath becoming a

live. The cables are run on wooden batten and fixed by means of link clips as in TRS wiring. The


great part of the cable employed is flat twin (the cable having two insulated conductors side by

side covered with red and black tape respectively and under one flat covering of lead alloy).

Three-core flat type cable is also used in certain cases as well as single core cables under a

circular sheath of lead alloy

Advantages

1. It provides protection against mechanical injury better than provided by 2. TRS wiring. 3. It is easy to fix and looks nice as it can be run in building without damaging

decoration and can be painted to suit colour scheme of the surroundings.

4. Its life is long if proper earth continuity is maintained throughout. 5. It can be use din damp situations provided protection against moisture effect

on the ends of the cable is given.

6. It can be used in situations exposed to rain and sun provided no joint is exposed.

Disadvantages

1. It is costlier than TRS wiring. 2. It is not suitable for places where chemical corrosion may occur. 3. In case of damage to insulation the metal sheath becomes alive and gives shock, so as to provide safety against electrical shock it is necessary that the sheath is properly earthed

and an earth wire is run side by side with it and all pieces are properly bounded or joined

together so that not a single cover is left unearthed.

4. Skilled labour and proper supervision is required. 5.


This wiring system is suitable for low voltage (up to 250 volts) installations. It may be

used in places exposed to sun and rain provided no joint is exposed. It may also be used in damp

places with a suitable protective covering. It should not be used in places where chemical

corrosion may occur.. This type of wiring is not very common in use these days except for some

small installations and distribution boards etc.

5. Conduit Wiring

In this system of wiring steel tubes, known as conduits, are installed on the surface of

walls by means of saddles or pipe hooks or buried under plaster and VIR or PVC cables are

drawn into afterwards by means of a GI wire of size of about 18 SWG. In damp situations the

conduits can be spaced from the walls by means of small wooden blocks fixed below the pipes at

regular intervals. In order to facilitate drawing of wires numbers of inspection fittings are

provided along its length. The conduits should be electrically and mechanically continuous and

connected to earth at some suitable point. The conduits used for this purpose are of two types

namely (i) light gauge (or split type) conduit and heavy gauge (or screwed type) conduit. Light

gauge or split conduit with a seam along its length is used for cheap work. It is not water tight or

even damp proof and is not permitted on medium voltage (i.e. on voltages higher than 250V).

Screwed conduit (solid drawn or with welded seam) is used for all medium voltage (250 V or

600 V) circuits and in places where good mechanical protection and absolute protection from


moisture is desired. In general the finish of the conduit is black stove-enamelled, there being a

smooth coating of enamel both on the inside and outside surface of the tube. Galvanized conduit

is also employed, especially in damp situation when the conduit is on the surface but under

ordinary conditions buried in walls it offers little, if any, advantage over good enamelled

conduits.

Advantages

1. It provides protection against mechanical damage. 2. It provides complete protection against fire due to short-circuits etc. 3. The whole system is water proof. 4. Replacement and alteration of defective wiring is easy. 5. Its life is long if the work is properly executed. 6. It is shock proof also if earthing and bonding is properly done.

Disadvantages

1. It is very costly system of wiring. 2. Its erection is not so easy and requires time. 3. Experienced and highly skilled labour is required for carrying out the job. 4. Internal condensation of moisture may cause damage to the insulation

unless the system outlets are properly drained and ventilated.


As this system of wiring provides protection against fire, mechanical damage and dampness so this is the only approved system of wiring for:

1. Places where considerable dust or puff is present such as in textile mills, saw mills, flour mills etc.

2. Damp situations. 3. In workshops for lighting and motor wiring. 4. Places, where there is a possibility of fire hazards such as in oil mills, varnish factories

etc.

5. Places, where important documents are kept such as a record room. 6. Residential and public buildings, where the appearance is the prime thing. The recessed

type conduit wiring is preferred for residential and public buildings.


CHOICE OF WIRING

The following factors should be considered before selecting a particular type of wiring.

1. Safety: The first and foremost consideration is safety to a person using electricity against leakage or shock. Where there is a possibility of fire hazard, conduit wiring is used.

2. Mechanical Protection: The wiring must be protected from mechanical damage during use.

3. Permanency: The wiring must not deteriorate unduly by action of weather, fumes, dampness etc.

4. Appearance: The wiring should he good looking. 5. Durability: The wiring must be durable. 6. Accessibility: In wiring system there should be facilities for extension, renewal or

alterations.

7. Initial Cost: The wiring selected should suit the pocket of the owner of the building. 8. Maintenance Cost: The wiring should have, as far as possible, the lowest maintenance

cost.

9. The other factors, in addition to above, to be kept in view while making the choice of wiring is load voltage to be employed, type of building etc.


Tools used in Electric Wiring

Some of the most commonly used tools are described below:

STUDY OF WIRING ACCESSORIES

Any device, associated with the wiring and electrical appliance of an installation, such as a

switch, a fuse, a plug, a socket-outlet etc. is called the wiring accessory. The cables, flexible

cords and various wiring accessories in common use are briefly described below.

SR. NO

WIRING ACCESSORIES

SIZE USE

1. Combination Pliers 15,20,25 cms For holding, twisting or cutting wires.

2. Round Nose Pliers or Flat Nose Pliers

10 cms For holding, twisting or joining the wires at narrow places.

3. Side Cutting Pliers(side cutter)

20 cms Cutting wire at narrow or ordinary places and for removing insulation.

4. Electrician Knife 10 cms It has two blades, one for removing insulation of wires and other for cleaning the wires.

5. Electric Soldering iron 25,40,65,125 W To solder the joints of wires and winding wires.

6. Cross peen Hammer 1/4 kg to 2 kg Used for fixing clip and making gitties hole in wall.

7. Ball peen Hammer 1/4 kg to 2 kg Best suited for chipping on teak wood batten, and riveting purpose in sheet metal works.

8. Tenon saw or Hand saw 30.5 cm & 40.5 cm

Used for cutting wooden boards, block casings etc.

9. Poker 10, 15 cm Used for making pilot holes for fixing wood screw.

10. Hand drill 3,6,12 mm Used for making holes in wooden blocks and boards.

11. Hacksaw 16,20,25,30 cms Used for cutting conduit G.I. pipes or mild steel.

12. Measuring Tape 10,20 mm Used for measuring the

dimension of the wiring. It is

made of steel or cotton cloth.

13. Wire Stripper & Cutter

Used for removing insulation of PVC wires and available with adjustable 22 SWG and onwards.

14. Files (Flat, round half) 3" to 4" To smooth the surface or corners of any iron board etc.

15. Crimping Tool 1.5,2.5,6mm As soldering on Aluminum is difficult, this plier is used to crimp the joint or lugs.


Switches

A manually operated device used for closing and opening or for changing the

connections of a circuit is known as a switch.

The switches used in internal wiring may be classified in various ways. According to the

type of base material they are classified as porcelain or bakelite switches. According to colour of

base they are either white or black or brown coloured switches. According to operation required,

they are classified as one way, two-way, centre off, double pole etc. switches.

1. One-way Switch

This type of switch consists of two terminals which can be easily seen from the back side

of the switch as well, without removing the cover. The switch is always connect* din series with the point (lamp, fan or socket-outlet) to be controlled. 2. Two-way Switch

The switch of this type consists of four terminals, two of them being short-circuited inside the switch. The switch of this type is usually used for the stair-case wiring or circuits where one point is to be controlled from two different places. 3. Two-way Centre off Switch

The switch of this type is just like a two-way switch but having three operations. In the

centre it becomes off. Such switches are used when two lamps are to be operated alternately.

5. Double Pole Switch

This is a combination of two one-way switches, which can be operated simultaneously as

ON-OFF terminals of both the switches, are connected together by a handle made of bakelite.

Such switches are used as interlinked switches when the load current is less than 5A and supply

voltage is under250V.Incaseeither of the voltage or current exceeds the limits mentioned above

DPI C switch is used. 5. Push-button Switches

Such switches are used for controlling the electric bells. When the knob is pressed, the circuit

is completed and the bell rings and as soon as the knob is left, the circuit becomes open. 6. Table Lamp Switch

This is a small on-off switch which is commonly used in table lamps.

7. Bed Switch

Such switches are used to switch off the table lamps or other lamps while going to sleep

or making the lamp on while getting up at night. It is connected in aeries with one of the two

flexible wires. The specialty with this switch is that fluorescent material is applied to its knob so

that it may glow at night and can easily be seen in darkness.


Socket-Outlets

The socket-outlets are used to supply electrical connections whenever required for electrical

appliances such as radios, table fans, table lamps, iron, stoves etc. Socket-outlets are of two

types two pin type and three pin type. Two pin socket-outlets have become obsolete now-a-

days. The three pin type socket-outlet has got three hollow terminals in which three pin plugs can

easily be inserted but not loosely. Two holes being of same size, are meant for making

connections to the flexible wire of the appliance and the third hole, which is bigger

comparatively, is meant for earth connections. Thus three holes or sleeves are for live, neutral

and earth connections. The three pin socket-outlets are also of two types:

1. 5 A for table fans, table lamps, radios etc, and 2. 15 A for power circuits as heater, stove, iron etc.

Three Pin Socket-Outlet Flush Mounting

Plugs

Plugs are used to take the supply from the socket-outlets for electrical appliances such as

table lamp, table fan, heater etc. Similar to socket-outlets plugs are also of two types namely two

pin and three pin. Two pin type plugs have become obsolete now-a-days. Three pin type plugs

consist of three pins usually made from brass. To the two pins which are thin and of same size,

flexible wires are connected and then covered up. To the third pin, which is thicker

comparatively, earth wire from the electrical appliance is connected. Similar to 3 pin-socket

outlets 3 pin plugs are also of two types5 A and 15 A. (see fig. 26.10)


Lamp Holders

As the name indicates the function of lamp holder is to support the lamp and also to connect it electrically. These are designed for quick removal and replacement of the lamp. Lamp holders are of many types. A few will be described here. Lamp-holders may be either of brass or bakelite type with porcelain interior. Brass holders are more durable but may give shock if connections are poor. Though bakelite holders are not durable, but do not give shock. 1.Pendant or Cored Grip Holders Such a lamp holder is used when the lamp is to be suspended from the flexible cord. Such a lamp

holder is hanged vertically downward from the ceiling with flu flexible cord, one end of which

makes electrical connections with the ceiling rose and other with the lamp holder and thus with

the lamp. Pendant Lamp Holder


PRACTICAL: 4

Aim: - To study the working of table fan and ceiling fan. Date: - / /

Theory:-

Fan is an essential home appliance nowadays and is available in different style and facili-

ties. Generally used types are table fan and ceiling fan. We can mount the ceiling fan on the

ceiling for providing wind to whole the room. As per IE rule the minimum height from floor to

fan must be2.5 meter. Table fan can be places on tabletop or any flat surface. But it has

minimum space limit compared to ceiling fan.

Construction

Main parts of a ceiling fan are 1. Winding 2. Capacitor & 3. Regulator

Winding of the motor can be done manually or by automated machine. Regulator may be

electronic type or resistance type. Electronic type regulator has negligible power loss and

compact size. But in the case of resistance type, resistances are connected in series with the

circuit; this may cause power loss as heat.

In table fan one permanent split capacitor run (PSC) motor is the heart of a fan. This motor

consists of two windings one as starting winding and other as running winding. Starting winding

of this motor has high resistance and low reactance but running winding has low resistance and

high reactance. One capacitor is connected in series with the starting winding and whole of this

circuit is put in parallel across running winding. In the case of ceiling fan these two windings are

placed in stator in the inner side of the fan. Rotor has no winding; it is the outer body of the fan.

Ceiling fan motor operates just in opposite manner as compared to general motor. That is actual

rotor of the motor is blocked and the stator is free to rotate. So ceiling fan runs in anticlockwise

direction. At the same time table fan motor is operated as normal case and so it runs in clockwise

direction. Capacitor connected in series with the starting winding should be value 2.5 micro

farad. Pyranel insulated foil paper capacitor is using for this purpose. It helps to provide a split

phase effect from single phase AC supply.


SERVICING

Problems and solutions normally occurring in fans are as follows

1. Fan is not working when supply is given o Check the supply at the consuming end. o Dismantle the fan from ceiling and remove the cover. Check the

windings, if it is burnt rewind it with proper gauge copper wire.

o Number of turns must be equal to the previous winding, because it may affect the speed of the fan. If starting winding is burnt, it alone can be replaced but in the

case of running winding we want change these two sets of windings.

2. Fan is not starting and will work when push to start

o Check the voltage at the consuming end o Dismantle the capacitor from fan and connect it to AC supply for 30 sec. Then

disconnect and short circuit the capacitor terminals. At that time we can hear

one spot sound if it working, otherwise it can be replaced by new one.

o Check the bearing of the motor; if it is dirty grease may be applied. o Induction type single phase energy meter


PRACTICAL: 5 Aim: - To study the working of induction type energy meter. Date: - / / Induction type instruments are used only for a.c measurements. These instruments can be

used either as ammeter, voltmeter or wattmeter. However, the induction principle finds its widest

application as an energy meter. Induction type single-phase energy meter is used invariably to

measure the energy consumption in any a.c circuit in a prescribed period where supply voltage

and frequency are constant. Energy meter is an integrating instrument which measures the total

quantity of electrical energy supplied to the circuit in a given period.

Principle:

The basic principle of induction type energy meter is electromagnetic induction. When

alternating current flows through two suitably located coils (current coil and potential coil)

produces rotating magnetic field which is cut by the metallic disc suspended near to the coils,

Thus an e.m.f is induced in the disc which circulates eddy currents in it. By the interaction of

rotating magnetic field and eddy currents, torque is developed and causes the disc to rotate.

Construction

An induction type single phase energy meters, as shown in fig. has the following main parts of

the operating mechanism. Driving system

Moving System

Braking System Recording mechanism

Driving System:- The driving system of the meter consists of two electromagnets,

1. Series magnet 2. shunt magnet

1. Series magnet:

It consists of a number of U- shaped laminations of silicon steel together to form a core. A

core of thick wire having a few turns is wound on both the legs of U-shaped magnet as shown

in fig. This coil is connected in series with load. Thus it is excited by the circuit current I and is

known as current coil. This magnet is placed below the aluminium disc and produces the

magnetic field se proportional to and in phase with the line current I.

2. Shunt Magnet

It consist of a number of M-shaped laminations of silicon steel assembled together to form a

core. A coil of thin wire having large number of turns is wounded on the central limb of the

magnet as shown m above: Fig. The coil is connected across the load. Thus it is excited by the


current proportional to the supply voltage and is known as, potential or pressure coil. This

magnet is placed above the aluminium disc.

In order to obtain deflecting torque, current in the pressure coil must lag behind the supply

voltage by 90. For this the copper shading band (Short circuiting copper ring) is provided on the

central limb of the shunt magnet. The phase difference of 90 is obtained by adjusting the

position of this shading band. The shading band acts as Short circuited transformer secondary.

Since its resistance Is negligibly small as compared to its inductance, therefore current

circulating in the shading band lags behind the supply voltage nearly by 90. Thus the shunt

magnet produced a field sh proportional to applied voltage. This field is in phase with the

current flowing through the pressure coil Ip but is in quadrature with the applied voltage.

Moving System:

It consists of a light aluminum disc mounted on a vertical spindle. The aluminium disc is

positioned in the air gap between series and shunt magnets, The spindle is supported by a cup

shaped jewelled bearing at the bottom end and has a spring jewel bearing at the top end. Since

there is no control spring the disc makes continous rotation under the action of deflecting torque.

Braking system:

A permanent magnet positioned near the edge of the aluminium disc as showin the Fig.

forms the braking system. When the aluminium disc moves in the field of the braking magnet,

flux is cat and currents are induced in the disc. The direction of induced current is such that it

opposes the rotation (lenz's law). Thus braking torque is produced. Since the induced current is

proportional to the speed of the disc (N) therefore braking torque (T ) is proportional to the disc

speed (ie) T. x N.

The position of braking magnet is adjustable and therefore, braking torque can be

adjusted by shifting the magnet to different radial positions. If the braking magnet is moved

towards the centre of the disc, flux cut the disc is less which reduces the induced current and thus

the braking torque is reduced. Hence by the inward movement of the magnet, braking torque

decreases but the speed of the disc increases and vice-versa.

The function of recording or registering mechanism is to record continuosly a number on

the dial which is proportional to the revolutions made by the moving system. The number of

revolutions of the disc is a measure of the electrical energy passing through the meter.


Working:

When the energy meter is connected in the circuit, the current coil carries the load current

and pressure coil carries the current proportional to the supply voltage. The magnetic field

produced by the series magnet (series coil) is in phase with the line current and magnetic field

produced by the shunt magnet (pressure coil) is in quadrature with the applied voltage (since the

coil is highly inductive). Thus a phase difference exists between the fluxes produced by the two

coils. This set up a rotating field which interacts with the disc and produces a driving torque and

thus, disc starts rotating. The number of revolutions made by the disc depends upon the energy

passing through the meter. The spindle is geared to the recording mechanism so that electrical

energy consumed in the circuit is directly registered in kWh.

The speed of the disc is adjusted by adjusting the position of the braking magnet. For

example, if the energy meter registers less energy than the energy actually consumed in the

circuit. Then, the speed of the disc has to be increased which is obtained by shifting the braking

magnet nearer to the centre of the disc and vice-versa.


Electric lamps

The first ever practical model of the incandescent lamp was invented in 1879. Since then,

there has been series of developments in the area of light source and lighting technology. The

first incandescent lamp was made with a carbon filament with a useful light output of only three

lumens per watt. A long time has gone by since then and today there are about 200 thousand

different types of demands keeping in view the wattage, size, applications, etc. It includes about

40,000 types of incandescent lamps alone. Lamp differ from each other in terms of luminous

flux, light, the colour of the light, their colour rendering characteristics, size and energy

consumption. Broadly, different types of lamps can be classified as follows:

1. Incandescent lamp (GLS) 2. Fluorescent lamps (FTL) 3. High Pressure Mercury Vapour lamps (HPMVL) 4. Halogen lamps 5. High Pressure Sodium Vapour Lamps (HPSVL) 6. Low Pressure Sodium Vapour lamps (LPSVL) 7. Metal Halide lamps 8. Mercury Blended lamps 9. Compact Fluorescent lamps

1. Incandescent Lamps:- Incandescent lamp has a history of over a century. The design of the lamp has changed many

times, but still it remains to be the most popular type due to its simple construction, easy

replacement and cheap cost. Incandescent lamps are available in wattage rating upto 1500W.

Construction

Fig.a illustrates the construction of a general lighting service (GLS) lamp. Incandescent

lamps work on the principle that visible light and infrared radiation are emitted as a result of

heating of the filament wire by a current passing through it. These emissions become noticeable

above 500C. Tungsten is usually used as the filament material since it has high melting point.

The diameter of the filament wire is determined by the operating current and the length of the

filament by the operating voltage. For normal voltages, the length will be too much and a coiled

coil arrangement is adopted to accommodate the long filament wire. The filament is mounted on

leads that carry the current.


(Fig.a Incandescent lamp construction)

To reduce the effect of vibration, additional filament supports are also employed. The

filament assembly is usually housed in a pear shaped glass bulb. The bulb diameter for 25W,

40W, 60W and 100W coiled coil type lamps is 60 mm. The size of the bulb is decided by the

maximum limit for cap temperature. For the same wattage if the bulb size is reduced, the cap

temperature will increase and eventually result in failure of mounting accessories.

Inside the lamp it may be vacuum or a filling of inert gas like argon or krypton with a

small percentage of nitrogen. The choice between vacuum and gas filling is made after

considering the following factors. Vacuum reduces heat loss and therefore helps to get the

highest temperature of the filament and hence more light output. But it also increases the

evaporation rate of tungsten, reducing its life. Filling with an inert gas reduces evaporation of the

filament material, but conducts heat away from the filament, reducing the temperature and the

light output. Generally vacuum is used for low wattage lamps (15W or below) and gas filling for

higher power lamps.

Performance

Incandescent lamp is the most widely used lamp because of its cheap cost and simple

usage. It is available in a wide range of voltage and wattage ratings and do not require any

additional accessories for starting or normal operation. They have excellent colour rendering

index and are used as automobile lamps, panel lamps etc. in addition to general lighting

purposes.

The major disadvantage of the incandescent lamp is its low efficacy. A typical 40W lamp

may have an efficacy of around 10 lumens/watt only. Compared to other types

of lamps, the life is also less - around 1000 hours.


2. Fluorescent Lamps

Fluorescent lamp is the most widely used discharge lamp. It is an energy

efficient lamp available in low and medium wattage range making it suitable for

domestic and commercial lighting purposes.

Construction

The construction of a standard fluorescent lamp is shown in Fig. It consists of a glass

tube of around 36 mm diameter and a length of 1200 mm. The inner surface of the tube is coated

with a fluorescent powder - usually phosphor coating. Tungsten wire electrodes with bi-pin cap

are provided at both ends. There is an electrode shield around each electrode to reduce the

blackening of the tubes due to deposition of evaporated tungsten. The tube is filled with an inert

gas such as argon to a pressure of 1.5 to 5 mm of mercury. A small drop-let of mercury is also

introduced into the tube. During normal operation this mercury vaporizes and helps to maintain

the discharge.

Operation

Fluorescent lamps are designed for switch start operation. A typical switch start circuit is

shown in Fig. The starter consists of two bimetallic contacts, housed in a small glass bulb filled

with a noble gas at low pressure. The contacts are positioned with a narrow separation between

them. When the normal voltage is applied, it creates a glow discharge between the bimetallic

contacts and due to heating they bend towards each other. The contacts touch each other for one


or two seconds and the current path is completed through the inductive ballast and the filament

electrodes. These current results in preheating the electrodes. As the bimetallic contacts touch,

the glow discharge stops and now the contacts cool down and leave apart to open the circuit. The

sudden break of current will induce a high voltage (600-1500V) in the ballast and is applied

across -the tube, which in turn trigger the discharge through the tube. The capacitor, which is

connected across the starter contact, is provided to reduce the radio interference due to switching

operations. The starter has no function once the lamp is started.

Like other discharge lamps, fluorescent lamps are also having a negative temperature

coefficient of resistance. This means the resistance of the tube decreases when temperature is

increased, resulting in increase of current. Therefore the ballast is essential during normal

operation also to regulate the lamp current. When the ballast is connected in series with the

circuit, it regulates the lamp current. The capacitor across the supply line is for power factor

improvement.

When there is a discharge through the lamp, it produces radiations mainly in the

ultraviolet region. This radiation is converted to visible radiation by the phosphor coating on the

inner side of the glass tube.

Performance

The luminous efficiency of the fluorescent lamp is around 75 lumens/watt, which is much

higher than incandescent lamps. The colour rendering index of this lamp is in the rage of 50-60

and this is sufficient for normal domestic or commercial lighting. Fluorescent tamps have an

expected life varying from 6000 to 20000 hours. One disadvantage with this lamp is that the

power factor of the circuit is low (around 0.5), but this problem can be solved to some extent by

connecting a capacitor across the supply.

Compact Fluorescent Lamps

Compact Fluorescent Lamps (CFLs) are now becoming

very popular. It is a smaller type fluorescent lamp that is even

more energy efficient. CFLs are available in wattage ratings of

5W, 7W, 9W, 11W, 13W, 18W, 23W etc. and usually they come

with an adapter having a cap similar to the incandescent lamp

cap so that the lamp can directly be fixed into an ordinary lamp

holder. The adapter contains necessary circuits for startup and

normal operation of the lamp. The principle of operation is very

similar to ordinary fluorescent lamps, but uses a thin tube. The

tube may be U shaped or having multiple folds. The light output

of an 11W CFL is equivalent to that of a 60W incandescent

lamp. This means the energy saving by the use of CFLs is

enormous.


PRACTICAL: 6

AIM: To study multi meter and perform difference functions of it. Date: - / /

THEORY:-

A multi meter is an instrument designed to measure two or more electrical quantities such

as voltage , current & resistance. Basically two types of multi meters are used: analog & digital.

Now a days mostly digital multi meters are preferred. In addition with above quantities advance

digital multi meters are used for checking diode, transistor as well as capacitance measurement.

CONSTRUCTION:-

It consists of moving coil instrument, a no of ammeter shunts, voltmeter multipliers,

rectifier and selector switches all in single casing. Selection of particular mode of measurement

required ( i.e. D.C. or A.C. )is effected by function selector switch & range selector switch can

be set to give a choice of several ranges of current, voltage & resistance. A suitable protection is

provided to the meter movement against possible overload during its use.

OPERATION :-

Circuit diagram shows basic circuitry of multimeter for the measurement of different

electrical quantities. A multiplier provides a high voltage range while shunt resistance provides

higher current range. A series rectifier make the measurement of A.C. voltage possible with the

same D.C. meter movement. Thus the same scales are used for both A.C. & D.C. current &

voltage. For resistance measurement a set of voltage from an internal battery is applied across the

resistance & resulting current is measured. By Ohms law, this current being inversely proportional to the resistance, scale is calibrated to give directly resistance in ohms to use. The

resistance scale is exactly reverse of the current scale i.e. full scale deflection of pointer

corresponds to maximum current in the range but on the resistance scale it corresponds to zero

resistance.

Even through the total ckt of multimeter is complex fig. A to fig. D shows separately the

simplified ckt diagram of different sections of typical multimeter ckt. Used for various


measurements. This fig. Is more or less self explanatory.

PROCEDURE :

1. Measure unknown D. C. voltage , A. C. voltage by connecting multimeter across the ckt. 2. Measure D.C. current and A.C. current by connecting multimeter in series with ckt. 3. Measure resistance and capacitance directly with out connecting supply. 4. Check Transistor & diode on multimeter.

OBSERVATIONS :

1. Value of unknown resistance = R = __________ohms. 2. Value of voltage across D.C. supply =V1 =___________Volts 3. Value of voltage across A.C. supply = V2 =___________Volt 4. Value of unknown capacitor = C = ____________farad. 5. Value of A.C. current in the ckt = I1 = __________Amps. 6. Value of D.C. current in the ckt = I2 = __________Amps

APPLICATIONS :

Being portable and compact instrument, multimeters are widely used in fields, shops &

laboratories to measure a wide range of D.C. Voltage & currents. A. C. voltage & currents,

resistance and capacitance measurements. It is also used to check continuity of conductors and

windings.


PRACTICAL:-1 DATE:-

Aim: To Study different electrical and electronics symbols.

Component name Symbol Symbol

Electrical Wire

Connected Wires

Not Connected Wires

SPST Toggle Switch

SPDT Toggle Switch

Pushbutton Switch

(N.O)

Pushbutton Switch

(N.C)

Earth Ground

Chassis Ground

Digital / Common

Ground

Resistor (IEEE)

Resistor (IEC)

Potentiometer (IEEE)


Potentiometer (IEC)

Variable Resistor /

Rheostat (IEEE)

Variable Resistor /

Rheostat (IEC)

Trimmer Resistor

Thermistor

Capacitor

Capacitor

Polarized Capacitor

2 workshop 2110017

Documents

lab bench

lab work

specific lab

lab period

study type of earthing

study of safety devices

study multi meter

study practicals date