Georgios T. Andreou

Selective Automation Upgrade in Distribution Networks Towards a Smarter Grid

Research on smart grid technologies has been advancing over the last years, producing novel practices concerning mainly the power distribution networks. However, in many countries these networks still operate in their traditional form, without offering the real-time operational characteristics which are essential for the utilization of the aforementioned practices. On the other hand, due to the extent of urban power distribution networks, as well as the substantial cost of medium voltage equipment, the full upgrade of these networks is in most cases not a feasible option. In this work, alternative options of selective automation upgrade in power distribution networks are offered, corresponding to the desired operational status of these networks. More specifically, the essential upgrades are analyzed for the implementation of reliability improvement and loss reduction techniques on such a network.

Enhanced Protection Scheme for Smart Grids Using Power Line Communications Techniques—Part II: Location of High Impedance Fault Position

An effective protection scheme against high impedance faults (HIFs) has to efficiently confront the issues of detection and location simultaneously. In Part I of this study the issue of detection is investigated, while in Part II a method that deals with the exact location of HIF position using an installed power line communication (PLC) system is elaborated. This method comprises specific test signal injections into the power grid after a HIF alarm is set. Using impulse responses that are recorded by the PLC devices, the location of the fault may be derived. A flowchart that describes the usage of the complete method for HIF detection and location is presented. The impulse responses that correspond to several fault cases are shown and the methodology that may lead to the fault location is explained. The effect of the fault type and its impedance on the efficacy of the method is highlighted. Finally, the model is applied to a line that is part of the Greek rural distribution system and its validity is tested.

Detection and Location of High Impedance Faults in Multiconductor Overhead Distribution Lines Using Power Line Communication Devices

An effective power system protection scheme has to be able to detect and locate all occurring faults corresponding to low and high impedance values. The latter category poses the greatest challenge for the protection schemes due to the low values of the related fault current. This paper extends previous work by the authors on the subject, aiming to achieve detection and location of high impedance faults (HIFs) in multiconductor overhead distribution networks utilizing power line communication (PLC) devices. Fault detection is proposed to be performed by a PLC device installed at the starting point of the monitored line and by using differences to the values of metrics related to input impedance at frequencies utilized by narrowband systems. Moreover, fault location can be derived by a response to impulse injection procedure utilized by all installed PLC devices along the line. The method is evaluated and validated in various simulation test cases concerning its ability to effectively detect and locate HIFs.

Enhanced Protection Scheme for Smart Grids Using Power Line Communications Techniques—Part I: Detection of High Impedance Fault Occurrence

Occurrence of high impedance faults (HIFs) in rural overhead power distribution networks may cause safety and economic issues for both public and the utility. Such faults may not be detected by the conventional protection schemes, so the development of a more sophisticated method is necessary. The forthcoming evolution of power networks to smart grids creates opportunities for new technologies to be implemented to that purpose. Utilities may transmit data that are necessary for the system operation using specific frequency ranges. A novel method utilizing these is proposed in this work. The monitoring of the networks input impedance in these frequency ranges can be used for detection of HIF occurrence, because such faults impose significant changes in its value. The proposed method is applied to single branch topologies, as well as to an existing topology of a Greek rural distribution system. Significant conclusions are derived in both cases. Moreover, the influence of several parameters, such as fault impedance and location and earths electromagnetic properties on the methods efficacy is examined. Also, it is shown that the implementation of the proposed method may be drastically simplified by focusing on the monitoring of specific frequencies rather than the entire frequency range under study.

Electrical Parameters of Low-Voltage Power Distribution Cables Used for Power-Line Communications

Many models proposed in the literature to describe low-voltage power distribution networks in consumer premises as communication media require knowledge of the electrical parameters of the cables comprising these networks. These parameters are nevertheless affected by a large number of factors which may vary greatly from case to case, making it thus very difficult to achieve an exact estimation about them. In this work, a study of the electrical parameters of two cable types widely used in residential low-voltage power distribution networks is presented. Moreover, a finite-element approach is used for the verification of the results of the theoretical model concerning the series impedance per unit length of the cable type under study with respect to its normal operational conditions

Load signatures improvement through the determination of a spectral distribution coefficient for load identification

In this paper a novel and simple methodology for developing distinct load signatures is proposed. The analysis relies on the exhaustive utilization of the information embedded in the harmonic behavior of a load, towards the formulation of an appropriate data form that could describe the behavior of a Low Voltage (LV) load in a unique and representative way. Based only on the current magnitude during one period of the steady state, a special coefficient is formulated under a simple procedure determining the spectral distribution of the current. A load identification algorithm is also developed and presented in order to examine the robustness and effectiveness of the resulting load signatures. The results are very promising since they indicate that uniqueness in load signatures is indeed added by the proposed technique and hence, the improvement of the effectiveness of the signatures could contribute in more efficient Nonintrusive Load Monitoring (NILM) algorithms.

Modeling of Medium-Voltage Power-Line Communication Systems Noise Levels

The implementation of power-line communication systems requires detailed knowledge of the channel properties, such as transfer function, noise levels, and channel capacity in order to assess the services that can be provided. In this paper, the interference scenario on overhead medium-voltage power distribution lines caused by external electromagnetic (EM) fields is examined by focusing on the noise induced. The external EM fields are considered to be the main source of occurring noise and a novel method capable to calculate the corresponding noise levels is presented. The proposed method is compared to other existing models and its strengths are highlighted. The effect of the induced noise to the overall data capacity of the power-line communication channel is examined. Eventually, the influence of several parameters, such as the magnitude and direction of propagation of the external EM field, network topology, earths EM properties, and different levels of emissions suggested by various organizations are investigated.

Event detection for load disaggregation in Smart Metering

The reduction of consumption is an objective of the Smart Grid paradigm. The pursuit of efficient solutions requires the knowledge that can be derived from each installations energy consumption measurements through Smart Metering. This work presents an event detection methodology, aimed to help in the disaggregation of the total measured energy consumption in an installation to a number of partial curves corresponding to individual appliances. The work has been conducted within the scope of the EU funded FP7 project “CASSANDRA - A multivariate platform for assessing the impact of strategic decisions in electrical power systems”.

Earth return path impedances of underground cables for the multi-layer case: a finite element approach

The lossy earth return path influences significantly the electrical parameters of underground power cables, especially in cases where transient simulation models are of interest. The use of approximations for the calculation of earth correction terms proves to be inaccurate at high frequencies or low earth resistivities. The infinite integral terms representing the earth influence are high oscillatory in cases of underground cables and therefore difficult to integrate numerically. The scope of this paper is to present and compare results, obtained by a novel numerically stable and efficient integration scheme to those obtained by a finite element method formulation for several single core cable configurations and for homogeneous and multi-layered earth. Significant differences between impedances are recorded, especially for high frequencies and low earth resistivities.

Performance of Commercially Available Residential PLC Modems

The scope of this work is to evaluate the performance of power line modems developed for use in residential communication networks. For this purpose, two sets of commercially available power line modems based on different specifications are tested in 20 different households representing the most usual residential power distribution networks in Greece. The results show the average throughput achieved in normal operational conditions by the two different modem types, as well as the limitations in their performance. Specific problematic situations are pointed out and explained. This process provides valuable information, concerning the usage of residential power distribution networks for communication purposes.