Static Load Model Research Articles

Composite laminate under influence of temperature and moisture

The static response of simply supported carbon/epoxy composite plates in a hygrothermal environment is carried out using the general purpose finite element program COSMOS. The static load model and the hygrothermal incorporation are solved separately. The hygrothermal effect is introduced by using empirical relations for degrading the material stiffness properties of the matrix. The corresponding ply properties are calculated using Mori-Tanaka method. A parametric study is conducted by varying the fiber volume fraction and the fiber orientation of the angle plies in the laminate.

Validation of the Dynamic Amplification Factor in Case of Historic Railway Steel Bridges with Short and Medium Spans

One of the significant parameters in design as well as fatigue assessment of railway bridges is the dynamic factor. The dynamic factor, also called dynamic amplification factor (DAF), must be applied to the static load model in order to take account of dynamic magnification of stresses and vibration effects in the bridge. The dynamic factor which actually enhances the static load effects depends on many parameters that are difficult to take into account with reasonable accuracy. The maximum bridge-span, train speed, self-weight, expansion joints if any is placed in bridge, the type of bridge supports and finally soil–structure interaction are among these parameters. This paper studies the variations of the analytical and experimental observations on steel railway bridge dynamics. For this purpose the measured stresses due to passing a locomotive through a historical steel railway bridge in Germany are compared with the calculated stresses contemplating the dynamic factor proposed by EN1991-2 [1] applied to the static load model of the same locomotive.

An active islanding detection scheme for inverter-based DG with frequency dependent ZIP–Exponential static load model

Abstract In this paper an analytical design method is proposed for constant voltage controlled inverter based DG with frequency dependent ZIP–Exponential static load model to obtain proper inverter output control and successful islanding detection. The proposed technique is aimed to eliminate the dependency of DG operation point on anti-islanding performance which is unavoidable in case of traditional control strategy. The generalized formulae are derived for calculating the upper and lower limits of the voltage gain, and it is recommended to select the voltage gain within the designed range for effective islanding detection. The proposed approach is tested in MATLAB/Simulink environment and result shows that the proposed scheme is found to be highly effective in islanding detection considering complex network configurations with single and multiple DG systems. The proposed control scheme is able to detect islanding within 10 ms (half cycle) from the event inception, showing the fastness of the developed technique. It is also observed that the percentage of voltage and current THD of the proposed scheme is within permissible limits, indicate that the power quality of the inverter is not degraded by the proposed control strategy, and thus overcomes the drawback of existing active anti-islanding techniques.

Fault location in power distribution systems considering a dynamic load model

<span>In the electrical power systems, load is one of the most difficult elements to be represented by an adequate mathematical model due <span>to its complex composition and dynamic and non-deterministic behavior. Nowadays, static and dynamic load models have been <span>developed for several studies such as voltage and transient stability, among others. However, on the issue of power quality, dynamic <span>load models have not been taken into account in fault location. This paper presents a fault location technique based on sequence <span>components, which considers static load models of constant impedance, constant current and constant power. Additionally, an <span>exponential recovery dynamic load model, which is included in both the fault locator and the test system, is considered. This last <span>model is included in order to consider the dynamic nature of the load and the performance of the fault locators under this situation. <span>To demonstrate the adequate performance of the fault locator, tests on the IEEE 34 nodes test feeder are presented. According to the <span>results, when the dynamic load model is considered in both the locator and the power system, performance is in an acceptable range.</span></span></span></span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span><p class="Abstractandkeywordscontent"> </p>

Fault location in power distribution systems considering a dynamic load model

<span>In the electrical power systems, load is one of the most difficult elements to be represented by an adequate mathematical model due <span>to its complex composition and dynamic and non-deterministic behavior. Nowadays, static and dynamic load models have been <span>developed for several studies such as voltage and transient stability, among others. However, on the issue of power quality, dynamic <span>load models have not been taken into account in fault location. This paper presents a fault location technique based on sequence <span>components, which considers static load models of constant impedance, constant current and constant power. Additionally, an <span>exponential recovery dynamic load model, which is included in both the fault locator and the test system, is considered. This last <span>model is included in order to consider the dynamic nature of the load and the performance of the fault locators under this situation. <span>To demonstrate the adequate performance of the fault locator, tests on the IEEE 34 nodes test feeder are presented. According to the <span>results, when the dynamic load model is considered in both the locator and the power system, performance is in an acceptable range.</span></span></span></span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span><p class="Abstractandkeywordscontent"> </p>

Partial factors for loads due to special vehicles on road bridges

The structural standards for bridge design are well calibrated to account for the general traffic loading and expected use of the structure. Consideration of special heavy vehicles on bridges is often regarded according to provisions for the general traffic model in standards that may be, however, inconsistent and problematic due to a number of reasons. This contribution identifies the characteristics of special vehicles and proposes the methodology for calibration of the related partial factors. Key steps of the methodology consist of assessing static load effect, dynamic amplification, model uncertainty, sensitivity factors and target reliability. Careful consideration of these influences then yields partial factors that correspond to the definition of special loading and can be modified to distinguish between design and assessment situations. It appears that the commonly accepted partial factor of 1.35 may be reduced for an increased ratio of permanent- to traffic loads, decreased target reliability and for controlled speed of the vehicle and/or its position on a bridge. When multiple crossings of the same vehicle or vehicles of the same type during a reference period are considered, it is proposed to keep the partial factor independent of the number of crossings while the characteristic value should be adjusted with respect to the expected number of crossings.

Estimation of composite load model with aggregate induction motor dynamic load for an isolated hybrid power system

It is well recognized that the voltage stability of a power system is affected by the load model and hence, to effectively analyze the reactive power compensation of an isolated hybrid wind-diesel based power system, the loads need to be considered along with the generators in a transient analysis. This paper gives a detailed mathematical modeling to compute the reactive power response with small voltage perturbation for composite load. The composite load is a combination of the static and dynamic load model. To develop this composite load model, the exponential load is used as a static load model and induction motors (IMs) are used as a dynamic load model. To analyze the dynamics of IM load, the fifth, third and first order model of IM are formulated and compared using differential equations solver in Matlab coding. Since the decentralized areas have many small consumers which may consist large numbers of IMs of small rating, it is not realistic to model either a single large rating unit or all small rating IMs together that are placed in the system. In place of using a single large rating IM, a group of motors are considered and then the aggregate model of IM is developed using the law of energy conservation. This aggregate model is used as a dynamic load model. For different simulation studies, especially in the area of voltage stability with reactive power compensation of an isolated hybrid power system, the transfer function ΔQ/ΔV of the composite load is required. The transfer function of the composite load is derived in this paper by successive derivation for the exponential model of static load and for the fifth and third order IM dynamic load model using state space model.

Improved modeling of equivalent static loads on wind turbine towers

This study presents a dynamic response analysis of operational and parked wind turbines in order to gain better understanding of the roles of wind loads on turbine blades and tower in the generation of turbine response. The results show that the wind load on the tower has a negligible effect on the blade responses of both operational and parked turbines. Its effect on the tower response is also negligible for operational turbine, but is significant for parked turbine. The tower extreme responses due to the wind loads on blades and tower of parked turbine can be estimated separately and then combined for the estimation of total tower extreme response. In current wind turbine design practice, the tower extreme response due to the wind loads on blades is often represented as a static response under an equivalent static load in terms of a concentrated force and a moment at the tower top. This study presents an improved equivalent static load model with additional distributed inertial force on tower, and introduces the square-root-of-sum-square combination rule, which is shown to provide a better prediction of tower extreme response.

Экспериментальное определение статических характеристик нагрузки электроэнергетических систем

Экспериментальное определение статических характеристик нагрузки электроэнергетических систем

Performance Analysis of Unbalance Radial Feeder with Time Varying Composite Load

The focus of this paper is to present performance indices for unbalance radial feeder having different characteristic and composition of time varying static ZIP load models. These provide a framework for benchmarking of distribution automation projects. 15 minutes characteristics time interval for load flow and load modeling are considered to meet smart grid implementation criterion. A forward-backward sweep method is employed for load flow solution. Developed performance indices were illustrated on modified IEEE 37 node test feeder. Performance indices are useful for analysis, operational, planning and integration of stochastic renewable sources.

Using Static Polynomial Load Models in “Rastrwin” Software Package for Power System Studies

Polynomial load model practical application has some specificity. Per unit static load model dependence on node rated voltage value is demonstrated in this paper. The assigned rated voltage values of load nodes with polynomial characteristics are to be invariant to avoid calculation complementary error appearance. If rated voltage correction is necessary condition, for example to obtain calculation convergence, the active and reactive power drawn under rated voltage and polynomial coefficients must be corrected too. Correcting calculation expressions are presented in the paper.

Modeling and simulation of static loads for wind power applications

This study aims to model and simulate static nonlinear loads with wind power generation to evaluate the impact of load models on wind power systems. Nonlinear loads are modeled as exponential load model, ZIP load model and combination of exponential/ZIP with an induction motor. The wind power generator is represented with a reduced-order doubly fed induction generator (DFIG) model. Developed models have been implemented in a grid-integrated wind power plant and simulated in MATLAB/SIMULINK. The effects of nonlinear loads into wind power plant are investigated in terms of bus voltages, angular speed, electrical torque, and d---q stator axes currents. Additional analyses are conducted to compare the behaviors of full- and reduced-order DFIG models under a selected loading condition. The results of this study indicate that the response of a system with DFIG is dependent of the load modeling and reduced-order DFIG model shows more stable trend than full-order DFIG model.

Static Load Model Determination Using Functional Approximation Based on Gaussian Pulses and its Comparison with ZIP Load Model

This paper describes a static load model based on functional approximation. The functional approximation has been achieved by selecting Gaussian pulses as basis function. Based on this a single layer neural network has been constructed, which can easily trained using δ-rule. A case study has also been reported. The load model as obtained using the proposed neural network has been compared with ZIP load model as obtained by least square estimator.

Dynamic Equivalent Method of Motor Loads for Power Systems Based on the Weighted

Dynamic equivalence can not only largely reduce the system size and the computation time but also stress the dominant features of the system [1]-[3]. This paper firstly recommends the basic concept of dynamic equivalent and the status of both domestic and abroad development in this area. The most existing equivalent methods usually only deal with static load models and neglect the dynamic characteristics of loads such as induction motors. In addition, the existing polymerization method which is based on the frequency domain algorithm of induction electric machines parameters takes a long time to equivalent for the large system, then the new method based on the weighted is proposed. Then, the basic steps for dynamic equivalence with the weighted method are introduced as follows. At first, the clustering criterion of motor loads based on time domain simulation is given. The motors with similar dynamic characteristics are classified into one group. Then, the simplication of the buses of motors in same group and network is carried out. Finally, parameters of the equivalent motor are calculated and the equivalent system is thus obtained based on the weighted. This aggregation method is applied to the simple distribution system of 4 generators. Simulation results show that the method can quickly obtain polymerization parameters of generator groups and the aggregation model retains the dynamic performance of the original model with good accuracy, the active and reactive power fitting error is smaller as well.

Impact of electric vehicle fast charging on power system voltage stability

The electric vehicle (EV) brings a sustainable future for the next generation of automobiles. Market penetration of EV has been increasing drastically in the recent past. However, EV integration into power grids adds more challenges for power system engineers worldwide. It is essential to evaluate potential grid impacts due to EV integration to guarantee consistent grid operation. Even though a number of power system impact studies have been performed covering several aspects of the problem, the impact on voltage stability has remained almost unattended. The lack of accurate load models to represent EV load for system stability studies is found to be a major gap. Hence, a static load model is developed in this study as an essential base for realistic stability studies. A specific EV load behavior which has not yet been revealed in the literature is identified during the study. Subsequently, the influence of EV load on power system voltage stability is evaluated under different scenarios. The study has discovered that integration of EV fast charging stations may significantly reduce the steady state voltage stability of the power grid.

Evaluation of the Effects of Nationwide Conservation Voltage Reduction on Peak-Load Shaving Using SOMAS Data

In this paper we propose a new method to evaluate the effects of nationwide conservation voltage reduction (CVR) on peak-load shaving, using substation operating results management system (SOMAS) data. Its evaluation is based on a national CVR factor, which is defined as the weighted average of CVR factors associated with all transformer banks and weighting coefficients are determined by the reconstructed loads corresponding to each transformer bank. To make use of the data resulting from nationwide CVR without installing additional measuring devices, we adopt a linearized static-load model with a linearizing parameter. SOMAS data are used to evaluate the effects of nationwide CVR on peak-load shaving in the Korean power system. Evaluation results show that the national CVR factor of the Korean power system has small values in the summer season and large values in the winter season. This means that the effect of nationwide CVR on peak-load shaving in the Korean power system presents stronger benefits during winter months.

Approximate Analytical Method of Load-Settlement Relation for Composite Foundation with Lateral Restriction

Considering reinforcement zone and natural foundation as a whole, the displacement component formulas satisfy with the displacement boundary conditions were constructed based on some hypotheses. Considering friction influence under foundation, a approximate analytical algorithm of foundation deformation was established under embankment loads by the variational method of displacement, and the approximate analytical formula on the relationship between the load and the average settlement was derived. The static load model tests were carried out in laboratory to verify the feasibility of this method proposed in this paper. Key words: load-settlement relation; variational method of displacement; embankment load; composite foundation

Studying Voltage Stability in Power System Considering Load Dynamics

This paper investigates on-load tap changer OLTC effect on voltage stability. Chaos theory used in this analysis is via the calculation of the maximum power transmission. Resulted chaotic behavior is exhibited by singular induced bifurcation which clearly shows the voltage stability of the power system with OLTC from a singular induced bifurcation point of view. The paper is organized as follows: 1) increasing in the maximum reactive power via increasing the ratio of OLTC and the possibility of voltage collapse decrease under the same load command. 2) Noting that the voltage instability is directly affected by the load characteristics, shown via the effect of OLTC on the voltage instability under different static load models. 3) Studying voltage stability in state space and the effects of the generator excitation current limit, the OLTC and load dynamics on voltage collapse. In addition, a small-disturbance voltage stability region of a power system is constructed. The voltage stability of the system is determined by the dynamic characteristics of both the OLTC and the load.

Studying Voltage Stability in Power System Considering Load Dynamics

This paper investigates on-load tap changer OLTC effect on voltage stability. Chaos theory used in this analysis is via the calculation of the maximum power transmission. Resulted chaotic behavior is exhibited by singular induced bifurcation which clearly shows the voltage stability of the power system with OLTC from a singular induced bifurcation point of view. The paper is organized as follows: 1) increasing in the maximum reactive power via increasing the ratio of OLTC and the possibility of voltage collapse decrease under the same load command. 2) Noting that the voltage instability is directly affected by the load characteristics, shown via the effect of OLTC on the voltage instability under different static load models. 3) Studying voltage stability in state space and the effects of the generator excitation current limit, the OLTC and load dynamics on voltage collapse. In addition, a small-disturbance voltage stability region of a power system is constructed. The voltage stability of the system is determined by the dynamic characteristics of both the OLTC and the load.

Improved Power Flow Initialization of Dynamic Studies with Non-linear Composite Load Model

A power flow solution using a static constant MVA load model is a straightforward approach to initialize power system dynamic simulations. Using this model to represent induction motor load, however, may not be suitable due to a natural mismatch between initial bus scheduled powers and actual input powers that are computed afterward using their converged bus voltages. To avoid this mismatch occurrence, the Newton–Raphson power flow algorithm has been newly extended to incorporate non-linear characteristics of a composite load model in order to get an exact operating point of each individual induction motor and static load. The power flow solution of the applied 13-bus industrial power system reveals that the extended algorithm is capable of giving an exact active and reactive power input of the motors in correlation with their converged slips, internal bus voltages, and mechanical load torque characteristics and of voltage-dependent loads in relation to their exponent indices. Moreover, the computational efficiencies of the algorithm have been investigated using IEEE 14-bus and 57-bus networks. The results show that embedding induction motor and static exponent load models directly into the power flow mismatch function and Jacobian can improve computational efficiency since the power flow solution is well converged in a satisfactory quadratic manner.