Future Power Networks Research Articles

Recovery time analysis in a tri-axial HTS cable after an over-current fault

A tri-axial HTS cable with the advantage of compact structure, low heat loss, and low cost is a perfect solution for future distribution power network demand. In our previous research, a typical single line to ground (SLG) fault simulation was carried out in an adiabatic condition. A stabilizer layer thickness design of the tri-axial HTS cable based on a calculation of maximum temperature rise in the worst condition was proposed. However, in practical application, after the quenched cable is removed from the network by a breaker, a recovery time is also a very important parameter to decide if the cable is allowed to reconnect to the power network. In this paper, a one-dimensional computational fluid dynamics (CFD) analysis is carried out to simulate the transient thermal behavior of the cable. The result shows that it takes time to recover the cable temperature to the steady-state operation level due to a low thermal conductivity of the insulation layer. Since the cable is cooled by forced liquid nitrogen (LN2) flow, there is a temperature gradient along the cable. The temperature of LN2 gradually rises after the fault until the warmed coolant runs out of the cable.

Wide-Area Monitoring, Protection, and Control of Future Electric Power Networks

Wide-area monitoring, protection, and control (WAMPAC) involves the use of system-wide information and the communication of selected local information to a remote location to counteract the propagation of large disturbances. Synchronized measurement technology (SMT) is an important element and enabler of WAMPAC. It is expected that WAMPAC systems will in the future reduce the number of catastrophic blackouts and generally improve the reliability and security of energy production, transmission, and distribution, particularly in power networks with a high level of operational uncertainties. In this paper, the technological and application issues are addressed. Several key monitoring, protection, and control applications are described and discussed. A strategy for developing a WAMPAC system in the United Kingdom is given as well.

Multi-agent Microgrid Power Management

AbstractMicrogrids are a promising means to broadly integrate distributed energy resource (DER) systems. Seen as an enabling technology within smart grid infrastructure, microgrids offer solutions for both customers and system operators of future power networks. However, the optimal management and control of many generation, load, and storage assets local to a microgrid presents as a daunting challenge. In this paper, an agent-based control architecture for microgrids, capable of coordinating and cooperatively achieving multiple user-defined objectives in real-time is presented. Herein, the authors present fundamental properties required by a decentralized microgrid multi-agent system (MAS), define agent capabilities that support resilient operations, and discuss aspects of the microgrid MAS necessary to smoothly transition between system states. The microgrid MAS developed allows control decision-making to be shifted to a lower hierarchical level, capitalizing on the ability of distributed agents to self-order and cooperate towards an optimal power management solution, given assigned goals. As smart grid technologies continue to evolve, the microgrid operational concepts discussed, along with robust power management and control issues, will play an increasingly significant role.

A secure decentralized data-centric information infrastructure for smart grid

In recent years the power grid has been undergoing transformative changes due to the greater penetration of renewable energy sources and increased focus on power demand shaping. These innovative transformations on the grid require a flexible IP-based communication grid that is reliable and secure. In this article we describe an IPbased decentralized and data-centric information infrastructure that can reliably, securely, and cost-effectively support the operation and innovative applications of the next generation grid. The proposed infrastructure differs from a typical distributed system since it addresses the specific requirements of power applications such as security, distributed data sources, latency sensitive data transactions and real time event updates. The work presented here paves the way for a future data-centric power network infrastructure.

Agent-based coordination techniques for matching supply and demand in energy networks

There is a lot of effort directed toward realizing the power network of the future. The future power network is expected to depend on a large number of renewable energy resources connected directly to the low and medium voltage power network. Demand side management (DSM) is an important element for reaching this goal. Demand side management is concerned with actions that reshape the energy consumption pattern for the end-users during peak time or during times when consumption exceeds generation. To control and coordinate the operation of the network with these new characteristics efficiently and with a certain degree of reliability, intelligent coordination approaches are required. The intermittency and variability of renewable energy resources, the large number of distributed consumption and generation units, and the local operation constraints for these units should be considered when designing the appropriate control and coordination systems. Agent-based systems are proposed and being implemented to control and coordinate the operation of different entities inside the future power network. By using agent technology we can satisfy the local constraints of different entities while simultaneously satisfying global goals by using coordination approaches for coordinating and adapting the agents' actions. Approaches developed rely on two control types for altering demand: price-based control (indirect control) and direct-load control. In this survey article we review previously and currently developed agent-based coordination approaches that depend on direct-load control for matching supply and demand in the power network of the future.

2層型契約ネットプロトコルを用いた配電系統事故復旧の分散処理システム

Distributed processing system for restoration of electric power distribution network using two-layered CNP is proposed. The goal of this study is to develop the restoration system which adjusts to the future power network with distributed generators. The state of the art of this study is that the two-layered CNP is applied for the distributed computing environment in practical use. The two-layered CNP has two classes of agents, named field agent and operating agent in the network. In order to avoid conflicts of tasks, operating agent controls privilege for managers to send the task announcement messages in CNP. This technique realizes the coordination between agents which work asynchronously in parallel with others. Moreover, this study implements the distributed processing system using a de-fact standard multi-agent framework, JADE(Java Agent DEvelopment framework). This study conducts the simulation experiments of power distribution network restoration and compares the proposed system with the previous system. We confirmed the results show effectiveness of the proposed system.

Energy and exergy analysis of a micro-compressed air energy storage and air cycle heating and cooling system

Energy storage systems are becoming more important for load leveling, especially for widespread use of intermittent renewable energy. Compressed air energy storage (CAES) is a promising method for energy storage, but large scale CAES is dependent on suitable underground geology. Micro-CAES with man-made air vessels is a more adaptable solution for distributed future power networks. In this paper, energy and exergy analyses of a micro-CAES system are performed, and, to improve the efficiency of the system, some innovative ideas are introduced. The results show that a micro-CAES system could be a very effective system for distributed power networks as a combination that provides energy storage, generation with various heat sources, and an air-cycle heating and cooling system, with a energy density feasible for distributed energy storage and a good efficiency due to the multipurpose system. Especially, quasi-isothermal compression and expansion concepts result in the best exergy efficiencies.

RETRACTED: UK scenario of islanded operation of active distribution networks with renewable distributed generators

This paper reports on the current UK scenario of islanded operation of active distribution networks with renewable distributed generators (RDGs). Different surveys indicate that the present scenario does not economically justify islanding operation of active distribution networks with RDGs. Anti-islanding protection schemes currently enforce the renewable distributed generators (RDGs) to disconnect immediately and stop generation for grid faults through loss of grid (LOG) protection system. This greatly reduces the benefits of RDG deployment. With rising RDG penetration, much benefit would be lost if the RDGs are not allowed to island only due to conventional operational requirement of utilities. For preventing disconnection of RDGs during LOG, several islanding operation, control and protection schemes are being developed. Technical studies clearly indicate the need to review parts of the ESQCR (Electricity Safety, Quality and Continuity Regulations) for successful islanded operations. Commercial viability of islanding operation must be assessed in relation to enhancement of power quality, system reliability and supply of potential ancillary services through network support. Demonstration projects under Registered Power Zone and Technical Architecture Projects should be initiated to investigate the usefulness of DG islanding. However these efforts should be compounded with a realistic judgement of the associated technical and economic issues for the development of future power networks.

A GA Based Transmission Network Expansion Planning Considering Voltage Level, Network Losses and Number of Bundle Lines

Transmission Network Expansion Planning (TNEP) was studied considering voltage level, network losses and number of bundle lines using decimal codification based genetic algorithm (DCGA). TNEP determines the characteristic and performance of the future electric power network and directly influences the operation of power system. Up till now, various methods have been presented for the solution of the Static Transmission Network Expansion Planning (STNEP) problem. However, in all of these methods, STNEP problem has been solved regardless of voltage level of transmission lines. For this reason and according to various voltage levels and different number of bundle lines used in real transmission network which caused different annual losses, STNEP was studied considering voltage level, network losses and number of bundle lines using genetic algorithm. Genetic Algorithms (GAs) have demonstrated the ability to deal with non-convex, nonlinear, mixed-integer optimization problems, like the TNEP problem, better than a number of mathematical methodologies. The proposed method was tested on an actual transmission network of the Azerbaijan regional electric company, Iran, to illustrate its robust performance. The results were shown that considering the network losses in a network with different voltage levels and the number of bundle lines considerably decreased the operational costs and the network can be satisfied the requirement of delivering electric power more safely and reliably to load centers.

DCGA based evaluating role of bundle lines in TNEP considering expansion of substations from voltage level point of view

Transmission network expansion planning (TNEP) is an important component of power system planning. It determines the characteristic and performance of the future electric power network and influences the power system operation directly. Up till now, various methods have been presented for the solution of static TNEP (STNEP) problem. However, in all of them, the role of bundle lines in TNEP problem considering the expansion of substations from the voltage level point of view has not been investigated. Thus, in this paper, the role of bundle lines in STNEP problem is being studied considering expansion cost of substations from the voltage level point of view using decimal codification genetic algorithm (DCGA). The effectiveness of the proposed idea is tested on an actual transmission network of the Azerbaijan regional electric company, Iran. The results reveal that bundle lines have effective role in transmission expansion planning and subsequent determining the network arrangement. In addition, considering the bundle lines in a power system is caused that the expansion cost of lines and substations decreases and therefore the total expansion cost of network is minimized. Also, it can be said, although cost of bundle lines are more than those which have not bundle conductor, constructing this type of lines in a transmission network with different voltage levels prevents useless expansion of unbundled lines in separate corridors and therefore the network expansion planning is optimized.

Sensitivity of Small Disturbance Angle Stability to the System Parameters of Future Power Networks

The incorporation of renewable energy sources for the sustainable electricity production is undertaking a more prominent role in electric power systems. Thus, it will be an indispensable incident that the characteristics of future power networks, their prospective stability for instance, get influenced by the imposed fea- tures of sustainable energy sources. One of the distinctive attributes of the sustainable energy sources is exhibiting the stochastic behavior. This paper investigates the impacts of this stochastic behavior on the small disturbance rotor angle stability in the upcoming electric power networks. Considering the various types of renewable energy sources and the vast variety of system configurations, the sensitivity analysis can be an efficient breakthrough towards generalizing the effects of new energy sources on the concept of stability. In this paper, the definition of small disturbance angle stability for future power systems and the iterative-stochastic way of its analysis are presented. Also, the effects of system parameters on this type of stability are described by performing a sensitivity analysis for an electric power test system.

Discontinuous Dynamics of Electric Power System With DC Transmission: A Study on DAE System

Transient stability of power systems with dc transmission is an important problem for planing and operation of future power networks. A differential-algebraic equation (DAE) system is proposed for transient stability analysis of a practical ac/dc power system which includes one synchronous generator operating onto both ac and dc transmissions. When transient stability analysis is performed using the DAE system, its solutions that represent dynamics of the ac/dc power system become discontinuous. This is because a constraint set, which is a set of variables satisfying algebraic equations of the DAE system, discontinuously changes at the onset of fault occurrence and clearing. We numerically and analytically examine such discontinuous solutions of the DAE system and associated transient dynamics of the ac/dc power system. The discontinuous nature of solutions shows that enhancement of transient stability via dc transmission is characterized by a dynamical system on a constraint set or a manifold controlled by input as installation of dc transmission.

42-V/3-V Watkins-Johnson converter for automotive use

In this paper, the Watkins-Johnson (WJ) converter was found to best step down the future automotive 42-V power network to 3 V or lower for the supply of microcontrollers and semiconductors. The particularity of the WJ converter is that it only employs a tapped-inductor and three other components. The use of a tapped-inductor is well-known and gives an extra-degree of freedom by the insertion of the winding ratio of the tapped-inductor into the transfer function of the WJ converter. It also permits the duty cycle to be adjusted to a value at which the efficiency of the converter is improved. The converter can be slightly modified and used as a multiple output converter while employing few components, diminishing the weight, size, cost, and complexity of a system. Practical test results for the single-output WJ converter are presented.

Plug in to grid computing

This article discusses the potential benefits of grid computing for future power networks. It is also intended to alert the power system community to the concept of grid computing and to initiate a discussion of its potential applications in future power systems. Much like the Web, the grid can operate over the Internet or any other suitable computer networking technology. Grid computing offers an inexpensive and efficient means for participants to compete (but also cooperate) in providing reliable, cheap, and sustainable electrical energy supply. It also provides a relatively inexpensive new technology allowing the output of embedded generators to be monitored and, when necessary, controlled. Basically, the ability of grid-enabled systems to interact autonomously is vital for small generators where manned operation is likely to be viable.