TEMPERATURE-RISE OF ROTATING ELECTRICAL MACHINES AS AFFECTED BY COLD TEMPERATURE MEASUREMENT

ABSTRACT

Determination of temperature-rise, of rotating electrical machines by resistance measurement, has become a problem of practical interest to all electrical manufactures. This paper describes the governing features of such measurements and thereby projecting certain recommendations. Major deductions are solely derived on experimental basis which prove to be a valuable tool to practising engineers in the heat-transfer area. Major emphasis is laid not only on the basis of accurate assessment of winding resistance, but also on the cold temperature of the winding. A clear distinction is brought out between ambient temperature and cold temperature of the winding. Paraphrasing the intutive question that is well answered here is “How one is able to determine the temperature rise of the machine accurately” and hence to appreciate the efficacy of optimization of design. The results of temperature variation on randomly chosen two days in winter and a day in summer are presented. The recommendations made here are applicable to tropical countries where there is a large difference in day and night temperature. The physical cause for this difference is also described.     

Growth and characterisation of lead zirconate titanate (30/70) on indium tin oxide coated glass for oxide ferroelectric-liquid crystal display application

Abstract

The growth and characterisation of sol-gel lead zirconate titanate (PZT) (30/70) thin films on indium tin oxide (ITO) coated glass have been investigated using X-ray diffraction (XRD), transmitting electron microscopy (TEM) and atomic force microscopy (AFM). Perovskite crystallised at 550°C in a random orientation, and all films showed characteristic rosette formations. A seeding and crystallisation model has been proposed to describe the rosette formation process, which is based on the ease of PbO diffusion through the film. The effect of drying temperature on annealed film properties has been examined and when optimised has been shown to improve electrical properties and film flatness. Incorporation of the PZT films into small prototype liquid crystal displays has been done. Application of pulsed poling voltages to the displays has resulted in bulk alignment of the liquid crystal adjacent to poled regions of the PZT layer which remained after the poling voltages were removed.     

Pressurizing and sub-cooling effects on electrical breakdown of LN2 in modeled HTS coils

Pressurizing and sub-cooling of liquid nitrogen are considered to have advantageous aspects in electrical insulation and the critical current in high temperature superconducting (HTS) coils. This paper deals with experimental studies on bubble behavior and partial breakdown (PBD) characteristics in a simulated electrode system of HTS coils immersed in pressurized liquid nitrogen, following our previous reports with saturated liquid nitrogen at atmospheric pressure. The tested electrode system consists of a coaxial coil layer to a cylindrical electrode with an insulation barrier and spacers. A heater is mounted inside the coil electrode to generate boiling which appears on quenched superconducting coils. Liquid nitrogen is pressurized to 0.2 MPa under constant temperature of ~77 K. The experimental results show that the partial discharge (PD) voltage is affected markedly by the bubble behavior which depends on the applied pressure to liquid nitrogen. Pressurization suppresses bubble growth in the insulation space and increases the inception voltage of PD. The charge quantity associated with a single PD at a given applied voltage increases with the applied pressure, and deterioration of solid insulation such as spacers and barriers is accelerated compared to that at atmospheric pressure if the PBD occurred     

Design and Application of Micro-Spectrometer Based on Quantum Dots Photodetector

Abstract

In this article, a micro-spectrometer was developed based on quantum dots photodetector. The quantum dots photodetector has higher sensitivity than CCD, and its photoconduction gain has achieved 1.11E8 under 0.01 picowatt irradiation at liquid nitrogen temperature. In addition, the quantum dots micro-spectrometer is coupled to the microscopic imaging spectrometer to form a dual-model microscopic imaging spectrometer, which carries out spectral collection and comparison of biological samples. The experimental results show that the transmission spectra of rat skin obtained by the dual-model microscopic imaging spectrometer are consistent, and the comparison and verification of the two spectral measurement systems are realized.     

Investigation on structural and electrical properties of BZT ceramics synthesized at low temperature

Abstract

Due to environmental concerns, lead free ceramics such as KNN- NBT and BT have growing interest in applications such as actuators and sensors. Among them Barium Zirconate Titanate (BZT) has become most attractive because it is derived from two perovskite lattice i.e. Barium Titanate (BaTiO₃) and Barium Zirconate (BaZrO₃). It has been reported that Zirconium substitution in titanium lattice enhances the material properties. In the present paper BZT was prepared using solid state route. By adding a mixture of Li₂CO₃ as a sintering aid, the sample could be sintered at 1150?°C having around 94% of the theoretical density. Prepared samples were then subjected to XRD analysis. X-ray diffraction revealed the formation of single phase material. It is observed that the electrical properties of such low-temperature sintered samples are comparable with BZT samples prepared via conventional sintering at a high temperature. It is also observed that the curie temperature shift towards room temperature for a samples sintered at low temperature.     

Noise Test on Rotating Electrical Motors Under Load

ABSTRACT

The noise of the rotating electrical motor can be strongly influenced by the change in the loading conditions. In extreme cases a noise component of electromagnetic origin may increase by 36 dB or decrease by 24 dB upon loading.Protection of a human being from the noise depends on the noise characteristics of the el. machine under operating conditions. The standards relevant to the noise qualification measurements permit the use of the sound power level determined under no–load conditions, if the noise of the machine does not vary with the change in the load. This is a concession that is made because it is difficult to separate the noise level of the loading machine from the noise of the electric motor being investigated. This paper presents several methods, and their analyses, where the sound power level emitted by a loaded electrical motor can be determined experimentally in an industrial environment.Wide ranging experimental work has been made in this field, which will be be presented at the end of the paper.     

Structure property relations of BST thin films

Abstract

We report on the properties of thin BST films which were grown in a planetary multi-wafer MOCVD reactor which handles 5 six inch wafers simultaneously. The reactor is combined with a liquid delivery system which mixes the liquid precursors from three different sources: 0.35 molar solutions of Ba(thd)₂ and Sr(thd)₂ and a 0.4 molar solution of Ti(O-i-Pr)₂(thd)₂. Film growth on strongly (111)-textured Pt substrates is investigated within a wide parameter field. We focus on the properties of films with the composition Ba_0.7Sr_0.3TiO₃ and thickness between 10 and 130 nm. Topics to be discussed include: the change of the texture of the BST films, which is (100) for deposition temperatures above 600°C and changes to a random orientation at lower temperature, and a comparison of planar films with films on structured substrates. The electrical properties, e.g., permittivity and leakage current, are discussed in relation to the microstructure.     

A STATIONARY THERMAL MODEL FOR SMOOTH AIR-GAP ROTATING ELECTRIC MACHINES

ABSTRACT

A steady state heat transfer model applicable to rotating electrical machines with non salient poles is presented. Several cooling options are accounted for, ranging from the totally enclosed machine running in a high vacuum to the open ventilated one with axial and radial ducts. Sophisticated cooling systems, such as gas or water cooled windings, are not considered. The model includes such unusual levels of detail as radiation heat exchanges and prediction of the actual hot spot temperatures of the iron and windings. Peripheral results are the temperatures at other representative points and complete maps of the conduction, convection and radiation heat exchanges.

The resultant computer program may be used either to check the temperature rise constraints for a given design, or as a tool to analyze the performance of the cooling system of an actual machine or proposed design. Parametric studies can be easily performed, showing the sensitivity of the temperature rises and heat exchanges to variations of a particular dimension, loss, flow rate or material property.     

超高分子量聚乙烯用作低温电缆绝缘的试验研究

为了解决固体合成绝缘材料低温下的脆裂问题,本文研究了超高分子量聚乙烯用作低温电缆绝缘层的可能性。通过试验比较了各种电缆绝缘材料在低温下的脆裂情况,并在液氮温区中测定了 UHMW-PE 的电气绝缘性能。试验结果是满意的。     

Insulating materials evaluation for Cold Dielectric superconducting cables

The realisation of the so-called "cold dielectric" cable, where the insulation is kept at a cryogenic temperature, entails the choice of an optimised insulation system, with properties that are the best compromise between physical-electrical characteristics and design requirements. To this purpose, a specific study was planned to qualify different materials. On the basis of literature results, mostly carried out at liquid helium temperature, polypropylene laminate (PPL), paper, high-density polyethylene (HDPE) fiber and ethylene-propylene rubber (EPR) were chosen as potential candidates for the final use in liquid nitrogen. Electrical properties of materials were evaluated and compared by means of different models. Flat and cylindrical models were used to characterise the intrinsic properties of materials and determine the impact of the technological processes, respectively. Short term and long term tests were carried out at liquid nitrogen temperature and at different absolute pressures for the evaluation of electrical endurance. As far as short term tests are concerned, AC and lightning impulse (LI) breakdown step tests were performed. Long term tests were carried out under AC field; furthermore, power factor and partial discharge measurements were made to evaluate the impregnation process. The results of the whole testing procedure indicate that PPL shows the best behaviour for the application at cryogenic temperature in a superconducting cable.     

High voltage studies of dielectric materials for HTS power equipment

The discovery of high temperature superconductors (HTS) has triggered renewed interest in the study of dielectric materials at cryogenic temperatures. While considerable work was done in the 1970s and 1980s on dielectrics immersed in liquid helium for low temperature superconducting applications, there remains a need for dielectric research at liquid nitrogen temperature for HTS applications, requiring experimental data oriented toward practical situations. We report on AC breakdown (puncture and/or flashover), and impulse breakdown of solid materials in either vacuum or in liquid nitrogen. Solid materials which we examined, include fiberglass reinforced plastics, epoxies with and without filler, and polymeric tape. Combinations of some of these materials have also been studied at low temperatures. Additionally we have measured permittivity and dissipation factor for materials for which these parameters are not available at 77 K. Finally, we also discuss specific applications for HTS cables including breakdown and aging studies on model cables, with lapped tape electrical insulation, immersed in liquid nitrogen.     

HOMOPOLAR LINEAR SYNCHRONOUS MOTOR: STEADY STATE ANALYSIS AND EXPERIMENTAL RESULTS

ABSTRACT

The main electrical and mechanical performances of a homopolar linear synchronous motor (HLSM) are calculated using classical theories which are usually applied to rotating synchronous machines. An experimental study on a low-power test motor permits the verification of theoretical results. It cranes to evidence that simple theories are applicable under certain conditions to such a motor of original conception. A full scale operational motor proposed for a combined propulsion and magnetic suspension system for high speed ground transportation is designed through extrapolation.     

Some microwave applications of BaSrTiO3 and high temperature superconductors

Abstract

The group at the University of Colorado has been working on the applications of BaSrTiO₃ and high temperature superconductors to microwave circuits and systems with support from Superconducting Core Technologies, NASA and ONR. This work has included the development of a voltage tunable oscillator, a phase shifter, and a voltage tunable phased array antenna system. An important aspect of this program is the lattice match between the high temperature superconductor and the ferroelectric materials which enables us to grow thin films of either material on each other. By choosing the appropriate barium stronium ratio we are able to obtain changes in the dielectric constant of 5 to 1 in bulk capacitors at 77 K, the liquid nitrogen boiling temperature. Phase shifts of a little less than 126° at 10 Ghz have been obtained by applying 5 volts on a one centimeter coplanar line. The proposed phased array systems should enable us to point the beam radiated from the antenna in an arbitrary direction using two control voltages of less than 50 volts. We believe this approach leads to the possibility of inexpensive electronically scannable antenna systems which could be used for mobile communications with satellites and cellular systems.     

MOV在不同介质中的雷电冲击特性

为较好实现MOV内部过电压新保护方法,试验研究了MOV在空气、变压器油和液氮3种绝缘介质中的雷电冲击响应特性,进一步运用ANSYS有限元软件仿真分析了液氮介质中MOV在遭受雷击时的热特性。试验结果表明,MOV在多种介质中有效限制了雷击过电压,利于保护并联于MOV后的设备器件,其中以液氮介质中限压效果最好,平均低于空气介质中约200V;ANSYS仿真结果表明,在MOV与液氮的接触面上存在局部气化并产生气泡的可能性,严重威胁到液氮绝缘介质的电击穿强度,基于此讨论了改善MOV表面热梯度分布,提出了避免液氮局部气化的方法,为MOV应用于超导设备内保护提供了参考。     

IMPEDANCE SPECTROSCOPY STUDY ON TRAP-CONTROLLED SPACE-CHARGE-LIMITED CONDUCTION OF Cr-DOPED SrTiO3 THIN FILMS

ABSTRACT

The electrical conduction properties of 0.2% Cr-doped SrTiO₃ thin film in metal–insulator–metal (MIM) structure was investigated by using dc and impedance spectroscopic measurements at room temperature. The dc measurement shows that the electronic conduction is the trap-controlled space-charge-limited current (SCLC) conduction. The impedance study shows that the electrical conduction is bulk-limited conduction. The behavior of the bulk resistance obtained in the equivalent circuit model from the impedance analysis is also consistent with the trap-controlled space-charge-limited conduction with exponential trap distribution.     

Dielectric behaviour of neutrophil gelatinase associated lipocalin detected by alpha relaxation process

ABSTRACT

We have investigated alpha (α) relaxation process and its temperature evolution in electrical double layer (EDL) around neutrophil gelatinase-associated lipocalin (NGAL), anti-lipocalin2 (anti-LCN-2) and their conjugate in phosphate buffer. The dielectric permittivity (20 Hz to 1 MHz) of α-relaxation process for LCN-2 and anti-LCN-2 shows variation with temperature. This happens due to unfolding of various microstates of protein at measured temperature intervals. The DSC thermograms of LCN-2, anti-LCN-2 and their conjugate predict that the multiple unfolding domains are parallel to the shifts in real dielectric permittivity at a particular temperature.     

Electrical properties of 3-component piezoelectric thick films by screen printing method

Abstract

PZT(52/48) thick films with Pb-based complex oxide (PCW) additive were prepared on Pt/TiO₂/YSZ/SiO₂/Si substrate by screen printing method. PCW addition and PZT sol application are performed to fabricate high density PZT thick film and to lower sintering temperature. With the increase of sintering temperature, electrical properties of screen-printed films were improved. Further, for the sol-gel treated thick films, the electrical properties were improved as compared to only screen-printed films. For the PZT-0.12PCW thick films with sol-treated and sintered at 900°C, the remanent polarization (P_r) was about 23.8 μC/cm² at the applied filed of 150 kV/cm², the dielectric permittivity (Ω_r) was 1024 at the frequency of 100 kHz, and the piezoelectric coefficient (d₃₃) was 339 pC/N at the applied pressure of 1 atm. Finally, the application of these PZT thick films to piezoelectric actuator is described.     

AC breakdown properties of bamboo pulp-ice composite system at cryogenic temperature

In recent years, biomaterials have attracted attention in various fields in response to environmental problems. We pay attention to bamboo because it naturally decomposes and is characterized by its excellent elasticity and water absorption properties. We had proposed a bamboo-ice composite system as a substitute for the glass fiber reinforced plastics (GFRP) in electrical insulation systems at cryogenic temperatures. In this paper we will report the AC breakdown properties of a bamboo pulp-ice composite system at liquid nitrogen temperature. The bamboo pulp-ice composite system had AC breakdown strength comparable with GFRP and can be easily molded in various shapes. We consider that the bamboo pulp-ice composite system is promising as a substitute for the GFRP in the electrical insulating systems at cryogenic temperatures     

PIEZOELECTRIC RESPONSE OF PZT NANOSTRUCTURES OBTAINED BY FOCUSED ION BEAM

ABSTRACT

Pb(Zr_x,Ti_{1 - x})O₃ (PZT) microscale island (1μ m～ 100 nm) was fabricated by Focused Ion Beam (FIB) before and after its crystallization. In the first case the FIB etching is realized on amorphous films and a post annealing treatment, at the crystallization temperature of the PZT films, is necessary to cristallize the film in the perovskite phase. In the second case the etching are made on crystallized films. Local electrical properties were evaluated by piezoresponse force microscopy (PFM) technique and the degradations induce in the films are studies by Raman spectroscopy. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases.     

Electrical characterizations of MgTiO3 thin films grown on Si

Abstract

We have analyzed MgTiO₃ thin films grown on the Si substrate with/without SiO₂ using pulsed laser deposition (PLD). We find that MgTiO₃ thin films start to crystallize at 600°C, causing electrical instabilities in the MIS capacitors above this temperature. Detailed analysis by XRD technique reveals that structural differences of MgTiO₃ thin films were not obvious below 600°C, whereas the electrical characteristics changes as a function of deposition temperature and the presence of thermally grown SiO₂. We observe that the decrease of deposition temperature results in the increase of leakage current and anomalous positive charge (APC) density. These drawbacks were effectively suppressed by growing 100A SiO₂ layer on the Si substrate prior to the deposition of MgTiO₃ thin films.