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Energy saving issues occupy a leading position in all control systems. This article provides a detailed analysis of control systems and is conducted by considering the complexity of implementation and response to the control action. The implementation of energy-saving control systems is directly related to the selected control system and the proposed energy-efficient algorithm. A system with direct torque control is proposed, which provides energy savings in the mechanisms for moving goods. A detailed analysis of the implementation of systems with direct torque control is carried out. New methods to save energy in the control system by minimizing the stator current have been proposed. [ABSTRACT FROM AUTHOR]

Energy saving issues occupy a leading position in all control systems. This article provides a detailed analysis of control systems and is conducted by considering the complexity of implementation and response to the control action. The implementation of energy-saving control systems is directly related to the selected control system and the proposed energy-efficient algorithm. A system with direct torque control is proposed, which provides energy savings in the mechanisms for moving goods. A detailed analysis of the implementation of systems with direct torque control is carried out. New methods to save energy in the control system by minimizing the stator current have been proposed.

In the late 19th century, the three-phase induction motor was the central element of productivity increase in the second industrial revolution in Europe and the United States. Currently, it is the main load on electrical systems in global terms, reaching approximately 70% of electrical energy consumption in the industrial sector worldwide. During the 20th century, electric motors underwent intense technological innovations that enabled significant performance gains. Thus, this work analyses the performance changes in squirrel-cage rotor three-phase induction electric motors (SCIMs) with mechanical powers of 3.7 kW, 37 kW, and 150 kW and speed ranges corresponding to two poles and eight poles, connected to a low voltage at a frequency of 60 Hz and tested between 1945 and 2020. The study confirms accumulated performance gains of above 10% in some cases. Insulating materials for electrical conductors have gone through several generations (cotton, silk, and currently, varnish). Improvements to the housing for cooling, the bearings, the quality of active materials, and the design were the elements that enabled the high gains in performance. The first commercial two-pole SCIM with a shaft power of 4.4 kW was marketed in 1891, with a weight/power ratio of 86 kg/kW, and until the 2000s, this value gradually decreased, eventually reaching 4.8 kg/kW. Between 2000 and 2020, this ratio showed a reversed trend based on improvements in the performance of SCIMs. More active materials were used, causing the weight/power ratio to reach 8.6 kg/kW. The MEPS (minimum energy performance standards) of SCIMs had an essential role in the performance gain over the last three decades. Data collection was via tests at the Electrical Machines Laboratory of the Institute of Energy and Environment of the University of São Paulo. The laboratory has a history of tests on electrical equipment dating from 1911. [ABSTRACT FROM AUTHOR]

The relevance. The share of electricity generated by installations based on renewable energy is constantly growing, and therefore the need for the development of power supply systems and automatic control of electrical machines underlying wind and hydro generators is still relevant. As part of such alternating current generator sets, synchronous electric machines, induction generator with phase and squirrel-cage rotor are used. Frequency converters installed in the stator and rotor circuits of induction motor make it possible to control their excitation, however, to start generation, additional external power sources must be used. Due to the residual magnetization in the magnetic circuit, it is possible to ensure the process of guaranteed self-excitation of the induction generator by connecting the capacitor banks to the electrical circuit of its stator without using an additional external power source. The proposed method of non-stationary capacitor excitation makes it possible to ensure the adaptation of the generator set to the change in operating modes under conditions of decentralized power supply. The main aim of the research is to study the proposed voltage stabilization system of induction generator with a short-circuit rotor with variable capacitor excitation as part of a renewable energy source. Methods. To achieve the goal of the research, theoretical and experimental research methods were used. Theoretical research methods include the theory of differential equations, methods for the numerical solution of ordinary differential equations, the theory of electric drives, the theory of electrical machines, numerical methods for approximating data. The basis of experimental research is testing an induction generator with non-stationary capacitor excitation on a developed test bench in order to obtain load characteristics and oscillograms of voltages on the stator windings of an induction generator with a short-circuit rotor in different operating modes. Results. An original experimental setup with a unit imitating the operation of a turbine, an electromechanical energy converter in the form of an induction generator with a short circuit with non-stationary capacitor excitation has been developed and manufactured. The control system is made in the form of a galvanically isolated module integrated with the power unit in a moisture-resistant design using a wireless Bluetooth communication interface. A method for switching capacitor banks using thyristors as a controlled switch with two-way conduction is described and tested. The analysis of the obtained load characteristics shows the fundamental possibility of ensuring a guaranteed generation of electricity with voltage stabilization within the limits of load power variation. The system of automatic switching of capacitors with a capacitance varying depending on the power consumption applied as part of the experimental setup made it possible to provide an acceptable time for dynamic response to a disturbing effect under nonstationary load.

Purpose. Development of a method for calculating mechanical characteristics of induction motors, taking into consideration saturation of the magnetic path and displacement of the current in the rotor bars. Methodology. The algorithm is based on calculating the steady-state mode of induction motor operation for a set slip, described by a system of non-linear algebraic equations of electrical equilibrium, whereas the mechanical characteristic is evaluated as a set of steady-state modes using parameter continuation method. The idea of the steady-state mode calculation consists in determining vectors of currents and flux linkages of the motor circuits, using which makes it possible to evaluate the electromagnetic torque, active and reactive powers, etc. Results. The study resulted in the development of a method and algorithm for calculating static characteristics of induction motors, which allows looking into the effect of different laws of voltage regulation on the mechanical characteristics, depending on the frequency change. Originality. An algorithm for calculating mechanical characteristics of the squirrel-cage induction motor was developed based on the mathematical model of the induction motor in which electromagnetic parameters are calculated using real saturation curves for the main magnetic flux and leakage fluxes, and displacement of the current in the rotor bars is evaluated by presenting the rotor winding as a multi-layer structure. Applying the transformation of the electrical equilibrium equations into the orthogonal axes enabled a significant reduction of calculation volume without impairing the accuracy of the results. Practical value. The developed algorithm allows studying the effect of different laws of scalar regulation of the voltage on the mechanical characteristics of the induction motor in order to obtain the necessary torque-speed curves for their optimization. It can be used for programming frequency converters.

Permanent magnet adjustable speed drive (PMASD) has been widely applied to regulate the speeds of large pumps and fans for energy-saving. For improving the torque density and simplifying the actuator of traditional PMASD, a novel squirrel-cage rotor (SCR-) PMASD with a non-rotary mechanical flux adjuster (MFA) is proposed in this paper. An analytical model considering the slot effect and the MFA shifting is established to analyze the magnetic field and the output torque efficiently for the initial design of the proposed drive. The air-gap flux density distributions obtained by the analytical model are verified by two-dimensional (2D-) finite element analysis (FEA). During the speed regulation process, the torque characteristics, power, loss, and efficiency of the drive under different MFA shifting distances are compared with the 2D-FEA and experimental results. The analysis and measured results show that the proposed drive can achieve a wide speed regulation range. [ABSTRACT FROM AUTHOR]

In the late 19th century, the three-phase induction motor was the central element of productivity increase in the second industrial revolution in Europe and the United States. Currently, it is the main load on electrical systems in global terms, reaching approximately 70% of electrical energy consumption in the industrial sector worldwide. During the 20th century, electric motors underwent intense technological innovations that enabled significant performance gains. Thus, this work analyses the performance changes in squirrel-cage rotor three-phase induction electric motors (SCIMs) with mechanical powers of 3.7 kW, 37 kW, and 150 kW and speed ranges corresponding to two poles and eight poles, connected to a low voltage at a frequency of 60 Hz and tested between 1945 and 2020. The study confirms accumulated performance gains of above 10% in some cases. Insulating materials for electrical conductors have gone through several generations (cotton, silk, and currently, varnish). Improvements to the housing for cooling, the bearings, the quality of active materials, and the design were the elements that enabled the high gains in performance. The first commercial two-pole SCIM with a shaft power of 4.4 kW was marketed in 1891, with a weight/power ratio of 86 kg/kW, and until the 2000s, this value gradually decreased, eventually reaching 4.8 kg/kW. Between 2000 and 2020, this ratio showed a reversed trend based on improvements in the performance of SCIMs. More active materials were used, causing the weight/power ratio to reach 8.6 kg/kW. The MEPS (minimum energy performance standards) of SCIMs had an essential role in the performance gain over the last three decades. Data collection was via tests at the Electrical Machines Laboratory of the Institute of Energy and Environment of the University of São Paulo. The laboratory has a history of tests on electrical equipment dating from 1911.

In a squirrel-cage induction motor, because the rotor windings are assembled from conductor bars short-circuited by end rings, the number of poles is not an intrinsic characteristic of the windings, as it occurs in the case of wound rotor windings, but it is a consequence of the distribution of the currents induced in the bars. However, since the motor works, the number of stator and rotor poles must necessarily be the same, and the explanation of why this occurs is usually left to physical considerations. The paper proposes the analytical proof that in a squirrel-cage induction motor, the number of rotor poles is the same as that of the stator. The proposed demonstration is based on the determination of the air gap flux density distribution generated by any set of currents circulating in the rotor bars, without any hypothesis about their waveform. The distribution is expressed as sum of infinite space harmonics, for each of which a current space vector can be defined. First, the special case of sinusoidal stator currents is addressed, and then the general one of stator currents having any waveform. In this way, it is possible to show that the only nonzero rotor current space vector is the one corresponding to the space harmonic having a number of poles as that of the stator. [ABSTRACT FROM AUTHOR]

The intermediate ring (IR) in the novel squirrel‐cage rotor is vulnerable to electrical faults for its relatively small dimension. With the investigation of IR current features, this study mainly proposes an optimisation design strategy of IR to avoid excessive thermal stress at a start‐up instant. The amplitude and phase relations of various rotor currents are reflected in the proposed current phasor diagram. In terms of the internal distribution of one concrete current, the circuit analysis theory is applied by dividing the whole conductor into multiple subconductors. The leakage flux around the conductors is simplified, respectively, according to the spatial symmetry. With reference to the existing bar design, the IR design scheme is mainly guided by two essential principles regarding the current‐related parameters. Finally, the validity of the designing process of IR is verified by the coupled simulations and temperature‐rise experiments. The surface temperature of the designed IR is not the highest, and the partial temperature difference is limited and reasonable. [ABSTRACT FROM AUTHOR]

Copyright of Electrical Engineering & Electromechanics is the property of National Technical University, Kharkiv Polytechnic Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Broken rotor bars in induction motors can be dependably detected by analyzing the current signatures under sufficient motor load conditions. Detection becomes less dependable under light motor load conditions. There are also cases in which tolerable motor operating conditions generate current signatures similar to those of motors with broken rotor bars. These cases may present security concerns when the detection element is set to trip the motor and to send alarms. In this paper, we aim to achieve the following: show how broken rotor bars cause characteristic current signatures; show how to detect broken rotor bars with a zero-setting protection element, which uses the current signature method; use cases with different motor operating and fault conditions to analyze the performance of the zero-setting broken bar protection element; identify cases when the current signature method is dependable and cases when security is a concern, and present solutions to address security concerns. [ABSTRACT FROM PUBLISHER]

It is difficult to apply conventional online motor current signature analysis techniques for diagnosis of rotor faults for closed-loop induction motor drives for many applications due to the masking effect of the feedback current controller and/or variable frequency or load operation. Relying solely on traditional offline inspection techniques during regular maintenance does not allow frequent monitoring of rotor problems and is inconvenient since it requires rotor disassembly and/or manual rotor rotation. In this paper, a new automated technique for testing voltage source inverter-fed squirrel-cage induction machines at a standstill for rotor faults is proposed. The main concept is to use the inverter to excite the machine with a pulsating field at a number of angular positions to observe the variation in the impedance pattern due to broken rotor bars, whenever the motor is stopped. An experimental study on a 7.5-hp induction motor verifies that broken bars can be detected with high sensitivity and reliability. It will be shown that the proposed method can provide automated and reliable assessment of rotor condition frequently without motor disassembly, manual rotation, or additional instrumentation. The proposed test can also provide rotor quality assessment independent of variations in motor or load operating conditions since it is a standstill test. [ABSTRACT FROM AUTHOR]

Power-saving electric drives created by modernizing traditional three-phase induction motors for draw benches are presented. Power-saving induction motors have cos φ = 1.0 and power efficiency ηp = 80–90%. Each kilowatt of rated power of an energy-saving induction motor makes it possible to save approximately 300–750 kW h of electric power per year. [ABSTRACT FROM AUTHOR]

New mathematical relationships for the contactless determination of the active resistance of the rotor winding, excitation circuit inductance, and the electromagnetic time constant of the rotor are presented for an operating motor. The relations include parameters that are available for direct measurement in the control system or known from the design documentation and needed for calculations. We have revealed new interdependences between the basic parameters of operating frequency-controlled induction motors for any mode at different saturations of the magnetic circuit and any temperature of stator and rotor windings. [ABSTRACT FROM AUTHOR]

This paper presents the nonlinear modeling of a permanent-magnet induction machine (PMIM). The PMIM has a permanent-magnet (PM) rotor that is free to rotate inside a squirrel-cage rotor. The internal self-excitation from this PM rotor allows the PMIM to operate at a higher power factor. Utilizing a duality between magnetic and electric circuits, an electrical equivalent circuit that can accurately include the nonlinearity of the excitation circuit is derived. Based on this equivalent circuit, a measuring method of circuit parameters and a calculation method of the steady-state performance are explained. In addition, the generating characteristics of the PMIM in the grid-connected mode are theoretically calculated to verify the validity of the derived equivalent circuit, and the results are confirmed through experiments. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(1): 58–67, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10189 [ABSTRACT FROM AUTHOR]

This paper presents a new structure for a self-regulated, self-excited, single-phase induction generator. The generator has two sets of electrically isolated stator windings, a single-phase main winding and a three-phase auxiliary winding. It employs a standard squirrel-cage rotor. Three shunt capacitors are connected across the auxiliary winding, while a single-phase load is connected across the main winding in series with a series capacitor. For analysis and design of this new generator, an equivalent circuit is derived using the method of symmetrical coordinates. Based on the equivalent circuit, the steady-state performance of the generator is theoretically calculated, and the results are verified through experiments. In addition to a self-regulating feature, the proposed generator has the advantage of balanced three-phase excitation. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 68–78, 2002 [ABSTRACT FROM AUTHOR]

• High temperature superconducting induction/synchronous motor. • Fully superconducting motor by the use of BSCCO tapes. • Nonlinear resistances of superconducting windings and nonlinear inductances of silicon steel core. • Quantitative characterization of load characteristics. This paper reports an optimal technique to design a fully superconducting motor. A 50-kW-class fully superconducting induction/synchronous motor with both rotor and stator windings was fabricated from bismuth–strontium–calcium–copper-oxide (BSCCO) tapes and quantitatively characterized. The toroidal structure was adopted for the stator windings in order to increase their critical current in the iron core, and a squirrel-cage structure was used for the rotor windings. The three-phase AC loss was measured in atmospheric liquid nitrogen (77 K), and characterized as a function of the stator current and its frequency. Nonlinear self-inductance as well as mutual- inductance of the silicon steel core was estimated based on experimental and analytical methods. These nonlinear parameters were introduced into the voltage equations and then coupled with the equation of motion. The measured load characteristics were quantitatively reproduced despite complex nonlinear parameters. [ABSTRACT FROM AUTHOR]