automatic induction motor

8/2/2019 Automatic Induction Motor

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INTRODUCTIONMan is an ambitious creator. He has conquered the world

of science and has reached to this 21ST century. In pre-cuts of perfection. He has

cared much for automation and product quality which is directly co related to

electronics.

In this fact developing society, electronic has come to stay

as the most important branch of Engineering. Electronic devices are being used in

almost all the industries for quality control and automation. They have become a fast

replacement of present workers army which is engaged in processing and assembling

of the factory.

Great strides taken in the industrial applications of

electronics during recent years have demonstrated that this versatile tool can be of

great importance in increasing production. Efficiency and control. The rapid growth

of electronic technology appears as a formidable challenge to the beginners. The

purpose of this introduction is the presentation of elementary knowledge of modern

electronics.

The branch of engineering which deals with current

conduction through a vacuum or gas or semiconductor and study of flow of electrons

through these is known as Electronics.


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Electronics essentially deals with electronic devices and

their applications. As ELECTRONIC DEVICE is that in which electrons flow through

a vacuum or gas or semiconductors. Such devices have valuable properties which

enable is function and behave as a friend as man today.

Electronics has gained much importance due to its

numerous applications in industries. In Industries, electronic circuits and electron

devices are used in system on apparatus which quite useful.

Electronic devices are capable of performing lots of

different types of function.


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PURPOSE OF PROJECTAn engineer discover new ideas and identifies opportunities

in various sectors of national economy. He explores the possibilities of starting

adventures infield of agriculture, trade, industry, transport and communication etc.

An engineering project is a combination of numerous

activities on the part of entrepreneurs, organisers, designers, workers and etc. project

is a reflection of hard but harmonious labour on the part of above agencies.

The engineer is the key element in any project work and it

is not possible to attain success for every engineer. An engineer should posses certain

qualities and characteristics to achieve success in project or task undertaken. The

characteristics which contribute to engineers success in his.

Technical competence, better judgement, intelligence,

leadership, self confidence, attitude of creativeness, honesty and emotional stability.

The engineering project is a perfect co-detail of the

practical aspects of humanity and economics. The project provokes an engineer to

deal problem from a standpoint of view of the society. The engineer ultimate

aim is to do and dedicate himself for the society.


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INTRODUCTION OF THE PROJECT

Automatic induction motor starter with programmable timer.

Induction motors are popular due to their low-cost, sturdy

construction, fast pick-up , low maintenance expenditure and good efficiency. The

DOL ( direct-on-line ) starters and star/delta starters used for starting and running of

induction motors provide coarse type of protect ions against voltage fluctuations and

single phasing. Induction motors are very sensitive to low voltage and single phasing

during which they draw a heavy current and can burn out unless switched of within

few seconds of occurrence of such conditions. This makes the requirement of a

sensitive protective device absolutely essential to avoid burning of induction motors

under such conditions.

The circuit of an automatic starter, incorporating the

important features given below, is described here. It is meant to be used in

conjunction with a DOL starter.

1. Under-voltage and over-voltage cut-out.2. Single phasing prevention.3.Automatic start on resumption of proper conditions.4. 24-hour programmable off timer (on completion of actual runtime of the motor).5. Specially suited for remote operation of induction motor.


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INTRODUCTION OF INDUCTION MOTORWith the almost universal adoption of a.c. system of

distribution of electric energy for light and power, the field of application of a.c

motors has widened considerably during recent years. As a result, motor

manufacturers have tries, over the last few decades, to perfect various types of a.c.

motors suitable for all classes of industrial drives and for both single & three phase

a.c. supply. This has given rise to bewildering multiplicity of types whose proper

classification often offers considerable difficulty. Different a.c. motors may however,

be classified and divided into various groups from the following different points of

view:

1. AS REGARDS THEIR PRINCIPLE OF OPERATION

A) Synchronous motors

i) plain and ii) super-

B) Asynchronous motors

a) Induction motors

i) Squirrel cage {single, double}

ii) Slip-ring (external resistance)

b) Commutator motors


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i) Series {single-phase, universal}

ii) Compensated {conductively, inductively}

iii) shunt {simple, compensated}

iv) repulsion {straight , compensated}

2. AS REGARDS THE TYPE OF CURRENT

i) single phase

ii) three phase

3. AS REGARDS THEIR SPEED

i) constant speed

ii) variable speed

iii) adjustable speed

4. AS REGARDS THEIR STRUCTURAL FEATURES

i) open ii) enclosed

iii) semi-enclosed iv) ventilated

v) pipe-ventilated iv) riveted frame eye etc.

PRINCIPLE OF INDUCTION MOTOR

As a general rule, conversion of electrical power into

mechanical power takes place in the rotating part of an electric motor .In demotors,

the electrical power is conducted directly to the armature (i.e. rotating part) through

brushes and commutator . Hence, in this sense, a dc motor can be called a

conduction motor. However , in a c motors, the rotor does not receive electric power

by conduction hut by induction in exactly the same way as the secondary of a 2-


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winding transformer receives its power from the primary. That is why such motors are

known as induction motors. Infact, an induction motor can be treated as a rotating

transformer i.e. one in which primary winding is stationary but the secondary is free

to rotate.

Of all the a. c. motors, the polyphase induction motor is the

one which is extensively- used for various kinds of industrial drives. It has the

following main advantages and also some disadvantages :

Advantages :

1. It has very simple and extremely rugged, almost unbreakable construction(especially squirrel-cage type).

2. Its cost is low and it is very reliable.3. It has sufficiently high efficiency. In normal running condition. No brushes are

needed, hence frictional losses are reduced. It starting arrangement is simple

especially for squirrel-cage type motor.

Disadvantages:

1. Its speed cannot be varied without sacrificing some of its efficiency.2. Just like a. d. c. shunt motor, its speed decreases with increase in

load.

3. Its starting torque is somewhat inferior to that of a. d. c. shuntmotor.


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Construction

An induction motor consists essentially of two main parts :

a) a stator and b) a rotor.

a) Stator

The stator of an induction motor is. in principle, the same

as that of a synchronous motor or generator . It is made up of a number of stampings

which are slotted to receive the windings. The stator carries a 3 phase winding and is

fed from a 3phase supply. It is wound for a definite number of poles the exact number

of poles being determined by the requirements of speed. Greater the number of poles,

lesser the speed and vice versa. The sattor windings, when supplied with 3 phase

currents, produce a magnetic flux which is of constant magnitude but which revolves

(or rotates) at synchronous speed (given by Ns =- 120f/P). The revolving magnetic

flux induces an e.m.f. in the rotor by mutual induction.

b) Rotor

i) Squirrel-cage rotor : Motors employing this type of rotor are known assquirrel-cage induction motors

ii) Phase wound or wound rotor :- Motors employing this type of rotor arevariously known as phase-wound motors or wound motors or as slip -

ring motors.


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THE CIRCUITAs the circuit being described is required to be used with a DOL starter, the internal

diagram of the same is given in Fig. 1. The three phases (R. Y, and B) entering the

starter are passed via fuses Fl, F2. and F3. The current rating of the fuses would

depend on contactor and motor current ratings. The three phases from the DOL

starter are extended to the automatic starter circuit of Fig. 2 via points marked R ', Y',

and B'. The other points which are to be extended to Fig. 2 are marked C through F.

All the points marked identically in Figs I and 2 are to he connected together.Functions of switches and relays. To understand the

circuit operation, it is essential to know the effect of switches S1 through S6 and

contacts of relays RLI and RL2 in on and off conditions. These are discussed below.

When switches S1 and S2 are off, only manual operation of

the DOL starter, without protections offered by the circuit of Fig. 2, is possible. The C

and D points are shorted (via switch S1 in off position) whereas E and F points

remain open. in this state, relay contacts have no effect on the DOL starter operation.

The motor can be switched on by momentary operation of start switch s6. Please note

that red ( R ) phase is always connected to one side of the EM (electromagnetic) coil

of contactor. The blue ( B ) phase gets extended to the other side of contactor coil

through switch S6 (in depressed state) , normally made contacts of stop switch s5 (red

button) and shorted C and D points (via switch S1 in off position). Once the contactor

coil is energised, it is latched via its own contact marked '5 ' and closed dry run


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points D1 and D2 to provide alternate path for B phase to the contactor coil. All three

phases (R. Y, and B) are extended to the induction motor via the closed contacts of the

contactor, and the motor runs.

When switch SI is on and switch S2 is off, the red (R) phase

connection to transformer XI through, while yellow (Y) phase is already connected to

bottom end of transformer X2. In this state, sensing circuit and B- Y phase detector

circuits of Fig. 2 are effective. If all phases are available and voltages are within

proper limits, relay RL1 will get energized (as explained later in the text) to close

contacts C and D. However, contacts E and F remain open irrespective of the state of

relay RL2 (contacts of relayRL2 come in parallel with the contacts of start switch,

provided switch S2 is on. Thus in this condition, although safety circuits are

functional, auto starting is not feasible. Manual start button S6 has to be pressed for

starting the induction motor. This mode of operation is termed here as mode 1.

When switches SI and S2 are both on. then the sensing

circuit (for under/over voltages and single phasing) as well as auto start circuits are

operational. The effect of switch S1 and relay RL1 has already been explained above.

Relay RL2, which remains, on for a short while, along with tenderization of relay RLI,

acts in the same way as momentary depression of start switch S6 to provide auto

start/restart facility when 3-phase voltages are within limits. This is termed here as

mode 2 operation.

Switch S3 is used for automatic switching off of the

induction motor after it has operated for a pre-programmed period selected with the


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help of rotary switch S4. During mode 1 (switch 1 on and switch 2 off) operation

when switch 3 is on, the induction motor will be switched off when programmed on-

time' is completed or whenever power fails. However, after power resumes (and if all

phase voltages are within limits), the motor can be restarted with the help of start

switch manually, provided the programmed period is not over. During mode 2 (both

switches S1 and S2 on)operation if switch S3 is on, the motor will keep restarting

automatically whenever power resumes (or all 3-phase voltages become all right)

until the programmed running period is over.

Power supply. The power supply for the schematic circuit

of Fig. 2 is derived from R and Y phases, using two mains transformers with primary

voltage rating of 230V AC connected in series across it through DPDT slide switch

S1. Their secondaries rated at 6V-0-6V AC, 200mA are also connected in series to

realise 12V-0-12V output across rectifier diodes Dl and D2, connected as full-wave

rectifiers. The output of rectifier, after some smoothing by capacitor C1. is used for

the purpose of sampling of under/over voltage conditions. The output across capacitor

C1, after passing through diode D3, is further filtered by capacitor C3 before

regulation by 9-volt regulator 7809 (ICI). The regulated output of ICI regulator is

used for powering the entire circuit. No heat sink is required for regulator 7809.

When two transformers (X1 and X2) are used in this

fashion, the AC output voltage should be checked after connecting the secondaries of

both transformers in series. If no voltage is present across anodes of diodes Dl and

D2 then either primary or secondary connections need be reversed (but not both).


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INTEGRATED CIRCUIT 4060

DESCRIPTION:

Integrated circuit 4060 is a sixteen pin CMOS integrated

circuit. It is a twelve stage Ripple Carry Binary Counter. The counters are advanced

one count on the negative transition of each clock pulse. The counters are reset to the

zero state by a logical I at the reset input independent of clock.

CHARACTERISTICS ;

1. It has wide supply voltage range from Iv. To I 5v.2. Integrated circuit 4060 had high noise immunity s 0.45 VDO.3. Its lower power Transistor Logic is Fan out of two driving 741. or one driving

74LS.

4. Maximum speed of operation is 8 MHz. Tip. At = 10 volts.5. It is used Schmitt trigger clock input.

ABSOLUTE MAXIMUM RATING :-

7. Its .supply voltage VDD is -0.5v. to + 18v.

2. Its input voltage VIN is -0.5v. to + 0.5v.

3. It has storage temperature of Ts -65o

C to 150o

C

4. It has package Dissipation

a) . In Dual-in-line 700 MW.

b) In Small-out-line 500 MW


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5. It has head temperature (T,) of 260o

C

6. Soldering is within 10 sec. Nods.

RECOMMENDED OPERATING CONDITION :

Its supply voltage VDD is +3 volts to + 15 volts and

input voltage Vin is volts to VBD. Its operating temperature range ( T1) is 10o

C to +

85o

C.

INTEGRATED CIRCUIT LM 393DESCRIPTION.

LM 393 is eight pin linear IC consisting of two opamps. It

has two independent processing voltage comparators having offset voltage

specification as low as 2 mV designed specifically to operate on single power supply

over a wide range. Operation from split power supply current drain is independent of

magnitude of power supply voltage. These comparators also have a unique

characteristics that the input common-mode voltage includes ground even if operated

eight single power supply voltage.

Application areas includes limit comparators. Simple

analog to digital converter, pulse, square wave any time delay generator. It has a

wide range of Vco. MOS clock timers multivibrators and single voltage digital logic


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gates. This series was designed to interface directly with TTI and CMOS logic where

its law power drain is a distance advantage over other standard comparators.

SILENT FEATURES :

1. If gives wide supply voltage range. Dual supply varies from 2 VDC to 36 VDCand 1.0 VDC to 18 VDC.

2. If gives very low supply current drain about 0.4 MA.3. It is independent of supply voltage.4. It has low triasing current nearly about 25 mA and input offset current upto 5

nA.

5. Maximum offset voltage is about3 mV.6. Its input common mode voltage range includes ground.7. Its differential input voltage range to power supply voltage.8. At 4 MA current its output low saturation voltage is 250 mV.9. Its output voltage is compatible with TTl, DTL, ECL and CMOS logic system.

ADVANTAGES :-

1. It is a high precision comparator.2. If eliminates need power supply.3. It reduces Vos drift over temperature.4. It is compatible with all forms of logic.5. Power drain is suitable for battery operation.


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INTEGRATED CIRCUIT 7809DESCRIPTION:

IC-7809 is a three terminal positive regulator, it is self

contained having fixed voltage capability upto 1.5 amperes load current and input

voltage upto 15ov. It has a unique feature to set the output voltage on chips. The 7809

version is now much improved with load regulation characteristics.

Though designed as fixed voltage regulator the output

voltage can he increased through us of simple voltage divider. The low quiescent

drain current of device insures good regulation when this method is used. In this we

give positive dry battery voltage to input terminal of 4809 and get + 9v. regulated

output voltage from o/p terminal of IC.

SILENT FEATURES :

1.

Ifs output voltage is 9 v.

2. The maximum output current is I ampere.3. Its output impedance Ro is 30 milli ohm.4. The minimum input voltage required for operation is greater than 3v.5. It has terminal load protection.


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INTEGRATED CIRCUIT 555

A 555 monolithic timing ckt. Is a highly stable controller capable of producing an

accurate time delay or oscillation. Additional terminals are provided for triggering

or resulting if desired. In the time delay mode of operation, the time is precisely

controlled by one external resistive and capacitive for a stable operation as an

oscillator, the free running frequently and the duty cycle are both accurately

controlled. With two external resisters and capacitors. The ckt. May be triggered 7

reset on falling waveform and the output structure can source or sink upto 200 ml. Or

drive TTL ckt. Fig.4.5 shows pin-diagram of IC555.

The NE versions are similar except for minimum

temperature ratings. The general purpose type NE555 operates reliably only over

a range of 0 degree centigrade to 70 degree centigrade.

FEATURES

1. Timings from microseconds to hours2. Operates in both stable & monostable modes3. Adjustable duty cycle4.

High current output, can source or sinks zero ma.

5. Output can drive TTL6. Temperature stability of 0.005/ deg. Centigrade.7. Normally ON and normally OFF output.


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APPLICATIONS .

1. Precision Timings2. Pulse Generation3. Sequential Timing4. Time delay generation5. Pulse width modulation6. Pulse position modulation7. Mission pulse detection

ABSOLUTE MAXIMUM RATINGS :--

1. 7. Supply voltage- + 18 volts2. 2. Power dissipation - 60 mw3. Operating Temperature Range - 0 deg. Ceg. To 70 deg. Ceg.4. NE - 5555. Storage Temperature Range - 65 deg. Ceg. To 150 deg. Ceg.6. Lead Temperature- + 300 deg. Ceg. ( Soldering 60 sec. )

The external connections facilities for free tuning and self triggering mode for

operation are shown. The three equal register R for the deference level of upper

comparator at 2/3 vcc. There reference levels are required to control.


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STUDY OF COMPONENTSApart from different ICs and gates we have used many

other components such as

a) Capacitorb) Transistorsc) Resistorsd) Diodes

Lets discuss these components one by one is short.

a) CAPACITOR :

It is a system of electrical conductors and insulators the

principle characteristic of which is capacitance. The simplest form consists of two

parallel metal plates separated by layer of air or some other insulating material that

is, dielectrode such as ceramic, mica etc. The capacitor C of such a parallel plate

capacitor is given by :-

Where E = Permitivity of farad meter

A = Area of the plate

D = Distance of separation between plates

Hence, we can said that capacitor is the property of a

system which enables it to store Electrical Charge when a potential difference

exists between the conductors separated by a dielectric. The SI unit of

capacitance is farad. Fig. (4.1) shows capacitance.


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The types of capacitors are :-

1. Electrolite Capacitors2. Air Capacitors3. Paper Capacitors4. Polystyrene Capacitors5. Ceramic, mica, glass Capacitors

The operating range of frequencies is different for these

different capacitors in general each type of capacitors is based in its own operating

range.

b) TRANSISTORS

It is a semiconductor device capable of amplification in a

similar to thermionic values. It consists of two PN semiconductor junction back to

back forming either PNP or NPN structure.

c) RESISTORS :-

A resister is an electrical component which when made part

of an electrical ckt is intended to introduce a definite amount of d.c. resistance in very

compact form. In many application the amount of ckt.

Current to a predetermined value Resisters are made in many sizes and shapes and in

a variety of materials. The wire wound type makes use of a special alloy wire or

ribbon as the resistance element and is wound on an insulting form with or without a

ceramic covering.


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Another type of fine resisters consists of a thin film of metal

deposited. On insulating form. Both the carbon and the deposited metal types are low

current units and are available in resistance values from several ohms to as high as

mega ohm and is having voltage rating from watts to 2 watts. As shown in fig. (4.3)

These types of carbon and deposited metal types are

connected by means of wire leads called pigtails.

d) DIODES :--

The diodes are generally formed by diffusing a P -type

region and an N - type region in the same crystal structure. There are different types

of semiconductor diodes.

1. Zener Diodes.2. Point Contact Diodes.3. Light Emitting Diodes (LED)4. Photo Diodes5. Tunnel Diodes6. Varacter Diodes

But our ckt. Contains LED i.e. Light emitting diode. So let

us take a brief look at these diodes.

Light Emitting Diodes [ LED ]

LEDs are now a day being used in almost all instruments.

In last decade upto electronics technology has developed very rapidly and a number


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of new Opto-electronic product have come in the market of various types, sizes &

colours of LEDs have been developed to unit all requirements.

LEDs is infect a diode which emits light when it is reversed

biased, it does not conducts and hence does not emit light. When the diode is in

forward biased, electrons are moved from N-side conduction band to the P-side

valance band. In making this transitions the electrons cross the energy gap 'E.g.' that

separates the two bands and hence they radiate energy. In ordinary rectifier diode

this energy is given off as heat but in Light emitting diode it radiate as light.

When LEDs are to used in the ckt. Where the operating

voltage are much more than the forward voltage v.f. (2F), then first Precaution to be

taken is to see that the LED does not exceed the maximum rated forward current ( 35

ma maximum ).

Polarity of LED :

It is shown as in fig. The electrode with small area in an

anode and the other with larger area in an anode and other with larger area in

cathode. Usually in red LEDs the terminal is shorten than the other. The shorter

terminal is called cathode and longer terminal is called anode.

LM78XX Series Voltage Regulators

General Description

The LM 78 XX series of three terminal regulator is

available with several fixed output voltages making them useful in a wide range of


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applications. One of these is local on card regulation, eliminating the distribution

problem associated with single point regulation. The voltage available allow these

regulators to be used in logic systems instrumentation, HiFi, and other solid state

electronic equipment. Although designed primarily as fixed voltage regulators these

devices can be used with external components to obtained adjustable voltages and

current.

The LM78XX series is available in an aluminium TO-3

package which will allow over 1.0 A load current if adequate heat sinking is provided.

Current limiting is included to limit the peak output current to a safe value. Safe area

protection for the output transistor is provided to limit internal power dissipation. If

internal power dissipation becomes too high for the heat sinking provided, the

thermal shutdown circuit takes over preventing the IC from overheating.

Considerable effort was expanded fop make the LX78XX

series of regulators easy to use and minimise the number of external components. It is

not necessary to bypass the output, although this does improve transient response.

Input bypassing is needed only if the regulator is located far from the filter capacito r

of the power supply.

RELAYS :-

The name relay is given too board class

electromechanical switches in which contacts are opened and/or closed by various in

the conditions of one electric circuit and thereby affect the operation of other devices


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in the same or other electric ( usually control or signalling) circuits. The term "relay "

does not over devices, such as magnetic starters, contractors, and the like, intended to

switch power circuits.

Relays are very common components of automatic Control

systems. There may be a total of several hundred various relays in some of them.

The way a relay acts is represented by its static

characteristic which relates its output y to its input x. This is a stepped relationship.

The output y jumps from y1 to y2 only after the input x has changed to x2 ( the

subscript 0 stand for operate ). Any further increase in x will not affect the

value of y. As the value of x falls stands for release, the value of y again decreases

stepwise.

The principal parameters of relays follows :

a) The operate value of a relay is the minimum value of aphysical quantity that will allow the operated load or retractile force of the relay to

un operate, or release, it. Thus release is the opposite of operate.

b) The release value of a relay is the maximum value of aphysical quantity that will allow the operated load or retractile force of the relay to

unoperate, or release, it. Thus release is the opposite of operate.

c) The power consumption of a relay is the amount of powertaken by the relay in a given duty.

d) The operate time is the interval required for a relay to startits contents and to complete its function after a control signal has been


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applied to its coil.

e) The waiting time in operate is the time required for thepull of the electromagnet to become equal to the back tension, so that any further

increase in the pull will cause the relay to pick up.

f) The motion time in operate is the time that elapses, afterthe armature just starts off, until the relay completes its intended function.

The relays are utilised in automatic control system as

transducers for an intermittent (desecrate ) control of actuating mechanisms by means

of low-power electric signals.

The form of the relay is in a large measure determined by

the form of the parameter it checks ( temperature, pressure rate of

rotation) and the type of actuating mechanism (pneumatic, hydraulic, electric) which

the relay controls. Accordingly, all relays are classified as electric, pneumatic,

hydraulic, electropneumatic, etc.

All relays are classified as :

i. Electromagnetic.ii. Moving-coil.

iii. Inductive.iv. Electronic

According to power of control signal, electric relay sub-divided into :

i) Low power ( less than 1 W )


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ii) Medium-power (from l to W )

iii) Hifh-power ( 10 W )

Finally according to pick-up time into quick :

i) Quick-response.

ii) Normal

iii) Delay.

iv) Time relays.

Now we will discuss the various types of relays in details.

A NATURAL ELECTROMAGNETIC RELAY :

The principle of operation of a relay consists in the fact

that when the control current is fed to the -winding of the electric magnet its core

gets magnetised and attracts the armature. The movement of the armature closes ( or

opens ) the contract of the controllable electric circuit.

The relays used for signal multiplication and separation of

electric circuits operating in a common scheme, or as amplifier s of relay action.

These relays can be utilised for direct current of any polarity and for alternating

current.

Electromagnetic relays are designed with a hinged or pull

in armature.TRANSFORMER :-

A transformer is a static ( or stationary ) piece of

apparatus by means of which electric power in one circuit is transformed into electric


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power of the same frequency in another circuit. It can raise or lower the voltage ion a

circuit but with a corresponding decrease or increase in current. The physical basis

of a transformer is mutual induction between two circuits linked by a common

magnetic flux. In its simplest form, it consists of two inductive coils which are

electrically separated but magnetically linked through a path of low reluctance as

shown in fig.

The two coils posses high mutual inductance. If one coil is

connected to a source of alternating voltage, an alternating flux is set up in the-

laminated core, most of which is linked with the other coil in which it produces

mutually induced e.m.f. (according to faradays laws of Electro-Magnetic Induction e

= Mdl/dt. ) if the second coil circuit is closed, a current flows in it and so electric

energy is transferred from the first coil to the second coil. The first coil. in which

electric energy is fed from the a. c. supply mains, is called primary winding and the

other from which energy is drawn out, is called secondary winding. In brief, a

transformer is a device that

i) Transfers electric power from one circuit other.ii) It does so without a change of frequency,iii) If accomplishes this by electromagnetic induction andiv) Where the two electric circuits are in mutual inductive influence of each

other.


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TRANSFORMER CONSTRUCTION:

The simple elements of a transformer consist of two coils

having mutual inductance and a laminated steel core. The two coils are insulated

from each other and the steel core. Other necessary parts are : some suitable

container for the assembled core and windings, a suitable medium for insulating the

core its windings from its container : suitable bushings ( either of porcelain, oil-filled

or capacitor - type ) for insulating and bringing out the terminals of windings from

the tank.

In all types of transformers, the core is constructed of

transformer sheet steel laminations assembled to provide a continuous magnetic path

with the minimum of air gap included. The steel used is of high silicon content, some

times heat treated to produce a high permeability and low hysteresis loss at the usual

operating flux. Densities. The eddy current loss is minimised by laminating the core,

the laminations being insulated from each other by a light coat of core - plate varnish

or by an oxide layer on the surface. The thickness of laminations varies from 0.35 mm

for a frequency of 50 Hz to 0.5 mm for a frequency of 25 Hz. The core laminations are

joined as shown in fig.

Constructionally, the transformers are of two general types. Distinguished from each

other merely by the manner in which the primary and the secondary coils are placed

around the laminated steel core. The two types are known as

1. CoreType and2. Shelltype


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FABRICATION UNITAn etched or printed circuit consists of a thin layer of

copper foil. The final is shaped by etching the copper in a chemical. The copper foil

acts as a wire, or conductor in the ckt. Components parts like resistors, transistors

and capacitors are soldered to the conductive foil to complete the electrical path and

circuit.

Production of PCBs.

The transfer of the conductor pattern -which on the film

master on the copper clad laminate is done by two methods. They are

1. Photo Printing

2. Screen printing

But in our circuit we have used screen printing method so

we study only about this.

SCREEN PRINTING METHOD :-

PCB production by photographic printing method is

expensive though accurate. The screen process uses a resist ink applied throughout a

stencil or mask to the surface of the blank circuit board. The stencil is produced and

attached to the fine mesh, metal, polyester, nylon or silk screen. The resist ink is kept

forced through openings in the stencil on to the surface of the blank board. This


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process produces a positive of the cleb on the copper foil. When dry, the board is

ready for etching. In our project instead of stencil we used positive of artwork.

Etching Process

The etching solution is prepared in non metallic plate. For

preparing etching solution take one part of ferrite chlorides in power form with two

parts of water heat the solution upto 40o

C to 50o

C till the vapour just starts forming,

add a small quantity of HCL for fast etching action the quantity of solution required

should be just enough to immerse the PCB. Give some base to the PCB so that it does

not touches the bottom of the container. Always keep the printed circuit side on the

upper side. For fast action of etching stir the solution without disturbing PCB. By this

process the copper other than the areas which are covered by point is etched away.

Continue the process for 45 min. By holding the board in light it can be seen that,

whether the board is completely etched or not ?

After few boards have been etched the colour of the

solution changes from yellow to green. Wash the board under running water and

remove the paint. After etching give a coat of varnish to the PCB so that it remain

shining.

SELECTION AND MOUNTING OF COMPONENTS ON PCB :

The careful assembly of the PCB is as relevant for the final

equipment reliability as the circuit design or PCB design and fabrication. Assembly

technique can vary widely from case to case.


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i) Mounting of resisters, capacitors and diodes

The bending of the axial component lead is done in a

manner to guarantee an optimum retention of the component on the PCB while a

minimum trace is introduced on the solder joint. During bending the component lead

no damage to the component should occur. The bend lead should fist into the holes

perpendicular to the board so that any trace on the component lead junction is

minimised.

Component are generally mounted on only one side of the

PCB. In double sided PCBs, the component side is usually opposite to the pager

conductor pattern side Unless otherwise detached by special design requirement.

The uniformity in orientation of polarised components like

diodes, resisters. IC etc. is determined during the design of PCB.

ii) Mounting if ICs :

It is never expected to put the ICs directly on the PCB and

then soldered. The IC sockets are available in the market. These sockets are available

in the market. These sockets are first mounted and leads of the sockets are soldered.

After completion the IC is transferred in the socket.

After the component mounting and soldering the extra part

of the lead coming out, must be cut with a cutter. It is recommended that before

soldering the lead the extra portion of the lead must be cut and then soldered. The

lead cutting after soldering is still common in the smaller industries -where hand

soldering is used.


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By keeping all above information in mind we fabricate total

unit after testing of each component and after preparing power supply for unit. The

circuit works successfully and we get results which are given in chapter Conclusion

& Results

Under/over voltage cut-out. This section comprises an 8-

pin dual comparator LM393N (IC3) in DIL (dual -in-line) package. The output of the

two comparators (at pins 1 and 7) has been combined in a wired-OR fashion. This

output is high as long as sampled voltages being monitored are within precept limits.

When sampled voltages are out of limits, the wired-OR output goes low.

Here IC2(a) is used as over-voltage detector, while IC2(b )

is used as under-voltage detector. The 4.2V developed across Zener D4 is used as

reference voltage for both the comparators. The potmeter VR1 is so adjusted that

when the phase-to-phase (R-Y) input voltage across primary of transformer (X1 and

X2 combined) is less than a specific desired level (sav 350V RMS), the voltage at it s

contact goes less than 4.2 volts. Thus, the output of comparator IC2( b ) and also the

wired-OR output goes low, irrespective of output of'comparatorIC2 (a). Similarly,

potmeter VR2 is so adjusted that when the voltage between R-Y phases exceeds

certain desired value (say 480V AC RMS), the voltage at its wiper contact goes higher

than 4.2 volts, and the output of comparator IC2( a ) goes low. Thus, we observe that

whenever the R-Y phase-to-phase voltages are beyond acceptable limits, the output of

comparator goes low to switch off the motor after a delay of four seconds, as

explained in the following section.


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On/off time delay. The popular NESS 5 timer is so

configured as to provide an on-time delay of 12 seconds after all conditions are

suitable (i.e. all 3 phases are present and the phase-to-phase voltages are also within

limits), if all conditions are all right (at the time of start-with slide switch S1 in on

position), capacitor C4 will he charged via resistors R2 and R4 .which would take

about 12 seconds to make pin 2 of 555 high, so that its output (at pin 3) goes low

to cut off transistor T3. As a result, base of transistor T4 gets forward biased via

resistor R9 (andR13 ) to energise relay RL1 to short points C and D (refer Figs 1 and

2) through its contacts, and energise contactor in the DOL starter of Fig. 1 via the

start switch ( in pressed state) or due to energisation of relay RL.2 for short duration

with switch S2 on (explanation covered under Auto start unit subheading ). Thus

motor starts after an on-time delay of 12 seconds.

When compactor IC2 senses under-voltage or over-

voltage condition, its output goes low and capacitor C'4 discharges via resistance R4.

This will take about jour seconds before it causes pm 2 of IC3 logo low or its output

to go high, which in turn causes de-energisation of relay RLI to eventually switch off

the motor. This is the off-time delay which allows the motor not to s-witch off if the

voltage returns to normal state within this 4-second period. If the voltage does not

return to normal state within this period then only the motor is s-witched off. This

avoids unnecessary switching off of the motor during momentary voltage fluctuations.

Single-phase cut-out. When a single phase failure occurs,

the motor will continue to run on remaining two phases, drawing heavy load current.


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This would result in overheating of windings and its eventual burning in a short time

if it is not disconnected. The single-phase cut-out circuit employed here is very simple

and it has the capability to sense all three phases , including low voltage condition of

phase B. Sensing of under-voltage and over-voltage condition of R and Y phases is

already taking place, as described earlier.

Phase failure of R and/or V phase (s) results in no supply

to the circuit and relays RBI and RL2 will he in de-energised state and the motor is,

therefore. Switched off. In Y-B single phase detector part of the circuit, the diode D12

in Y phase path rectifies the voltage before potential divider network, comprising

resistors R16 and R17, reduces the voltage with respect to phase B. Capacitor C7

smooth the voltage across resistor R17. If this voltage is greater than 27V, zener D11

as well as the diode inside opto-coupler IC4 will conduct. As a result, base of

transistor T2 is pulled to ground and it is cut off. This causes the compactor output to

he applied to pin 2 of timer NE555 without any change (modification). But in case the

B-phase voltage is very low, or if it is missing altogether, transistor T2 will he biased

to saturation condition, discharging capacitor C4 via resistor R5. As a result, pin 2 of

timer 555 would go low immediately and eventually switches off relay RLI to cut off

the con factor in DOL starter as well as the motor.

Auto start unit. The necessity auto start unit has, if late,

increased due to frequent power interruptions, including single phasing. Many auto

start units are available in the market. The auto start circuit comprises the circuitry


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around relays RL1 and RL2 (and their contacts), slide switches SI and S2, and the

DOL, starter.

During normal conditions, the out-put of timer NE555 will

initially go high for 12 seconds on resumption of power or when normal state is

reached. The capacitor C.6 will he charged through resistor R11. However, the base

of transistor T5 will he held to ground potential by diode D6, which is forward biased

due to the condition of transistor T3. As a result, relay RL2 will he in off state due to

non-conduction of transistor T5. When NE555 IC changes its out-put state from high

to low after 12 seconds, diode D6 will he reverse-biased due lo the positive voltage at

anode of diode D6. Capacitor C6 will get discharged via resistor R11 and transistor

T5 will come to conduction stale due to the positive voltage at its base. As a result,

relay RL2 will get energised. The discharge action of capacitor C6 continues for

about two seconds (which is sufficient to bring the electromagnetic relay of DOL

starter to on position). Once the starter EM relay energises, it is latched as explained

under Functions of relays and switches subheading. After two seconds, the base of

transistor T5 will fall to ground potential and relay RL2 will he switched off.

However, relay RLI will continue to he on and hold the motor in on stale.

Timer, The timer is built around 14-stage CMOS counter

CD 4060 which has an on-chip oscillator. The timing component, comprising resistor

R24 and capacitor C8, is selected lo gel an approximate off -time delay of 20 minutes

at Q7, 45 minutes at Q8, 1.5 hours at Q9, 3hours at Q1O, 6 hours at Q11, 12 hours at


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Q12 , and 24 hours at Q13 out-put. The timer is not affected by power cuts as it is

provided with a backup, using a 9V, PP3 battery. The timer function comes into play

when switch S3 is flipped to on position.

When power fails, transistor T6 will cut off due to absence

of any forward bias voltage at its base. This forward biases diodeD14, which makes

pin II of the counter high and the counter suspends further counting. When power

resumes, the counter proceeds further and the time count is thus not lost. The same

thing occurs when an unhealthy condition of line is detected. Pin 3 of timer 555 goes

high and diode D13 causes suspension of counting. When the final count is reached,

the corresponding output pin of IC5 goes high. The IC5 output is coupled to pin 11

via diode D12 to suspend the counting. At the same time this high output is also

connected to the base of transistor T3, which starts conducting and takes the base of

transistor T4 to cut-off. As a result relay RL1 de-energises to switch off the motor.

To set the counter timing, first set the value of time by

rotary switch S4 and then flip switch S3 on to start the timer. To reset the timer push

switch S3 to off' and then switch it on again.

LED indicators. LED1, when on indicates that switch S1is

on and R-Y phase supplies and 9V output from the regulator ICI are available. LED2,

when on, indicates that relay RL1 has energised. LED3 is on when switch S3 is on and

9V supply from IC1 for timer is available.


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An actual-size, single-sided PCR for the circuit of Fig. 2 is

shown in Fig. 3 . The component layout/or the PCB is given in Fig 4. All switches,

relays, and transformers are to he mounted externally. As the B-Y phase detector

circuit contains high voltages, it is recommended to cut out the phase detector part up

lo opto-coupler from the PCB and install the same externally. Only the output leads

from the opto-coupler may be soldered on to the- points provided on the PCB.


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Part list

Semiconductors :

IC 1 - 7809 fixed regulator + 5 volts

IC 2 - I.M393 Voltage compactor

IC 3 - NE555 timer

IC 4 - CD4060 14-stage ripple counter oscillator

IC 5 - MC2TE opto-coupler

T2,T3 - BC 547 npn transistor

T4,T5,T6 - 2N2222 switching transistor

D 1-D3,D5-D10,

D12-D16 - 1N4007 rectifier diode

D4 - 4.2V, 0.5W zener

D11 - 27 V, 0.5 W zener

LED1-1.ED3 - Coloured LED

Resistors : all 1 4W, + 5% metal carbon film, unless stated otherwise

R 1, R5, R8-R10, R12

R15, R18, R21 - 1kilo-ohm

R2, R22 - 22-kilo-ohm

R3, R7, R19,

R20, R25 - 10-kilo-ohm


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R4 - 47-kilo-ohm

R6 - 220-kilo-ohm

R11, R 14 - 4.7-kilo-ohm

R15 - 470-kilo-ohm

R16, R17 - 47-kilo-ohm 1 W

R22 - 22kilo-ohm

R23 - 1-mega-ohm

R24 - 100kilo-ohm

R26 - 22-kilo-ohm 1W

VR1, VR2 - 4.7-kilo-ohm potmeter

Capacitors :

C1,C8 - uF, 25V electrolytic

C2 - 1000uF, 25V electrolytic



C5 - 0.0uF ceramic disc




C10 - 4.7uF, 25V electrolytic


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Miscellaneous

R1,1,RL.2 - 0V,150ohm SPSP relay

S1,S2,S3 - Slide switches DPDT

X1,X2 - 250V primary to 6V-0-6V,

200 mA see transformer

- Battery PP9VS4 - Rotary switch single-pole

7-throws

- DOL starterBergstrip connectors-male/female


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REFERENCE

i) Electrical Engineering : by B. L. THAREJA

ii) Electronics For You.(Dec.99)

iii) Data Hand Book.

automatic induction motor

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