Total Unbalance Research Articles

Distortion and Unbalance Assessing Indices Using Commercial Analysers

Power quality monitoring is assuming an increasing importance because of the large diffusion of nonlinear and time-varying single-phase and three-phase loads and their interactions with the power supply system. This has made that the industrial electrical consumer systematically uses measure equipment to evaluate the electric power quality. The measurements show that the harmonics of the waveforms are variable along with the time due to the changes in the load conditions and in the system configuration. Thus, the electrical users dispose of a great quantity of data from such of the three phases of the supply. Therefore, it is necessary to find a way to characterize this great group of registered data. Thus, the objectives of this work are: firstly, to propose two indices, a three-phase total demand distortion index and a three-phase total unbalance index; secondly, this paper proposes a simple way to characterize the groups of data in an statistical way which make easy its representation. The study carried out is applied to the data recently registered in an electrical power system.

Modal balancing for ball bearing-rotor system using nonlinear normal modes

Rotor dynamic balancing procedure relies on the linearisation hypothesis of the rotor system. However, some mechanical elements constituting a rotor system behave in various nonlinearities, such as the contact force and radial internal clearance between rolling balls and races for a rotor-bearing system. To balance a nonlinear rotor system, the traditional modal balancing method must be extended. This paper investigates the modal balancing method for a rotor-bearing system based on nonlinear normal modes (NNMs). The proposed algorithm includes three main steps. First, compute the NNMs and express nonlinear modal shapes using complex Fourier series. Second, describe the unbalance response as a complex amplitude containing higher harmonics. Third, estimate the correction coefficient of each harmonic, then compute the unbalance correction of each mode of interest until the total unbalance corrections are obtained. Hertz contact force and two different sizes of radial internal clearances of the ball bearings are considered during the balancing simulation. The responses after balancing with NNMs are present and compared with the linear modal method to demonstrate the accuracy and effectiveness of the proposed method.

Unbalanced Source Detection in Power Distribution Networks by Negative Sequence Apparent Powers

Distribution network unbalanced operation is among crucial power quality concerns. Detecting the unbalance sources and their contribution to the network total unbalance with high precision is a prerequisite to alleviate this challenge. To do so, this letter proposes a new method based on load and branch negative sequence apparent power vectors. The inner product decomposition algorithm is employed to specify the contribution of each downstream unbalanced load on a given branch or node unbalance index. Accordingly, the unbalanced loads compensating for the others can also be discriminated. Referring to simulations, the proposed method outperforms the existing techniques in terms of efficiency and accuracy.

Optimal Operation of Active Distribution Network Involving the Unbalance and Harmonic Compensation of Converter

The massive accessing of unbalance and nonlinear loads to a power distribution network may cause serious problems on power quality and result in additional power loss and safety risks. Distributed generation (DG) with a converter interface has a flexible adjusting ability and can provide certain unbalance and harmonic compensations to power distribution networks. In this paper, an optimal operation method of an active distribution network (ADN) involving the unbalance and harmonic compensation of a converter was proposed. First, the power regulating characteristics of DG were analyzed. Second, an optimization model was constructed to minimize ADN power loss, sum of harmonic voltage squares, and total unbalance of the negative sequence voltage, and multiple constraints, such as converters and network, were considered in the model. Third, the optimization model was transformed into a semidefinite programming model based on the characteristics of the nonconvex and nonlinear original model, thus assuring global convergence and decreasing difficulties in problem solving. Finally, the validity of the proposed algorithm was verified by using IEEE 33-node and 123-node test systems.

Multiple-degree-of-freedom rotor model with total unbalance and possible contact on stator

Mathematical model for the flexible rotor which has static and dynamic unbalance and enabled slip rolling on the compliant stator is developed. Also, rotation inertia, gyroscopic effect, bearings characteristics, internal hysteresis, and external viscous friction are included. The matrix approaches are used. The proposed model allows investigating the dynamic effect of total unbalance and stator displacements as an elastic and solid body on basis of the ordinary differential equations.

A novel feeding topology for DC electric arc furnaces utilizing PWM-AC choppers

SUMMARY The main contribution of this paper is the study of a new feeding system for direct current (DC) electric arc furnaces. This system includes pulse-width modulation-alternating current (PWM-AC) choppers along with six-pulse diode rectifier. In contrast with traditional power supplies such as 12-pulse thyristor-based rectifier and 12-pulse diode rectifier–DC chopper-based power supplies, the proposed configuration stands out because of the reduced number of rectifier units and output reactors. Furthermore, the proposed power supply system is free of any current/power-sharing problems, and only one proportional-integral controller is sufficient to control the DC arc current or its power. It is shown through analysis and simulation that in comparison with traditional feeding systems, the proposed topology can lead to smaller input filter size, total unbalance and harmonic distortion reduction, and power factor improvement. Copyright © 2012 John Wiley & Sons, Ltd.

New Distortion and Unbalance Indices Based on Power Quality Analyzer Measurements

Voltage and current waveform distortion are more prevalent on power systems today related to nonlinear loads. The proliferation of loads of this kind and their interaction with the power supply system is increasing the need to use power monitoring equipment to evaluate electric power quality. Measurements show that waveform harmonics and unbalance are variable over time due to changes in load conditions and in the system configuration. Thus, the electrical engineer has a large amount of data available from each phase, acquired using commercial Analyzers. Therefore, it is necessary to find ways to characterize this group of recorded data, to allow proper evaluation of the situation. Two indices, which can be calculated with these measurements, are proposed in this work: a three-phase total demand distortion index and a total unbalance index. In addition, this paper proposes an easy way to characterize the time-varying data to simplify their representation. The exposed procedures are applied to the data registered from an electrical power system, to show the performance of the proposed methods.

Traction System Unbalance Problem—Analysis Methodologies

This paper presents a novel methodology using a utility's existing software for the accurate prediction of total unbalance (UB) impact due to ac traction loads with emphasis on the estimation of negative sequence (N-Seq) current injection into utility generators. Traditionally, due to the requirement of complex 3/spl Phi/ power-flow simulation, UB analysis has been limited to the evaluation of UB voltage at the point of common coupling (PCC) without addressing whether supply of this N-Seq current would exceed the remaining margin of each utility generator. By using the salient feature that a utility's N-Seq network is basically "sourceless" as such for any N-Seq current injection at a specific node, the "contribution ratio" of each utility generator for that N-Seq current injection is fixed irrespective of the magnitude of that injection, this paper provides a solution to this important problem by using a utility's existing fault analysis software.

Evaluating power system unbalance in the presence of harmonic distortion

This paper presents a new method to evaluate power system unbalance in the presence of harmonic distortion. The balanced, the first unbalanced, and the second unbalanced components are obtained from the original three-phase current and voltage phasors of each harmonic component. The equivalent root-mean-square (RMS) value of three-phase voltage and current is then decomposed into the balanced fundamental, the unbalanced fundamental, the balanced harmonic, and the unbalanced harmonic components. The same decomposition is applied to the apparent power, and the system unbalance can then be evaluated through the proposed system total unbalance distortion factor. The unbalanced fundamental, the balanced harmonic, and the unbalanced harmonic distortion factors are defined. These distortion factors clarify the interleaving between the unbalance and harmonic distortion, and are suitable for unbalance evaluation in the presence of harmonics. Numerical examples are also presented to illustrate the application of the proposed method on the study and characterization of unbalance in power systems.

Evaluating Power System Unbalance in the Presence of Harmonic Distortion

This paper presents a new method to evaluate power system unbalance in the presence of harmonic distortion. The balanced, the first unbalanced, and the second unbalanced components are obtained from the original three-phase current and voltage phasors of each harmonic component. The equivalent root-mean-square (RMS) value of three-phase voltage and current is then decomposed into the balanced fundamental, the unbalanced fundamental, the balanced harmonic, and the unbalanced harmonic components. The same decomposition is applied to the apparent power, and the system unbalance can then be evaluated through the proposed system total unbalance distortion factor. The unbalanced fundamental, the balanced harmonic, and the unbalanced harmonic distortion factors are defined. These distortion factors clarify the interleaving between the unbalance and harmonic distortion, and are suitable for unbalance evaluation in the presence of harmonics. Numerical examples are also presented to illustrate the application of the proposed method on the study and characterization of unbalance in power systems.

Design and Performance of Compliant Thrust Bearings With Spiral-Groove Membranes on Resilient Supports

Novel thrust bearings, with spiral-groove, flexible membranes mounted on resilient supports, were designed and their performance convincingly demonstrated. Advantages of surface compliance were thus combined with the superior load-capacity of the spiral-groove geometry. Loads of 127–150N (29–33 lb) were comfortably supported on an area 42 cm2 (6.5 in.2), at speeds 43,000–45,000 rpm and mean clearances 15–20 μm (600–800 μin.), by these self-acting and air-lubricated bearings. Support-worthiness was proved under exacting conditions, when tested in conjunction with foil journal-bearings and a 19N (4.3 lb)-rotor, excited in a pitching mode by a total unbalance of 43 μm.N (6100 μin.oz).

高速度ミシンの不釣合と振動(第1報)

Unbalance and vibration of a Japan-made sewing machine (DDW-Type) were studied. Both the needle and its holder of this machine move up and down in its running condition, and therefore they produce unbalane force in its vertical direction. This unbalance force may, however, be cancelled by attaching a certain balance weight to its mainshaft, but by this attached balance weight a new unbalance force may be produced in the horizontal direction. Theoretically we are able to make the total unbalance force completely zero in one direction between the two (vertical and horizontal) directions, but at the same time that in another direction becomes maximum. Therefore, the practical sewing machine of DDW-Type is not made to become the state that the total unbalance force in one direction betw een the two may become zero or maximum in its running condition. This sewing machine has several parts of mechanisms, such as feeding mechanism, which move in only one direction. These parts of course produce unbalance forces in its running condition, but it may be seen from aforesaid facts that they cannot be cancelled by attaching any balance weight to its rotation part. All these unbalance forces in the machine were shown in this paper, and also it was found that in DDW-Type machine, the total unbalance forces are respectively equal to 2550 gr-cm in vertical direction, and 130 gr-cm in horizontal direction.