Development of Brush Lifting Gear for Slip Ring Motor.

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Dr. Ir. Md Nazri Bin Othman 2 July

“ I hereby declare that I have read through this report entitle “Development Of Brush Lifting Gear for Slip Ring Motor” and found that it has comply the partial fulfillment of

awarding the degree of Bachelor of Electrical Engineering (Industrial Power)”

Signature : ………...

Supervisor’s Name : ………...

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Mohd Khairy Bin Abd Mutalib 2 July

“ I declare that this report entitle “Development Of Brush Lifting Gear for Slip Ring Motor” is the result of my own research except as cited in the references. The report has not been accepted for any degree and is not concurrently submitted in candidature of any

other degree.

Signature : ………...

Name : ………...

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ACKNOWLEDGEMENT

Bissmillahirrahmanirrahim,

Alhamdulillah. Thanks to Allah SWT, whom with His willing giving me the opportunity to complete this Final Year Project which is title Development of Brush Lifting Gear for Slip Ring Motor. This final year project report was prepared for Faculty of Electrical Engineering, University Technical Malaysia Melaka (UTeM), basically for student in final year to complete the undergraduate program that leads to the degree of Bachelor of Electrical Engineering in Industrial Power. This report is based on the methods given by the university.

Firstly, I would like to express my deepest thanks to, Dr Ir. Md Nazri Bin Othman, a lecturer at Faculty of Electrical Engineering UTeM and also assign, as my supervisor who had guided be a lot of task during two semesters session 2011/2012. I also want to thanks the lecturers and staffs of Engineering Centre UTeM for their cooperation during I complete the final year project that had given valuable information, suggestions and guidance in the compilation and preparation this final year project report.

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ABSTRACT

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ABSTRAK

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TABLE OF CONTENTS

TITLE PAGE

ACKNOWLEDGEMENT ... iv

ABSTRACT ...v

TABLE OF CONTENTS ... vii

LIST OF TABLE ...x

LIST OF FIGURE ... xi

LIST OF ABBREVIATIONS ... xiii

LIST OF APPENDICES ...xiv

CHAPTER 1 ...1

INTRODUCTION...1

1.1 Theory Background ...1

1.1.1 The Concept of Rotor Slip ...3

1.2 Problem Statement ...5

1.3 Objective ...5

1.4 Scope ...5

CHAPTER 2 ...6

LITERATURE REVIEW ...6

2.1 Introduction ...6

2.2 Carbon Brush Lifting Gear System ...7

2.2.1 Advantages Of Brush Lifting System ...7

2.2.2 Design Requirements Of The Brush Lifting Device (BLD) ...7

2.3 Carbon Brush Wear ...8

2.3.1 Vibrations ...8

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TITLE PAGE

2.3.3 Maintenance ... 11

2.5 Slip ring ... 11

2.5.1 Basic slip ring ... 11

CHAPTER 3 ... 13

METHODOLOGY ... 13

3.1 Flow chart ... 13

3.3 Project Implementation Method ... 15

3.3.1 Fundamental study of the project. ... 15

3.3.2 Data analysis. ... 15

3.3.3 Result. ... 16

3.4 Project Planning ... 17

CHAPTER 4 ... 18

RESULT ... 18

4.1 Introduction ... 18

4.2 Result ... 18

4.2.1 Circuit Analysis. ... 18

4.2.2 Experiment Good and Poor Carbon Brushes. ... 19

4.2.3 Experiment for a Good and Poor Slip Ring. ... 22

4.2.4 Analysis Harmonic Current Peak to Peak in Matlab Software. ... 22

4.2.4.1 Carbon brushes. ... 22

4.2.4.2 Slip ring. ... 25

4.5 Design For Brush Lifting Gear ... 27

4.5.1 Brush lifting holder ... 28

4.5.2 Shorting system ... 29

4.5.3 Brush lifting function ... 30

CHAPTER 5 ... 31

ANALYSIS AND DISCUSSION ... 31

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TITLE PAGE

5.2 Discussion ... 31

5.2.1 Carbon Brush ... 32

5.2.2 Slip Ring ... 34

5.2.3 Harmonic ... 35

5.2.4 Design Brush Lifting Gear ... 36

CHAPTER 6 ... 37

CONCLUSION AND RECOMMENDATION ... 37

6.1 Introduction ... 37

6.2 Conclusion ... 37

6.3 Recommendation ... 38

REFERENCE ... 39

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LIST OF TABLE

TABLE TITLE PAGE

Table 3.1: Project activities. ... 17

Table 4.1 : Output current peak to peak at good carbon brush. ... 19

Table 4.2 : Output current r.m.s at good carbon brush. ... 19

Table 4.3 : Output current peak to peak at poor carbon brush. ... 20

Table 4.4 : Output Current r.m.s for poor carbon brush. ... 20

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LIST OF FIGURE

FIGURE TITLE PAGE

Figure 1.1 : The motor circuit ...2

Figure 1.2 : Characteristics with varying resistances...2

Figure 2.1 : Graph Time Versus Magnitude Of Brush Vibration ...9

Figure 2.2 : Brush Material Rated Current Metal Content ... 10

Figure 2.3 : Basis slip ring... 12

Figure 2.4 : The slip ring device. ... 12

Figure 3.1 : Flow Chart for Proses Implementation The Project... 14

Figure 4.1 : Circuit diagram wound rotor motor for experiment. ... 18

Figure 4.2 : Actual circuit in experiment. ... 19

Figure 4.3 : Current waveform for a good carbon brush... 20

Figure 4.4 : Current waveform for a poor carbon brush. ... 21

Figure 4.5 : Current waveform r.m.s for good and poor carbon brushes. ... 21

Figure 4.6 : Peak to peak current waveform for good and poor slip ring. ... 22

Figure 4.7 : Current waveform peak to peak for a good carbon brushes. ... 23

Figure 4.8 : Current waveform peak to peak for a poor carbon brushes. ... 23

Figure 4.9 : Harmonic level for a good carbon brushes. ... 24

Figure 4.10 : Harmonic level for a poor carbon brushes... 24

Figure 4.11 : Waveform current peak to peak for a good slip ring... 25

Figure 4.12 : Waveform current peak to peak for a poor slip ring. ... 25

Figure 4.13 : Harmonic level for a good slip ring. ... 26

Figure 4.14 : Harmonic level for a poor slip ring. ... 26

Figure 4.15 : Brush lifting gear all part view. ... 27

Figure 4.16 : All part brush lifting holder. ... 28

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FIGURE TITLE PAGE

Figure 4.18 : All section brush lifting gear. ... 30

Figure 5.1 : Circuit diagram rotor and slip ring. ... 32

Figure 5.2 : Torque-speed characteristics for R2 increasing. ... 33

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LIST OF ABBREVIATIONS

AC - Alternating Current

DC - Direct Current

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LIST OF APPENDICES

APPENDIX TITLE PAGE

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CHAPTER 1

INTRODUCTION

This project is about 'Development of brush lifting gear for slip ring motor', in this chapter contain :

a. Background project. b. Objective of the project. c. Project scope.

d. Problem statement. e. Project report layout.

Background project explain development of brush lifting gear for slip ring motor, while the objective explain project the purpose of the objective are made like study system for carbon brush lifting gear. Project scope on the other hand tell steps to achieve this project. Problem that faced when undertaking the project this would be recounted in problem statement.

1.1 Theory Background

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generated by continuous operation in decreasing speed, frequent acceleration, or acceleration with large inertia load [1].

Figure 1.1 : The motor circuit [3].

Figure 1.2 : Characteristics with varying resistances [4].

Base on the Figure 1.2 the red waveform is the characteristics for the resistance and the blue waveform is the characteristics for the current in the external resistance. The operations are :

a. The T1 is low rotor resistance and the C1 is typical starting current.

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( 1.4 )

( 1.5 ) 1.1.1 The Concept of Rotor Slip

Three-phase wound rotor induction machines can be used to furnish, at their slip-ring terminals, a three-phase source of variable and frequency. For this application, the wound rotor is connected to normal voltage and frequency supply. The voltage induced in rotor and its frequency are directly proportional to the operating slip [2].

=

=

where E, is the rotor electromagnetic fields (EMF) where motor is at standstill and fs is the stator frequency. When the rotor is running in the same direction as its synchronously rotating magnetic field, the slip is :

= −

For small slip, the rotor frequency is low. If the direction of the synchronously rotating magnetic field is opposite to the rotor direction, the slip is :

= − −

− = +

The slip will be greater than unity, the rotor voltage will be larger and its frequency will be larger than of the stator. The slip rings of the wound rotor can thus become a power source of variable voltage and frequency.

The three-phase induction motor essentially consists of two part : stator and rotor. The stator connected to a three phase power supply. Due to the phase shift of 120⁰ between each successive phases, a rotating magnetic field is produced and governed by the following expression [2].

=

( 1.3 ) ( 1.1 )

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( 1.6 )

( 1.7 )

( 1.8 )

Where f is the system frequency, P is the number of poles and nsync is the speed of the magnetic field’s rotation.

There are two different magnetic field passes over the rotor which can be placed inside the stator. One is called a wound rotor. A wound rotor has a complete set of three-phase windings that are mirror images of the windings on the stator. The three three-phases of the rotor winding are usually in Y-connection and at the end of the three rotor, wires are tied to slip rings on the rotor’s shaft. The rotor windings are shorted through brushes riding on the slip rings. Wound rotor induction motors therefore have their rotor currents accessible at the stator brushes, where that can be examined and where extra resistance can be inserted into the rotor circuit [2].

= = ( − )

The equations 1.6 shows the mechanical power is shaft power, while the power converted from mechanical to electrical.

=

The equation 1.7 shows the simplest equation for the motor circuit. The only element in equivalent in the circuit where the power consumed is in the resistor R2/s, while the rotor

copper losses are the power which would be consumed in a resistor of value R2.

=

When the R2/s in the motor circuit is increase, value of current I will decrease. The

equations 1.8 as show power crossing the resistance from the stator circuit to the rotor circuit. It is equal to power absorbed in the resistance R2/s [2].

where :

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1.2 Problem Statement

A slip ring applications have been widely used on slower speed of wound rotor motor. The amount of the maintenance for the motor increases as to check the wear and tear of the slip ring regularly. The uneven surface of slip ring due to continuous contact with carbon brush may produce unstable current of the motor which subsequently will increase the power loss of the motor. By having brush lifting gear for slip ring, it will reduce the contact duration and minimize the wearing process of the slip ring.

1.3 Objective

There are some objectives of development of brush lifting gear for slip ring motor. The objectives are :

a. To understand the problem pertaining carbon brushes and slip ring of wound rotor motor.

b. To develop brushes lifting gear slip ring for wound rotor motor.

1.4 Scope

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter discus about the summary of the transactions, journals, proceedings, original reports and book. This source is very helpful in finishing the project. The purpose is to discuss about for perspective and method that used so that project can be studied and produced. This chapter is also act as reference to the project in problem solving. Project comprehension is important as guide and result something the study could not be valued without compared to theory. This chapter also sets out briefly on theory related materials that are being used in project so that comprehension related can be increased. Topic which include in this chapter were related development carbon brush lifting gear for slip ring motor.

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2.2 Carbon Brush Lifting Gear System

The wound rotor motor is one of the solution for these applications. For a high torque capacity with controlled current, the motors start with a liquid rheostat (variable resistor) in series with the winding rotor. The wound rotor motor works on the same principle of an induction motor. The slip ring and brush arrangement will convert the rotating winding rotor to ends stationary terminal. The sole purpose of brush or ring assembly is to allow an external resistance to be connected in series with the slip windings while starting the rotor. Normally, this resistance is disconnected by shorting the winding terminals once the motor reaches the rotor operation and the becomes electrically like the squirrel cage motor. Once the rings are short-circuited, there is no need of brushes to slip rings contact. Hence the brushes can be lifted to avoid wear [1].

2.2.1 Advantages Of Brush Lifting System

The advantages for this system are :

a. Constant and continuous motor performance for years.

b. No premature wearing of the brushes and collector rings. Thus reduced break for maintenance and substitution of brushes.

c. Clean brush section due to low carbon dust from brushes, promote higher insulation life.

d. Low extra cost due to increased brush and collector rings lifespan.

2.2.2 Design Requirements Of The Brush Lifting Device (BLD)

The projected functionalities of the BLD are:

a. Brushes shall be in contact with slip ring with required spring pressure while machine is stationary.

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c. Once machine reached its required operational speed, the rotor winding terminals shall be short circuited.

d. The shorting mechanism shall able to conduct the maximum rated current with no temperature issues.

e. There shall be no relative motion between rotor and shorting mechanism. f. Brushes shall be lifted from slip ring surface to avoid brush wear.

g. Brushes shall be secured in holders for further operations.

h. The shorting shall precede the brush lifting. This means the brushes shall be lifted only after the shorting mechanism is fully connected in the short-circuit position. i. The whole operation shall be friendly for automation with a manual override. j. System shall be reliable.

2.3 Carbon Brush Wear

This part will discuss about factor that causes wear to the carbon brush’s operation motor which are :

a. Vibration. b. Current Density. c. Maintenance.

2.3.1 Vibrations

All vibrations impair the contact between brush and slip ring. It may have as its origin: bad balance, defective running, bad alignment and exterior to the machine itself, gearing coupling and driven or driving equipment. A slip ring in a bad or deformed condition gives rise to faults which should be attenuated if not suppressed[4].

The vibratory system constituted by the brush, the spring and the brush holder with its support, can enter into resonance. This is generally followed by serious deterioration of the brush and even also of the brush holder [4].

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dominant frequencies of several specific brushes. Assuming unchanged generator balance, the brush vibration will increase slowly over a long period of time, because of collector-ring wear. If vibration increases to high levels, the brushes are no longer able to maintain contact with the ring around its entire periphery and they start bouncing and arcing. Under such conditions, arc erosion of the ring surface quickly deepens existing valleys. If peaks and valleys develop in the ring periphery, higher vibration frequencies will result and there will be higher forces on the brush. Since acceleration is proportional to the square of the frequency, these forces may become quite high [4].

Monitor the vibration of selected brushes weekly and plot vibration magnitude against time. If vibration begins to increase rapidly with time, investigate the condition immediately and take corrective action [4].

Figure 2.1 : Graph Time Versus Magnitude Of Brush Vibration [5].

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2.3.2 Current Density

The actual current a brush can carry is widely influenced by operating conditions such as type of ventilation, continuous or intermittent duty, speed and other factors. The published data sheet ratings for electrographite brushes are generally conservative, some allowance having been made for short term overloads above those listed in the published data [3].

The current carrying capacity of a brush depends ultimately on the operating temperature. On well-ventilated machines having small brushes with larger surface area in proportion to their volume and where brushes cover only a small percentage of the commutator or ring surface, conventional current densities for electro graphite grades can often be doubled without seriously jeopardizing their performance [3].

On the other hand, increasing the current density without making provisions for maintaining a suitable low brush temperature may reduce the brush life dramatically. In practice, low current density in a machine caused by running a machine below full rated load is potentially more damaging than a moderate overload. For good operating temperature and performance as a general rule, the actual operating current density should be not lower than 60% of the published rated current density [3].

Brush current densities vary widely depending on the motor design and loading, and brushes may be graphite, electro graphite or metal graphite grades. The current in the brushes on this application is AC (Alternating Current at slip frequency). For wound rotor motors, the current densities may vary over a larger range, but the brush current density and ring material are the main factors in selecting brush grades [3].