TOPIC

PROJECT REPORT ON INDUSTRIAL AUTOMATION

(AC & DC Motors, Transformers, Windings, Testing and PLC )

Submitted to: G.E. MOTORS (PVT) LTD.13/1, G.T Road, Sheoraphuly

Hoogly .Pin: 712223

Submitted by : SAMPAD ACHARYA

KALYANI GOVT. ENGG COLLEGE

ROLL:10201612090

Date of submission:

ACKNOWLEDGEMENTSI would like to thank teachers and all helpers of G.E. MOTORS for their invaluable help and advice. I would also like to thank my group members who gave me a lot of help and support .www.youtube.com and http://www.google.co.in websites also helped me a lot.

CONTENTS INTRODUCTIONANALYSIS

DC Motor Principle of Operation of DC Motors Construction of DC Motor

Main magnetic field Armature winding Commutator and brush

Insulation

AC Motors Principle of Operation of AC Motors Direction of induced E.M.F & the Laws

on which the AC Fundamental depends:Faraday’s Law, Fleming’s Right-hand Rule, Lenz’s Law

Conducting Material Insulation

Transformer Working Principle and Basic

Characteristics

Regulation of Transformer Transformer Rating Efficiency of Transformer

Construction Classification Transformer Equivalent Circuit

PLC Basic Operations Logic Symbols Logic Diagram

CONCLUSION

INTRODUCTION For the advancement of technologies two main streams are responsible- Mechanical Power and Electrical Modifications.

We are the students of Electrical Engineering from KALYANI GOVT. ENGG. COLLEGE . we have enlisted our names for a training at G.E Motors PVT LTD.

There we have got a practical idea about five basic fundamentals for the advancement of technologies-

1) Fundamentals of AC Current,2) Nature and properties of DC Current,3) Working principles of Transformers.4) Winding and working principle of both AC & DC machine5) PLC programming

Mechanical power requires to make different types of machines according to needs.

We all have learnt theoretically about Ohm’s law, Faraday’s law, electromagnetism etc but for this training we have come to know about the practical significances about all that we have learnt.

We gained the ability to design PLC circuit and run the program.

ANALYSISD.C. MOTORS

The DC machine that converts electrical power into mechanical power is called DC motor. The dc motor basically works on the principle that when a conductor carrying current is placed in the magnetic field, mechanical force acts on the current carrying conductor and as a result conductor starts rotating in a direction depending upon the direction of current and the field and is given by Fleming’s left-hand rule

Working Principle of DC Motor: Direct current (DC) motors are widely used to generate motion in a variety of products. Permanent magnet DC (direct current) motors are enjoying increasing popularity in applications requiring compact size, high torque, high efficiency, and low power consumption.

In a brushed DC motor, the brushes make mechanical contact with a set of electrical contacts provided on a commutator secured to an armature, forming an electrical circuit between the DC electrical source and coil windings on the armature. As the armature rotates on an axis, the stationary brushes come into contact with different sections of the rotating commutator

Permanent magnet DC motors utilize two or more brushes contacting a commutator which provides the direct current flow to the windings of the rotor, which in turn provide the desired magnetic repulsion/attraction with the permanent magnets located around the periphery of the motor.

The brushes are conventionally located in brush boxes and utilize a U-shaped spring which biases the brush into contact with the commutator. Permanent magnet brushless dc motors are widely used in a variety of applications due to their simplicity of design, high efficiency, and low noise. These motors operate by electronic commutation of stator windings rather than the conventional mechanical commutation accomplished by the pressing engagement of brushes against a rotating commutator.

A brushless DC motor basically consists of a shaft, a rotor assembly equipped with one or more permanent magnets arranged on the shaft, and a stator assembly which incorporates a stator component and phase windings. Rotating magnetic fields are formed by the currents applied to the coils.

The rotator is formed of at least one permanent magnet surrounded by the stator, wherein the rotator rotates within the stator. Two bearings are mounted at an axial distance to each other on the shaft to support the rotor assembly and stator assembly relative to each other. To achieve electronic commutation, brushless dc motor designs usually include an electronic controller for controlling the excitation of the stator windings.

Construction of DC Motor: The main constructional parts of a D. C. Motor can be classified in three parts and these three are given below :

Main Magnetic Field and Supporting System Armature Winding and Supporting System Commutator and Brush Arrangement

There are three types of d.c. motors-

1. DC shunt motor.

2. DC series motor.

3. DC compound motor

DC Shunt motor:

It is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Fleming's Left-hand rule and whose magnitude is given by

Force, F = B I L Newton

DC series motor:

The series motor provides high starting torque and is able to move very large shaft loads when it is first energized.

The advantage of a Series Motor is that it develops a large torque and can be operated at low speed. It is a motor that is well-suited for starting heavy loads; it is often used for industrial cranes and winches .

DC compound motor:

DC compound motor is essentially a combination of Series DC motor and Shunt DC motor.

These types of motors are two types:-

1. Cumulative Compound Motors2. Differential Compound Motors

DC compound motors are desirable for a variety of applications because it combines the characteristics of a series-wound motor and a shunt-wound motor. The DC compound motor has a greater torque than a shunt motor due to the series field; however, it has a fairly constant speed due to the shunt field winding. Loads such as presses, shears, and reciprocating machines are often driven by compounded motors.

DC GENERATOR

    An electrical Generator is a machine which converts mechanical energy (or power) into electrical energy (or power). The types of DC generators are similar to that of a DC motor

Principle :

   It is based on the principle of production of dynamically (or motionally) induced e.m.f (Electromotive Force). Whenever a conductor cuts magnetic flux, dynamically induced e.m.f. is produced in it according to Faraday's Laws of Elect+romagnetic Induction. This e.m.f. causes a current to flow if the conductor circuit is closed.

   Hence, the basic essential parts of an electric generator are :

              A magnetic field and

             A conductor or conductors which can so move as to cut the flux.

Construction :

    A single-turn rectangular copper coil abcd moving about its own axis in a magnetic field provided by either permanent magnets or electromagnets. The two ends of the coil are joined to two split-rings which are insulated from each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip rings.

  DC GeneratorA dc generator is an electrical machine which converts mechanical energy into direct current electricity. This energy conversion is based on the principle of production of dynamically induced emf.

Construction:

Above figure shows the constructional details of a simple 4-pole DC generator. A DC generator consists two basic parts, stator and rotor. Basic constructional parts of a DC generator are described below.

1. Yoke: The outer frame of a generator or motor is called as yoke. Yoke is made up of cast iron or steel. Yoke provides mechanical strength for whole assembly of the generator (or motor). It also carries the magnetic flux produced by the poles.

2. Poles:  Poles are joined to the yoke with the help of screws or welding. Poles are to support field windings.  Field winding is wound on poles and connected in series or parallel with armature winding or sometimes separately.

3. Pole shoe: Pole shoe is an extended part of the pole which serves two purposes, (i)to prevent field coils from slipping and (ii)to spread out the flux in air gap uniformly.

Armature core (rotor)

4. Armature core: Armature core is the rotor of a generator. Armature core is cylindrical in shape on which slots are provided to carry armature windings.

5. Commutator and brushes: As emf is generated in the armature conductors terminals must be taken out to make use of generated emf. But if we can't directly solder wires to commutator conductors as they rotates. Thus commutator is connected to the armature conductors and mounted on the same shaft as that of armature core. Conducting brushes rest on commutator and they slides over when rotor (hence commutator) rotates. Thus brushes are physically in contact with armature conductors hence wires can be connected to brushes. 

Commutator

                          

AC MOTOR:

An AC motor is an electric motor driven by an alternating current.

Ac Motor Construction:

The AC induction motor comprises 2 electromagnetic parts:

Stationary part called the stator Rotating part called the rotor, supported at each end on bearings

The stator and the rotor are each made up of:

An electric circuit, usually made of insulated copper or aluminum, to carry current A magnetic circuit, usually made from laminated steel, to carry magnetic flux

The stator :

The stator is the outer stationary part of the motor, which consists of:

The outer cylindrical frame of the motor, which is made either of welded sheet steel, cast iron or cast aluminum alloy. This may include feet or a flange for mounting.

The magnetic path, which comprises a set of slotted steel laminations pressed into the cylindrical space inside the outer frame. The magnetic path is laminated to reduce eddy currents, lower losses and lower heating.

A set of insulated electrical windings, which are placed inside the slots of the laminated magnetic path. The cross-sectional area of these windings must be large enough for the power rating of the motor. For a 3-phase motor, 3 sets of windings are required, one for each phase.

Figure 1: Stator and rotor laminations

The rotor :

This is the rotating part of the motor. As with the stator above, the rotor consists of a set of slotted steel laminations pressed together in the form of a cylindrical magnetic path and the electrical circuit. The electrical circuit of the rotor can be either:

Wound rotor type, which comprises 3 sets of insulated windings with connections brought out to 3 sliprings mounted on the shaft. The external connections to the rotating part are made via brushes onto the sliprings. Consequently, this type of motor is often referred to as a slipring motor.

Squirrel cage rotor type, which comprises a set of copper or aluminum bars installed into the slots, which are connected to an end-ring at each end of the rotor. The construction of these rotor windings resembles a ‘squirrel cage’. Aluminum rotor bars are usually die-cast into the rotor slots, which results in a very rugged construction. Even though the aluminum rotor bars are in direct contact with the steel laminations, practically all the rotor current flows through the aluminum bars and not in the lamination.

AC Motor Working Principle:

In both induction and synchronous motors, the stator is powered with alternating current (polyphase current in large machines) and designed to create a rotating magnetic field which rotates in time with the AC oscillations. In a synchronous motor, the rotor turns at the same rate as the stator field. By contrast, in an induction motor the rotor rotates at a slower speed than the stator field. Therefore the magnetic field through the rotor is changing (rotating). The rotor has windings in the form of closed loops of wire. The rotating magnetic flux induces currents in the windings of the rotor as in a transformer. These currents in turn create magnetic fields in the rotor, that interact with (push against) the stator field. Due to Lenz's law, the direction of the magnetic field created will be such as to oppose the change in current through the windings. The cause of induced current in the rotor is the rotating stator magnetic field, so to oppose this the rotor will start to rotate in the direction of the rotating stator magnetic field to make the relative speed between rotor and rotating stator magnetic field zero.

For these currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field ( ), or the magnetic field would not be moving relative to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field as seen by the rotor (slip speed) and the rotation rate of the stator's rotating field is called "slip". Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as asynchronous motors. [7] An induction motor can be used as induction generator, or it can be unrolled to form the linear induction motor which can directly generate linear motion.

SINGLE-PHASE MOTORS

Induction Motors

If two stator windings of unequal impedance are spaced 90 electrical degrees apart and connected in parallel to a single-phase source, the field produced will appear to rotate. This is called phase splitting.

In a split-phase motor, a starting winding is utilized. This winding has a higher resistance and lower reactance than the main winding (illustration shown below). When the same voltage VT is applied to the starting and main windings, the current in the main winding (IM) lags behind the current of the starting winding IS (illustration shown below ). The angle between the two windings is enough phase difference to provide a rotating magnetic field to produce a starting torque. When the motor reaches 70 to 80% of synchronous speed, a centrifugal switch on the motor shaft opens and disconnects the starting winding.

Single-phase motors are used for very small commercial applications such as household appliances and buffers.

Ac Motor commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.

Rotating Magnetic Field From 2-Phase Supply

As with a 3-phase supply, a 2-phase balanced supply also produces a rotatingmagnetic field of constant magnitude. With the exception of the shaded-polemotor, all single-phase induction motors are started as 2-phase machine. Onceso started, the motor will continue to run on single-phase supply.Let us see how 2-phase supply produces a rotating magnetic field of constantmagnitude. Fig shows 2-pole, 2-phase winding. The phases X and Yare energized from a two-phase source and currents in these phases arc indicatedas Ix and Iy the fluxes producedby these currents arc given by;Y m sint and X m sin(t 90) m costHere m is the maximum flux due to either phase. We shall now prove that this2-phase supply produces a rotating magnetic field of constant magnitude equalto m.

Working principle of 1 phase induction motor

3- PHASE MOTORS

SQUIRREL CAGE INDUCTION MOTOR

In induction, the AC power supplied to the motor's stator creates a magnetic field that rotates in time with the

AC oscillations. The induction motor stator's magnetic field is therefore changing or rotating relative to the

rotor. This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding,

when the latter is short-circuited or closed through an external impedance. The rotating magnetic flux induces

currents in the windings of the rotor; in a manner similar to currents induced in a transformer's secondary

winding(s). The currents in the rotor windings in turn create magnetic fields in the rotor that react against the

stator field. Due to Lenz's Law, the direction of the magnetic field created will be such as to oppose the change

in current through the rotor windings. The cause of induced current in the rotor windings is the rotating stator

magnetic field, so to oppose the change in rotor-winding currents the rotor will start to rotate in the direction of

the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque

balances the applied load. Since rotation at synchronous speed would result in no induced rotor current, an

induction motor always operates slower than synchronous speed. The difference, or "slip," between actual and

synchronous speed varies from about 0.5 to 5.0% for standard Design B torque curve induction motors. The

induction machine's essential character is that it is created solely by induction instead of being separately excited

as in synchronous or DC machines or being self-magnetized as in permanent magnet motors.

For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating

magnetic field ( ); otherwise the magnetic field would not be moving relative to the rotor conductors and no

currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the

magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio

between the rotation rate of the magnetic field induced in the rotor and the rotation rate of the stator's rotating

field is called slip. Under load, the speed drops and the slip increases enough to create sufficient torque to turn

the load. For this reason, induction motors are sometimes referred to as asynchronous motors. An induction

motor can be used as an induction generator, or it can be unrolled to form a linear induction motor which can

directly generate linear motion.

\

SLIP RING INDUCTION MOTOR

The slip ring induction motor has two distinctly separate parts, one is the stator and other is the rotor. The stator circuit is rated as same in the squirrel cage motor, but the rotor has coils similar to that of the stator windings which are brought out by means of slip rings.

            A slip ring (in electrical engineering terms) is a method of making an electrical connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels or electrical rotary joints, are commonly found in electrical generators for AC systems and alternators and in packaging machinery, cable reels, and wind turbines.

        A slip ring consists of a conductive circle or band mounted on a shaft and insulated from it. Electrical connections from the rotating part of the system, such as the rotor of a generator, are made to the ring. Fixed contacts or brushes run in contact with the ring, transferring electrical power or signals to the exterior, static part of the system.

Winding coil of 3 phase induction motor stator

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling.

If a load is connected to the secondary, current will flow in the secondary winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np. The windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical.

Basic principles:

An ideal transformer. The secondary current arises from the action of the secondary EMF on the (not shown) load impedance.

The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism) and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils. If a load is connected to the secondary winding, the load current and voltage will be in the directions indicated, given the primary current and voltage in the directions indicated (each will be alternating current in practice).

Induction law:

The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:

where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil and Φ is the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicularly to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for Vs and Vp gives the basic equation for stepping up or stepping down the voltage

Np/Ns is known as the turns ratio, and is the primary functional characteristic of any transformer. In the case of step-up transformers, this may sometimes be stated as the reciprocal, Ns/Np. Turns ratio is commonly expressed as an irreducible fraction or ratio: for example, a transformer with primary and secondary windings of, respectively, 100 and 150 turns is said to have a turns ratio of 2:3 rather than 0.667 or 100:150.

Ideal power equation

The ideal transformer as a circuit element

If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient. All the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the input electric power must equal the output power:

giving the ideal transformer equation

This formula is a reasonable approximation for most commercial built transformers today.

If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is transformed by the square of the turns ratio. For example, if an impedance Zs is attached across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the primary circuit appears to the secondary to be (Ns/Np)2Zp.

Detailed operation

The simplified description above neglects several practical factors, in particular, the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit.

Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance. When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core.: The current required to create the flux is termed the magnetizing current. Since the ideal core has been assumed to have near-zero reluctance, the magnetizing current is negligible, although still required, to create the magnetic field.

The changing magnetic field induces an electromotive force (EMF) across each winding. Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VS measured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the "back EMF". This is in accordance with Lenz's law, which states that induction of EMF always opposes development of any such change in magnetic field.

Types (based on supply)

1- phase 3- phase/polyphase

Types (based on construction or application )

Autotransformer Instrument transformers

Autotransformer

In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where electrical connections are made. An autotransformer can be smaller, lighter and cheaper than a standard dual-winding transformer however the autotransformer does not provide electrical isolation.

A variable autotransformer is made by exposing part of the winding coils and making the secondary connection through a sliding brush, giving a variable turns ratio. Such a device is often referred to by the trademark name Variac.

Poly phase transformers

For three-phase supplies, a bank of three individual single-phase transformers can be used, or all three phases can be incorporated as a single three-phase transformer. In this case, the magnetic circuits are connected together, the core thus containing a three-phase flow of flux. A number of winding configurations are possible, giving rise to different attributes and phase shifts.[63] One particular polyphase configuration is the zigzag transformer, used for grounding and in the suppression of harmonic currents.

Instrument transformers

Instrument transformers are used for measuring voltage and current in electrical power systems, and for power system protection and control. Where a voltage or current is too large to be conveniently used by an instrument, it can be scaled down to a standardized low value. Instrument transformers isolate measurement, protection and control circuitry from the high currents or voltages present on the circuits being measured or controlled.

Current transformer

Current transformers, designed for placing around conductors

A current transformer is a transformer designed to provide a current in its secondary coil proportional to the current flowing in its primary coil.

Voltage transformers (VTs), also referred to as "potential transformers" (PTs), are designed to have an accurately known transformation ratio in both magnitude and phase, over a range of measuring circuit impedances. A voltage transformer is intended to present a negligible load to the supply being measured. The low secondary voltage allows protective relay equipment and measuring instruments to be operated at a lower voltages.

Both current and voltage instrument transformers are designed to have predictable characteristics on overloads. Proper operation of over-current protective relays requires that current transformers provide a predictable transformation ratio even during a short-circuit.

PLCs

A programmable logic controller (PLC), also referred to as a programmable controller, is the name given to a type of computer commonly used in commercial and industrial control applications. PLCs differ from office computers in the types of tasks that they perform and the hardware and software they require to perform these tasks. While the specific applications vary widely, all PLCs monitor inputs and other variable values, make decisions based on a stored program, and control outputs to automate a process or machine. This course is meant to supply you with basic information on the functions and configurations.

Basic PLC Operation

The basic elements of a PLC include input modules or points, a central processing unit (CPU), output modules or points, and a programming device. The type of input modules or points used by a PLC depends upon the types of input devices used. Some input modules or points respond to digital inputs, also called discrete inputs, which are either on or off. Other modules or inputs respond to analog signals. These analog signals represent machine or process conditions as a range of voltage or current values. The primary function of a PLC’s input circuitry is to convert the signals provided by these various switches and sensors into logic signals that can be used by the CPU.

We have studied some programs. Those are:

1) Star-Delta Starter2) 1 light blinking3) 2 lights blinking4) AND gate OR gate5) One switch on another off 6) 3 phase induction motor forward reverse stop

Now for 6 here, the motor’s breaking is natural breaking. So when the motor’s direction in changed, it cannot instantly change its direction. When motor’s supply is cut down, it will have a natural breaking, during which its speed reduces and finally comes to rest. Our assumption is that, the motor takes 7 seconds to completely stop. So when the motor is instructed to change direction by the user, PLC cuts off its supply, till it comes to rest and then, it changes its direction, using the direction changing circuits ( forwardmtr, reversemtr ) . In order to be on the safer side, an off-delay timer of 10 seconds ( greater than 7 seconds) is used, to activate the motor direction changing circuits

LOGIC DIAGRAM OF THREE PHASE INDUCTION MOTOR

So the total logic diagram is :

CONCLUSIONFrom our technical studies we just can achieve theoretical knowledge . but if we have to know how it really works we must have to know it from the core .This training has given us the chance to achieve the practical knowledge. Now we know about windings , working principle of AC DC motors generators TRANSFORMRES. Beside having those knowledge we learnt about a new programming . That is PLC Programming. This interesting subject just drawn our attentions.