Stator Coils Research Articles

Experiment and Analysis on the New Structure of the Coilgun With Stepped Coil Winding

In this paper, a new structure of coilgun with stepped coil winding was designed. The performance of this structure was investigated and compared to the conventional coilgun with uniform diameter stator coil (UDSC) winding. It can be seen from the results that the trigger position of this new structure moves forward with respect to the conventional coilgun. In order to compare the results, the inductance of the two coils is set to the same. If the initial voltage of the capacitor is lower, as the armature at the optimum trigger position, the muzzle velocity of armature in the conventional UDSC coilgun is relatively larger. Conversely, if the initial voltage of the capacitor is higher, the muzzle velocity of armature in the new structure coilgun is relatively larger. According to the simulation results with the increase of voltage, the difference is more and more obvious. Through the single-stage preliminary experiment in our laboratory, the results were in good agreement with the simulation results. And the trigger position is more forward, so the interaction time between the armature and the coil will be longer. Besides, the coil with stepped structure will increase the efficiency of the coilgun when the voltage level is higher.

Rotary-Reciprocating Movement Switched-Reluctance Machines With Consequent Axially Shifted Poles

A new switched-reluctance machine (SRM) topology with combined rotary and reciprocating rectilinear movement is introduced in this paper. The topology of this machine is based on the conventional radial-flux SRM with a modified rotor structure. Unlike the other rotary-translational electromechanical systems which have separate units, one for rotary motion and another for translational reciprocating motion, the proposed machine achieves combined rotary-reciprocating (RR) movement with just one set of stator coils around each pole identical to the conventional SRM. By exciting each pole of the stator, both radial and axial magnetic flux will be produced in the air gap of the machine. As a result, the electromagnetic reluctance torque around the axis of the rotation and the reluctance force along the axis of translational movement are produced. Details of the rotor structure and machine operation are presented. Magnetic equivalent circuit (MEC) analytical equations are derived for four operational points within the RR motion cycle. Finite-element analysis (FEA) is utilized to validate the analytical MEC equations. The output performance profiles are simulated for two example machines using static 3-D FEA to investigate the impact of the axial displacement of the consequent poles. In addition, a sensitivity analysis is carried out to investigate the impact of the rotor pole angle on the torque and force production of the machine. The dynamic behavior of the proposed structure is analyzed and discussed for two displacements of the consequent axially shifted poles.

DC and AC Current Transport Characteristics of the HTS Stator Coils in an HTS Induction/Synchronous Motor

We developed and characterized an especially designed stator for a 50 kW class high-temperature superconducting induction/synchronous motor (HTS-ISM). The so-called ring windings are introduced for the stator in order to increase the critical current in the iron slots. DC and ac current transport tests are carried out in liquid nitrogen (77 K). It is found that the stator can carry a large dc current and show adequately small ac loss at low frequencies. Our report shows the possibility of the further improvements of efficiency and torque density in fully HTS-ISM.

Stator Design and Performance of Superconducting Motors for Aerospace Electric Propulsion Systems

Hybrid electric propulsion has been identified as a potential solution to the ambitious environmental emissions and noise targets of the aerospace industry. Superconducting machines may be the key component of that topology enabling the high power densities and efficiencies needed in aerospace. Fully superconducting machines, however, are not a mature technology. This paper looks at the different machine design configurations focusing on the stator magnetic circuit of a fully superconducting motor. The motor has been designed for an aerospace distributed fan propulsion motor with an aerospace benchmark specification of 1 MW. The AC fully superconducting machine includes superconducting bulk magnets mounted on a conventional rotor core and an MgB2 superconducting wire wound stator. The AC losses in the stator winding are particularly sensitive to exposure to the main rotor field so different screening solutions were used to shield the superconducting windings from the rotor field. The effectiveness of the screening techniques for the stator coils and the impact on the machine performance and weight were evaluated for different stator designs, such as full stator core and air core with and without flux diverters. Various combinations of pole numbers, diverter geometries, and magnetic materials have been checked. Results show that there is a tradeoff between stator iron losses and superconducting losses.

Aging of stator coil interconductor insulation of high voltage asynchronous motor

This paper investigates winding's aging of high voltage asynchronous motor. The paper is in a form of an experimental research manuscript. The long time experiments are performed on samples taken from new and used windings. Additional impregnated samples were also examined. The samples differ according to the technological process during the winding fabrication. During the experiment are determined: the breakdown voltage, the partial discharge threshold voltages and the curves of lifetime. Based on the obtained results, it was found how winding fabrication process affects insulation and insulation aging. It is suggested how it is possible to reduce the influence of the winding fabrication process on the inhomogeneity of its structure and the unevenness of its aging.

Grading electric field in high voltage insulation using composite materials

Localized overstress due to electric field concentration is a threat to the long-term performance of the insulation in almost all high voltage apparatus. Resistive field grading using field grading materials (FGMs) may be a solution to this problem. Insulation matrixes such as ethylene propylene diene monomer, epoxy, or silicone rubbers, blended with fillers such as ZnO microvaristors, are reported to possess field dependent conductivity with greater and more stable nonlinearity than traditional FGMs [1]. Their application in high voltage apparatus such as bushings [1], cable accessories [2]–[4], insulators [5], [6], and stator coils [7] has been studied recently. It is well known [8] that the most important parameters for FGMs are the nonlinear coefficient α and switching field Eb; the challenge is to tailor these two parameters to a specific application. FGMs can function effectively in most cases when α >10 [9], but the adjustment of Eb is more complex.

Calculation of Magnetic Field for Cylindrical Stator Coils in Permanent Magnet Spherical Motor

Calculation of Magnetic Field for Cylindrical Stator Coils in Permanent Magnet Spherical Motor

Design and Construction of a Mini Hydro Turbine Model

This research is aimed at design and construction of a mini hydro turbine generator that can be made available at the consumer level, so as to improve the generation and availability of power at lower rate without pollution to the environment so as to help boost power generation, quality of power to its power consumers in developing countries. Pelton’s wheel design was used for the turbine research. Water stored in a tank or reservoir at a three meter height contains potential energy, this water is allowed to fall on the turbine wheel which drives the turbine. The potential and kinetic energy available in the water is converted to mechanical energy by rotating the runner connected to the turbine blade. The runner is connected to the rotor part of the alternator (containing the permanent magnet) and the stator (containing the windings) which is kept at permissible air gap to the rotor for effective induction. The voltage is tapped out from the stator as a single phase output, which is used to power household utilities and other machineries which need power supply. The result obtained was gotten from the various tests carried out on this research the tests includes water flow rate test, stator coil resistance test, output voltage test, power quality test and rotational speed test. The output power result shows that domestic power could be generated at individual residential level this will help improve and stabilize the power in the national grid.

Design and testing of a coil-unit barrel for helical coil electromagnetic launcher.

A coil-unit barrel for a helical coil electromagnetic launcher is described. It provides better features of high structural strength and flexible adjustability. It is convenient to replace the damaged coil units and easy to adjust the number of turns in the stator coils due to the modular design. In our experiments, the highest velocity measured for a 4.5-kg projectile is 47.3 m/s and the mechanical reinforcement of the launcher could bear 35 kA peak current. The relationship between the energy conversion efficiency and the inductance gradient of the launcher is also studied. In the region of low inductance gradient, the efficiency is positively correlated with the inductance gradient. However, in the region of high inductance gradient, the inter-turn arc erosion becomes a major problem of limiting the efficiency and velocity of the launcher. This modular barrel allows further studies in the inter-turn arc and the variable inductance gradient helical coil launcher.

New prognostic neural method by discrete wavelet transforms for electromechanical flight controls affected by progressive faults

Progressive failures affecting onboard electromechanical actuators (EMA), especially if related to primary flight commands, could be a critical issue for the aircraft reliability and, in the worst cases, could compromise its safety. In the last years strong interest is expected by the development of prognostic algorithms able to provide an early identification of the precursors of EMA progressive failures. In this work authors proposes a new prognostic method based on two artificial neural networks (ANN), a basic and an enhanced feedforward neural network, performing the fault detection and identification of two critical progressive faults often affecting the EMA brushless motor (i.e. turn-to-turn short circuit of a stator coil and rotor static eccentricity); in order to identify a suitable data set able to guarantee an affordable ANN classification, the said failures precursors are properly pre-processed by a Discrete Wavelet Transform, extracting several features used as input of the proposed prognostic algorithm.

Partial-Discharge Measuring Produces Uncertain Results: Important Quality Assesment Updates for Stator Windings

The petrochemical industry considers the offline partial-discharge (PD) measurement an important quality assessment for new medium-voltage motor and generator stator windings. A recent edition of American Petroleum Institute (API) Standard 541 [1] requires an instrument to be compliant with International Electrotechnical Commission (IEC) Standard 60270 [3] for PD measurements on sacrificial stator coils and proposes 100 pC for guidance on acceptance criteria until more data becomes available. Given the industry's faith in PD as an acceptance test based on a representative sample, it warrants closer scrutiny. The characteristic PD distribution pattern produced by each test instrument provides information on the origin of the discharges and, therefore, can be used to determine what type of defect has produced them. This article shows how external factors such as instrument selection, testing environment, and time interval between tests can influence PD test results.

Fuzzy logic principles for an induction motor direct torque control application

In the article three induction engine torque direct control system designing methods are compared: classical; width-pulse voltage modulation is set according to the output of "Switching table" block; based on fuzzy logic mathematical apparatus. The direct torque control systems structure and particular blocks included in are considered. Numerical methods in order to determine the harmonic composition of such values as the electromagnetic torque, the stator coil voltage and current at low rotor rotation speeds are described. The obtained results analysis is given.

Magnetic Field Model for Permanent Magnet Spherical Motor With Double Polyhedron Structure

This paper presents an analytical method for calculating the magnetic field for a permanent magnet spherical motor (PMSM) with double polyhedron structure. For the PMSM, stator coils and cylindrical permanent magnet (PM) poles locate at the fixed point of octahedron and hexahedron, respectively, and provide the uniform magnetic field. To analyze the magnetic field in the spherical coordinate, the cylindrical PM pole is approximated as a dihedral cone pole using geometrical equivalence principle. Moreover, considering the characteristics of hexahedron structure, a virtual equatorial layer is emphasized, and the corresponding periodic boundary condition can be built for solving the Laplace equation related to the virtual equator. Then, the Tait–Bryan rotation transformation is applied three times; thereby the overall magnetic field of the PM poles is obtained by the superposition principle. Both simulations and experiments are conducted to demonstrate the effectiveness of the proposed method. The results indicate that the analytical modeling can represent the magnetic field of the PMSM with a high precision.

A stepping micromotor based on ferrofluid bearing for side-viewing microendoscope applications

This paper reports a catheter-based electromagnetic micro rotary motor targeting at enabling side-viewing microendoscopes designed for the Raman spectroscopic modality. The micromotor uses the magnetic rotor that is levitated with thin ferrofluid layers inside the polymeric tube and electromagnetically driven with the stator coils circumferentially patterned around the tubular substrate. The device with a new miniaturized design is both theoretically and experimentally shown to provide performance benefits over the preceding design, including 4×higher revolution speeds per given power and >95% reduction in temperature rise at low-speed operation. The precision stepping control of fabricated prototypes with angular steps down to 22.5° is demonstrated with an average positioning error as small as <2%. This is achieved with only two stator coils defined on the tube substrate via controlled power distribution to the coils, uniquely enabling fine stepping actuation with a limited number of stator coils that could be integrated within a microendoscope device. The developed micromotor is suitable for application to side-viewing Raman probes that typically require fine circumferential stepping of laser beam.

New Hybrid‐Excited Motor Using Armature Windings as Field Flux Source

SUMMARYIn this paper, a new hybrid‐excited motor is proposed. Its unique feature is that it has no field exciting coil, despite being a type of bypass yoke core (BYC) hybrid‐excited synchronous motor. Based on finite element analysis (FEA), the following facts are clarified. Since the stator coil magnetomotive force (MMF) and claw poles rotate at the same speed and in the same direction, they are motionless relative to each other. Since the claw poles are located at one of its ends near the BYC surface with a gap, it receives immovable magnetization by the stator coil MMF through the BYC; then the claw poles can supply a magnetic field flux via the BYC. This flux via the BYC increases the total torque, because its torque is added the two other torque components: the permanent magnet torque and claw poles reluctance torque. In addition, the magnetic polarity and the amount of the flux of the claw poles can be varied by controlling the armature current phase angle.

Improved Model of Synchronous Generators Internal Faults Based on Circuit-Coupled FEM

A precise simulation of the internal faults of synchronous generators is crucial for the design of the main protection scheme; therefore, an accurate model is necessary. In this paper, based on the circuit-coupled finite element method (CCFEM), an improved model of a synchronous generator with internal faults is proposed, wherein the localized model of each stator coil is built as per its actual structure. Using this model, the internal fault occurring inside the coil can be accurately simulated, better approximating the location of the actual fault point; thus, the fault currents can be calculated more accurately. The accuracy of the improved model is verified by a dynamic simulation experiment. Moreover, the electromagnetic magnitudes, such as the air gap flux density, fault currents, field current, and all the damper currents are investigated in detail, under fault conditions, thereby revealing the fault characteristics more clearly and providing a basis for designing protection schemes.

Efficient Thermal Cooling Structure for a Motor

SUMMARYThe rated output of a motor is determined based on the value of the load current at which the temperature of the motor's parts reaches the permissive limit. Especially, the temperature of the stator coil is considered in many cases. In this research, in order to attain the higher rated output of a motor, a new thermal cooling structure that decreases the rise in the temperature of the stator coil is proposed. Next, based on the proposed structure, a prototype motor was manufactured and evaluated. The results demonstrated the superior performance of the proposed structure in comparison with the conventional structure. Moreover, the press‐formed coil which is devised with the purpose of enhancing the desired effect is also explained herein.

Diagnosis of Stator Faults Severity in Induction Motors Using Two Intelligent Approaches

Three-phase induction motors are the primary means of transformation of electrical energy into mechanical energy in industry, since they are robust and present low cost. However, despite being robust, these machines are subject to electrical or mechanical faults. Thus, identifying a defect in a running motor may decrease the risk of possible damage. This paper proposes an alternative approach to identify defects in the stator of these motors, by analyzing current signals in the time domain. In addition, it presents the determination of the consequent fault severity by means of two proposals: 1) a multiagent system with a classifier behavior; and 2) a neural estimator. The faults observed are related to short circuits between turns in the stator coil of 1% to 10%. Experimental results are observed with motors of different powers, under various adverse situations of electrical feed and a wide range of load conditions on the machine shaft.

Study on the Rotation Properties and the Design Issue of Non-Contact Rotating System Using HTS Bulks and Permanent Magnets

In previous study, non-contact rotating system consisting of the ring-shaped high temperature superconducting (HTS) bulks, ring-shaped permanent magnets (PMs) and stator coil was proposed. In this system, HTS bulks were magnetized by PMs and PMs were levitated with strong restoring force. In our previous study, we have constructed the rotating system with the ring-shaped HTS bulks with ID 20 mm, OD 60 mm, and 15-mm thickness. However, since these bulks costs too much, we switched to use HTS bulks with ID 20 mm, OD 60 mm, and 5-mm-thickness to miniaturize the system. However, this system have potential to fail the radial stability of rotating shaft. Therefore, we focused on the rotating and the radial restoring force in terms of the stability of the rotating shaft in the rotating system with 5-mm thickness HTS bulks.

Analytical Modeling of Interturn Short Circuit for Multiphase Fault-Tolerant PM Machines With Fractional Slot Concentrated Windings

Interturn short-circuit faults that occur inside stator coils are difficult to cope with compared with terminal short-circuit faults. A general analytical model for interturn short-circuit faults is developed that employs a novel T-type equivalent circuit. When this model is used to investigate the impact of interturn short-circuit faults in permanent-magnet (PM) machines with fractional slot concentrated windings (FSCW), the model delivers fault response predictions that agree very well with results from the finite element analysis. The model is used to show that the 24-slot/14-pole FSCW PM machine is vulnerable to very high interturn fault currents, even when the remaining turns are shorted, offsetting its advantage of low magnetic coupling between phases. FSCW-PM machines that employ aligned coils in phase windings can effectively suppress their interturn fault currents. Experimental verifications are provided for the 24-slot/22-pole FSCW PM prototype machine (with two aligned coils per phase) under the single-turn short-circuit fault.