Start-up Of Induction Motor Research Articles

Detection of High-Resistance Connections in Industrial Power Systems During Induction Motor Start-up

We propose a methodology for detecting and isolating high-resistance connections (HRC) in industrial power systems during induction motor (IM) start-up. Negative sequence components are analyzed during the IM start-up transient in different points of the electric system of an industrial plant. The effects of HRC are evaluated using an analytical model of an industrial power system in steady state and validated with numerical simulations obtained of a transient model. These results show not only the possibility to detect HRC but also its isolation from unbalance voltage conditions of the grid. In addition, an approximation of the total power of motors affected by the HRC is calculated with our proposal. This power and the electric one-line diagram of the industrial plant allow us to determine the location of HRC. Finally, the proposal is validated by using experimental results obtained in a meat processing industry.

Identification of Voltage Sag Sources in the Electrified Railway Power Supply System Based on CNNs

In order to solve the problems of long classification time and low accuracy of traditional voltage sag source identification methods, on the basis of CNNs, the author conducts an in-depth study on the identification of voltage sag sources in the electrified railway power supply systems. Firstly, study and research from three methods of line fault analysis, simulation verification method, and power quality analysis method are conducted. In order to improve the classification and identification of compound-voltage sag sources when the distribution network contains harmonics, the author proposes a new method for the classification and identification of compound-voltage sag sources based on the eigenvalue synthesis method. Among them, according to the different voltage sag waveform characteristics caused by different composite voltage sag sources, the three-phase voltage unbalance is defined, and the result is obtained by combining the compound-voltage sag source including single-phase grounding with the voltage sag source compounded by induction motor startup and transformer input. After experiments and research, the proposed method is verified by simulation experiments, the results show that the method can classify and identify the types and fault sequences of the compound-voltage sag sources well, and the identification accuracy rate is higher than 96%.

Conformable fractional order controller design and optimization for sensorless control of induction motor

PurposeIn recent years, use of sensorless control methods for electrical motor-based variable speed drive systems has been increasing rapidly to compensate the increasing costs in industrial systems. Also, use of induction motors is popular for a long time to decrease the cost of these industrial systems. This study aims to design an effective controller to improve the sensorless speed control performance of induction motor. To achieve this, a conformable fractional order proportional integral (CFOPI) controller is designed.Design/methodology/approachThe system is modeled based on small signal analysis by using the input–output data, experimentally. To do this, system identification toolbox of Matlab is used. The proposed controller is established on conformable fractional integral approach proposed by Khalil et al. (2014). CFOPI controller coefficients are optimized using particle swarm optimization method on the created small signal-based simulation model of the system to minimize the integral time absolute error. To prove the success of the proposed method, a traditional fractional order proportional integral (TFOPI) controller is tested under the same experimental system with the CFOPI controller.FindingsTFOPI and CFOPI controllers are tested with the optimum parameters. Reference and actual speed trends are obtained for both methods. In induction motor start-up test, settling-times are measured as 8.73 and 8.44 s and steady-state oscillations are 2.66% and 0% (almost) for TFOPI and CFOPI controllers, respectively. In variable referenced speed tracking test, CFOPI performs well at all speed levels, while TFOPI fails to reach the reference speed at most speed levels.Practical implicationsProposed CFOPI control method can be easily implemented in industrial systems, thanks to its simple algorithm. digital signal peripheral interface controller (dsPIC) based driver circuit with designed CFOPI controller used in this study can be applied directly to industrial systems such as elevators, conveyors, cranes and drills. Moreover, it can improve the performance of induction motor-based variable speed drive systems.Originality/valueThe proposed method provides robust performance for induction motor used in control systems. Additionally, it does this by using less complex algorithm written on the processors according to the traditional fractional order controllers.

유도전동기 기동용 변압기의 용량 산정에 관한 연구

Induction motor have the advantage of simple structure, robustness, low-price and easy maintain. Therefore, it is most widely used in the industrial field. The induction motor has two disadvantages when starting. The first is that the power factor is low and the second is that the voltage drop due to the high starting current is large. Therefore, many studies have been conducted to reduce such shortcomings. If the voltage drop on the same bus increases, it affects other loads as well, so the system should be designed so that the voltage drop is as low as possible. Although the previous research focused on improving the induction motor start-up method, this research introduces a method that can improve the voltage drop through the change of the capacity of the transformer. Therefore, in this study, we applied the calculation method of the capacity of the emergency generator to the transformer and analyzed the voltage drop that occurs automatically when the induction motor is directly started. In order to verify the analysis, it was confirmed that the actual circuit was very similar as a result of comparative analysis by applying an analytical method and an analysis program.

Modelling of soft starters for automated electric drive

In this paper we investigated the conditions of favorable start-up of fixed-speed induction motors in order to increase the functional reliability of the engines. The methods of controlled soft start of induction electric motors with a squirrel-cage rotors are investigated. The study of the mathematical model of induction motors for determining the dependencies of reducing the dynamic component of the transient electromagnetic moment and the magnitude of the starting current. A computer simulation to identify the effectiveness of different methods of controlled start-up of induction motor was carried out. To generate the starters’ models, the MatLab modelling application, Simulink and SimPowerSystems block libraries were used. Based on the results of transient processes simulation in MatLab, the comparative characteristics for different methods of starting an induction motor were given.

Magneto-structural simulation of an induction motor start-up using nodal magnetic forces in Elmer

For reduction of vibrations and noise of electrical machines, the computation of the magnetic force distributions and the ensuing deformations are needed. Here we utilize nodalforce method in open-source Finite Element software Elmer to compute the force distributions and the vibrations of an induction motor during start-up.

Development of a device providing resource-saving start-up of induction motors under reduced voltage

Electromechanical and thermal transients at start-up of squirrel-cage induction motors in reduced voltage conditions are the object of research. One of the most troubled places in these processes is sufficient difficulty diagnosing of resource consumption of induction motors with heavy start-up in reduced voltage conditions and timely facilitation of such regimes with a view to resource saving. To determine the diagnostic parameters of starting modes for induction motors at reduce of supply voltage it is necessary to identify the dependence of start-up duration depending on the parameters of the «motor – working machine» system and their impact on the thermal insulation wear in motor during period after start-up. Therefore, the main way to increase the operational reliability of induction motors is to develop technical device for diagnostics of additional thermal insulation wear in induction motor. We use such methods as: analysis method and mathematical modeling method. It is grounded that pulse of squared starting current can take as diagnostic parameter of additional thermal insulation wear of induction motor. Investigation of thermal insulation wear shows that the thermal transient at the start-up is adiabatic. Main thermal insulation wear is during period after start-up. The dependence of additional thermal insulation wear on the pulse of squared electric current of induction motor allows to select pulse set point of squared starting current of proposed device, which will facilitate the starting mode of the motor. A structural diagram of the device for diagnostics of additional thermal insulation wear in squirrel-cage induction motor during period after start-up is proposed.

Advanced Rotor Fault Diagnosis for Medium-Voltage Induction Motors Via Continuous Transforms

A number of field case studies for rotor fault diagnosis on medium-voltage induction motors operating in a petrochemical plant are presented in this paper. The methodology employed is based on analyzing the induction motor startup current with advanced signal processing tools (continuous transforms) that enable a capture of a “complete picture” of the rotor condition. Indeed, unlike the classical tools that often rely on the detection of few fault frequencies, these new tools allow extraction of the evolution of a wide range of fault components during the startup transient and steady-state evolutions, which enables improved reliability. This is crucial in medium-high-voltage motors, where a false diagnosis may result in significant expense due to inspection, repair, or forced outage. An additional contribution of the study is its immunity to external voltage supply disturbances, which introduce components that are not related to the failure and which are difficult to detect with classical tools. The results of this study prove how the advanced continuous tools enable an improved visualization of the fault components, distinguishing them from the other components that are not linked to the failure.

A proposal for the study of voltage sag in isolated synchronous generators caused by induction motor start-up

This study presents a proposal based on controlled capacitor switching at the moment of three-phase induction motor start-up, when such motors are fed by isolated synchronous generators. This procedure allows for the mitigation of voltage sag that occurs during this transitory period, since a large portion of the reactive power requested during the motor start-up is provided by capacitor banks, thereby relieving a portion of current from the synchronous generator, and with it mitigating the voltage sag. Traditionally, oversizing of the generator was used, under the pretext of mitigating voltage sag. This proposal represents not only an economy, but also power optimization, developed through the motor-generator group, leading to a greater working life.

Pursuing optimal electric machines transient diagnosis: The adaptive slope transform

The aim of this paper is to introduce a new linear time-frequency transform to improve the detection of fault components in electric machines transient currents. Linear transforms are analysed from the perspective of the atoms used. A criterion to select the atoms at every point of the time-frequency plane is proposed, taking into account the characteristics of the searched component at each point. This criterion leads to the definition of the Adaptive Slope Transform, which enables a complete and optimal capture of the different components evolutions in a transient current. A comparison with conventional linear transforms (Short-Time Fourier Transform and Wavelet Transform) is carried out, showing their inherent limitations. The approach is tested with laboratory and field motors, and the Lower Sideband Harmonic is captured for the first time during an induction motor startup and subsequent load oscillations, accurately tracking its evolution.

회전속도에 따른 유도기의 무효전력 변화 분석

Induction machine requires a rotating magnetic field for energy conversion. The current to generate a rotating magnetic field is the magnetization current. This magnetization current corresponds to the reactive power. Reactive power is higher than active power at start-up of induction motor. As the rotation speed is increased, their magnitudes are reversed each other. The active power is higher than the reactive power at near the synchronous speed. This paper is dealing with the analysis result for the changes of the magnetizing current and reactive power when the induction machine is operating as a motor or generator near synchronous speed.

A soft-startup device for an induction motor with supply-network voltage control

The use of a thyristor voltage converter to limit voltage dips during the induction motor startup is considered. It is shown that the traditional solution—the current-cutoff startup mode—does not solve the problem of maintaining the residual voltage at supply-network bars during the motor startup at a level, at which the uninterrupted operation of other equipment connected to this supply network is provided. To limit the voltage dips during the startup, it is necessary to control the supply voltage during the startup. A control-system structure of the thyristor soft starter, which implements a closed loop of supporting the supply-network voltage during the startup, and the synthesis procedure of a controller in this structure are proposed. It is shown that the controller, which is created based on a simplified object model, gives acceptable results in practical use. Results of modeling and experimental data that show the operability of the proposed approach are presented. The desired supply-network voltage is directly set to the input in the system with the voltage control, and the possibility of maintaining this voltage during the induction-motor startup with the structural and parametric variations in the supply network and load is provided with high accuracy and adequate quality of transient processes.

Analysis of transients at startup of cage induction motor: Acceleration stage

For the in-depth analysis of transients in a rotating induction motor the method of constant velocity is proposed, which allowed us to obtain analytical expressions for the currents and electromagnetic torque of the motor when selecting the d-q model as a starting point. The results of the theoretical analysis of transient currents and electromagnetic torque at the startup of the induction motor with a cage rotor are shown and the influence of the motor rotational frequency on them is determined. The results of the computer simulation of the induction motor startup confirm the validity of the analysis using the method of constant velocity.

TORQUES IN INDUCTION MACHINES DUE TO LOW-FREQUENCY VOLTAGE/CURRENT HARMONICS

Harmonic torques in induction machines can be generated by spatial and time harmonics. Stator and rotor slotting, rotor eccentricity, and multiple armature reactions cause space harmonics. Time harmonics originate in the non-sinusoidal wave shape of the terminal voltage. In addition, the interaction of space and time harmonics may generate side-band frequency torques, which can be of integer, non-integer (inter, fractional), or sub-harmonic order h within the frequency range from 0 to 60 Hz - appearing within the fundamental torque characteristic near zero speed. This paper analyzes and computes harmonic torques of induction machines due to low-frequency (f h < 60 Hz) components of the terminal voltage/current. The analysis suggests that the amplitude of low-frequency voltage/current harmonics must be restricted to a few percentage of the fundamental voltage not to jeopardize the start-up of induction motors.

Applications of the Fault Decoupling Device to Improve the Operation of LV Distribution Networks

The aim of this paper is to present the operating principle of a new resonant device, called the fault decoupling device (FDD), able to improve power quality in electrical distribution systems. In low-voltage networks, this device can be employed in order to mitigate voltage dips due to faults or large induction motor startup. Moreover, in the presence of distributed-generation (DG) units, the FDD allows one to obtain various benefits such as a reduction of the fault current in each node of the network and an increase in the voltage at the DG unit node. In order to show the performances of the FDD, analytical studies and computer simulations were carried out which took into account various working operation conditions. Finally, the prototype of the FDD as well as the preliminary experimental results are presented.

Self-excited induction generator controlled by a VS-PWM bidirectional converter for rural applications

This paper concerns an application of a three-phase cage induction machine (IM) as a self-excited generator connected to the AC side of a voltage-source PWM bidirectional inverter. The generator is supposed to be driven by a low-head unregulated shaft hydraulic turbine. The proposed system is intended to be applied in rural plants as a low-cost source of high-quality AC sinusoidal regulated voltage with constant frequency. Simulation results are obtained based on the /spl alpha//spl beta//spl gamma/ stationary reference frame model of the IM. The experimental results demonstrated that the system presents satisfactory behavior when feeding AC loads and during the startup of induction motors.

COMPREHENSIVE METHOD FOR TRANSIENT MODELING OF SINGLE PHASE INDUCTION MOTORS INCLUDING THE SPACE HARMONICS

ABSTRACT In this paper a method which enables the simulation of single phase induction machines during transient as well as steady state is presented. The approach, based on the winding functions, makes no assumption as to the necessity for sinusoidal MMF and therefore include all space harmonics in the machine. The parameters of the model are directly calculated from the geometry and winding layout of the machine. The results are shown to be in good agreement with the solution obtained by a conventional d-q model for symmetric conditions. However, the developed method is then extended to include the effect of skewing of the rotor bars. Furthermore, the effect of stator and rotor slot numbers on the single phase induction motor start-up is explored.

Static VAR compensators for reducing energy losses in large industrial loads

Fast and controlled regulation of voltage and reactive power may be obtained in large industrial installations which include repetitive or frequent start-up of induction motors by using static VAR compensators (SVCs) to control start-up time and inrush transient current and to maintain consumed and reactive power at minimum levels. Consequently, reduced energy losses and kW generation savings are expected. For a typical industrial load, these savings are evaluated quantitatively and are proved to be sufficient to justify the application of SVCs for energy saving purposes, accompanied by whole system performance improvements. Matching of reactive power demand during normal running conditions contributes to a decrease in energy loss and to increases in motor currents and torques.