Signature :... Supervisor s Name :... Dr. Ir. Md Nazri Bin Othman 2 July

Transcription

1 i 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 :... Dr. Ir. Md Nazri Bin Othman Date : 2 July

2 ii 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 :... Mohd Khairy Bin Abd Mutalib Date : 2 July

3 To my beloved mother and father iii

4 iv 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. Deepest thanks and appreciation to my parents, family, close friends, and others for their cooperation, encouragement, constructive suggestion and full of support for the report completion, from the beginning till the end. Also thanks to all of my friends and everyone, that have been contributed by supporting my work and help myself during the final year project report till it is fully completed. Last but not least, my thanks to Faculty of Electrical Engineering, University Technical Malaysia Melaka (UTeM).

5 v ABSTRACT Wound rotor motor or slip ring was one induction machines where rotor containing one set coils that are terminated in slip ring where external resistance can be connected. The purpose of this project is to develop brush lifting gear for slip ring of wound rotor motor and understand the problem pertaining carbon brush and slip ring. Wound rotor motor has the rotor windings connected to an external resistance through carbon brushes and slip rings assembly. When the brushes are in continuous contact with the slip rings during normal operation of the motor, the brushes and the slip rings will experience premature wearing. Once the motor reaches the normal operation speed, there is no need to have the external resistance in the circuit and the brushes to slip rings contact can be ceased. The development for this project is to lift up the carbon brushes immediately after the motor has reached to its steady state speed. As the result it will minimize the amount of wear and tear of the slip ring and hence will avoid instability on the running current.

6 vi ABSTRAK Motor rotor atau gelincir cincin merupakan salah satu aruhan motor di mana rotor mengandungi satu set gelung yang bersambung dengan gelincir cincin untuk menghubungkan rintangan luar motor. Tujuan projek ini adalah untuk membangunkan satu peralatan mengangkat berus karbon untuk motor rotor gelincir cincin. Motor ini mempunyai belitan rotor yang berhubung di antara gelincir cincin dengan berus karbon. Semasa motor beroperasi secara normal, berus karbon akan bersentuhan dengan gelincir cincin yang akan mengalami separa kehausan. Sebaik sahaja motor mencapai kelajuan yang diperlukan, rintangan luar tidak diperlukan di dalam litar motor dan berus karbon dan gelincir cincin boleh dipisahkan. Projek ini adalah untuk mengangkat berus karbon sebaik sahaja motor telah sampai kepada kelajuan yang diperlukan oleh beban. Sebagai hasil keputusan, jumlah haus dan lusuh gelincir cincin dapat diminimumkan dan dapat mengelakkan ketidakstabilan arus elektrik yang mengalir pada motor.

7 vii 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 INTRODUCTION Theory Background The Concept of Rotor Slip Problem Statement Objective Scope...5 CHAPTER LITERATURE REVIEW Introduction Carbon Brush Lifting Gear System Advantages Of Brush Lifting System Design Requirements Of The Brush Lifting Device (BLD) Carbon Brush Wear Vibrations Current Density... 10

8 viii TITLE PAGE Maintenance Slip ring Basic slip ring CHAPTER METHODOLOGY Flow chart Project Implementation Method Fundamental study of the project Data analysis Result Project Planning CHAPTER RESULT Introduction Result Circuit Analysis Experiment Good and Poor Carbon Brushes Experiment for a Good and Poor Slip Ring Analysis Harmonic Current Peak to Peak in Matlab Software Carbon brushes Slip ring Design For Brush Lifting Gear Brush lifting holder Shorting system Brush lifting function CHAPTER ANALYSIS AND DISCUSSION Introduction... 31

9 ix TITLE PAGE 5.2 Discussion Carbon Brush Slip Ring Harmonic Design Brush Lifting Gear CHAPTER CONCLUSION AND RECOMMENDATION Introduction Conclusion Recommendation REFERENCE APPENDICES... 40

10 x LIST OF TABLE TABLE TITLE PAGE Table 3.1: Project activities Table 4.1 : Output current peak to peak at good carbon brush Table 4.2 : Output current r.m.s at good carbon brush Table 4.3 : Output current peak to peak at poor carbon brush Table 4.4 : Output Current r.m.s for poor carbon brush Table 4.5 : Output Current peak to peak for good and poor slip ring

11 xi 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 Figure 2.3 : Basis slip ring Figure 2.4 : The slip ring device Figure 3.1 : Flow Chart for Proses Implementation The Project Figure 4.1 : Circuit diagram wound rotor motor for experiment Figure 4.2 : Actual circuit in experiment Figure 4.3 : Current waveform for a good carbon brush Figure 4.4 : Current waveform for a poor carbon brush Figure 4.5 : Current waveform r.m.s for good and poor carbon brushes Figure 4.6 : Peak to peak current waveform for good and poor slip ring Figure 4.7 : Current waveform peak to peak for a good carbon brushes Figure 4.8 : Current waveform peak to peak for a poor carbon brushes Figure 4.9 : Harmonic level for a good carbon brushes Figure 4.10 : Harmonic level for a poor carbon brushes Figure 4.11 : Waveform current peak to peak for a good slip ring Figure 4.12 : Waveform current peak to peak for a poor slip ring Figure 4.13 : Harmonic level for a good slip ring Figure 4.14 : Harmonic level for a poor slip ring Figure 4.15 : Brush lifting gear all part view Figure 4.16 : All part brush lifting holder Figure 4.17 : All part shorting system... 29

12 xii FIGURE TITLE PAGE Figure 4.18 : All section brush lifting gear Figure 5.1 : Circuit diagram rotor and slip ring Figure 5.2 : Torque-speed characteristics for R 2 increasing Figure 5.3 : Slip ring function in motor

13 xiii LIST OF ABBREVIATIONS AC DC RMS - Alternating Current - Direct Current - Root Mean Square

14 xiv LIST OF APPENDICES APPENDIX TITLE PAGE APPENDIX A Table 4.1 : Output current peak to peak at good carbon brush. 40 APPENDIX B Table 4.2 : Output current r.m.s at good carbon brush 45 APPENDIX C Table 4.3 : Output current peak to peak at poor carbon brush. 50 APPENDIX D Table 4.4 : Output Current r.m.s for Poor Carbon Brush. 55 APPENDIX E Table 4.5 : Output Current peak to peak for good and poor slip ring 60 APPENDIX F Matlab coding for good and poor carbon brushes 65 APPENDIX G Matlab coding for slip ring 67

15 1 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 The wound rotor or slip ring motor is a type of one induction machines where rotor containing one set coils that are terminated in slip ring where external resistance can be connected. Its sole purpose is to allow resistance to be placed in series with the rotor windings while starting as show in Figure 1.1. This resistance is shorted once has motor started to reach its required speed. Generally wound rotor motors initiates with secondary resistance in rotor circuit. This resistance therefore reduces to allow the motor gains its speed. The secondary resistance can be designed for continuously service dissipate heat

16 2 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. b. The T2 is moderate rotor resistance and the C2 is moderate starting current. c. The T3 is moderately high rotor resistance and the C3 is low starting current. d. The T4 is high rotor resistance and the C4 is very low starting current.

17 The Concept of Rotor Slip Three-phase wound rotor induction machines can be used to furnish, at their slipring 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]. E r = se 2 ( 1.1 ) f r = sf s ( 1.2 ) where E, is the rotor electromagnetic fields (EMF) where motor is at standstill and f s is the stator frequency. When the rotor is running in the same direction as its synchronously rotating magnetic field, the slip is : s = n s n r n s ( 1.3 ) 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 : s = n s n r n s = 1 + n r n s ( 1.4 ) 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]. n syn = 120 f P ( 1.5 )

18 4 Where f is the system frequency, P is the number of poles and n sync 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 threephase windings that are mirror images of the windings on the stator. The 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]. P mech = T mech ω mech = I 2 2 R 2 s ( 1 s ) ( 1.6 ) The equations 1.6 shows the mechanical power is shaft power, while the power converted from mechanical to electrical. P = I 2 2 R 2 s ( 1.7 ) 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 R 2 /s, while the rotor copper losses are the power which would be consumed in a resistor of value R 2. I 2 2 = P R 2 s ( 1.8 ) When the R 2 /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 R 2 /s [2]. where : n s = slip speed of the motor n sync = speed of magnetic fields n r = mechanical shaft speed of rotor

19 5 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 The main target of this project is to develop the carbon brush and slip ring lift up mechanism for slip ring wound rotor motor. This method is designed to lift up the carbon brush after the motor has reached its steady state speed.

20 6 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. This project is to develop brush lifting gear for slip ring of wound rotor motor. Wound rotor motor has the rotor windings connected to an external resistance through carbon brushes and slip rings assembly. When the brushes are in continuous contact with the slip rings during normal operation of the motor, the brushes and the slip rings will experience premature wearing. The development for this project is to lift up the carbon brushes immediately after the motor has reached to its steady state speed. As a result, it will minimize the amount of wear and tear of the slip ring and hence, will avoid instability on the running current.

21 7 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] 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 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. b. The rotor winding shall be connected through the slip rings, brushes and external resistor.

22 8 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 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]. Excessive collector vibration can cause brush bounce, arcing, and ultimately, a flashover. Thus, it is important to monitor the magnitude of brush vibrations, and the

23 9 dominant frequencies of several specific brushes. Assuming unchanged generator balance, the brush vibration will increase slowly over a long period of time, because of collectorring 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]. Loss of continuous contact is caused by excessive brush vibration, which can be cured only by reconditioning the collector-ring surface. This assumes that the shaft excursion caused by unbalance is acceptable [4].

24 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]. Figure 2.2 : Brush Material Rated Current Metal Content [3].