Karuna Kalita

Practical Implementation of the Bridge Configured Winding for Producing Controllable Transverse Forces in Electrical Machines

It is now evident that the value of endowing rotating machines with the capability to produce transverse forces in addition to their normal torque-producing function can be extremely high. The bridge configured winding is a cost-saving connection scheme for electrical machines to exploit transverse magnetic forces on the rotors. The winding scheme retains the machines three-phase terminals such that ordinary motor inverters can be employed for the normal torque-producing function while providing separate terminals for transverse force action. This paper describes the practical implementation of such a winding connection in a conventional electric machine and demonstrates that controllable transverse forces can be produced.

Self-bearing switched reluctance motor: A review

A switched reluctance motor is a variable speed motor in which switching of current results in the production of torque and power. Due to the doubly salient structure of switched reluctance motor high acoustic noises and vibrations are produced along with torque ripple. In order to overcome these hindrances bearing-less switched reluctance motor was introduced as a solution to this problem. The motoring action of a switched reluctance motor can be combined with a magnetic bearing action to get a single unit called self-bearing switched reluctance motor. It is an electromagnetic device that has the capability of supporting the rotor on its own, generating magnetic forces by the windings on its stator. This paper presents an extensive literature survey on self-bearing switched reluctance motor and its recent developments including its various purposes in industrial applications. Details of its working principle, design methodologies, winding designs, control strategies and some prototype developments have been studied and presented.

A strategy for achieving accurate bending by multi-pass laser line heating

Laser bending has emerged as a promising technique to bend sheet metals by thermal residual stresses in the last two decades. Several mathematical models are available to predict the bend angle after the laser bending process. However, due to the limitations in the mathematical models and precision of input parameters, the sufficiently accurate prediction of bend angle is not possible. In this work, a strategy is proposed for choosing the parameters of multi-pass laser line heating for obtaining an accurate bend angle when the accuracy of prediction is known. The guidelines have also been provided for ascertaining the accuracy of prediction. The strategy is verified with experiments for three different materials.

Stability Analysis of a Rigid Rotor Supported on Gas Foil Bearings Under Different Loading Conditions

Gas foil bearings (GFBs) has been considered as an alternative to traditional bearings in turbopumps, turbocompressors, and turbochargers. The popularity of this bearing has motivated the researchers and people from industries to explore its capabilities. In this context, a nonlinear transient analysis of a rigid rotor supported on airfoil bearing under unidirectional constant load and unidirectional periodic load is carried out. The nondimensional form of the Reynolds equation is discretized using Finite Difference Method while the Crank–Nicolson method and Newton–Raphson method are used to obtain the pressure at every time step. Mass parameter, which is a function of the speed of the rotor, has been considered as the parameter of stability. It has been observed that a rotor stable under unidirectional constant load can be unstable under unidirectional periodic load.

Modeling and analysis of bearingless switched reluctance motor equipped with specialized stator winding

Conventional switched reluctance motor undergoes extensive vibration and undesirable acoustic noise caused by the production of significant amount of radial force. The reason behind this is the non-uniformity in air-gap of the motor which can be controlled in order to make it more efficient. A viable solution to pacify this problem is the introduction of bearingless technology with a special winding scheme called bridge configured winding in switched reluctance motor. Various designs of winding have been introduced by researchers to produce radial force which can be utilized in order to make the motor bearingless. This paper presents the incorporation of a single set winding called bridge configured winding in a 12/8 switched reluctance motor capable of producing both torque and controllable radial force, which can be used for bearingless operation of the motor. An analytical model of a 12/8 switched reluctance motor equipped with bridge configured winding is developed considering the effects of magnetic saturation of the motor. A mathematical model is obtained by solving the magnetic equivalent circuit of the proposed design. Also a finite element model of the design is developed in ANSOFT Maxwell 2D in order to verify the developed analytical model.

Vibration Control in Electrical Machines Using Built-in Actuator

The magnetic field within electrical machines causes an electromechanical interaction between the electrical and mechanical dynamics of the system. A relatively small asymmetry of flux distribution in the air gap creates an unbalanced magnetic force which tends to pull the rotor towards the stator in the direction of the highest flux density. This unbalanced magnetic force (or pull) in an electrical machine is exploited in so-called self-bearing or bearing-less electrical machine where, as well as functioning as a motor or generator, the machine can also produce transverse forces perpendicular to the rotation axis. The presence of magnetic field of pole pair p is due to the main supply of the motor and the presence of magnetic field of pole pair \( p \pm 1 \) is due to the asymmetry present in the magnetic field or due to the eccentric rotor motion. So, the presence of magnetic field of pole pair \( p \pm 1 \) will produce an unbalanced magnetic force in the air gap. This paper addresses a special type of stator winding scheme having parallel branches and a novel Wheatstone-bridge type connection in order to achieve direct control on the unbalanced components of stator magnetomotive force (MMF) whilst having no effect on the torque-producing components of the stator MMF. An Finite Element code has been developed in MATLAB and used as the basic tool for this investigation. It has been demonstrated in case of an induction motor that a controllable force in the air gap can be produced. The results from numerical model have been verified by experimental results.

Performance Analysis of Gas Foil Bearing with Different Foil Pivot Configuration

A numerical model is developed in order to find out the performance characteristics of gas foil bearings. The static performance analysis of gas foil bearings has been carried out using an elastic foundation model of the foil. The steady state results have been compared with the experimental and theoretical results available in the literature. The characteristics of the bearing have been investigated with change in foil pivot position. It has been shown that the load carrying capacity is different for different foil pivot positions. Besides effect of bearing parameters like eccentricity ratio, length to diameter ratio, compliance coefficient, and bearing number on the load carrying capacity with different foil pivot positions have been studied.

Passive Contra-Magnetized Parallel-Airgap Serial Flux Magnetic Bearings

Conventional magnetic bearings accomplish a specific load capacity, defined as the ratio of maximum sustainable weight to the total self-weight, of up to 35:1. In this paper, the authors introduce a class of passive magnetic bearings that comprise a large number of parallel airgaps and discs and can deliver specific load capacities substantially higher than 35:1. Two-dimensional planar, two-dimensional axi-symmetric, and three-dimensional finite-element analysis (FEA) have been undertaken to predict the force capability of the bearings. An unoptimized prototype passive magnetic bearing is constructed to demonstrate the concept and its force-carrying capacity. The experimental results are then compared with those obtained from the FEA. Further optimization of the bearings is done across the whole design space comprising tens of thousands of models using an automatic mesh generator in conjunction with solving the FE models in nested loops.