Apostolos N. Milioudis

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.

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”.

High impedance fault evaluation using narrowband Power Line Communication techniques

Occurrence of High Impedance Faults in urban overhead power distribution networks can cause economical and safety issues for both the public and the utility. These faults may hardly be detected using conventional protection methods, so a sophisticated system has to be developed to deal with the problem. In this work the usage of high frequency ranges and specifically the Cenelec A Band frequency range is examined for the detection of such kind of faults by monitoring the input impedance of the system. High impedance faults can cause significant deviation to the overall impedance at specific frequencies. Several branched overhead Medium Voltage topologies are examined and significant conclusions are extracted. Furthermore, a parametric analysis is conducted with respect to the earths electromagnetic properties, i.e. ground resistivity and relative permittivity, regarding their impact on the efficacy of the method. Finally, the occurrence of fault at all possible locations of a transmission line is examined and also analyzed.

Modelling for on-line partial discharge monitoring on MV cables by using a modified Universal Line Model

The overall cable insulation condition can be monitored continuously by the implementation of an on-line partial discharge (PD-OL) monitoring system. It can both detect and locate the sources of PDs and also assess the insulation condition by using past data. The utilization of an accurate electromagnetic transient model is crucial for the accuracy of the system. Therefore, the well known Universal Line Model (ULM) is chosen to be used for the modelling of PDs propagation through underground medium voltage (MV) cables. For that purpose the ULM is properly modified in order to be able to take into account the PDs occurring among the two terminals of a cable section. The proposed approach also indicates the way that frequency dependent cable terminations can be included as well as the time varying noise existent at the points of measurements.

Siting and sizing of Photovoltaic Systems subject to several parameters

In this paper a methodology regarding the siting and sizing of Photovoltaic Systems (PVS) under the consideration of several parameters is presented. In the proposed algorithm equal distribution of the available PVS is initially considered and at the next level appropriate coefficients are formalized in order to quantify each respective parameter. The initial equal distributed capacity of PVS is being resized due to the impact of various critical parameters. Moreover, the participation of each parameter to the resizing procedure is being defined by respective weight factors. In the paper, the Interconnected Greek Transmission System (IGTS) is examined as the test case and useful conclusions are depicted regarding the algorithms results. The proposed algorithm could constitute a useful guideline for efficient allocation of PVS in regard to specific predefined requirements and in turn it could define the most appropriate solution among a number of alternatives.