Network Operating Conditions Research Articles

Distributed State Estimation for Interconnected Synchronous Generators

In contrast to the traditional centralised power system state estimation methods, this paper investigates the optimal filtering problem for distributed dynamic systems. Specifically, the interconnected synchronous generators are modelled as a state-space linear equation where sensors are deployed to obtain measurements. As the synchronous generator states are unknown, the estimation is required to know the overall operating conditions of large-scale complex power networks. Basically, the proposed algorithm is based on the minimization of the mean squared estimation error, and the optimal gain is computed by exchanging information with their neighboring estimators. Afterwards, the convergence of the developed algorithm is proved so that it can be applied to real-time applications in modern smart grids. Finally, simulation results demonstrate the efficacy of the developed approach.

Edge-centric Computing for Smart Water Supply: Management and Service

The smart water supply management system targets for the efficient water supply network management, optimization, and water supply service provisioning. It is an essential component of smart city application. The smart water management system monitors the water supply network operation status via installed sensors (e.g. water pressure, flow speed, water leakage etc) in a large scale. It analyzes the potential risk in the distribution network and integrates the water supply information in a user friendly GUI. It is efficient and cost effective to detect the abnormal situations and take corresponding measurements without much human interference. The water service system provides the users many traditional and new value-added services.

Optimal use of thermal energy storage resources in commercial buildings through price-based demand response considering distribution network operation

Energy storage resources (ESRs) inherent in building structures are a viable, attractive option to improve power system operation by providing demand-side flexibility. This paper proposes a two-stage optimisation framework for price-based demand response of commercial buildings that include variable speed heat pumps (VSHPs). The proposed framework aims at assisting commercial building aggregators to devise a beneficial strategy for exploiting thermal ESRs in response to electricity prices. Specifically, in this paper, the thermal dynamics of VSHPs are modelled in detail using a set of piecewise linear equations for two different methods of room temperature control. The energy consumption and reserve provision of VSHPs, as well as plug-in electric vehicles, are then co-optimised considering the operating conditions of distribution networks (DNs) for the pre- and post-contingency states of wind power generation. Simulation case studies are performed to estimate the effects of building ESRs on the optimal operation of power systems and commercial buildings under various conditions characterised by: (1) temperature control methods, (2) ESR penetration levels, and (3) DN operational constraints.

Optimization of a natural gas distribution network with potential future extensions

A model of a pipeline network for gas distribution is developed considering supply of gas, either from external gas networks or as injected biogas or gasified liquefied natural gas (LNG) at terminals. The model is based on mass and energy balance equations for the network nodes, equations of the pressure drop of a compressible gas in the pipes, as well as expressions of gas compression in compressor nodes. The model is applied within an optimization framework where the optimal supply of natural gas to the customers is studied under a multi-period mixed integer nonlinear programming (MINLP) formulation, considering possible extensions of the pipeline network to new sites as well as potential supply of the gas from LNG terminals. The natural gas network in Finland is used in a case study, which determines the network's size and operation conditions. The results illustrate that the model can tackle complex gas supply problems and that it finds interesting alternatives where the optimal gas flow is reversed between the periods. The findings reveal the conditions under which it is beneficial to upgrade existing connections by parallel pipelines, extend the pipeline to new sites, or to re-gasify LNG and inject it into the network.

Analysis of critical operating conditions for LV distribution networks with microgrids

Increase in the penetration of Distributed Generation (DG) in distribution networks, raises the risk of voltage limit violations while contributing to line losses. Especially in low voltage (LV) distribution networks (secondary distribution networks), impacts of active power flows on the bus voltages and on the network losses are more dominant. As network operators must meet regulatory limitations, they have to take into account the most critical operating conditions in their systems. In this study, it is aimed to present the impact of the worst operation cases of LV distribution networks comprising microgrids. Simulation studies are performed on a field data-based virtual test-bed. The simulations are repeated for several cases consisting different microgrid points of connection with different network loading and microgrid supply/demand conditions.

Uncertainty of Voltage Profile in PMU-Based Distribution System State Estimation

Distribution system state estimation (DSSE) tools are required to estimate the real operating conditions of power distribution networks. The accuracy of the quantities estimated through DSSE plays a key role in the effectiveness of the management and control functions. This paper presents a comprehensive mathematical analysis aimed at highlighting the most important factors affecting the accuracy of the voltage profile obtained by means of weighted least squares estimators. The proposed analysis shows the way in which the uncertainty components of the voltage estimations depend on the measurement system available on the field. In particular, this paper considers synchrophasor measurements provided by phasor measurement units and hybrid measurement systems also presenting conventional devices. Tests performed on a 95-bus network prove the validity of the theoretical analysis and show the importance of the results also from a meter placement perspective, emphasizing the requirements needed to achieve specific accuracy targets.

On user association and multiple access optimisation in 5G massive MIMO empowered ultra dense networks,

AbstractUltra network densification and massive multiple‐input and multiple‐output are considered major 5th generation technology enablers, promising huge capacity gains as they offer proximity, spectral and spatial reuse benefits. Towards succeeding in harnessing the anticipated gains, a systematic treatment of radio resources management challenges encountered in such network deployments is of utmost importance. In this respect, we introduce and study in detail the user‐association and multiple‐access optimisation aspects of massive multiple‐input and multiple‐output ultra dense networks. We derive for the first time to the best of our knowledge a series of mathematical programming models for computing the optimal user‐association decisions and assessing the impact of two multiple access candidate approaches, namely, frequency domain and spatial domain multiple access. We support the work with an extensive performance evaluation study, which reveals the rate scaling performance trends of the different approaches, considering various network operation conditions, as well as obtain useful design insights for future setups employing the particular technologies. Copyright © 2016 John Wiley & Sons, Ltd.

Optimal operation of large district heating networks through fast fluid-dynamic simulation

Optimization of the operating conditions of district heating networks is usually performed limiting the analysis to the primary energy related with heat production. An additional aspect that should be considered is the role played by the pumping system. Pumping may contribute to about 10% of the total primary energy consumption, especially in large networks or when small temperature levels are applied. Furthermore, the increasing share of waste heat or renewable energy sources from distributed producers requires a flexible and efficient pumping system. A further aspect which pumping strategy should face is system operation when malfunctions in the plants, pumps or pipes occur.Optimization of the pumping system requires the use of detailed simulation tools, which may need significant computational resources, especially in the case of large networks. A reduced model, based on Proper Orthogonal Decomposition combined with Radial basis functions (POD-RBF model) is proposed in this paper. This approach allows maintaining high level of accuracy despite reductions of more than 80% in the computational time. This make the approach effective tool for control strategy operations. An application to a large district heating network shows that reductions of about 20% in the pumping request and effective management of failures are possible.

Data collection using miniature aerial vehicles in wireless sensor networks

Energy constraints of sensor nodes in wireless sensor networks (WSNs) is a major challenge and minimising the overall data transmitted across a network using data aggregation, distributed source coding, and compressive sensing have been proposed as mechanisms for energy saving. Similarly, use of mobile nodes capable of relocating within the network has been widely explored for energy saving. In this study, the authors propose a novel method for using miniature aerial vehicles for data collection instead of actively sensing from a deployed network. The proposed mechanism is referred as data collection fly (DCFly). It is suitable for data collection from WSNs deployed in harsh- undulating terrain with the base station located far from the sensing region. The DCFly is compared with data collection based on multi-hop data aggregation and data collection with mobile sinks. The numerical results justify that the proposed data collection mechanism is effective and efficient for use in WSNs. 1 Introduction Wireless sensor networks (WSNs) are deployed in an area to be monitored, referred to in this paper as the sensing region, for diverse applications such as habitat and environmental monitoring, battlefield surveillance, and industrial monitoring. Using active node mobility in the network, overall communication in the network can be reduced and specifically nodes close to the base station (BS) could be prevented from draining out. Various utilities that are possible using active node mobility in the network are: mobile relay, mobile data mule, and mobile BS. Alternatively, in-network data processing mechanisms such as data aggregation, network coding, and compressive sensing could be utilised for minimising the overall communication of the network. These two approaches, that is, node mobility, and in-network processing have been extensively explored individually and independently. This paper presents a mechanism for data collection using a data collection fly (DCFly). The DCFly would aerially collect data from the network. This is the first work that explores the potential of using miniature aerial vehicles (MAVs) for collecting data, collectively involving node mobility and in-network data processing. The underlying framework adopted in this paper has been presented in our preliminary work (1). The remaining paper has been structured as follows: in Section 2, previous work relating to node mobility and in-networking data processing has been presented. Section 3 provides an insight into factors governing optimal number of cluster heads (CHs) and inter-relation with position of BS, data collection operation by the DCFly; these aspects influence the network architecture. The factors governing the DCFly's possible use in the sensing region and the network operational conditions considered for evaluation are presented in Section 4. The DCFly's governing factors formulated as an optimisation problem to determine the feasible operational utility are presented in Section 5. The optimum number of clusters that can be covered by a single DCFly are presented in Section 6, along with the comparative evaluation of the proposed DCFly with a multi-hop data aggregation mechanism (referred as DA mechanism). The DCFly-based data collection is also compared with data collection from the network relying on mobile elements (MEs) in Sections 6.1 and 6.2. Finally, this paper is concluded in Section 7. 2 Related work As stated earlier, the methods for minimising the energy consumption in the network can be broadly categorised into node mobility and in-network data processing-based mechanisms.

Experimental Evidence of the Discharge Law in Private Tanks Connected to Water Distribution Networks

In almost all the Mediterranean countries, users store water resources in private tanks usually located on the rooftops. These local reservoirs are usually connected to the water distribution network (WDN). In such cases, network-operating conditions can be far from design ones, thus, specific models have to be developed to correctly simulate the WDN. Here, a new mathematical model able to reproduce the tank emptying/filling cycles is proposed. Specifically, through experimental analysis a new mathematical formulation of the emitter law is proposed.

Operating principle of Soft Open Points for electrical distribution network operation

Soft Open Points (SOPs) are power electronic devices installed in place of normally-open points in electrical power distribution networks. They are able to provide active power flow control, reactive power compensation and voltage regulation under normal network operating conditions, as well as fast fault isolation and supply restoration under abnormal conditions. Two control modes were developed for the operation of an SOP, using back-to-back voltage-source converters (VSCs). A power flow control mode with current control provides independent control of real and reactive power. A supply restoration mode with a voltage controller enables power supply to isolated loads due to network faults. The operating principle of the back-to-back VSCs based SOP was investigated under both normal and abnormal network operating conditions. Studies on a two-feeder medium-voltage distribution network showed the performance of the SOP under different network-operating conditions: normal, during a fault and post-fault supply restoration. During the change of network operating conditions, a mode switch method based on the phase locked loop controller was used to achieve the transitions between the two control modes. Hard transitions by a direct mode switching were noticed unfavourable, but seamless transitions were obtained by deploying a soft cold load pickup and voltage synchronization process.

Evaluation of Node and Link Importance Based on Network Topology and Traffic Information

For awareness of the network situation, this paper proposes a set of indicators that can assess the importance of nodes and links combining with network topology and traffic information, their generating algorithm is given at the same time. Under the premise of determined network routing protocols, this algorithm is capable of assessing the importance of nodes and links based on the structure and operation state of network. In this way, it can show the special property of the unit position in the network, and can reflect the impact to each part due to the network state change so that network administrators can manage network reasonably.

Operation State Evaluation of Distribution Network Based on Attribute Mathematics

Distribution network can implement self-healing when real-time operation state can be mastered comprehensively and operation change tendency can be predicted. Firstly the evaluation index system of operation state was constructed from five aspects (safety, reliability, quality, economy and adaptability). Then, distribution network’s operation network evaluation model was established on the basis of attribute mathematics theory, which could transform this problem into calculation problem of operation state’s attribute measure. Analytic hierarchy process was used to determine the weights of indexes. Finally the process for evaluating operation state was given. The simulation results show that this model can get accurate operation state of distribution network.

Security‐oriented cooperation scheme in wireless cooperative networks

This study proposes a security-oriented cooperation (SOC) scheme, which first determines one of the three possible cooperation scenarios, namely the jammer only, relay only and the relay-jammer pair, according to the security requirement and network's operational conditions. After determining a cooperation scenario, then, the selection of a relay or/and a jammer as well as their transmit power are jointly optimised with the objective to attain a good trade-off between security performance and energy consumption. The performance of the networks employing the proposed SOC is investigated here over finite-state Markov channels. The studies and results explain that the proposed SOC scheme constitutes one of the promising SOC schemes. It belongs to a generalised cooperative security scheme, which adapts according to the specific security requirement and communication environments.

Real-Time Simulation of Pipe Network Based on EPANET

Hydraulic simulation models of water pipe networks (WPN) are routinely used for operational investigations and network design purposes. However, their full potential is often never realized because in the majority of cases, they have been calibrated with data collected manually from the field during a single historic time period and reflects the network operational conditions that were prevalent at that time. They were then applied as part of a reactive investigation. An urban water distribution network real time simulation system based on EPANET system using OPC (object linking and Embedding for Process control) communication was built in this paper. In order to make real-time simulation of water distribution network, the real-time data was collected every 15 minutes, the real time data were received and sent into water distribution network simulation model by OPC communication of EPANET system. The real-time data included total head of reservoir, flow rate, pressure, pump operation information. The real-time simulation system can give timely warning of changes for normal network operation, providing capacity to minimize customer impact and comparing the simulation results with the real-time data collected. The real time simulation system of urban water pipe network solved the problem of data input and user interaction compare to traditional network model. It offers a way for the development of intelligent water network.

Online Data Validation for Distribution Operations Against Cybertampering

In recent development of ubiquitous computing on home energy management systems, additional IP-based data collection points are utilized to acquire electricity usage directly from consumers. As cybertampering can disrupt the accuracy of billing information, a well-structured cyberdefense mechanism is required to validate the availability and integrity of metering data for a customer billing center. This paper proposes an online data validation framework to verify home energy meters (EMs) in a secondary network with real-time measurements from feeder remote terminal units (FRTUs) in primary network. A potential cybertampering is identified based on three levels: 1) feeders; 2) subsystems; and 3) customers. This framework attempts to identify malicious consumers and their locations based on historical consumption pattern and network operating conditions in real time. The proposed framework is demonstrated to detect tampering activities using a realistic 12.47-kV distribution network. Results show that the data validation framework can accurately identify subsystems with tampered meters. This framework allows the system operator to restrict the search area to a manageable number of meters in a subsystem.

Comprehensive definition of thermal losses taking into account to the conditions of thermal networks

The article presents an analytical evaluation of heat losses through the thermal in- sulation of pipelines, taking into account the actual operating conditions of thermal networks. Calculations confirmed a significant influence of the main operational factors on the increase in heat loss and the possibility of energy saving in heating networks.

New Smart Passive Graphical Islanding Detection Method

As there is still a great argument on islanding detection methods, this paper presents a new smart passive graphical islanding detection method. The new method depends on measuring the instantaneous variation in phase voltage angle (θ) related to the instantaneous variation in phase voltage magnitude (V) and drawing the relationship between them. The traditional passive methods have performance deficiencies. On the other hand, the active methods are more accurate islanding detection methods, but perturb the electrical system. So, the need for a new detection method which can be accurate, doesn't affect the system behavior, and through which both active and passive methods disadvantages can be avoided is an essential requirement. The continuous updates in Wide Area Monitoring, Protection and Control (WAMPC) technology and Phasor measurement units (PMU) facilitate the idea of measuring and tracing the voltage angle variation. The concept of the new proposed smart passive islanding detection method depends on observing the behavior of the variation of voltage magnitude versus the voltage angle variation (V - θ) of the bus which connects the suggested island with the main power grid. During islanding, sometimes the variation of the voltage magnitude is not significant to be detected, especially in case of low power island. The variation of the voltage angle presents an accurate indication with high sensitivity to the different sorts of system transients. The angle variation behavior differs in load changing, islanding, faulted network, and normal operation conditions. The relationship between (V - θ) is confirmed by the graphical relationship between their derivatives (dV/dt - dθ/dt). V versus θ and dV/dt versus dθ/dt are studied and analyzed in this research to verify the concept of the new method. The new proposed smart method is applied to four different power systems having the same main power grid. The wind electrical power generation unit of the studied power systems has different generation and loading capacities in each of the four studied cases. The studied cases are classified into low, high, and medium (with two different loading status) wind electrical power generation capacity. For each studied case, the system normal operation, load disconnection, islanding, and three phase fault conditions are discussed. In the four studied cases, the results verify the completely different graphical behaviors for each transient condition. So, the concept of the new method is verified.

DZ50: Energy-efficient Wireless Sensor Mote Platform for Low Data Rate Applications

A low cost and energy e_cient wireless sensor mote platform for low data rate monitoring applications is presented. The new platform, named DZ50, is based on the ATmega328P micro-controller and the RFM12b transceiver, which consume very low energy in low-power mode. Considerable energy saving can be achieved by reducing the power consumption during inactive (sleep) mode, notably in low data rate applications featured by long inactive periods. Without loss of generality, spot monitoring in a Smart Parking System (SPS) and soil moisture in a Precision Irrigation System (PIS) are selected as typical representative of low data rate applications. The performance of the new platform is investigated for typical scenarios of the selected applications and compared with that of MicaZ and TelosB. Energy measurements have been carried out for di_erent network operation states and settings, where the results reveal that the proposed platform allows to multiply the battery lifetime up to 7 times compared to MicaZ and TelosB motes in 10s sampling period scenarios.

Energy-aware cooperative networks: enabling technologies, operation design, and benchmarking

Cooperative Communication Networks (CCNs) have recently emerged as a promising technology for improving spectral efficiency and extending overall network coverage. CCNs have also managed to generate significant interest in the research community for their role in optimizing Energy Efficiency (EE) in next-generation networks. However, envisioning CCN as an energy-saving solution is met with many unresolved problems and significant challenges. In this article, we discuss the enabling technologies for energy-aware CCNs, the challenges behind employing these technologies and the open research issues. We also discuss the lack of benchmarking EE metrics and a performance evaluation framework. We propose an EE scheme for a heterogeneous WiFi-sensor network to address these issues and present a measurement- based methodology to evaluate the proposed scheme. The scheme is designed using Markov Decision Process (MDP). The implementation of the scheme in the proposed testbed demonstrates its ability to provide 63 percent energy-saving in the WiFi network and 82 percent in the sensor network in low traffic network operational conditions.