Maximum Loadability Research Articles

Optimal incorporation of multiple distributed generation units based on a new system maximum loadability computation approach and vortex searching algorithm

In this paper, the optimal incorporation of distributed generation (OIDG) units for the maximization of the system‟s loadability is investigated (based on sizing and siting). To this end a new computational approach for computing maximum loadability of the system is developed. This approach has been compared with the classical one on different radial test systems (RTS) and is found to be faster and more accurate. The OIDG problem is formulated mathematically as an optimization problem with the objective function to maximize system‟s loadability, the imposed constraints are; voltage limits, thermal limits and DG penetration level. The optimization algorithm used is to solve the OIDG problem is the Vortex searching algorithm (VS). The tested radial distribution systems are the standard 33-bus and 69-bus systems. This paper also discusses some other interesting findings about VS algorithm.

Optimal incorporation of multiple distributed generation units based on a new system maximum loadability computation approach and vortex searching algorithm

In this paper, the optimal incorporation of distributed generation (OIDG) units for the maximization of the system‟s loadability is investigated (based on sizing and siting). To this end a new computational approach for computing maximum loadability of the system is developed. This approach has been compared with the classical one on different radial test systems (RTS) and is found to be faster and more accurate. The OIDG problem is formulated mathematically as an optimization problem with the objective function to maximize system‟s loadability, the imposed constraints are; voltage limits, thermal limits and DG penetration level. The optimization algorithm used is to solve the OIDG problem is the Vortex searching algorithm (VS). The tested radial distribution systems are the standard 33-bus and 69-bus systems. This paper also discusses some other interesting findings about VS algorithm.

Voltage stability constrained line‐wise optimal power flow

The purpose of optimal power flow (OPF) is to optimise an objective function subject to a set of operating constraints. It remains an active research area because of using the bus-wise power balance equations, which leads to a non-linear solution space, resulting in OPF yielding local optimal solutions, thereby causing significant economic loss. In this study, first, a new line-wise OPF (LWOPF) formulation is proposed. Thereafter, a maximum loadability factor, as a voltage collapse indicator, is derived and combined with LWOPF constraints to form a voltage stability constrained LWOPF (VSCLWOPF) model. As the line-wise power balance equations are based upon the square of voltage magnitudes, it results in significant improvement in the solution space and lower-order terms in all computational steps. The LWOPF and VSCLWOPF formulations, are solved using non-linear optimisation technique, tested on several benchmark and real power systems. Results show that the proposed LWOPF is accurate, provides monotonic convergence, and scales well for large systems. It provides a better solution and is consistently faster, up to twice the speed of MATPOWER, due to reduced computational needs. Results of VSCLWOPF show that, for the same voltage stability level, the solution costs less than that obtained by classical bus-wise OPF.

A graph theory application for fast and efficient search of optimal radialized distribution network topology

The topological changes and re-configuration can be brought into an existing power network by operation of sectionalizing switches on the feeder lines. Distribution networks can be operated either in meshed or in radial configuration. While primary meshed distribution networks have advantages like lower short circuit current, reduced overall conductor length and increased reliability and fault tolerance, the radial networks on the other hand stand-out on their merits of simple installation and easier relay coordination. An optimal radial network can operate at higher efficiency owing to its reduced power losses and can offer higher voltage stability. Transformation of a primary meshed network to a radially reconfigured optimal network requires selection of the “best” set of switches on the feeders that are to be opened or closed so that each feeder can be operated close to its maximum loadability limit and the resulting optimal network operates at its lowest feasible value of power loss and highest voltage stability index. This theoretical concept of optimal power network radialization is however difficult to implement in practice due to the heavy computational burden and unacceptably long searching time as the number of feasible alternative configurations is usually massive for large power networks. Given the extent of the search space, the heuristic search approaches are usually more practical and common in power network reconfiguration. This paper presents a novel guided search approach based on Edmond’s Maximal Spanning Tree Algorithm to achieve the optimal radial configuration for an arbitrary power network rapidly and efficiently. Efficacy of the proposed method has been tested on 30-node and 57-node mesh distribution networks with encouraging results.

Preparation, Characterization and Evaluation of Curcumin Nanodispersions Using Three Different Methods – Novel Subcritical Water Conditions, Spontaneous Emulsification and Solvent Displacement

Abstract Curcumin as a lipophilic bioactive compound can be incorporated into water-based formulations when it turns into curcumin nanodispersions. In fact, nanodispersion systems, increase curcumin bioavailability, solubility and stability, and furthermore increase curcumin uses in aqueous food and pharmaceutical formulations. Present study focuses on the preparation of curcumin nanodispersions under subcritical water conditions (temperature of 120 °C and pressure of 1.5 bar for 2 h) and using selected another two different methods namely, spontaneous emulsification and solvent displacement. Lecithin as carrier oil, Tween 80 as emulsifier and polyethylene glycol as co-surfactant, with a ratio of 1:8:1, were used in all the preparation techniques. Obtained results indicated that curcumin nanodispersions with smallest mean particle size (70 nm), polydispersity index (0.57), curcumin loss (5.5%) and turbidity (0.04 Nephelometric Turbidity Unit), and maximum loading ability (0.189 g/L), loading efficiency (94.5%) and conductivity (0.157 mS/cm) were obtained under subcritical water conditions. The results also exhibited that the prepared spherical curcumin nanoparticles in the water by this technique had desirable physical stability as their mean zeta potential value was (−12.6 mV). It also observed that, as compared to spontaneous emulsification and solvent displacement methods, the prepared curcumin nanodispersions via subcritical water method had highest anti-oxidant and antibacterial activities.

A comparison of the effectiveness of voltage stability indices in an optimal power flow

Voltage stability is very important, as without it voltage collapse will occur. There is therefore a need to incorporate the consideration of voltage stability into the optimal power flow (OPF). This paper presents a comparison of the effectiveness of five voltage stability indices (VSIs) when incorporated in an OPF. The improved particle swarm optimization (IPSO) algorithm is used to solve the OPF problem. The five VSIs investigated are the L‐index, fast voltage stability index (FVSI), line stability index (Lmn), online voltage stability index (LVSI), and voltage collapse proximity indicator (VCPI). The effectiveness of each VSI is considered in the terms of the generation cost, emission, transmission loss, and voltage stability. The IEEE standard 14‐, 30‐, 57‐, and 118‐bus test systems are used for the comparison. It is found that considering each voltage stability index as part of the objective function for the OPF provided different values of generation cost, emission, transmission loss, and maximum loadability. The results suggest that FVSI and Lmn provide the minimum generation cost values for all test systems, while VCPI and LVSI provide lower emission values for most systems. VCPI gives the lowest transmission losses for all systems, and the L‐index provides the maximum loadability for most systems. Incorporation of these indices into the OPF can provide the optimal values in different terms, and the most suitable voltage stability index will depend on the situation and size of the system, which needs to be judiciously chosen. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Multi‐objective approach to maximise loadability of distribution networks by simultaneous reconfiguration and allocation of distributed energy resources

In recent years, continuously increasing load demand and deficiency of capital resources vis-a-vis a competitive electricity market have forced transmission and distribution utilities worldwide to maximise the efficiency and utilisation of their existing infrastructure. This study presents a multi-objective approach to maximise the loadability of distribution networks by simultaneous reconfiguration and optimal allocation of distributed energy resources using a comprehensive teaching-learning-based optimisation algorithm. The proposed technique is based on the e-constraints method and uses a graphical approach for network reconfiguration. Loadability enhancement is validated on the IEEE 33-bus and 69-bus radial distribution systems. Several case studies are carried out to demonstrate the effectiveness of the proposed approach in reducing the network active power losses, improving the kVA loading margins and enhancing the voltage profiles while considering voltage and thermal limit constraints. Results show that maximum loadability is obtained with simultaneous network reconfiguration and multiple DER allocation with varying power factors.

Maximum Loadability Enhancement with a Hybrid Optimization Method

Nowadays, a power system is operating in a stressed condition due to the increase in demand in addition to constraint in building new power plants. The economics and environmental constraints to build new power plants and transmission lines have led the system to operate very close to its stability limits. Hence, more researches are required to study the important requirements to maintain stable voltage condition and hence develop new techniques in order to address the voltage stability problem. As an action, most Reactive Power Planning (RPP) objective is to minimize the cost of new reactive resources while satisfying the voltage stability constraints and labeled as Secured Reactive Power Planning (SCRPP). The new alternative optimization technique called Adaptive Tumbling Bacterial Foraging (ATBFO) was introduced to solve the RPP problems in the IEEE 57 bus system. The comparison common optimization Meta-Heuristic Evolutionary Programming and original Bacterial Foraging techniques were chosen to verify the performance using the proposed ATBFO method. As a result, the ATBFO method is confirmed as the best suitable solution in solving the identified RPP objective functions.

Optimal multiple installation of DG and capacitor for energy loss reduction and loadability enhancement in the radial distribution network using the hybrid WIPSO–GSA algorithm

ABSTRACTIn the electric power system, the majority of loads connected to the distribution side are inductive loads, thereby resulting in enhanced energy loss and reduced voltage stability and maximum loadability. In this study, in order to overcome these issues, optimal multiple installation of distributed generation (DG) and capacitor are presented with minimisation of total apparent power loss () taken as the main objective function. The optimal DG and capacitor planning problem are solved using a hybrid configuration of the weight improved particle swarm optimisation (WIPSO) algorithm and gravitational search algorithm (GSA) called the hybrid WIPSO–GSA algorithm. Moreover, the total economic benefit due to optimal DG and capacitor installation are also established by considering essential cost parameters for the total planning period. The proposed methodology is tested on standard 33-bus and Indian 85-bus radial distribution systems. The superiority of the proposed technique is also illustrated by comparing the results with other optimisation techniques.

CONTINUATION POWER FLOW OF AN UNBALANCED THREE-PHASE FOUR-WIRE DISTRIBUTION SYSTEM


 A continuation power flow algorithm for an unbalanced three phase four wire distribution system is presented. The proposed algorithm is used to trace the loci of the voltage of the different phases of an unbalanced three-phase distribution system. The locus of the neutral voltage for a wide range of loading conditions is also obtained. The proposed technique is applied on a typical unbalance three phase radial Iraqi distribution system. The results obtained reveal the effectiveness of the continuation technique for exploring all the possible solutions and the determination of maximum loadability of the distribution feeder.
 

Determination of Maximum Loadability by a Mixed Complementarity Formulation of the Adjusted Power Flow Problem

The ever-increasing demand for power leads to increased loading on the power system. It is necessary to determine the maximum loadability of power systems so that a sufficient margin can be maintained. Maximum loadability can be determined by solving the power flow equations successively while increasing the loading gradually; conventionally, the unadjusted power flow problem is solved. This also helps in determining the voltage profile with respect to loading. However, determination of loadability margin by the solution of adjusted power flow problem is challenging in the presence of certain limits such as the limits of tap-changing and phase-shifting transformers, and the operating limits of Flexible AC Transmission Systems (FACTS) controllers. In the course of determination of maximum loading, it is likely that these limits are encountered. A novel method for systematic handling of these limits is presented in this paper. A Mixed Complementarity Problem formulation is proposed for inclusion of the limits of tap-changing and phase-shifting transformers, and FACTS controllers. The proposed method is tested on the IEEE 300 bus system and the WSCC 9 bus system in the presence of FACTS controllers.

Techniques for the Identification of Critical Nodes Leading to Voltage Collapse in a Power System

AbstractThis paper proposes two techniques for the identification of critical buses in a power system. The technique of Network Structural Theory Participation Factor (NSTPF) depends on the network structural interconnection of buses as captured by the admittance matrix of the system and is formulated based on the fundamental circuit theory law using eigenvalue decomposition method. Another power flow based technique which depends on the system maximum loadability, the system step size among other factors is also proposed. Traditional power flow based techniques are used as benchmarks to determine the significance of the proposed methods. To ensure voltage stability enhancement, STATCOM FACTS device is installed at the selected weak load buses of the practical Nigerian 24 bus and IEEE 30 bus test systems. The results of the simulation obtained show that, the suggested approach of NSTPF is more suitable in the identification of weak buses that are liable to voltage instability in power systems as it requires less computational burden and also saves time compared to techniques based on power flow solutions.

Transversality enforced Newton–Raphson algorithm for fast calculation of maximum loadability

The authors propose a novel modification of the conventional Newton–Raphson load flow solver for characterisation of the maximal system loadability. Within the proposed approach, the standard power flow equations are extended with (i) an algebraic representation of maximal and minimal voltage level conditions and (ii) with the so-called transversality condition restricting the set of solutions to the boundary of the solvability region. Solutions to this extended system of equation characterise the maximal load levels for which the solution of power flow equations exists and satisfies the standard feasibility constraints on voltage levels. The resulting system of equations is non-singular and can be solved with just a few standard Newton–Raphson type iterations. Different possible choices of transversality conditions are discussed together with fast algorithms for evaluating the transversality conditions and their gradients. Implementation of the algorithm is described in detail, and its performance is validated on several IEEE cases.

Optimal Power Flow of Radial Networks and Its Variations: A Sequential Convex Optimization Approach

This paper proposes a sequential convex optimization method to solve broader classes of optimal power flow (OPF) problems over radial networks. The non-convex branch power flow equation is decomposed as a second-order cone inequality and a non-convex constraint involving the difference of two convex functions. Provided with an initial solution offered by an inexact second-order cone programming relaxation model, this approach solves a sequence of convexified penalization problems, where concave terms are approximated by linear functions and updated in each iteration. It could recover a feasible power flow solution, which usually appears to be very close, if not equal, to the global optimal one. Two variations of the OPF problem, in which non-cost related objectives are optimized subject to power flow constraints and the convex relaxation is generally inexact, are elaborated in detail. One is the maximum loadability problem, which is formulated as a special OPF problem that seeks the maximal distance to the boundary of power flow insolvability. The proposed method is shown to outperform commercial nonlinear solvers in terms of robustness and efficiency. The other is the bi-objective OPF problem. A non-parametric scalarization model is suggested, and is further reformulated as an extended OPF problem by convexifying the objective function. It provides a single trade-off solution without any subjective preference. The proposed computation framework also helps retrieve the Pareto front of the bi-objective OPF via the $\varepsilon $ -constraint method or the normal boundary intersection method. This paper also discusses extensions for OPF problems over meshed networks based on the semidefinite programming relaxation method.

Chip-Based Multicapillary Column with Maximal Interconnectivity to Combine Maximum Efficiency and Maximum Loadability.

On the basis of our previous work on the design of pillar array columns for liquid chromatography, we report on a new pillar array design for high-efficiency, high volumetric loadability gas chromatography columns. The proposed pillar array configuration leads to a column design which can either be considered as a packed bed with perfectly ordered and uniform flow paths or as multicapillary columns (8 parallel tracks) with a maximal interconnectivity between the flow paths to avoid the so-called polydispersity effect (dispersion arising from the inevitable differences in migration velocity between parallel flow paths). Despite our relative inexperience with column coating, and most probably (not supported by data) suffering from the same problem of stationary phase pooling in the right-angled corners of the flow-through channels as other chip-based GC devices, the efficiencies obtained in a L = 70 cm long and 75 μm deep and 6.195 mm wide chip for, respectively, quasi-unretained and retained components (k = 7) went up to N = 60 000 and 12 500 under isothermal conditions using H2 as carrier gas and a downstream restriction. Under programmed temperature conditions (Ti = 80 °C, Tf = 175 °C at 30 °C/min, and a H2 flow of 0.4 mL/min), a peak capacity of 170 was obtained in 3.6 min. For retained compounds, the optimal flow rate is found to be on the order of 0.4 mL/min, achieved at an operating pressure of 2.3 bar. Intrinsically, the column combines the efficiency of a 75 μm capillary with the volumetric loadability of a 240 μm capillary.

Loadability analysis based on short‐circuit power

This study describes a loadability analysis in power systems based on short-circuit power (SSC) at a load bus as a parameter space. This analysis determines the maximum loadability based on a proposed voltage stability indicator called voltage-power stability indicator (VPSI). VPSI is calculated by processing two consecutive sets of voltage magnitude and power measurements, both recorded at the same bus of a power system. By maximising VPSI under load changes, one can obtain information concerning the SSC. Then, the loadability value can be calculated based upon SSC. The results demonstrate that a simple relation between the SSC and power load can be used to determine the loadability of the power system. This work highlights the advantage of obtaining the loadability in SSC parameter space because system changes or load changes produce the same effect into the SSC domain, allowing better determination of the maximum loadability.

Application of swarm based intelligent computing algorithms for dynamic evaluation of maximum loadability of transmission network

This work proposes the application of soft computing techniques to evaluate the optimal location and control settings of Flexible AC Transmission System (FACTS) devices inorder to improve the Maximum Loadability (ML) of pool, hybrid model of deregulated power system during scheduled outages like single (N-1) and double (N-2) contingencies. Particle Swarm Optimization (PSO), Hybrid Particle Swarm Optimization (HPSO) algorithms are applied for optimizing the solution. In this case study, three different FACTS devices are considered namely, series type Thyristor Controlled Series Compensator (TCSC), shunt type Static Var Compensator (SVC) and series – shunt type Unified Power Flow Controller (UPFC). To reduce the Installation Cost (IC) of these devices, they are optimally located in the system, based on priority indices like Contingency Severity Index (CSI) and Fast Voltage Stability Index (FVSI). This proposed approach uses Newton Raphson Power flow equations with voltage, real and VAr power, settings of FACTS devices as constraints. Hybrid structure is modeled using bilateral transactions. The problem is simulated using IEEE 57 bus system. The ML of transmission system obtained for various numbers, settings and locations of FACTS devices are compared both numerically and graphically. It is concluded that HPSO provides better result with minimum Time of Computation (ToC) and quicker convergence.

Application of Artificial Bee Colony Algorithm in Power Flow Studies

Artificial bee colony (ABC) algorithm is one of the important artificial techniques in solving general-purpose optimization problems. This paper presents the application of ABC in computing the power flow solution of an electric power system. The objective function to be minimized is the active and reactive power mismatch at each bus. The proposed algorithm has been applied on typical power systems. The results obtained are compared with those obtained by the conventional method. The results obtained reveal that the ABC algorithm is very effective for solving the power flow problem in the maximum loadability region. Index Terms: Artificial Bee Colony, Maximum Loadability, Power Flow, Swarm Artificial Technique

Simulation of Distance Relay for Load Encroachment Alleviation with Agent Based Supervision of Zone 3

Cascaded tripping of power lines due to mal-operation of zone-3 distance relays has been one of the main causes of many previous blackouts worldwide. Encroachment of load into zone-3 characteristics during stressed system operation conditions is a basic factor for such mal-operation of the relays. By improving the operation of zone-3, it is possible to prevent mal-operations so that cascaded line tripping can be avoided. For proper study of the behavior of distance relay during faults and load encroachment phenomenon, we must build a model of distance relay, so in this paper a modeling study of distance relay is implemented using MATLAB/Simulink program. However, this model is distinguished from previous models that, examines in detail the third zone of distance relay. Many cases are simulated with changing line loading and fault location to ensure the capability of the relay to detect the fault and thus the maximum load ability limit of distance relay is obtained. In order to prevent cascading events caused by hidden failures in zone-3 relays, agent based relay architectures have been suggested in the recent past. In such architectures each zone-3 relay contains agents that require communication with other agents at various relevant relays in order to distinguish a real zone-3 event from a temporary overload. In this paper, a local master agent is consulted by all zone-3 agents before a tripping decision is made. The master agent maintains a rule base which is updated based on the local topology of the network and real time monitoring of the status of other relays and circuit breakers. Cisco Packet Tracer program is used for running communication network simulations. The result of the simulation indicate that the time estimated to send and receive a packet data unit (PDU) message between one relay to anther can satisfy the communication requirement for the proposed scheme with fiber media.

Mitigating Congestion in a Power System and Role of FACTS Devices

Congestion management refers to avoiding or relieving congestion. In transmission lines, congestion management is one of the most important issues for the reliable operation of power system in the deregulated environment. Restructuring has brought considerable changes in all possible domains including electric supply industry. By virtue of restructuring, electricity has now become a commodity and has converted into a deregulated one. The traditional regulated power system has now become a competitive power market. In the present scenario, the real time transmission congestion is the operating condition in which the transfer capability to implement all the traded transactions simultaneously is not enough due to either some expected contingencies or market settlement. Thus, congestion is associated with one or more violations of the physical, operational, and policy constraints under which grids operate. Thus, congestion management is about managing the power transmission and distribution among valuable consumers priority-wise. Placement of FACTS (Flexible Alternating Current Transmission System) devices for generation rescheduling and load-shedding play a crucial role in congestion management. FACTS devices are used to enhance the maximum load ability of the transmission system. FACTS increases the flexibility of power system, makes it more controllable, and allows utilization of existing network closer to its thermal loading capacity without jeopardizing the stability. FACTS technology can boost the transfer capability in stability limited systems by 20–30%. As a result, more power can reach consumers with a shorter project implementation time and a lower investment cost. This review work unites the various publications on congestion management in past few decades.