Detection and classification of single and combined power quality disturbances using fuzzy systems oriented by particle swarm optimization algorithm

This paper presents the results of an experimental study on derating of an induction motor under different voltage unbalanced conditions and its comparison with the NEMA standard MG1 voltage unbalance derating graph. During the derating tests the 4 kW squirrel cage induction motor temperature rise was kept constant at the rated value and the windings temperature was measured on-line by means of an accurate digital thermal monitoring system with nine thermocouples positioned in both stator and rotor circuits. The obtained results show that the positive sequence voltage plays an important role in the derating performance of the induction motor under unbalanced conditions, and that the unbalance voltage indices currently used do not allow for accurately measuring this influence.

Experimental study of the effect of positive sequence voltage on the derating of induction motors under voltage unbalance

This paper analyzes the voltage notches in ac/dc converters and the problems that they create. Voltage notch disturbs the voltage's waveform and excites the natural frequencies of the system. In some systems, these excisions create considerable high-frequency oscillations in the voltages of the converter and the adjacent buses; this can damage capacitor banks, create parallel resonance, and generate radio disturbances. This paper analyzes the effect of snubber circuits on the voltage oscillations that arise from commutation. It also presents the theoretical foundation and analytical derivation that are used to calculate notch depth and the frequency of oscillations. To achieve accurate and applicable results, various loads of the converter, the dc current ripple, and the characteristic impedance of the system are considered. Several experimental results are shown in order to illustrate the effects of changes in the system and converter parameters on the voltage waveform of the converter. Computer simulations and experimental results indicate the accuracy of the theoretical relations. The proposed equations make it possible to effectively study the harmonic and power quality in networks that include high-power converters.

/pdf/evaluating-voltage-notch-problems-arising-from-ac-dc-2356whws79.pdf

Evaluating Voltage Notch Problems Arising from AC/DC Converter Operation

This paper presents a study of the influence of the positive sequence voltage on the derating of three-phase induction motors under voltage unbalance and its comparison with the NEMA derating curve. Three criteria for derating induction motors under unbalanced voltages are presented: the rated current, the rated equivalent current and the rated losses. These criteria are theoretical and experimentally analyzed. A 4 kW three-phase induction motor was used in the study. The paper suggests that the positive sequence voltage must be considered together with the Voltage Unbalance Factor VUF (or Percent Voltage Unbalance PVU) index for derating purposes. If only the VUF (or PVU) index is taken into account, a facility user cannot appropriately derate the motor.

Influence of the positive sequence voltage on the derating of three-phase induction motors under voltage unbalance

This paper presents a generic hybrid optimization methodology based on space mapping techniques for the design of various high voltage pulse transformer structures used in klystron modulators. It is using two dimensioning models with different levels of complexity: a coarse model based on 2D FEA less accurate but cheaper to evaluate and a fine 3D FEA model more accurate but time consuming. A specific correction mechanism is applied to align the 2D FEA dimensioning model with the more accurate 3D FEA dimensioning model. With a suitable selection of the correction factors, the convergence of this hybrid optimal design methodology is obtained with a limited number of time consuming 3D FEA simulations. The method is applied to the optimal design of a monolithic high voltage pulse transformer for the CLIC klystron modulator. The influence of the klystron operating voltage on the size of the optimal pulse transformer is evaluated with the proposed design methodology.

/pdf/hybrid-design-optimization-of-high-voltage-pulse-1x2ith4588.pdf

Hybrid design optimization of high voltage pulse transformers for Klystron modulators

High voltage and high frequency pulses are widely used in industrial applications such as klystron modules, radar application, plasma technology, and so on. Transforming such a pulse with magnitude of thousands volt requires special transformers. Considering its frequency requirements which vary from hundreds to thousands Hertz, effects of parasitic capacitance may change the expected results. In this paper a specific method is proposed to optimize the design of both high voltage (HV) and low voltage (LV) windings, to reach the best rise time and overshoot performance. This method is based on both calculations of equivalent circuit and finite element analysis (FEA). Among the various topologies represented in the literatures, cone winding type pulse transformer is selected in which by changing its windings angle, it can be modified to parallel winding type. Initially analytical study in pulse transformer rise time equivalent circuit is performed to find the best cone angle between the windings and also the best distance between the bottom of windings to reach the optimum output parameters of pulse transformer such as fast rise time and minimum overshoot. In this analysis the lumped parameters of the equivalent circuit are calculated based on the stored energy between the windings. Afterwards sensitivity of the response to the load and source parameters variations is calculated in order to find the best distance and the angle between the windings. In the meantime, the distributed parasitic capacitances are extracted by using FEA to exert as circuit elements, in the electromagnetic model of pulse transformer. Finally a transient analysis is executed on the pulse transformer model containing distributed capacitances. The results of this analysis prove that the winding design using the distributed elements effects shows good results considering pulse shape.

Optimal winding design of a pulse transformer considering parasitic capacitance effect to reach best rise time and overshoot

The losses in electrical machines causes decreasing of machine lifetime and breaking down of insulation. Therefore, in order to extend the insulation life, it is critical to monitor the stator and rotor temperature and protect the motor under thermal overloading conditions. However, the stator winding and insulation is designed for safety operation but the winding temperature can be risen under special conditions such as motor stall, jam, overload, unbalanced operation, and situations where the cooling ability of the motor is accidentally reduced. In this study the effect of unbalance supplying voltage on the motor temperature rising has been investigated. For this purpose, by construction of the rotor and stator monitoring system, different unbalancing types have been applied on the 1.1 kW / 50 Hz/ 1400 rpm motor and by doing different tests such as lock rotor, no-load and etc the effect of any type of unbalancing on the temperature rising has been investigated.

Investigation of unbalance supplying voltage on the thermal behavior of Squirrel Cage Induction motor using monitoring system

A new method for computing convection heat transfer coefficients in axial flux permanent magnet synchronous machines (AF-PMSMs) is introduced. The method is based on a two-step finite element analysis (FEA). In the first step, a simple 2D model is introduced and fluid flow and temperature fields are studied using computational fluid dynamic (CFD) technique. Convective heat transfer coefficients for all heat transfer surfaces of the model are extracted from CFD analysis and are then used as inputs to a 3D thermal finite element model. Two case studies are considered to check the accuracy of the abovementioned two-step method. One of the case studies is an air-cooled AF-PMSM that has air inlet and outlet on its enclosure and the other case is a totally enclosed AF-PMSM. The correctness of the mentioned method is verified by practical measurements on the second case. In addition, an experimental set-up is conducted to measure the temperature of different parts of the second case. It is observed that the results of the two-step CFD-FEA model are in good agreement with the experimental data. In the other case, the effect of inlet air velocity on heat transfer coefficients, as well as the thermal behaviour of the machine are explored.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-epa.2019.0514

New finite element based method for thermal analysis of axial flux interior rotor permanent magnet synchronous machine

In this paper, voltage notch have been analyzed based on theoretical equations at during commutation time of a AC/DC converter. Depth of voltage notch in the converter busbar, depend on several parameters: feeder system impedances (Xs), converter impedance that placed between feeder and converter (Xt) and fire angle of controllable converters (Figure 1). By the way, characteristics variation of notch depth and wide according to system impedances and DC current of converter load, are presented. Main matter of this paper, discuss about oscillation frequency of converter voltages during commutation time. These frequencies depend on system impedances size (Xs+Xt), capacitor banks in network and capacitors size of snubber circuits. In final conclusion experimental results that obtained from a controllable AC/DC converter have been compared with simulation and theoretical results.

The problems of voltage notch phenomena in power AC/DC converters

In this paper Islanding fault of rectifier and inverter substations are studied in HVDC system both in back to back and long transmission line systems. The effect of system short circuit ratio (SCR), are studied too. System’s controller action, pulse blocking of faulty converter and rectifier changing operation to inversion mode are three control schemes that studied here. Finally the results compared with each other and with system that has no control action and the best method for each fault are determined. All of these simulations are done using MATLAB- SIMULINK.

D. Habibinia

Papers

Optimal winding design of a pulse transformer considering parasitic capacitance effect to reach best rise time and overshoot

Investigation of unbalance supplying voltage on the thermal behavior of Squirrel Cage Induction motor using monitoring system

New finite element based method for thermal analysis of axial flux interior rotor permanent magnet synchronous machine

The problems of voltage notch phenomena in power AC/DC converters

Study of inverter and rectifier substations islanding fault in HVDC system, and comparison between different control-protective methods