Design And Construction A Motor Soft Starter For A Three Phase Motor

Electrical Electronics Engineering | Engineering

A motor soft starter for a three-phase motor is a sophisticated electronic device utilized to mitigate the initial inrush current and mechanical stress during motor startup, thereby prolonging motor lifespan and enhancing operational efficiency. It functions by controlling the voltage and current supplied to the motor, gradually ramping up the power to achieve a smooth start-up process. This device incorporates various components such as semiconductor devices like thyristors or silicon-controlled rectifiers (SCRs), microcontrollers, and sensing circuits to monitor parameters like voltage, current, and temperature. Through precise modulation of power delivery, it ensures a gentle start for the motor, reducing electrical and mechanical shocks while enabling seamless integration into diverse industrial applications.

DEDICATION

This project is dedicated to Almighty God for his protection, kindness, strength over my life throughout the period and also to my — for his financial support and moral care towards me.Also to my mentor — for her academic advice she often gives to me. May Almighty God shield them from the peril of this world and bless their entire endeavour Amen.

ACKNOWLEDGEMENT

The successful completion of this project work could not have been a reality without the encouragement of my — and other people. My immensely appreciation goes to my humble and able supervisor Mr. — for his kindness in supervising this project. My warmest gratitude goes to my parents for their moral, spiritual and financial support throughout my study in this institution.
My appreciation goes to some of my lecturers among whom are Mr. —, and Dr. —. I also recognize the support of some of the staff of — among whom are: The General Manager, Deputy General manager, the internal Auditor Mr. — and the —. Finally, my appreciation goes to my elder sister —, my lovely friends mercy —, —, — and many others who were quite helpful.

ABSTRACT

This paper describes a student project that studies the design of a Soft-Starter for three phase Alternating Current (AC) Induction Motor. Starting a large motor that utilizes an AC Converter will eliminate the need to draw a large amount of current during the transient period, thereby insuring that starting a large motor will not disturb adjacent power lines.

On the demand side, the protection of consumer equipment and appliances from damage and total destruction due to phase failures is an issue of paramount importance mainly in parts of the world with unsteady supply of electricity. In this work we took a detailed look into what a phase failure is and the possible causes. Then we finally explain the details of a method we have developed that detects cases of phase failure and takes the appropriate measure that will save the consumer loads from damages.

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

ABBREVIATION

CHAPTER ONE

1.0 INTRODUCTION

1.1 BACKGROUND OF THE STUDY

PROBLEM STATEMENT
AIM AND OBJECTIVE OF THE STUDY
ADVANTAGES OF SOFT STARTER
DISADVANTAGES OF SOFT MOTOR STARTER
APPLICATIONS OF SOFT STARTER
LIMITATION OF THE STUDY
SCOPE OF THE STUDY

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

3.0 METHODOLOGY

3.1 SYSTEM BLOCK DIAGRAM

3.2 SYSTEM CIRCUIT DIAGRAM

3.3 SOFT STARTER CIRCUIT DESCRIPTION

3.4 PHASE FAILURE AND SEQUENCE PROTECTION CIRCUIT

3.5 PHASE FAILURE DETECTOR AND SEQUENCE PROTECTION CIRCUIT DIAGRAM

3.6 PHASE FAILURE DETECTOR AND SEQUENCE PROTECTION MODE OF OPERATION

CHAPTER FOUR

4.1 INSTALLATION OF THE COMPLETED DESIGN

4.2 CONSTRUCTION PROCEDURE AND TESTING

4.3 CASING AND PACKAGING

4.4 ASSEMBLING OF SECTIONS

4.5 TESTING OF SYSTEM OPERATION

CHAPTER FIVE

CONCLUSION
RECOMMENDATION
REFERENCES

CHAPTER ONE

1.0 INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Our industries use various kinds of machines. The induction machine is one of the most used three phase AC machine which is almost 70% of the motors used in industries. Their robust construction and high efficiency makes it the best choice for every industrial sector. But they do require protection devices and equipment used for their safe operation so it can operate safely and prevents any potential damage to the motor and also increase their life span. The most essential equipment used for three phase induction motor is a motor starter.

The soft starter is a type of motor starter that uses the voltage reduction technique to reduce the voltage during the starting of the motor.

The soft starter offers a gradual increase in the voltage during the motor startup. This will allow the motor to slowly accelerate & gain speed in a smooth fashion. It prevents any mechanical tear & jerking due to sudden supplying of full voltage.

The torque of an induction motor is directly proportional to the square of current. & the current depends on the supply voltage. So the supply voltage can be used to control the starting torque. In a normal motor starter, applying full voltage to the motor generates maximum starting torque which possess mechanical hazard to the motor.

Therefore we can say that a soft starter is a device that reduces the starting torque & gradually increase it in a safely manner until it reaches it rated speed. One the motor attains its rated speed, the soft starter resumes the full voltage supply through it.

During motor stopping, the supply voltage is gradually reduced to smoothly decelerate the motor. Once the speed reaches zero, it breaks the input voltage supply to the motor.

The main component used for the regulation of voltage in a soft starter is a semiconductor switch such as a Thyristor (SCR). Adjusting the firing angel of the thyristor regulates the voltage supplying through it. Other components such as OLR (overload relay) used for overcurrent protection is also used.

1.2 PROBLEM STATEMENT

Connecting the motor to power supply draws a huge amount of current in the stator winding due to this low impedance called inrush current. The alternating current in the stator generates a rotational magnetic field (RMF) that induces current in the rotor windings.

The rotor current generates its own magnetic field that try to cancel its cause & starts rotating in the direction of RMF. Thus the rotor experience torque & as its speed starts increasing the slip of the motor decreases (i.e. the rotor RMF speed approaches near stator RMF speed). Since the slip is reduced, the impedance of the rotor increases & the motor start drawing normal rated current.

The High inrush current is 5-8 time larger than the full load rated current of the motor. Induction motor cannot tolerate such amount of current as it can quickly damage or burn the windings, reducing the performance & lifespan of the motor. Such high currents can also cause huge dip in the line voltage which is dangerous for other appliances connected to the same line.

In order to prevent such high inrush current, we use motor starters that reduces the initial current for a short duration. Once the motor gains certain speed, the normal power supply is resumed. It also offers protections against low voltage & overcurrent.

1.3 AIM AND OBJECTIVES OF THE STUDY

The main aim of this work is to build a motor soft starter for a three phase electric motor. The objectives of this work are:

To help you reduce mechanical wear and tear on startup.
To reduce energy costs.

To minimize loss of production hours from equipment

1.4 ADVANTAGES OF SOFT STARTER

Advantages of Soft Starter are as follows:

Smooth Startup: Unlike conventional motor starter, it provides very gradual increase of voltage thus speed that results in a very smooth startup. There is no mechanical stress whatsoever or jerks that can damage the motor.

Acceleration & Deceleration Control: It offers a fully adjustable acceleration & deceleration of the motor. Varying the firing angle slowly or quickly can control the acceleration during startup & deceleration during stopping of motor. This is used in application where startup acceleration needs to be adjusted.

No Power Surges: Since the conventional motor starter allows full voltage across the motor, a huge inrush current start flowing into the motor that cause a power surge in the circuit. the soft starter limits such current thus preventing the power surges.

Multiple Startups: Some applications require the motor to start & stop multiple times in small period of time. such motor if used with a conventional starter will experience overheating due to high starting current. However, soft starters drastically increases the number of startups for a motor in a specific duration.

Reduction of Overheating: The motor overheating is a very serious problem. It occurs due to the high winding current during its startup. The soft starter allows a very small amount of starting current which prevents the overheating of motor.

Increased Life Span: The soft starter as compared to a conventional starter improves the life time of the motor. it is due to the smooth operation & absence of electrical & mechanical stress on the motor.

Less Maintenance: Due to its smooth operation, the induction motor is less likely to have any mechanical faults, which is why it require less maintenance as opposed to conventional motor starter.

Efficiency: A conventional motor starter supply full voltage (very high inrush current) to the motor that consumes too much energy. A soft starter significantly reduces it & allows a gradual increase in energy consumption. Also the power switches are controlled using very low voltage level. It improves the overall efficiency of the motor.

Compact & Small Size: The soft starter has a very compact design that takes up very small space. Unlike other motor starters, it has very small size.

Low Cost: compared to other starters such as VFD, this sure does cost cheaper.

1.5 DISADVANTAGES OF SOFT MOTOR STARTER

No Speed regulation: The soft starter only allows the control of input voltage supply i.e. from 0 volts to line voltage with a fixed line frequency. Since the frequency is constant the motor speed is constant & only regulates by the load connected with it. The speed of induction motor is regulated by varying the supply frequency below or above the line frequency according to the need. Such feature is only available in VFD (variable frequency drive).

Heat dissipation: The semiconductor switches inside the soft starter dissipates some energy in the form of heat. Therefore, it also requires heat sinks for cooling the power switches.

Reduced starting Torque: Since it reduces the input voltage that corresponds to the input current which is directly proportional to the starting torque of the induction motor, it significantly reduces the starting torque.

1.5 APPLICATIONS OF SOFT STARTER

The soft starter is used in industries & is more appropriate to be used for motors that run on a constant speed.

Fans: The huge fans used in industries runs at a constant speed. However, they do require the startup protection. A soft starter is a best option for such fans.

Conveyor belts: The conveyor belts in industries are used for moving objects & it needs extra care. The sudden jerks during starting or stopping using conventional starter may misalign the belts, damages the belt due to mechanical stress & damage the objects placed on it. It requires a smooth starting & stopping offered by a soft starter

Motors using belt & pulleys: The motor that drives load through belts & pulleys cannot tolerate the sudden jerks. It wears the belt that couples it to the load. A soft starter offers a smooth starting for such motor applications.

Water or liquid Pump: Any type of pump connected with a motor requires a smooth starting & stopping due to the sudden pressure building inside the pipes. A conventional starter may generate enough pressure at startup to break the line. A soft starter offer gradual increase in the pressure to such liquid pumps. However, there is no speed control of the pump during normal operation. A VFD is a better choice for variable pump speed.

1.7 LIMITATION OF THE STUDY

Electrical motor starters are usually used for heavy power rated motors. Small motors below 1Hp does not require motor starter due to their high impedance. However, they do need overcurrent protection that is available in DOL starter.

1.8 SCOPE OF THE STUDY

The scope of this work covers building a motor starter to safely start and stop an electric motor. The induction motors draws a huge amount of current at starting. It is due to the low impedance of the windings of the motor at standstill.

PROJECT DESCRIPTION

Format = Microsoft word

Chapters = 1-5 chapters

Price: N3,000.

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