Francesco Muzi

Vibro-acoustic techniques to diagnose power transformers

This paper deals with new procedures based on vibro-acoustic techniques to diagnose power medium-voltage/low-voltage (MV/LV) transformers. The normal operating machines can be monitored and checked from a remote, dedicated diagnostic center where information is received directly from the field. The diagnostic method adopted and the experimental test results are reported. Tests have been performed either in the laboratory or directly in the field on transformers in normal operating conditions. The laboratory tests related the transformer vibrations to internal anomalies. The suggested monitoring and diagnostic system allows one to usefully schedule preventative maintenance, reduce costs, and improve the quality of power distribution.

Acoustic signal processing to diagnose transiting electric trains

This paper deals with a method based on vibroacoustic techniques to diagnose electric trains and other important railway components. The proposed method can detect the following main subsystems: pantographs, electrical contact lines, rails, bogies, wheels, etc. Signal-processing techniques are thoroughly applied to acoustic vibrations that are directly acquired on the field when the train is transiting. Signals are picked up, processed, and stored by acquisition systems installed along the railway on structures jointed to the soil. The processed data can be sent to a remote dedicated diagnostic center to get continuous monitoring and supervision of the railway system. The received diagnostic information can be conveniently used to improve safety, to schedule a correct maintenance, and to reduce costs. The results of the experimental tests conducted to validate the method during an extensive measurement program are reported and commented.

Variable-window algorithm for ultra-high-speed distance protection

This paper presents a new concept in ultra-high-speed distance relays for power line protection. The idea is based on the use of a sampling window shorter than usual to speed commutation. The reduction in protection time is obtained through a variable window that is expanded sample by sample until a satisfactory precision is reached in the calculation of fault quantities. The right window length is obtained automatically via software and time-by-time change depending on the characteristics of the fault. The algorithm is based on the equation associated to the R-L fault circuit, whose solution is obtained using the phase-modified Fourier transform. To validate the proposed procedure, a large number of simulations are performed with reference to an existing 150 kV subtransmission line. In comparison with other solutions, the relay proposed here is very cost-effective and makes it possible to achieve ultra-high-speed fault localization not only on EHV networks but also on HV distribution networks.

A real-time harmonic monitoring aimed at improving smart grid power quality

It is well known that network analyzers perform reliable estimations of the Total Harmonic Distortion (THD). A distorted signal is actually decomposed in real time into its harmonic components using the Fourier transform. The implemented algorithm requires a 200ms observation window in order to meet both the necessary accuracy and standard requirements. Though the adopted observation time is compatible with the dynamic behavior of large generators, it is however not acceptable for small distributed generators (DG). Moreover, DGs are usually intermittent energy sources connected to a distribution network through inverters with time constants of dozens of microseconds. For this reason, smart grids with a massive presence of distributed renewable generation have to be monitored by fast algorithms in order to guarantee high levels of power quality. Actually, a remarkable distortion of the voltage waveform, which may also be due to a malfunctioning inverter, can cause for instance an incorrect behavior of digital protection systems. Herein a fast algorithm for the estimation of voltage harmonics is introduced, which, contrarily to algorithms currently adopted for the discrete Fourier transform, can be implemented also in non-updated, low performing microprocessors. The proposed method uses a second order generalized integrator that refers to the SOGI-based Frequency Locked Loop (SOGI-FLL). A number of simulations were performed in order to validate the method, and the results showed that the time response of the algorithm is less than 20 ms, which means the method can be profitably used to improve smart grid power quality.

Symmetrical Components and Digital Signal Processors for Smart Grid Protection

The paper presents a study on asymmetric faults with explicit reference to smart grids. The kinds of faults examined are: single phase ground fault, double phase ground fault, phase-phase short circuit, three-phase short circuit and single phase interruption. As a matter of fact, the complexity of smart grids requires new targets for protective systems in terms of reliability, timeliness and security. In comparison with traditional methods, the digital protections of the latest generation are very effective, versatile and programmable, allowing to simulate all network components effortlessly and therefore exactly. This new scenario also requires a revisitation of the theories underlying power system protection, so as to target them to the latest requirements. The results of a case study concerning a single-phase fault clearing and subsequent, automatic network reconfiguration are reported and illustrated.

A Predictive Model for the Automated Management of Conditioning Systems in Smart Buildings

The paper describes a technological basis for dynamic actions targeted to an effective, real-time control of air conditioning systems in smart buildings with a focus on energy management. The proposed procedure could be extended to more complex systems, usually including a number of prosumer (producer and consumer) nodes, connected to a smart grid and remotely controlled by a Distributed System Operator (DSO) in distributed control and monitoring systems. Accurate, continuously-recorded local weather data are then used to make decisions aimed at both reducing energy consumption and assuring pre-established comfort levels. The amount of saved energy can be estimated by observing a buildings energy performance under the action of different meteorological agents through data mining and machine learning methods. Moreover, some possible advantages from real-time exploitation of a buildings thermal inertia are shown. The proposed on-line management was also validated through laboratory experimental tests, whose results are reported and discussed.

Implementation of a new control system for low voltage switchboards

A new kind of control system to remotely manage an LV switchboard is presented. The main feature of the system is an optimal load management that allows both to optimize end-use energy consumptions and increase the level of supply continuity. An interesting application of the switchboard lies in the management of LV installations connected to smart grids, where the consumer - also named “prosumer”- can produce energy, usually from renewable sources as in the case of photovoltaic generation. In applications of this kind traditional switchboards are not able to manage bidirectional power flows, loads, and generators at same time. The proposed control system is provided by a user-friendly interface developed in a Microsoft Visual Studio environment, which is also described in the paper.

Improvement of the dispatching preplanning process in day-ahead electricity market using a sequential method

This paper proposes a sequential loading method, which finds the hourly changes of frequency and optimal load distribution between power stations. The method solves to minimize the aggregate cost in the electric power system (EPS). The method also calculates the surplus or deficit of an active power in EPS, hourly power flows of each transmission lines, active power losses in the networks. Computed and analyzed the optimal regimes of Mongolian EPS by the proposed method. The result confirmed that the method can potentially benefit to supply of frequency regulation. Developed software allows doing day-ahead market planning and intraday market preplanning in EPS, which improves electricity market model.

An effective procedure for voltage control in HV systems receiving remarkable energy from DG

The high levels of energy produced by Distributed Generation (DG) may create some problems to the voltage control of transmission systems if a great amount of active power crosses transformers and autotransformers from lower to higher voltage level (reverse power flow). In addition DG is usually intermittent and often does not participate to the voltage regulation process. This situation may be accepted as long as the power from renewable sources (wind and solar PV) is much lower than the power generated by conventional power stations. However, due to the large amount of DG now installed, in such situations as favorable weather conditions and low electrical load, the production from traditional power plants might become negligible compared to the production from distributed renewable sources. Under these conditions, which are occurring more and more frequently in Italy, the blackout risk becomes increasingly high. The present work shows that DG increase is not only just another problem to solve, but it can also be seen by the system operator as an opportunity to adopt proactive actions towards an effective voltage control. With this in mind, the use of a practical procedure is suggested whose validity was demonstrated first theoretically and then through a number of field tests which were suitably reported and commented.

Maximizing energy injections of distributed generation in rural areas

Since its introduction, distributed generation (DG) has surely allowed the exploitation of otherwise unrecoverable energy resources dispersed on the territory, though posing a series of as yet unsolved problems connected to smart grid operation. One of these inconveniences is the automatic DG disconnection in weak network. Actually, for a DG system to be able to inject power into a grid, the voltage value in its interconnection node must be increased. If voltage exceeds a certain limit, the current Protection System Interface (SPI) will disconnect the generator resulting in the total loss of the energy produced at that node. This paper proposes a number of solutions to the issue, making specific reference to inconveniences that actually occurred in DG systems installed in some Italian rural areas, but that might as well affect areas with higher load densities. During a first phase of the study, the current situations were analyzed and then a circuit model was implemented in a Matlab-Simulink environment to obtain an accurate system simulation. The DG taken into consideration mainly involved photovoltaic systems connected to LV networks, of different sizes and supposedly working in different operating conditions, depending on load demand and weather conditions. The results of the numerical simulation were properly illustrated and discussed, so as to establish the actual validity of the proposed solutions.