Transients in Single-Phase Induction Motors: A Study of the Transient Torque Characteristics of an Unloaded Single-Phase Capacitor-Start Induction Motor

The thesis describes a study of the transient torque characteristics of an unloaded single-phase, capacitor-start induction motor. A review of published works on the study of transient torques in induction motors is made in Chapter 1. Though there have been attempts to calculate transient torque characteristics of single-phase Induction motors for zero speed and constant speed conditions, there does not appear to have been any attempt at an experimental study of the problem. Experimental investigation avoids the limitations normally involved in theoretical calculations. A systematic experimental investigation necessitates the exercise of control over the point-on-wave of closing the supply to the motor and equipment to detect transient torques, under both free-rotor and blocked-rotor conditions. After an exhaustive survey of possible methods of detecting transient torques under these conditions (Appendix I), it was decided to use a d.c. excited, drag-cup, two-phase induction generator as an accelerometer in the former case and a stator reaction detecting scheme using a precision load cell for the latter case. The calibration of the accelerometer is described In Appendix II and the design of the stator reaction detecting scheme in Appendix III. The attempt to design and develop a p.-on-w. control and the actual one used are described in Chapter 2. The operational details and calibration of the p.-on-w. switch are also described in detail. It was found to be very important to have the accelerometer rigidly coupled to the shaft of the motor. For the stator reaction detecting scheme, it was necessary that the natural frequency of the stator suspension should be at least about 450 c/s. Results obtained simultaneously by the two detecting methods show satisfactory correspondence. Chapter 3 deals with the investigation of transient torques with free rotor. The effect of pointx-on-wave of closing the supply voltage is studied in detail at a reduced terminal voltage of 140V. The results show that the initiation of the transient torques is governed by point-on-wave. The transient torques have a maximum near 0 point-on-wave and are almost completely absent for 90. Speed effects are discussed and It is found that speed plays an Important part in determining the value of maximum peak torque. Speed also introduces dynamic braking torque which affects the mean torque pattern. Free-rotor investigations with different applied voltages are described, and their results discussed. The importance of speed effects is well demonstrated by these results. The duration of the line frequency component of the transient torque is almost entirely governed by speed except for very long run-up times. The appearance of a double line frequency pulsating torque also seems to be speed dependent. With short run-up times, the machine overspeeds before finally attaining its no-load speed. Variation in speed effects with differing acceleration and the effect of saturation on the torque peaks are discussed. Experiments to study the effect of switching on while the motor is running are reported. The results show that the dynamic braking torque assumes greater importance when re-closing is done near no-load speed and 0 point-on-wave. Investigation of the stalled-rotor transients is presented in Chapter 4. This investigation was carried out both by experiment and by computation. The experimental results show that the initiation of transient torques depends on the point-on-wave in much the same way as in the free-rotor case. In the absence of speed effects the magnitude of torque peaks does not show an Increase over the initial value and the transient torques decay with their 'natural' electrical time constants. The principal component has a very long time constant. Transient current equations are derived based on the actual two-axes arrangement of the windings. Experimentally determined machine constants are substituted in these equations and the resulting current expressions are solved for instantaneous values using a digital computer. Instantaneous values of torque are computed from the Instantaneous values of currents. The various components of the transient torque are discussed. Computed transients compare favourably with experimental results. The approach, systems used, and results obtained are discussed in a general fashion. Blocked-rotor results and free-rotor results are compared with a view to determining the degree to which the former results can be applied to the latter condition. It is thought that the very large dynamic braking torque that can be obtained during re-closing while the rotor Is rotating, my be of some practical significance

Kinetics of Reaction Between o-Substituted Benzoate Ions & Phenacyl Bromide

805-80

The Extraction of Mint Oil from Mint Leaves: A Study

Essential oils are a diverse group of natural products. Oils are the important source of aromatic and flavoring chemicals in food, industrial, and pharmaceutical products. Essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds derived from the different parts of the plants. Various extraction methods are used in the manufacture and extraction of essential oils from the plant materials. Essential oils are produced using several techniques like water distillation, steam distillation, hydro diffusion, maceration, solvent-free microwave extraction, solar distillation and CO2 supercritical fluid extraction, etc. These extraction and expression methods are used to remove the oils from the dried/fresh plants (or) machines to squeeze the oil out of the plants. Out of all the extraction methods, supercritical carbon dioxide method is more efficient. The present report is an attempt to list out the various methods of extraction of essential oil from the different parts of the mint leaves and their merits and demerits. The world production and consumption of essential oils and perfumes are increasing very fast. Production technology is an essential element to improve the overall yield and quality of essential oil. The traditional technologies pertaining to essential oil processing are of great significance and are still being used in many parts of the globe. Water distillation, water and steam distillation, steam distillation, are the most traditional and commonly used methods

Mother Tongue Influence on English Pronunciation: A Case study in College Students

Mother tongue interference can affect students’ English speaking skill especially in pronouncing the words intrinsically. Considering Tamil language is the dominant mother language used by students at College level, the students as EFL learners often use their mother tongue in daily communication and at campus, and College students pronounce English words in a different way. This study investigated the forms of Tamil language interfering students in pronouncing English words, and how they were interfered. This was a descriptive study in the field of English pronunciation elaborated in a qualitative way. Recorded interviews and pronunciation testing were the main techniques of collecting data. Interview guide, validated pronunciation test, and document analysis were the instruments. In conclusion, the interference was positive since Tamil language’s phonemic sounds have some similarities to those of English, so this condition does not potentially change the meanings of English words

Oxidation of Acetonaphthones by Hexacyanoferrate(III)

14

Properties of cotton, tencel and cotton/tencel blended ring- spun yarns

Yarn characteristics of pure cotton, 67:33 cotton/tencel blend, 33:67 cotton/tencel blend and pure tencel have been studied. Blending is done at draw frame. Machinery parameters are kept constant for studying the effect of fibre parameters on yarn characteristics. It is observed that the addition of tencel increases single yarn strength significantly at the higher tencel composition. Presence of tencel improves the elongation property. Packing fraction of tencel and tencel blended yarn is found to be more than that of cotton. Swelling diameter of pure cotton yarn is found to be lower than those of pure tencel and tencel/cotton blend yarns. Hairiness (H) decreases with the addition of tencel in the blend. It is also observed that the coefficient of friction (yarn- to- metal) of blend yarn reduces with the addition of tencel fibre in the blend

Dimensional stability of cotton, tencel and tencel/cotton blend plain weft knitted fabrics

Pure cotton, 33/67 tencel/cotton, 67/33 tencel/cotton, and pure tencel yarns of 30 Ne count have been produced in the cotton spinning system and then used for knitting plain weft structure with three ranges of tightness factor to study their dimensional stability. Then knitted fabrics are subjected to dry, wet and tumble dry relaxations. Courses per inch(cpi), wales per inch(wpi), fabric thickness and areal density are measured at the end of each relaxation. Constants k1, k2, k3, k4 values for stitch density, cpi, wpi and loop shape factors are calculated using measured stitch length. Test results are subject to multilevel factorial analysis to determine factor contribution to the dimensional changes. It is found that the fibre contribution to the shrinkage is very less as compared to the contribution made by stitch length and relaxation treatments. Similarly, the quantum of length and width shrinkage is determined primarily by the stitch length (tightness factor). This is also confirmed by the calculation and comparison of loop shape factor. Thickness of the fabric is influenced significantly by relaxation treatment and fibre composition. Areal density is primarily determined by relaxation treatment and stitch length rather than by fibre composition. Hence, it is concluded that tencel and cotton are similar in dimensional characteristics