Influence Of Load Characteristics Research Articles

Influence of Load Characteristics on Three-Phase Short Circuit and Demagnetization of Surface-Mounted PM Synchronous Motor

Three-phase short circuit (3PSC) is a critical condition that may cause irreversible demagnetization of surface-mounted permanent magnet synchronous motor (SPMSM). In the literature, 3PSC current was often calculated under constant rotor speed condition. However, due to the disturbance of current and electromagnetic torque during 3PSC, the rotor speed usually changes, which influences 3PSC current and electromagnetic torque in turn. This article investigates the 3PSC responses and demagnetization of SPMSM under typical types of loads, such as gravitational lift torque (GLT) load, dry fiction torque (DFT), viscous friction torque (VFT), torque square of speed (TSS), and constant power (CP) load etc. It shows that different load types can lead to different 3PSC responses and demagnetization. Moreover, since the d-axis short circuit (SC) current is more detrimental to demagnetization, this article focuses on the influence of different load characteristics on the d-axis peak SC current. The investigation shows that the d-axis peak current under GLT load can be larger or smaller than that under constant speed load, whereas the 3PSC currents under DFT, VFT, TSS, and CP loads are all smaller than that under constant speed load. In addition, the influence of initial q-axis current, temperature, and machine dimension on the d-axis peak SC current is also investigated. According to the analysis results, some guidelines are given for the demagnetization check when designing an SPMSM. Furthermore, experiments are conducted to validate the theoretical analysis.

Analysis of the influence of train load characteristics on the water damage of slab tracks

High-speed train load is one of the main factors that causes the failure of a slab track and is also the direct cause for producing water pressure in the cracks. Hence, choosing the right loading method is the key to analyze the water damage of slab tracks. In order to identify the distribution characteristics of the vertical force acting on the slab track, the analytic expression of fastener load was derived, and the field test was conducted to verify the theoretical model. According to the distribution characteristics of fastener load and the area of crack filled with water, the loading method was presented to analyze the water damage of slab tracks, and the influence of loading characteristics on the hydrodynamic pressure and crack propagation was analyzed. The results show that the distribution of fastener load in the main affected zone approximately accords with the Gaussian distribution under the single wheel load. When under the action of double wheels, the superimposed effect makes the second derivative of the loading function to increase by 99.93%. The superimposed effect of three or more wheels is less than 1% and can be ignored. Considering that the hydrodynamic pressure is highly sensitive to the second derivative of loading function, the load applied on the track slab should be in the form of a bogie, and different loads should be applied step by step based on the time series. The distribution of hydrodynamic pressure along the crack is approximately equal to the cubic polynomial, and the pressure peak appears at the crack tip. Also, the pressure is proportional to the square of the running speed of the train. In the region with abundant rainwater and a poor drainage system, reducing the train speed and taking timely measures such as grouting can effectively reduce the water damage of slab tracks.

Research on the Influence of Load Characteristics of Distributed Power Grid on Electric Energy Metering

As a large number of Distributed Generation Connecting Electric Grid put into operation, there are many impacts on power metering of power grid due to the problems of large fluctuation of load and frequent reverse of power, injecting DC component and harmonic component into power grid, generating voltage deviation, voltage fluctuation and flicker, and voltage unbalance. Measurement accuracy of traditional metering devices is difficult to guarantee. Therefore, the adaptability of traditional metering devices in the distributed power grid environment and the improvement of new technical methods to the Distributed Generation Connecting Electric Grid need to be studied. In this paper, through the analysis of the field operation data, it is proposed that the load fluctuation and frequent reverse of power can be solved by using the bidirectional and wide-range metering gateway meter; by analyzing the influence of the secondary transformer on the DC component, it is proposed that the influence of the DC component on the power metering can be almost ignored under the 0.5% DC component injection of the Distributed Generation Connecting Electric Grid. By analyzing zero flux technology, phase matching technology and high frequency sampling technology, a method to solve the problem of synchronous sampling of voltage and current under the influence of harmonics is proposed. By analyzing the point product and harmonic algorithm, the sampling rate requirement of accurate measurement of electric energy is proposed. A series of reasonable technical means and requirements are put forward in this paper, which greatly improves the power metering problem under the Distributed Generation Connecting Electric Grid.

Grey Relational Grade Based Quantitative Analysis of the Factors Influencing the Load Characteristics of A Power Grid

Regarding analysis of load characteristics of a power grid, there are multiple factors that influence the variation of load characteristics. Among these factors, the influence of different ones on the change of load characteristic is somewhat different, thus the degree of influence of various factors needs to be quantified to distinguish the main and minor factors of load characteristics. Based on this, the grey relational analysis in the grey system theory is employed as the basis of mathematical model in this paper. Firstly, the main factors affecting the load characteristics of a power grid are analysed. Then, the principle of quantitative analysis of the influencing factors by using grey relational grade is introduced. Lastly, the load of Guangzhou power grid is selected as the research object, thereby the main factor of temperature affecting the load characteristics is quantitatively analysed, such that the correlation between temperature and load is established. In this paper, by investigating the influencing factors and the degree of influence of load characteristics, the law of load characteristics changes can be effectively revealed, which is of great significance for power system planning and dispatching operation.

Interface behavior of a bi‐material plate under dynamic loading. Cohesive interface debonding

The paper deals with the elastic and cohesive interface behavior of pre‐cracked bi‐material ceramic‐metal structures under dynamic time harmonic load. The shear lag model as well as the Fourier method is applied to find the dynamic response of the considered bi‐material structure, assuming the cohesive interface behaviour, accompanied before of the elastic‐brittle one. In both cases, the growth of debond length is not considered, e.g. at a given loading condition the only corresponding debond length is found. The inertia forces of the already elastic debond parts of the bi‐material structure are neglected. Appropriate contact conditions are proposed in order to fit together both elastic and cohesive solutions. The numerical predictions for the cohesive debond length of the bi‐material structures is calculated by the aid of the corresponding value of the elastic debond length at the same loading condition. The influence of loading characteristics i.e. frequencies and amplitude fluctuations on the debond length and the interface shear stress distribution is discussed. The parametric analysis of the results obtained is illustrated by examples of the modern ceramic‐metal composites on metal substrates and is depicted in figures.

Precracking and interfacial delamination in a bi-material structure: Static and dynamic loadings

The behavior of a precracked bi-material structure interface under given static and dynamic axial loading is an interest object in the present paper. Firstly, it is shown that the shear-lag model is a proper tool to analyze a delamination process in a precracked bi-material structure undergoing static loading. Secondly, the “shear-lag model” is applied to the structure under dynamic loading. To solve the problem for an interface delamination of the structure and to determine the debond length along the interface, our own 2D boundary element method (BEM) code is proposed in the case of static loading, and the shear-lag model together with the Laplace transforms and half-analytical calculations are used in the case of dynamic loading. The interface layer is assumed as a very thin plate compared with the other two. The parametric (geometric and elastic) analysis of the debond length and interface shear stress is done. The results from the 2D BEM code proved the validity of analytical solutions to the shear-lag model. In the dynamic case, the influence of loading characteristics, i.e., frequencies and amplitude fluctuations on the shear stress and the value of debond length for an interval of time, is discussed. The analysis of the obtained results is illustrated by an example of the modern ceramic-metal composite, namely cermet, and depicted in figures.

Interface delamination of bi‐material structure under dynamic time harmonic loading

AbstractThe interface behaviour between two layers of 2D elastic structure under dynamic time‐harmonic load is studied. The “shear lag model” is adopted and applied to the dynamic response of bi‐material structure, assuming the elastic‐brittle behaviour of the interface. The Laplace transforms together with half‐analytical calculations are used to obtain the shear stress and elastic debond lengths along the interface at sinusoidal load. Parametric analysis of the obtained results is illustrated by an example of the modern ceramic‐metal composite, so called cermet, and depicted in figures. The influence of loading characteristics, i.e. frequencies and amplitude fluctuations on the shear stress and the value of debond length for a small interval of time, is discussed.

Influence of load characteristics on the power/voltage stability of HVDC systems. I. Basic equations and relationships

The influence of load characteristics on the power stability of a specific HVDC system configuration has been shown. This points to a more fundamental influence of load characteristics on the power/voltage stability of HVDC systems in general. Thus, a fundamental analysis of the influence of load characteristics on the power/voltage stability of three typical HVDC system configurations is carried out in this two-part work. Three aspects are treated; (i) the basic power/voltage stability equations incorporating load characteristics, the effect of load characteristics and system parameters; (ii) the relationships between the maximum power and voltage sensitivity based methods for all the configurations incorporating load characteristics; and (iii) the most unfavourable load characteristics with respect to degrading power/voltage stability margins and the sensitivity of these margins to load characteristics. This paper presents points (i) and (ii) while part II deals with point (iii).

Dynamic stability and optimal excitation control of doubly excited synchronous machine: Influence of load characteristics

Abstract This paper is concerned with the effects of connected loads on the optimal excitation control and dynamic stability of power systems, incorporating doubly excited synchronous generators. The system studied is made up of a generating unit with local load and a transmission line connecting the machine to an infinite bus. A number of operating conditions are examined, and different system parameters used in order to identify effects attributable to the regulators, tie-line reactance, and the characteristics of the local load. For purposes of comparison, corresponding results of dynamic stability studies are also presented for the system with a conventional synchronous machine.