Design And Construction Of Forward And Reverse Control Of An AC Motor Using Timer Relay

ABSTRACT

Manually, the direction of rotation of any three-phase motor can be reversed by changing any of the motor leads. Since the motor is connected to the power line regardless of which direction it operates. In this work, instead of changing the direction of the motor manually a timer relay was used which is a type of relay constructed with a kind of “shock absorber” mechanism attached to the armature which prevents immediate, full motion when the coil is either energized or de-energized. This addition gives the relay the property of time-delay actuation.

This work deals with forward reverse of an ac motor delta used in every electrical industry involving industrial process automation control technology.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PURPOSE OF THE PROJECT
• OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• APPLICATION OF THE PROJECT
• LIMITATION OF THE PROJECT
• PROBLEM OF THE PROJECT

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF THE STUDY
• DESCRIPTION OF AN AC INDUCTION MOTOR
• REVIEW OF OPERATING PRINCIPLES OF AN AC INDUCTION MOTOR
• HISTORICAL BACKGROUND OF AN AC INDUCTION MOTOR
• REVIEW OF RELATED STUDIES
• REVIEW OF DIFFERENT TYPES AC MOTOR CONTROL

CHAPTER THREE

SYSTEM METHODOLOGY

• DESIGN METHODOLOGY
• MATERIAL USED
• YSTEM DIAGRAM
• SYSTEM OPERATION
• DESCRIPTION OF ELECTRICAL PARTS USED

CHAPTER FOUR

• THERMAL OVER LOAD RELAY
• MOTOR STARTER WITH OVERLOAD PROTECTION

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                                     BACKGROUND OF THE STUDY

Three phase star-delta motors are constructed similarly to a direct online single phase motor, but the terminals for each winding are not terminated within the motor, instead they are brought out of the motor for control wiring to connect to.

Three phase star-delta motors are used for maximum talk, where the motor will try to start under a heavy load. A star-delta motor starts in two stages, controlled by equipment connected to it.

Forwarding and reversing of an ac motor is done using a push button switches. Depending on the choice of the operator, starting the circuit is selected via the forward or the reverse push button switches. When the forward push button switch is selected, the command is transferred to the relevant forward function of the circuit which activates the forward main coil (blue). The relevant auxiliary contacts of the forward main coil (blue) would then be actuated opposite its normal state, that is, a normally open contact would eventually switch to a close contact whereas a normally close contact would switch to an open contact.

The forward main contact (blue) closes to activate the star coil (brown) together with the timer coil (green), hence placing the motor terminal in the power circuit connected to a star configuration. After an elapsed time is reached, the timer contact (green) will release the star coil (brown) and transfers the command to the forward delta mode as a result of a completed circuit with the closing of the timer contact (green) along with the awaiting initially closed forward main contact (blue), thereby permitting power flow to the forward delta coil (dark blue). This final stage places the motor terminal in the power circuit configured to a delta connection.

Another forward main contact (blue) is connected in parallel across the forward push button switch to serve as a latching switch that keeps the forward main coil maintained energized after the operator releases the forward push button switch.

Conversely, when the reverse push button switch is pressed by the operator, all the related contacts of the reverse main coil (red) is activated which holds the reverse main coil maintained activated after releasing the reverse push button switch, then energizes the star coil (brown) and the timer coil (green), then switches to the reverse delta mode (orange) after the specified time set on the timer expires.

To manually interrupt the circuit, the operator only needs to press the stop push button switch to deactivate any energized coil in the control circuit to instantaneously isolate the power source to the motor. Another interrupting contact is the thermal overload contact (purple) which serves as an automatic shutoff switch that instantaneously opens the control circuit to shut down the motor when overload current greater than the rated capacity is detected from the electric motor.

Interlock contacts are also strategically placed on the control circuit as a protective measure. An auxiliary contact from the star contactor (brown) is connected in series before the two delta contactor coils to isolate both the forward delta coil and the reverse delta coil when the star contactor coil is active. Likewise, auxiliary contacts from both the forward and the reverse delta coils are also placed in series before the star coil to isolate power to the star coil should any one of the two delta coils be active to ensure the absence of power flow to the star coil when  the control circuit is actively in the delta mode.
Auxiliary contacts from both forward and reverse coils are also placed opposite each coil so that one cannot activate without the other one deactivated first, meaning, the normally-closed forward main contact (blue) connected before the reverse main coil (red) will not permit the activation of the reverse main coil (red) while the forward main coil (blue) is activated, conversely, the normally-closed reverse main contact (red) connected before the forward main coil (blue) will not also permit the activation of the forward main coil (blue) while the reverse main coil (red) is activated.

The same condition applies to both the forward and the reverse delta coils. The opposing interlock contacts placed before the forward and the reverse delta coils also provides protective action by preventing the simultaneous activation of the forward and the reverse delta coils at the same time, that is, the normally-closed reverse main contact (red) connected before the forward delta coil (dark blue) will not permit the activation of the forward delta coil (dark blue) while the reverse main coil (red) is active, and the normally-closed forward main contact (blue) placed before the reverse delta coil (red) will not also permit the activation of the reverse delta coil (red) while the forward main coil (blue) is active.

To facilitate for a further understanding about the concept of the forward reverse star delta electric motor control circuit, a flowchart diagram is provided to serve as a schematic representation of the sequence of operation of the reversible star delta electric motor control circuit.

1.2                                              PURPOSE OF THE PROJECT

A large number of motors are being used for general purposes in our surroundings from house-hold equipments to machine tools in industrial applications. The electric motor is now a necessary and indispensable source of power in many industries. The function and the applications of these motors are wide-ranging. For the many applications, the forward and reverse control of the motor plays a major role, which can be done using a wide range of control strategies.

The main purpose of this work is to control the forward and backward of an ac motor using timer relay.

1.3                                        OBJECTIVE OF THE PROJECTGenerally direction control of an ac motor can be achieved by pressing the switch connected the input parameters of the motor such as current, voltage etc. However the objective of this work is to control ac motor direction (that is forward and backward) using timer relay.

1.4                                         SIGNIFICANCE OF THE PROJECT

Can be used to drive small conveyor belts in 2 directions and with dimmer would be able to handle both directional control and speed control.

It is also possible to use this circuit for any robotic application where directional control is needed with speed control such as RC helicopters’ or aircrafts’ propellers. “Single Phase Induction Motor Speed Control Using PWM AC Chopper Fan Applicaitons”

1.5                                                 SCOPE OF THE PROJECT

This work deals with forward reverse of an ac motor delta used in every electrical industry involving industrial process automation control technology.

Depending on the choice of the operator, starting the circuit is selected via the forward or the reverse push button switches. When the forward push button switch is selected, the command is transferred to the relevant forward function of the circuit which activates the forward main coil (blue). The relevant auxiliary contacts of the forward main coil (blue) would then be actuated opposite its normal state, that is, a normally open contact would eventually switch to a close contact whereas a normally close contact would switch to an open contact. The forward main contact (blue) closes to activate the star coil (brown) together with the timer coil (green), hence placing the motor terminal in the power circuit

1.6                                          APPLICATION OF THE PROJECT

This work is used in the following devices:

• Automatic gates
• Electronic bikes
• Swing machines
• Robotic controls
• Mobile air condition fans
• Ac operated drill machines
• Winding machines
• Electronic door controllers
• Electronic chairs (beauty parlor. Etc.)

1.7                                           LIMITATION OF THE PROJECT

This device only control the forward and reverse of the motor and is not able to control the motor speed.

1.8                                              PROBLEM OF THE PROJECT

The timer relay which acts as a switch is quite expensive compare to other types switches which are used as an external electrical equipment. This switch is the most troublesome parts of the device. This switch suffers from mechanical wear, which affects the motor performance.