AC Induction Research Articles

Energy Cost Savings in Motive Power

AbstractMotive power accounts for over 65% of the average UK industrial electricity bill; however, in the water industry this percentage is nearer to 90%. During 1994, UK industry spent almost £3000 million on the energy used by motors – mainly attributable to AC induction motors, with pumps and fans being the most common motor applications.Many techniques can be used to reduce the cost of running motors, from simple good‐housekeeping measures to sophisticated electronic controls. This technical note reviews a selection of these techniques using independent case studies from the Department of the Environment's ‘best practice programme’to illustrate the cost savings; the use of software to predict energy savings is also discussed.

Parameters influencing the expression of mature glial-cell-line-derived neurotrophic factor in Escherichia coli.

Factors governing expression in Escherichia coli, namely promoters, fusion partners, targeting signals, host strains, growth temperature of cultures and inducer concentrations, were investigated to elucidate their influence on the accumulation of mature glial-cell line-derived neurotrophic factor (GDNF). The present study provided evidence indicating that translational and/or post-translational events were more important in determining overall accumulation of the target protein than was transcription. Under the control of the strong inducible tac or T7 promoter, no direct correlation between transcript abundance and final yield of recombinant protein was observed. GDNF was also recalcitrant to being produced in a soluble form in E. coli. Direct expression resulted in the exclusive localization of GDNF in inclusion bodies, regardless of whether the protein was produced in the cytoplasm or targeted to the periplasm. The fusion approach was found to be the most efficient method, as it resulted not only in the highest level of GDNF produced, albeit primarily in inclusion bodies, but also in the accumulation of small amounts of soluble proteins. Using different host strains, low inducer concentration or sub-optimal growth temperature did not result in any detectable shift towards solubility. Persistent localization in inclusion bodies, low levels of expression as a native protein and in vivo proteolysis of soluble fusion forms appeared to be influenced by structural features located at the N-terminus of GDNF. Deletion of this region was found to result in substantial alleviation of these problems.

Involvement of iclR and rpoS in the induction of acs, the gene for acetyl coenzyme A synthetase of Escherichia coli K-12

Two independent pathways in Escherichia coli convert acetate to acetyl CoA: reversal of acetate production by phosphotransacetylase and acetate kinase, and the acetyl-CoA synthetase (Acs) pathway that scavenges acetate. We investigated acs gene expression by using a cat transcriptional fusion. It was observed that acs expression varies depending on the carbon sources used and occurs in the stationary phase of growth even in the absence of acetate. Mutations in iclR for the repressor of the glyoxylate shunt and in rpoS for the stationary phase sigma factor reduced the consumption of acetate mediated by Acs, indicating that both are involved in acs regulation.

A transputer-based adaptive speed controller for AC induction motor drives with load torque estimation

In this paper, we design and implement an adaptive speed controller that can estimate load torque for AC induction motor drives employing a transputer-based parallel processing technique. The adaptive speed controller, which precedes the field-oriented control loop, consists of a two-degree-of-freedom controller and a feedforward load-torque compensator. The two-degree-of-freedom controller is designed by a pole-placement technique with polynomial manipulations. Its parameters are adjusted adaptively in terms of estimated model parameters. Estimating the model parameters entails a second-order least-squares estimator with constant trace to avoid estimator windup. The design of the feedforward compensator is based on an estimated load-torque model. Estimating the load torque entails a first-order least-squares estimator with variable forgetting factor and covariance resetting, the purposes of which are to detect any slow or sudden changes of torque disturbance, respectively. The resulting adaptive controller is implemented in parallel by IMS T800-20 transputers. Experimental results demonstrate the robustness of the proposed control method in contending with varying load and torque disturbance.

Optimum pole configuration of variable speed AC induction motors

Sometimes a user who is familiar with fixed speed AC induction motors may specify a variable speed AC requirement with a preconception of the number of motor poles. This is appropriate in the case of an application where the motor will be run "across-the-line", and is expected to run at the same speed and load as provided on inverter operation. If, on the other hand, "bypass" operation is not required, a more optimal choice of motor designs might be available. For example, an application requiring 3000 or 3600 RPM operation would demand a two-pole motor design if bypass (at 50 or 60 Hz) must be provided. However, when bypass is not required, it is often the case that a smaller motor can be provided in a four-pole design (utilizing 100 or 120 Hz base frequency) compared to a two-pole configuration. Another aspect of applying adjustable frequency power supplies to AC induction motors is that it allows an essentially infinite number of possible "base speeds", including base speeds in excess of 3600 RPM. In this paper the author discusses the number of poles required for fixed speed AC motors, DC motors, and adjustable frequency AC motors. Motor performance issues are also discussed.

Combination high-sensitivity alternating current susceptometer and high-frequency B–H looper

A combination high-sensitivity alternating current (ac) susceptometer and high-frequency B–H looper is described. Based on the well-known inductance technique, the design uses modern low-noise components and stable temperature control to achieve the high sensitivity. The mechanical assembly is designed for use inside a glass Dewar, enabling measurements to be made at any temperature between 4.2 and 300 K. Initial ac susceptibility can be measured over a frequency range of 10 Hz to 120 kHz with sensitivity of 1×10−8 emu, comparable to a superconducting quantum interference device (SQUID) magnetometer. B–H loops are measured at 2 kHz with a low duty cycle, damped oscillatory field pulse, and have sensitivity of 4×10−8 emu. The instrument can thus measure ac susceptibility at higher frequencies than ac-equipped SQUID magnetometers and commercially available inductive ac susceptometers, and can also measure B–H loops at much higher frequencies and with greater applied fields than steady-state loop tracers.

Inductive anomaly of two-dimensional electrons in the Wigner solid regime

We have investigated the small-signal frequency response of the GaAs AlGaAs two-dimensional electron system in the reentrant insulating phase around the ν = 1 5 fractional quantum Hall liquid from 0.2 to 2 MHz in the presence of a DC bias. When the sample is DC biased above the nonlinear conduction threshold, the insulating state exhibits an inductive AC response as the imaginary component of the conductivity ( Im σ xx ) becomes negative. Moreover, Im σ xx shows a broad minimum near a frequency which increases with increasing DC bias, in a manner consistent with the washboard oscillations of a magnetic-field-induced Wigner crystal.

Dependency of Escherichia coli cell-division size, and independency of nucleoid segregation on the mode and level of ftsZ expression.

Expression of ftsZ in strain VIP205 is dissociated from its natural promoters, and is under the control of an inducible tac promoter. This abolishes the oscillation in ftsZ transcription observed in the wild type, allowing different levels of ftsZ expression. We demonstrate that this construction does not affect the expression of other genes, and has no effects on replication or nucleoid segregation. A shift in IPTG from 30 microM, that supports division at wild-type sizes, to lower (6 microM) or higher (100 microM) concentrations, indicates that VIP205 cells can divide within a broad range of FtsZ concentrations. Analysis of the morphological parameters during the transition from one IPTG concentration to another suggests that the correct timing of ftsZ expression, and the correct FtsZ concentration, are required for division to occur at normal cell sizes. After a transient division delay during the transition to lower IPTG concentrations, cells in which ftsZ is expressed continuously (yielding 80% of the wild-type FtsZ levels) divide with the same division time as the wild type, but at the expense of becoming 1.5 times larger. A precise control of ftsZ expression is required for normal division, but the existence of additional regulators to maintain the correct timing during the cell cycle cannot be ruled out.

Suppression of transcription polarity in the Escherichia coli haemolysin operon by a short upstream element shared by polysaccharide and DNA transfer determinants.

Expression of the Escherichia coli hlyCABD operon encoding synthesis, maturation and export of haemolysin toxin was strongly dependent upon a 35 bp DNA sequence, spanning the element GGCGGTAG, located 2 kbp upstream. When the hly operon was placed under the control of the inducible tac promoter, expression remained dependent upon this element, when transcribed in its native orientation 3' of the promoter. The increase in ptac-directed transcription was strongest for the distal, export genes of the hly operon, and was particularly striking when ptac and the element were placed far upstream. The element did not influence transcript stability, and we suggest that it is a key component of a novel regulatory mechanism may suppresses transcription polarity within operons. The mechanism that be of widespread importance in bacterial gene expression because the 8 bp element is present in many Gram-negative species as an upstream component of operons encoding the production of toxins and the surface assembly of polysaccharides and components required for the conjugal transfer of DNA. We name it the ops element for operon polarity suppressor.

DSP-based robust control of an AC induction servo drive for motion control

A design method based on the internal model control (IMC) theory has been developed for the robust control of a low-power AC induction servo drive in application of high-performance motion control systems. Indirect vector control with software current control technique has been developed to achieve fast response decoupling control of the induction motor. An equivalent model representing the control dynamics of the decoupled AC induction motor is used for the analysis and synthesis of the IMC controller. To improve the control performance of the servo drive with given frequency-domain robustness specifications, a design procedure for the servo controller is developed based on the IMC theory. The proposed control scheme has been realized using the Texas Instruments TMS320C14 single-chip digital signal processor. Experimental results are given to verify the proposed design method.

Effect of PWM inverters on AC motor bearing currents and shaft voltages

This paper investigates AC induction motor shaft voltage problems, current flow through motor bearings and electric discharge current problems within bearings when operated under both pure sinewave and pulse width modulated (PWM) inverter sources. Experience suggests that PWM voltage sources with steep wavefronts especially increase the magnitude of the above electrical problems, leading to motor bearing material erosion and early mechanical failure. Previous literature suggests that shaft voltage-bearing current problems under 60 Hz sinewave operation are predominantly electromagnetically induced. It is proposed that under PWM operation these same problems are now predominantly an electrostatic phenomenon. A system model to describe this phenomenon is characterized and developed. Construction and test of a new electrostatic shielded induction motor (ESIM) verifies this model and is also a possible solution to the bearing current problem under PWM operation.

Regulatory impact on the application of AC induction motors

This article identifies the impact of current and future laws, regulations, codes, standards, and recommended practices affecting the specification, design, operation, and maintenance of electric motors. The intent is to provide the engineer with a user's guide to assure compliance. The purpose of the article is to identify existing and anticipated to the application of AC induction motors. Those areas where no apparent restrictions exist are also explored. It is important to understand that these constraints are, for the most part, in a constant state of review and possible change.

Analysis of the impact of pulse-width modulated inverter voltage waveforms on AC induction motors

The purpose of this paper is not to reveal any new technology or major breakthrough pertaining to the impact of pulse-width modulated (PWM) adjustable speed drives operating on AC motors. Nor is it to discuss the merits of the various designs of the drives. The applications are also well defined. The area where much confusion still exists deals with the voltage waveform impact on the motor performance, hence, this is the central theme of the paper. The author has assumed that the traditional fundamental sine-wave voltage is (except for starting or outside influences) a steady-state condition, with a maximum and an RMS value, whereas the voltage waveform supplied by a PWM drive can have significant harmonics and transients which may alter the motor performance characteristics and life expectancy. The effects of the maximum voltage, rate of rise, switching frequencies, capacitors, resonance, and harmonics are all considered.

Transcriptional regulation of the iron-responsive sigma factor gene pbrA.

In response to the intracellular iron concentration Pseudomonas fluorescens M114 coordinately regulates the production of pseudobactin M114, its cognate receptor PbuA, and a casein protease. Transcriptional initiation of this coordinate iron-stress response requires the sigma factor PbrA. PbrA is a member of the ECF (Extracytoplasmic function) subgroup of the sigma 70 family of eubacterial RNA polymerase sigma factors. Regulatory studies of the pbrA gene utilising promoter-lacZ transcriptional fusions demonstrate that expression of pbrA dictates the cellular response to iron. pbrA is transcribed in all phases of iron-limited growth but maximally at late-logarithmic to stationary phase. pbrA expression is independent of autoregulatory control but is strictly repressed in iron-rich conditions in a Fur-dependent fashion. Constitutive expression of pbrA from an inducible tac promoter permits the induction of PbrA-dependent transcription and pseudobactin M114 biosynthesis in high-iron conditions. A PbrA consensus sequences was derived from significant DNA sequence homologies observed within the "-25 bp" and "-16 bp" regions conserved among all PbrA-dependent promoters. The predicted PbrA target promoter consensus is homologous for the promoter recognition sites for other environmentally responsive ECF sigma factors.

Rotary pump drives

The most common drive for rotary pumps is the AC induction motor. It is, by far, the workhorse of modern industry. However, it is only one of a great variety of drive types and styles. This article will familiarize the reader with some alternatives that have been used with success. These alternatives often provide greater versatility and practicality under less than ideal circumstances.

Compact Vector Control Setup Based on the 80C196MC Microcontroller

AC motors are the electrical drives most frequently used in industrial applications. These drives are designed for operating at constant speed, a fact that makes them rather difficult to be used for control purpouses. Nowadays, there are several techniques for facing the problem of AC motor control, such as the Vector Control method. Nevertheless, their implementation normally implies high costs and a rather complex hardware design. This work presents a Vector Control System of AC induction motors, based on a high performance dedicated microcontroller. This setup enables a compact hardware design for the development of control algorithms of fast servo mechanism implemented with AC motors as actuators.

Direct expression of pig testicular (20β)-hydroxysteroid dehydrogenase in Escherichia coli

The cDNA coding for pig testicular 3 alpha/beta (20 beta)-hydroxysteroid dehydrogenase was expressed in Escherichia coli by placing it under the control of an isopropylthiogalactoside (IPTG) inducible tac promoter. Production of 3 alpha/beta (20 beta)-HSD was demonstrated by Western blotting and by catalytic activity with 5 alpha-dihydrotestosterone as a substrate for 3 alpha/beta-HSD, and progesterone and 17 alpha-hydroxyprogesterone as substrates for 20 beta-HSD in the presence of NADPH. The 3 alpha/beta (20 beta)-HSD enzyme was detected in a soluble fraction of the lysate of E. coli added to IPTG to induce the synthesis of the protein. Its molecular weight was estimated to be 30.5 kDa by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Recombinant 3 alpha/beta (20 beta)-HSD was purified to apparent homogeneity as determined by SDS-PAGE by column chromatography using DEAE-cellulose. The purified enzyme reduced not only steroids but also prostaglandins and other carbonyl compounds including aldehydes, ketones and quinones as demonstrated in native enzymes purified from pig testes. The amino terminus of the purified enzyme was serine which was coded next to the ATG start codon, and the sequence of the amino terminal 24 residues was identical with the coding amino acid in the cDNA; whereas, the amino terminus of the native 3 alpha/beta (20 beta)-HSD was not detected suggesting that the N-terminal amino acid was blocked.

Production in Escherichia coli of a functional murine and murine::human chimeric F(ab′) 2 fragment and mature antibody directed against human placental alkaline phosphatase

We report the production in Escherichia coli of a murine antibody IgG2b, a murine::human chimeric antibody IgG3 and the corresponding F(ab′) 2 fragments, all directed against human placental alkaline phosphatase, a tumor marker. The cDNA of the heavy chain of the mature antibodies and their fragments were linked up to the bacterial alkaline phosphatase signal sequence and were placed under control of the inducible tac promoter. Coexpression with the murine κ light chain resulted in production of functional dimeric, trimeric and tetrameric, mature antibodies and F(ab′) 2 fragments in the periplasm of E. coli in a yield of 200–300 μg 1 −1. High amounts of light and heavy chains were present also in the insoluble fraction.

Efficient expression, purification and characterization of hepatitis B virus preS1 protein from Escherichia coli

The complete (encoding 119 aminon acids, aa) or partial (encoding the N-terminal 90 aa) preS1 region gene of hepatitis B virus (HBV) was fused to the 3′-end of glutathione-S-transferase (GST) gene and expressed at 37 °C under the control of the inducible tac promoter in E. coli. The results showed that the fusion protein with the full length of preS1 was moderately expressed, about 10% of total cellular proteins, while the protein with the partial preS1 was highly expressed, about 33% of total cellular proteins but the half was degraded into the protein with about N-terminal 60 aa of preS1. Accordingly, GST fusion protein containing the N-terminal 56 aa of the preS1, which still encodes B-and T-cell epitopes and a hepatocyte receptor binding site, was expressed under the same induction conditions and was shown to be highly and stably expressed, about 37% of total cellular proteins. The fusion protein with the full length or N-terminal 56 aa of preS1 and the peptides were simply and successfully purified by affinity chromatography and were demonstrated to exhibit the antigenicity and immunogenicity of the preS1 antigen.

Epitaxial bilayer and trilayer heterostructures grown on LaAlO3 and SrTiO3(001) single crystals by laser ablation

High-quality S/I and S/I/S epitaxial heterostructures (S=YBa2Cu3Ox, l=SrTiO3) have been grown in situ on LaAlO3 and SrTiO3(001) single crystals, by the single-chamber pulsed laser deposition technique. YBa2Cu3Ox and SrTiO3 layers were deposited sequentially, at a substrate temperature Th=760 degrees C, and an oxygen pressure rho (O2)=300 mTorr. Structural data showed that the SrTiO3 layer, grown either on a YBCO film or sandwiched by two YBaCuO films, was strained in the (001) plane and exhibited an elongation of the lattice parameter in the (001) direction. This behaviour was consistent with the epitaxial growth of the S/I and S/I/S structures as revealed by the RHEED and ECP patterns. Ion milling in conjunction with AES analysis showed that the thicknesses of the interfacial regions were <or=35 AA, and resulted from residual roughness of the substrates. The critical temperature (Tc) and critical current density (jc) of the multilayers at 77 K, as determined by an inductive AC method, were found to be Tc=89.5 and 90.5 K, and jc=3 and 5*106 A cm-2, for trilayers and bilayers, respectively.