Chapter 1INTRODUCTION An electric motor converts electrical energy into mechanicalenergy. The reverse of this would be the conversion of mechanical energy intoelectrical energy and is done by an electric generator.In normal motoring mode, most electric motors operatethrough the interaction between an electric motor’s magnetic field and windingcurrents to generate force within the motor.
In certain applications, such asin the transportation industry with traction motors, electric motors canoperate in both motoring and generating modes toalso produce electrical energy from mechanical energy.Found in applications as diverse as industrial fans, blowersand pumps, machine tools, household appliances, power tools, and disk drives,electric motors can be powered by direct current (DC) sources, such as frombatteries, motor vehicles or rectifiers, or by alternating current (AC)sources, such as from the power grid, inverters or generators. Small motors maybe found in electric watches. General-purpose motors with highly standardizeddimensions and characteristics provide convenient mechanical power forindustrial use.
The largest of electric motors are used for ship propulsion,pipeline compression and pumped-storage applications with ratings reaching 100megawatts. Electric motors may be classified by electric power source type,internal construction, application, type of motion output, and so on. However,for a motor to work or achieve the purpose they are made to do whether inindustrial or workshop, they must be controlled. The direct, speed and torquemust be controlled by a controller.A motor controller is a device or group of devices that serves to govern insome predetermined manner the performance of an electric motor. A motorcontroller might include a manual or automatic means for starting and stoppingthe motor, selecting forward or reverse rotation, selecting and regulating thespeed, regulating or limiting the torque, and protecting against overloads andfaults. Different starting methods are employed for startinginduction motors because Induction Motor draws more starting current duringstarting.
To prevent damage to the windings due to the high starting currentflow, we use different types of starters.The simplest form of motor starter for the induction motor is the ForwardReverse starter. The Forward Reverse Motor Starter consists of aCircuit Breaker, Contactor and an Overload Relay for protection.
Typically, thecontactor will be controlled by separate start and stop buttons, and anauxiliary contact on the contactor is used, across the start button, as a holdin contact. 1.1 Overview The device connects a motor to apower source, such as in small appliances or power tools. The switch can bemanually operated or with a relay or contactor connected to some form of sensorto automatically start and stop the motor. The switch has several positions toselect different connections of the motor. This allows reduced-voltage startingof the motor, reversing control or selection of multiple speeds. Overload andover current protection may be omitted in very small motor controllers, whichrely on the supplying circuit to have over current protection. Small motors mayhave built-in overload devices to automatically open the circuit on overload.
Larger motors have a protective overload relay or temperature sensing relayincluded in the controller and fuses or circuit breakers for over currentprotection. An automatic motor controller may include limit switches or otherdevices to protect the driven machinery. 1.2 Project Idea Electric motors can run in both forward and reversedirection depending on the requirement of the application where it is to beinstalled.
For this type of application, a forward reverse motor controller isapplied to the control circuit of the electric motor to achieve this purpose.The device required for the possibility of this operation is the magnetic contactor. 1.3 Purpose of the project The purpose of this project is to design a device forstarting and stopping the motor. It includes forward or reverse rotation ofmotor, regulating the speed and limiting the torque. It will protect motoragainst overloads and faults.
1.4 Project Specifications The project has simplecontrol circuitry. It is most economicaland cheapest starter. It is simple to establish, operate and maintain. 1.5 Applications of the project The forward reversemethod is usually applied to low voltage, medium voltage and light startingtorque motors.The receivedstarting current is about 30 % of the starting current during direct on linestart and the starting torque is reduced to about 25 % of the torque.
Thisstarting method only works when the application is light loaded during thestart.If the motor is too heavily loaded, there will not be enough torque toaccelerate the motor up to speed before switching over to the delta position. 1.6 Project Plan Table 1 Project Plan Tasks Duration Source Person Literature Review 01 Week Muhammad Sheraz, Shams-Ud-Din Implementation of procedure 02 Week Muhammad Sheraz, Shams-Ud-Din Testing of project 03 Weeks Muhammad Sheraz, Shams-Ud-Din Final project and report submission 04 Week Muhammad Sheraz, Shams-Ud-Din Chapter 2LITERATURE REVIEW1 2 2.1 BackgroundTheory A starter turns anelectric motor or motor controlled equipment on or off, while providingoverload protection. Starters represent another evolution in motor control applications.
Contactors controlthe electric current flowing towards the motor. Their function is to repeatedlyestablish and interrupt an electrical power circuit.Overload Protectionprotects motors from drawing too much current, overheating, and from literallyburning out. 1 2.2 Related Technologies The relatedtechnologies of starters are discussed below.2.
2.1 Direct On line It consists ofsimple push button as the controller. When the start button is pressed, theswitch connecting the motor and the main supply is closed and the motor getsthe supply current.
In case of over current, the stop button is pressed, andthe bypass auxiliary contact is opened.2.2.2 Star Delta Starter The 3 windings arefirst connected in star connection and then after some time (decided by thetimer or other controller circuit) the windings are connected in deltaconnection.
In star connection, the current drawn is 0.58% of the normalcurrent and the phase voltage is reduced to 0.58%. Thus, the torque is reduced.
2.2.3 Auto Transformer starterIt consists of anauto transformer (A Transformer with a single winding tapped at differentpoints to supply percentage of it primary voltage across secondary) in starconnection, which reduces the voltage applied to the motor terminals.
Itconsists of 3 tapped secondary coils connected to the three phases. In thestarting period the transformer allows application of lower voltages to thethree windings. 2.
3 Related projects The projectsrelated to motor starters are discussed below 2.3.1 Motor start using Direct on Line(DOL) starterIn this method, themain heart of DOL starter is Relay Coil. Normally it gets one phase constantfrom incoming supply voltage. When coil gets second phase relay coil energizesand magnet of contactor produces electromagnetic field, due to this plunger,contactor will move, and main contactor of starter closes and auxiliary changesits position. NO will become NC and NC will become NO.2.
3.2 Motor start using Star- DeltastarterIn this method, thethree windings are first connected in star connection and then after some time(decided by the timer or other controller circuit) the windings are connectedin delta connection.2.3.3 Motor start using AutoTransformer starterIn this method, thestarting current is limited by using a three-phase auto transformer to reducethe initial stator voltage.It is provided withnumber of tapings. The starter is connected to one tapping to obtain the mostsuitable starting voltage.
The primary of the auto transformer is connected tothe supply line, and the motor is connected to the secondary of the autotransformer. 2.4 Limitations It does not reduce the starting current of the motor.High Starting Current:Very High Starting Current (Typically 6 to 8 times the FLC of the motor).Mechanically Harsh:Thermal Stress on the motor, thereby reducing its life.Voltage Dip:There is a big voltage dip in the electrical installation because of highin-rush current affecting other customers connected to the same lines.Therefore, it is not suitable for higher size squirrel cage motors.
High starting Torque:Unnecessary high starting torque, even when not required by the load, therebyincreased mechanical stress on the mechanical systems such as rotor shaft,bearings, gearbox, coupling, chain drive, connected equipment, etc. leading topremature failure and plant downtimes. 2.5 Problem Statement In some systems thestarting current of motor is required slow while in some systems startingcurrent is required fast, if current of the motor is not controlled accordingto the requirement then the system may damage. So that is why motor current isto be controlled as per the system requirements.
2.6 Summary The primaryfunction of forward reverse motor starter is to move the motor in forward andreverse direction to which it is connected. These are specially designedelectromechanical switches like relays. The main difference between a relay anda starter is that a starter contains overload protection for the motor. So, thepurpose of the starter is twofold, i.e., to switch the power automatically ormanually to a motor and at the same time protect the motor from overload orfaults.
Chapter 3 PROJECTDESIGN AND IMPLEMENTATION 3 3.1 Proposed Design Methodology The forward andreverse rotation of a motor can be caused by interchanging the connection ofany two of its three terminals. Contractors ‘F’ and ‘R’ are mechanicallyinterlocked. It means that if the contacts (1-2, 3-4, 5-6) of contractor R areclosed, contacts (1-2, 3-4, 5-6) of contractor F cannot be closed.When the contactsof contractor F are closed, L1 is connected to T1 through contact F (1-2), L2is connected to T2 through contact F (3-4), and L3 is connected to T3 throughcontact R (5-6).
The motor M runs forward.When the contactsof contractor R are closed, L1 is connected to T3 through contact R (1-2), L2is connected to T2 through contact R (3-4) and L3 is connected to T1 throughcontact R (5-6). The motor M runs reverse.Pressing the stoppush button de-energizes contactor F. This causes the contacts R (1-2, 3-4,5-6) to open and stop the motor M from running forward. Contacts F (11-12)close again maintaining contact F (13-14) open.Pressing thereverse push button energizes contactor R. Contactor R continually energizeseven if the reverse push button is released.
Contacts R (11-12) open to preventcontactor F to be energized. Contacts R (1-2, 3-4, 5-6) close to run motor M onreverse direction.Pressing the stoppush button again de-energizes contactor R. This causes the contacts R (1-2,3-4, 5-6) to open and stops the motor from running reverse. Contact R (11-12)close again maintaining contact R (13-14) open. 3.
2 Implementation Procedure Figure 1 Block Diagram Figure 2 Control Diagram 3.3 Details about Hardware Following components are used in project:Circuit breakerContactorsThermal overload relay Push buttonsIndicator lights Wires for connectionsThe chosen circuitbreaker is of 40 amperes. It protects the electrical circuit from damage causedby excess current.Two contactors areused for forward and reverse rotation.
They are used for switching of motorswitching circuits.One thermaloverload relay is used after two contactors. It protects the motor againstoverload.In the end, athree-phase motor is connected to relay. 3.4 Details about Final Design The completecircuit is placed in a wooden box. The upper lid of box is made up of plasticfiber.Three phasevoltages were supplied to the final circuit and it was connected to inductionmotor in delta connection.
When forwardpush button was pressed, the motor started to rotate clockwise. When reversepush button was pressed, direction rotation of motor changes. 2 Figure 3 Hardware 3.5 Summary The connections of motor are interchanged to make aforward reverse motor controller.
Firstly, the push button energizes theforward contactor to rotate motor in forward direction. Then motor is stoppedwith help of stop push button. After that the other push button energizesreverse contactor and motor rotates in reverse direction.Chapter4 TOOLSAND TECHNIQUES 4 4.1 Hardware Tools used The tools used inmaking of this project are push buttons, circuit breaker, contactors andthermal overload relay.4.1.1 Circuit Breaker A circuit breakeris an automatically operated electrical switch designed to protect anelectrical circuit from damage caused by excess current, typically resultingfrom an overload or short circuit.
The circuit breaker mainly consists of fixedcontacts and moving contacts. In normal “ON” condition of circuitbreaker, these two contacts are physically connected to each other due toapplied mechanical pressure on the moving contacts. Figure 4 circuit breaker 4.1.
2 Overload RelayThermal overloadrelays are economic electromechanical protection devices for the main circuit.They offer reliable protection for motors in the event of overload or phasefailure. The thermal overload relay can make up a compact starting solutiontogether with contactors. .Figure 5 overload relay 4.1.3 ContactorA contactoris an electrically controlled switch (relay) used for switching an electricalpower circuit. A contactor is typically controlled by a circuit which has amuch lower power level than the switched circuit, such as a 24-volt coilelectromagnet controlling a 220-volt motor switch.
3 Figure 6 contactor 4.1.4 Push ButtonA push buttonswitch is a small, sealed mechanism that completes an electric circuit when youpress on it. When it’s on, a small metal spring inside contacts two wires,allowing electricity to flow.
Figure 7 pushbutton 4.2 SummaryFour maincomponents are used in this project. Circuit breaker stops excessive current.Contactors move motor in forward and reverse direction.
Thermal overload relayprotects motor from damaging. Chapter 5PROJECT RESULTS ANDEVALUATIONAll the resultswere achieved. One push button was short circuited, it caused the whole circuitto stop working. With instructor’s help the mistake was corrected and circuitworked properly after that. Some modifications were made to final design. Twoindicators were added to show working of forward and reverse side. They workedproperly.
The project was not very efficient, it has some limitations, but itworked as the instructor wanted. 5 5.1 Presentation of the findings After making and modifying project at different stages the circuit wasable to run the motor in both forward and reverse direction.5.1.1 Hardware resultsThe first part ofproject was circuit breaker. It worked properly and tripped when excess amountof current was flown through its terminals.In next part twocontactors were connected in parallel.
When forward push button was pressed,the current flew from forward contactor and motor started running in forwarddirection. Because of interlocking current did not flow in reverse contactor.Similarly, whenreverse push button was pressed, the reverse contactor worked accordingly andstarted running the motor in reverse direction.The last part ofthe project contained overload relay. It was connected to keep the motor safein case of short circuit. When the push button caused short circuitry, motorremained safe because of overload relay.
The whole projectwas simple, and it worked fine. 5.2 Discussion on the findings The project wascompared with an already made controller. There were some limitations in thisdesign. It was rotating the motor in both directions.
The oldercontroller had star-delta starter connected to it. 1 It helped to run motor smoothly without any danger. The newdesign was not that efficient.This projectcontained light indicators, which showed direction of rotation of motor. 5.
2.1 Comparison with initial Project SpecificationsThe project waseasy and simple. Its only purpose was to rotate the motor in forward as well asin reverse direction.This result wasachieved from the project as it was claimed in proposal. 5.2.
2 Reasoning for short comings Some changings hadto make to the project because of unavailability of contactors of same values.This took a lot oftime and a new hardware was designed for the changed design. At the end, allresults were same. 5.3 Limitations of the working prototype The final workingprototype had some limitations in it. To run a motor in both directions, it hadto run in forward direction first. Then motor is stopped with help of stop pushbutton.
After that, it moved in reverse direction.By pushing reversebutton while motor was moving in forward direction may cause short circuitry.Similarly, pressing forward button while motor was moving in reverse directionmay cause short circuitry of project.To start the motor,delta motor connection was required. This connection was not added to theproject.
5.4 Recommendations and Future Work A delta motorconnection should be made part of this project to start the motor smoothly.Mechanicalinterlocking should be made better for the safety of the circuit.
A timer can beintroduced to stop the motor automatically after running in both directions. 5.5 Summary In this chapter,results of the project were discussed. All the parts of the project workedproperly. The project was compared with a standard working prototype.
It hadlimitations and short comings. The reasons of short comings were also given.In the end, somerecommendations were given to make this project better for future use.Chapter6 CONCLUSION AND FUTURE WORK The one mainproblem was faced because of unavailability of required contactor. Onecontactor worked for 180V and other was working for 220V. Because of this,whole circuit was changed.After working onthis project, it is concluded that this motor controller is very useful inmodern world.
It can be used in lifts to move the lift in upward and downwarddirections. It can be used in automatic doors to open and close them. It ischeap and easy to make.
It does not require modern techniques. Its uses wouldincrease in future. It can be used in modern cranes as well, which requiremovement in different directions. Bibliography 1 “Blogspot,” 26 November 2017.
Online. Available: https://motor-control-circuits.blogspot.com/2015/03/forward-reverse-motor-control.html. Accessed 4 January 2018. 2 “All About Circuits,” 3 july 2006.
Online. Available: https://www.allaboutcircuits.com/textbook/digital/chpt-6/motor-control-circuits/. Accessed 4 January 2018.
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Hubert, Electric Machines, 2nd ed., Delhi: Pearson Education Inc., 2010, pp. 307-315.