Wound Motors Research Articles

Minimally Invasive Approach to Access Vessels for Microvascular Anastomosis in Head and Neck Reconstruction.

To describe our technique, review indications, and evaluate the outcomes of the minimal access approach for recipient vessel identification in microvascular tissue transfer. Retrospective chart review of all patients who underwent microvascular reconstruction using the minimal access technique between 2015 and 2021. We report 236 cases, comprising 214 patients with a mean age of 60.2 years (3-88). The most common primary defect sites were the mandible (22.6%), cranium (14%), maxilla (13.2%), skull base (12.8%), and nose/nasal cavity (10.6%). Indications for free flap reconstruction included head and neck cancer extirpation (32.2%), osteoradionecrosis (29.7%), acquired deformity (14.0%), chronic wound (11.9%) and oral motor dysfunction (7.2%). Free flap donor sites used were the anterolateral thigh (84.3%), fibula (7.2%), and radial forearm (6.4%). Vessels utilized include superficial temporal (49.8%), facial (38.3%), angular (11.1%), and transverse cervical (0.4%). The overall complication rate was 14% (n = 33), with surgical complications at the recipient site accounting for 67.6% (n = 25). Flap failure occurred in 3.4% of procedures. Prior head and neck surgery and free flaps were associated with an increased risk of major recipient site complications (n = 20, p = 0.0257 and n = 14, p = 0.0117, respectively). Minimal access techniques allow consistent recipient vessel identification for microvascular-free tissue transfer. These approaches may be utilized in reconstructing a broad range of head and neck defects, are low morbidity, and contribute to an overall shorter length of stay. 2 Laryngoscope, 134:2177-2181, 2024.

ЭКСПЕРИМЕНТАЛЬНОЕ ИЗУЧЕНИЕ ЛЕЧЕБНЫХ СВОЙСТВ МАЗИ БИОСЕПТИН

Introduction. Due to the acquisition of resistance to antibiotics by pyogenic microbiota, the problem of local (medicinal) treatment of wounds has become more acute. Aim. Evaluation of the medicinal properties of Bioseptin ointment in vivo on a model of a purulent incised skin wound of research animals. Materials and object of the research. Bioseptin ointment was developed by LLC “Research Center”. The active principle of the ointment is a microbial association: bacteria Baсillus subtilis strain VKPМ B-7048 and Bacillus licheniformis strain VKPМ B-7038, which has high antagonistic activity against a wide range of pathogenic and opportunistic microorganisms. As an auxiliary component of the ointment, a dense nutrient medium is taken, used for growing cultures of B. subtilis and B. licheniformis in the process of obtaining a specific batch of ointment. The ointment is a combination preparation for topical use. The wound-healing effectiveness of the ointment was assessed in two groups (20 mice each) of healthy non-inbred mice with a body weight of 16 and 20 g of ICR colony of both sexes from the nursery State Scientific Center for Virology and Biotechnology “Vector” of Russian Federal State Agency for Health and Consumer Rights. The control group was a group of mice treated with the reference ointment Iruksol (20 mice per group). A model of a purulent wound in animals of these three groups was obtained by infecting incised skin wounds with a mixture of bacterial cells P. aeruginosa and S. Aureus. Treatment of mice was continued until their incised skin wounds healed. Every day, mice in all groups were assessed for wound area, percentage reduction in wound area (WAR) according to L.N. Popova’s method, rate of wound contraction, motor activity, appetite, dynamics and nature of wound healing. Every 3 days, changes in body weight were assessed, laboratory blood tests and histomorphological examination of the incised skin wound were performed. To obtain tissue samples, animals, according to the observation period were removed from the experiment by euthanasia using the method of cervical dislocation. Tissue samples excised from the wound and blood samples were examined on days 3, 6, 9, and 12 after skin wound formation. Samples for light microscopy were prepared and stained according to the methods. Viewing of preparations and microphotography was carried out on a Jenaval light microscope (Carl Zeiss, Jena, Germany). All data were processed statistically using Microsoft Excel and STATISTICA. Results and discussion. It was shown that almost until the end of treatment of purulent wounds in all groups of experimental animals with the control ointment Iruksol and Bioseptin ointment, negative dynamics of body weight was observed due to the expressed toxic effect of the purulent wound on the body of the research animals. The results of a blood test for hematological and biochemical parameters in the body of research animals of all three groups revealed changes characteristic of the development of a local infectious process and intoxication. Evidence was established of faster healing of purulent wounds in animals of groups 1 and 2 treated with Bioseptin and Iruksol ointments, respectively, compared to animals of group 3 (with a severe superinfected purulent wound). Moreover, complete visually observed wound healing in group 2 occurred in less than 9 days, in control group 1 and experimental group 3 on the 12th day of observation. Histomorphological study demonstrated the restoration of the structure of the skin in the wound as an organ with all its derivatives already on the 9th day in groups 1-2; in group 3 with a burdened purulent wound, complete restoration of the epidermal defect was not noted. Conclusion. Bioseptin ointment is promising as a drug for effective topical use in the treatment of infected wounds; the ointment has a significant antimicrobial effect. The microbial association (Bacillus subtilis strain ВКПМ B-7048 and Bacillus licheniformis strain ВКПМ B-7038) which is part of the Bioseptin ointment, promotes the cleansing of wounds, their granulation and faster healing compared to the control ointment Iruksol. The use of Bioseptin ointment for the treatment of complicated purulent wounds has been shown to be promising.

Экспериментальная оценка лечебных свойств мази на основе меланинов из природного сырья и глубинной культуры чаги

Introduction. Due to the acquisition of antibiotic resistance by pyogenic microbiota, the problem of topical (drug) treatment of wounds has worsened. Aim. Experimental evaluation of the antibiotic properties of melanin from natural raw material and a submerged culture of chaga (Inonotus obliquus) in vitro and the therapeutic properties of ointments prepared on the basis of these melanins in vivo. Materials and Methods. Melanins were obtained by alkaline hydrolysis. The antibiotic activity of melanins was determined by co-cultivation in a liquid medium of the studied samples with six cultures of test strains of gram-negative and gram-positive bacteria and two of yeast fungi. Ointments based on melanin from natural raw material and the submerged culture of chaga (Inonotus obliquus F-1244 strain) were obtained using two compositions of ointment base. The wound-healing efficacy of ointments was evaluated on three groups of mice. The control groups were mice untreated and treated with a comparison drug (Levomikon-TFF). The treatment of mice was continued until their incised skin wounds healed. Wound areas, motor activity, appetite, dynamics and character of wound healing were assessed daily in mice of all groups, as well as changes in their body weight every three days. Results. Melanins from natural raw materials and the submerged culture of chaga completely suppressed the growth of gram-positive spore-forming Bacillus cereus bacterium in a co-culture. Melanin from natural raw material of chaga on average suppressed the growth of the Staphylococcus aureus ATCC 6538 strain by an order of magnitude. Melanin from the submerged chaga culture completely suppressed the growth of a clinical isolate of the highly pathogenic Candida sp. Ft-5 strain from a deceased patient with generalized candida infection and, on average, inhibited the growth of the collection strain of yeast Candida albicans 620 by two orders of magnitude more intensively. It was found that ointments based on melanin from natural raw materials and the submerged culture of chaga, as well as ointment containing a fivefold increased concentration of melanin from natural chaga, do not have toxicity to experimental animals. Ointments containing 0.4 mg of melanin from natural raw material and the submerged chaga culture per 0.2 g of a single dose of ointment had the same wound healing efficacy, while not only were not inferior in this indicator to the combined antimicrobial comparison drug Levomikon-TFF, but also showed a tendency to more accelerated wound healing (on the 15–18th day of observation) compared with the process of wound regeneration in the group of animals treated with the drug of comparison. A more accelerated wound healing effect was demonstrated in experimental animals (already on the 12th day of observation) treated with a fivefold increased content of melanin from natural raw material of chaga, compared with mice treated with the comparison drug. Conclusion. Ointments containing melanin of chaga (Inonotus obliquus) have anti-inflammatory, regenerative properties and can be considered promising for topical treatment of wounds.

Partial Discharges in Electrical Machines for the More Electrical Aircraft. Part III: Preventing Partial Discharges

In this paper, the results obtained from lab tests on twisted pairs subjected to different voltage waveforms and atmospheric conditions are used to propose how to modify the IEC Std. 60034-18-41. The goal is to make the standard suitable for the More Electrical Aircraft (MEA). The results show that it is initially necessary to screen out materials through simple tests. The enhancement factors for temperature can be modified to consider reduced pressures and temperatures using a simple model. The aging enhancement factor can be reduced considering the reduced sensitivity of the partial discharge inception voltage (PDIV) at low pressures on the enamel thickness. Eventually, reference will be made to the drive discussed in Part I of this series to draw conclusions about the likelihood of partial discharge inception in a random wound stator and how to reduce it by modifying either the inverter or the stator insulation. Reference to a random wound motor is made throughout the paper.

Partial Discharge Phenomena in Electrical Machines for the More Electrical Aircraft. Part II: Impact of Reduced Pressures and Wide Bandgap Devices

This paper focuses on the inception of partial discharges within the insulation system of electrical actuators used for the More Electrical Aircraft (MEA). Since these machines should operate in the absence of Partial Discharges (PDs), the dependence of the PD Inception Voltage (PDIV) on voltage impulses typical of wide bandgap (SiC) devices is investigated at both 1 bar, reduced pressures close to those typical of aircraft cruising altitudes (150 mbar – 200 mbar) or lower (down to 5 mbar). Propagation issues are not dealt with here as results were obtained working on insulation models consisting of couples of wires twisted together (twisted pairs), thus knowing exactly the potential differences between all points of the insulation model. The results show that the rise times and the switching frequencies associated with wide bandgap devices have little impact on the PDIV. A model able to predict the PDIV of the turn/turn insulation of random wound motors (the most vulnerable part of the insulation) at different pressures is proposed. The model is also able to deal with temperature changes, with limitations that depend on the type on insulation systems.

A General Measurement Set-up Approach to Evaluate Insulation System Quality by Exploring PWM and DC biased waveforms

This article presents a novel test approach able to detect and evaluate PD characteristics when employing various wave shapes similar or close to what is used in different applications. The method covers the range from bipolar PWM with ultra-fast rise times to dc voltages with or without superimposed high -frequency content. Measurement results from tests on twisted pair aimed to resemble a random wound motor are presented. In particular, the influence of conductivity, permittivity, and rise time is explored by applying square- shaped waveforms. The PDs appearing after the unipolar flanks are compared with full -size bipolar voltage steps. One important observation presented is that when the zero voltage was reached and kept, the remaining charges within and surrounding the defect produced a PD pattern (PD echo) which resembles the charge amount present within the winding. Additionally, PWM shaped voltage waveforms superimposed on dc voltages present advantages when further evaluating the influence of material properties. Different step sizes are employed to represent dc voltage with or without superimposed voltage ripple to elucidate the influence on PD characteristics also on HVdc like applications. It can be concluded that higher frequency harmonics will result in considerably larger PD exposure. This article shows that during material evaluation, important common properties and guidelines can be found between these different waveform extremes, suggesting that a more efficient insulation coordination can be obtained selecting the most appropriate or time- efficient evaluation method.

Design and analysis of a novel wound rotor for a bearingless induction motor

ABSTRACTThe traditional squirrel-type bearingless induction motor (BIM) suspension winding generates induced current in its squirrel-cage rotor and affects the phase and amplitude of the suspension force. Based on the analysis of the spatial distribution of torque winding magnetic field and suspension winding magnetic field, a new type of wound rotor BIM is designed. Different from the squirrel-cage rotor, the wound rotor uses a special method of embedding a set of coils at any symmetrical four rotor slot positions, so as to only induce the torque winding magnetic field. The induced current, air-gap magnetic density, magnetic field line distribution, suspension force as well as electromagnetic torque of the traditional squirrel-cage motor and the new wound motor are analysed by Maxwell finite element calculation. The results show that the designed new wound BIM can not only effectively suppress the induced current of suspension winding, eliminating its influence on the suspension force, but also has a better starting performance.

Sample-Averaged Zero-Sequence Current Elimination PWM Technique for Five-Phase Induction Motor With Opened Stator Windings

The five-phase dual-inverter connected to the five-phase open-end winding induction motor (FPOEWIM) with a single dc source could result in the flow of common-mode current (CMC) through the common dc bus and motor phase windings. In addition, the FPOEWIM drive contains third-harmonic content which do not contribute for torque generation in a distributed wound motor. So, to nullify the CMC as well as the third-harmonic content the sample-averaged zero-sequence current elimination (SAZE) pulsewidth modulation (PWM) technique is proposed in this paper. Wherein, the concept of alternative clamping of the inverters is used with the generation of virtual vector to eliminate third-harmonic content and the effective time region is moved to eliminate the CMC in average sense. The detailed analysis of the proposed SAZE PWM technique is presented along with the simulation results and experimental verification.

전기차량에 적용한 Bang-Bang 제어기 연구

In order to establish the robust controller design technique of series wound motor driver system. This paper proposes a method of Bang-Bang controller using a series wound motor driver system under improperly variable load. A Bang-Bang controller structure is simpler than the structure of PID plus Bang-Bang controller. This paper shows that a general 8 bits microprocessor is used efficiently implementing such an algorithm. The calculation time of software is extremely small when compared with conventional PID plus Bang-Bang controller. Both nonlinear operating characteristics of digital switching elements and describing function methods are used for the analysis and synthesis. Real time implementation of Bang-Bang controller is achieved. Concept design strategy of the control and PWM waveform generation algorithms are presented in the paper.

Potential distribution on the stress grading system of high-voltage rotating machines –I measuring system

A surface potential measuring system has been developed utilizing a Pockels sensor to measure the potential distribution of the stress grading (SG) system of form wound motor coils. A Pockels BGO crystal is positioned just above (<1 mm) the SG, and the capacitively-induced voltage on the surface of the BGO crystal adjacent to the SG is measured by using Pockels effect of the BGO crystal. The sensing system is applicable to surface potential measurement over wide frequency region from 0.001 Hz to 100 MHz. The spatial resolution of the measuring system after enhancement through deconvolution is discussed with the result that the -3 dB spatial frequency of the measuring system is 0.22 cycle/mm which implies a resolution in the range of 4 mm.

Research on Identification of Induction Motor Parameters Based on Nameplate Data

A new method for identification of motor equivalent circuit parameters is proposed based on motor nameplate and particle swarm optimization (PSO). That is effective solution to the present problems of motor equivalent circuit parameters identification method. An accurate motor equivalent circuit is built by introducing an equivalent stray-loss resistance, mechanical loss, and slip loss of ring brushes contact for wound motor. The identification accuracy of motor equivalent circuit parameters is improved. An identification optimization model of equivalent circuit is established based on motor nameplate parameters and motor equivalent circuit’s calculating parameters. With PSO for solving optimization model is achieved a higher probability optimization goals. Finally, a group of equivalent circuit parameters to achieve the objective function value is randomly selected. The motor electrical parameters is calculated at different speeds with the equivalent circuit identified parameters and compared with the measured values. Experimental results demonstrate the proposed parameter identification method based on motor nameplate parameters and combining PSO optimization method is effective.

Partial discharge in electric motor fed by a PWM inverter: off-line and on-line detection

This paper deals with Partial Discharge (PD) detection in Pulse Width Modulation (PWM) inverter fed electric motors. The aim of this work is to detect PD activity in random wound motors, which is the main cause for premature breakdown of insulation system. Detection is performed thanks to a non-intrusive electromagnetic sensor. A high voltage power supply PWM has been built in order to test, offline, electric stators in conditions as close as possible to real electrical conditions. Then, on-line PD measurements have also been successfully carried out, in an engine test bench used to test and control electric vehicle (EV) powertrain.

The assessment of complications after spine surgery: time for a paradigm shift?

Background contextRecent years have witnessed a shift in the assessment of spine surgical outcomes with a greater focus on the patient's perspective. However, this approach has not been widely extended to the assessment of complications. PurposeThe present study sought to quantify the patient-rated impact/severity of complications of spine surgery and directly compare the incidences of surgeon-rated and patient-reported complications. Study designProspective study of patients undergoing surgery for painful degenerative lumbar disorders, being operated in the Spine Center of an orthopedic hospital. Patient sampleA total of 2,303 patients (mean [standard deviation] age, 61.9 [15.1] years; 1,136 [49.3%] women and 1,167 [50.7%] men). Outcome measuresPatients: Core Outcome Measures Index, self-rated complications, bothersomeness of complications, global treatment outcome, and satisfaction. Surgeons: Spine Tango surgery and follow-up documentation forms registering surgical details and complications. MethodsPatients completed questionnaires before and 3 months after surgery. Surgeons documented complications before discharge and at the first postoperative follow-up, 6 to 12 weeks after surgery. ResultsIn total, 615 out of 2,303 (27%) patients reported complications, with “bothersomeness” ratings of 1%, not at all; 22%, slightly; 26%, moderately; 34%, very; and 17%, extremely bothersome. Patients most commonly reported sensory disturbances (35% of those reporting a complication) or ongoing/new pain (27%) followed by wound healing problems (11%) and motor disturbances (8%). The surgeons documented complications in 19% of patients. There was a minimal overlap regarding the presence or absence of complications in any given patient. ConclusionsMost complications reported by the patient are perceived to be at least moderately bothersome and are, hence, not inconsequential. Surgeons reported lower complication rates than the patients did, and there was only moderate agreement between the ratings of the two. As with treatment outcome, complications and their severity should be assessed from both the patient's and the surgeon's perspectives.

Magnet Software Based Fault Analysis of Induction Motor Using Finite Element Analysis

Induction motor is one of the most commonly preferred motors used in the industry due to its long life & rugged construction. Faults occurring in an induction motor can significantly affect the performance of the motor and the drive which is running it. This project aims to study & analyze the faults which can occur internally in an induction motor .To implement fault analysis first the machine is modeled using MAGNET software. The motor is studied under healthy conditions. Subsequently faults are introduced & fault analysis is carried out. In the model of induction rotor bars are broken and the study is mostly based on magnetic field analysis of the motor under healthy conditions & under faulty conditions. The variation of starting torque with respect to increasing number of broken rotor bars is studied and a graph was plotted to show the variation. The stator winding currents produce a magnetic field that rotates in a counterclockwise direction. The changing magnetic field of the stator induces electromotive force in the rotor cage winding. The induced emf causes current to flow and magneto motive force in the rotor windings. In turn the rotor mmfs produce a magnetic flux pattern which also rotates in the air gap at the same speed as the stator winding field. Induction motors are the most commonly used prime movers in industrial applications. They are best suited for constant speed applications. Speed control can also be done with the help of power converter circuits. The 3-phase squirrel cage induction motor is the workforce of the industry as it is rugged & reliable. The interaction between the primary field and secondary currents produces torque from zero rotor speed onwards. The rotor speed at which the rotor currents are zero is called ideal no-load or synchronous speed. The rotor windings may be multiphase (wound motors) or made of bars short-circuited by end rings (cage rotors). All primary and secondary windings are placed in the uniform slots stamped into thin silicon steel sheets called laminations. The induction machine has a rather uniform air gap of 0.2 to 3mm.The secondary windings may be short circuited or connected to an external impedance or to a power source of variable voltage and frequency. Induction motors are the most commonly used prime movers in industrial applications. They are best suited for constant speed applications. Speed control can also be done with the help of power converter circuits. The 3-phase squirrel cage induction motor is the workforce of the industry as it is rugged & reliable. Electrical related faults are frequently occurring faults in three-phase induction machine which will produce more heat on both stator and rotor winding. This leads to the reduction the life time of induction machine. Stator winding fault in Induction Motors can be detected using Unknown Input Observer (UIO) & Extended Kalman Filter methods. They are used for speed estimation and fault detection methods respectively(1).Using analysis of permeance and MMF harmonics, frequency of air gap flux density harmonics which occur due to irregularities are calculated. It helps in detecting faulty ball bearing conditions (2). A procedure for electromagnetic design of three phase Induction Motor is discussed. This procedure is based on self-consistent equations. The electrical and magnetic properties are imposed by the user but the geometric dimensions are automatically calculated (3).The choice between Copper rotor bars and fabricated Aluminum rotor bars is discussed and debated. The fundamentals of rotor construction and basic information on how the Induction Motor works are discussed (10). The new IEC standard which defines the stator winding insulation requirement when the Induction Motor operates with Adjustable frequency drives (AFDs) is discussed. The

Speed and Power Control of a Slip Energy Recovery Drive Using Voltage-source PWM Converter with Current Controlled Technique

This paper introduces the speed and power control a slip energy recovery drive using voltage-source PWM converter with current-controlled technique. The slip energy occurred in the rotor circuit is transferred back to ac mains supply through a reactor and a step up transformer. The objective of the current-controlled technique is to increase power factor of the system and to reduce low order harmonics of the input line current. The drive system is designed and implemented using a voltage source inverter in conjunction with a boost chopper for DC link voltage, instead of a conventional drive using a 6 pulse converter or a Scherbius system. The slip power is recovered by the help of a voltage source inverter (VSI) based on a current-controlled technique. In order to keep the speed of the wound rotor induction motor constant over a certain range of operating conditions, the servo state feedback controller designed by a linear quadratic regulator (LQR) is also introduced and the PI controller designed by pole placement method is also introduced in control the slip power this paper. The overall control system is implemented on DSP, oller board. A 1kW wound motor is employed for testing. It is found that the motor speed can be controlled to be constant in the operating range of 600-1200rpm at no load and full load. It is also found that the harmonics of the input ac line current is reduced while the ac line input power factor is increased.

Considerations on Application of Surge-proof Magnet Wire for Inverter-fed Random Wound Motors

This paper discusses the lifetime evaluation of twisted pairs which was constructed by a surge proof magnet wire. Two kinds of twisted pairs were constructed; one is a conventional twisted pairs and the other is a special twisted pairs which has varnish treatment at both edge sides of it. The both lifetime characteristics were evaluated and the breakdown positions were also investigated. As a result, it was found that the lifetime of the edge parts of usual twisted pairs was about 50% shorter than that of the other positions. It was estimated that the partial discharge activity at the edge part is stronger than that at the other positions, by an ultraviolet light measurement or others. This paper also describes a concept and quality control method for the inverter fed random wound motor which was manufactured by using a surge proof magnet wire.

Posterior screw fixation in rotationally unstable pelvic ring injuries

Objective Although the stability of the pelvic ring primarily depends on the integrity of the posterior sacroiliac arch, lateral compression fractures with rotational instability are commonly treated by anterior fixation alone. The objective of the present study was to assess the outcome of patients with these fractures treated by posterior iliosacral screw fixation alone. Methods Patients with rotationally unstable lateral compression fractures of the pelvic ring (Young and Burgess LC I and LC II or AO/Tile B2) treated by percutaneous iliosacral fixation alone were included. Postoperative complications, need for secondary surgery, malunion, secondary fracture displacement and the time to full-weight bearing were documented. Results Twenty-five patients (13 female, 26 male; age: 56 ± 20 years) were treated by percutaneous screw fixation (14 bilaterally, 11 unilaterally). Mean follow-up was 6 ± 4 months, mean time to full weight bearing 9 ± 3 weeks. Revision surgery was necessary in two patients (8%) due to nerve irritation; an additional anterior stabilisation was needed in two other patients (8%) due to secondary dislocation. Wound infection or motor weakness were not encountered, non-union of the posterior arch did not occur. Non-union of the pubic rami, however, occurred in two patients. The presence of malunion of the pubic rami did not affect the time to full weight bearing. Conclusions Percutanous iliosacral screw fixation alone is a sufficient technique for the stabilisation of rotationally unstable pelvic fractures with low rates of complications or non-unions. It allows for a minimally invasive treatment thus being a useful option in patients who do not qualify for open anterior fixation.

Off-line PD testing of converter-fed wire-wound motors: when IEC TS 60034-18-41 may fail?

This paper reports and discusses qualification and type test procedures for random wound motors as specified in IEC Technical Specification 60034-18-41. Since laboratory tests dealing with off-line partial discharges measurements followed by life tests showed that motors qualified as good can fail in very short times, an extensive investigation on the causes of such discrepancy and, in particular, on the differences existing between the stresses applied during off-line tests and in service is described. In addition, the results of partial discharge measurements performed on crossed pairs are presented, highlighting how the differences in the applied voltage waveform can influence the Repetitive Partial Discharge Inception Voltage. Suggestions to improve the off-line test procedure and related equipment are eventually discussed.

Investigation of partial discharge with twisted enameled wires in atmospheric humid air by optical emission spectroscopy

We investigated the characteristics of the partial discharge (PD) with twisted enameled wires by optical emission spectroscopy (OES) in atmospheric humid air. The electric field strength in the gap of the twisted enameled wires during the discharges was estimated from intensity ratio of the spectrum bands of nitrogen molecules obtained by the OES. It was found that the electric field strength was increased when increasing the relative humidity, and the increasing rate was different depending on the temperature. The increase of the electric field strength in the gap of the twisted pair could be related to a reduction of PD inception voltage (PDIV) observed in the experiment. The reduction of the PDIV could be determined by not only dielectric properties of enameled wires such as permittivity and surface conductivity but also changes of the discharge phenomena in the humid air. In this study, effects of the increase of the permittivity of the enameled wire due to the moisture absorption into the insulating layer were quantitatively discussed as one of the candidates to explain the reduction of the PDIV in the humid conditions. On the other hand, the discharge current amplitude was decreased with the increase of relative humidity at high temperature. It was considered that the discharge could be quenched by dissociative electron attachment to the large number of water molecules. The observed PD phenomena with respect to the change of the humidity are very important for quality management of low voltage inverter-fed random wound motors.

Performance improvement of a slip energy recovery drive system by a voltage-controlled technique

This paper introduces the performance improvement of a slip energy recovery drive system for the speed control of a wound rotor induction motor by a voltage-controlled technique. The slip energy occurred in the rotor circuit is transferred back to ac mains supply through a reactor instead of a step up transformer. The objective of the voltage-controlled technique is to increase power factor of the system and to reduce low order harmonics of the input line current. The drive system is designed and implemented using a voltage source inverter in conjunction with a boost chopper for DC link voltage, instead of a conventional drive using a 6 pulse converter or a Scherbius system. The slip power is recovered by the help of a voltage source inverter (VSI) based on a space vector pulse width modulation (SVPWM) technique. In order to keep the speed of the wound rotor induction motor constant over a certain range of operating conditions, the servo state feedback controller designed by a linear quadratic regulator (LQR) is also introduced in this paper. The overall control system is implemented on DSP, DS1104’TMS320F240 controller board. The performance improvement of the proposed system is tested in comparison with the conventional Scherbius system and the modified conventional Scherbius system by a 12 pulse converter in conjunction with a chopper at steady state and at dynamic conditions. A 220 W wound motor is employed for testing. It is found that the motor speed can be controlled to be constant in the operating range of 450–1200 rpm at no load and full load. It is also found that the efficiency of the proposed system is remarkably increased since the harmonics of the input ac line current is reduced while the ac line input power factor is increased.