RICERCA

RICERCA

HV underground cables and overhead lines

This research would analyze the thermal limit (or Carrying Conductor Capacity) and the economical ampacity of the HV and UHV electrical cables and overhead lines.

This study are normally already available as result of the studies made in the ’60 by the main TSO (Transmission System Operators). The actual solutions of the conductors normally adopted (standard solutions) should be now reanalyzed taking into account the different economical values of the Joule and Corona losses and introducing the economical component correlated with the CO2 emission.

In the research also the high-temperature conductors are also considered (for OHV lines). 

 References

  1. M. Pompili, A. Posati “Multiconductors 400 kV Overhead Lines and their Environmental Impacts”, International Symposium CIGRE 2013, Auckland (NZ), September 2013; 
  2. G. Fioriti, A. Sturchio, M. Pompili, B. Cauzillo, “Failure Rates Reduction in Smart Grid Medium Voltage Distribution Lines: Influence of Temperature”, Annual Meeting AEIT 2014 – Trieste (Italy).
  3. L. Calcara, M. Pompili, B. Cauzillo, “Ampacity of MV Underground Cables: the Influence of Thermal Soil Resistivity”, 2015 International Youth Conference on Energy, May 2015 – Pisa (Italy)
  4. G. Fioriti, A. Sturchio, M. Pompili, L. Calcara, “Thermal Behavior of Distribution MV Underground Cables”, Annual Meeting AEIT 2015 – Napoli (Italy).

Life Cycle Assessment (LCA) of strategic electrical transformers and of large transformer fleets

Large electrical Operators and Utilities have in service some hundreds of HV power transformers with voltage levels in the range 130 - 500 kV (or above) and nominal powers of some tens of few hundred of MVA. These fleets of transformers represent assets of large economical value and unexpected failures may have large consequences, like unavailability of part of the system, loss of incomes, fires and explosions.

In several cases, the economic losses may be avoided adopting electrical schemes with appropriate redundancies but fire and explosion may be at the origin of others negative consequences with risks for human life and for the environment. In fact, HV transformers contain large quantities (several tens of tons) of mineral insulating oils and an internal electrical arch, releasing a large energy, may trigger fires and explosions.

The risk evaluation may be the key tool for classifying power transformers, mainly when belonging to large fleets, in iso-attention classes. The risk related to every unit may be defined as the probable losses due to a severe failure of the same transformers in a given period of time. This risk is formed by three partial components as in the following:

a) Causes of the failures, as for example:

  • overvoltage due to lightning strokes of the electrical substation or the incoming overhead lines;
  • short-circuit currents which have interested the transformer;
  • energizations;
  • temporary overloads;
  • other accidental and operational causes.

b) Probability that a failure may provoke a damage

c) Type of damages, as for example:

  • human injuries;
  • economical losses;
  • social-economic negative impacts.

The risk has the same dimensions of the damage which is at the origin of the same risk. Under some conditions, the risk may be expressed as in the following equation:

R = N · P · L     

where:

  • N is the number of dangerous events (like: lightning strokes, etc.). N is function of several parameter as the location of the substation, the number and the characteristics of the incoming overhead lines, etc;
  • P is the probability of one dangerous event may cause a damage. P is function of the capability of the transformers to withstand at the negative event without serious consequence: this capability may be considered as an “health index” (HI) of the transformer;
  • L is the average damage and is function of the economical asset of the transformer and its location (visibility, proximity to houses, etc).

 On the basis of this approach the following main conclusions may be depicted:

  • preventive and protective actions may reduce the risk: the efficiency of these actions differ with the type and status of the equipment and the related magnitudo of any possible accident;
  • new preventive systems (on-line monitoring systems, strategic prevention and intensive diagnostic plans carefully managed, etc.) are now available and their adoption may be taken in consideration;
  • when dealing with large fleets of equipment (like power transformers) the statistical approach on risk evaluation may be most helpful, giving also information in classifying each transformer and on which of them is more important to intervene.

 References

  1. M. Pompili, F. Scatiggio,  “Classification in Iso-Attention Classes of HV Transformer Fleets”, IEEE Transaction on Dielectric and Electrical Insulation, Vol 22, N. 5, 2015
  2. F. Scatiggio, M. Pompili. “Health Index: the TERNA’s Practical Approach for Transformers Fleet Management”, CIGRE Plenary Meeting 2014, Paris (France), August 2014;
  3. F. Scatiggio, M. Pompili, “Health index for transformers fleet management”, IEEE Electrical Insulation Conference, Ottawa (Canada), June 2013;
  4. M. Pompili, “On Health Index for Transformers Fleet Management”, IEEE DEI Italian Chapter My Transfo 2012, November 21-22, 2012, Turin (Italy).

Advanced liquid dielectrics and innovative evaluating test methods

This research deals with the activity of the IEC Technical Committee 10, “Fluids for electrotechnical applications”.

The main subjects concerns:

  • The use of vegetable oils (natural esters) in HV transformers.
  • The use of advanced test methods for the diagnostic of the insulating fluids and of the power transformers.

References

  1. M. Baur,  L. Calcara, M. Pompili, “Scatter Reduction of the 50-60 Hz Breakdown Voltage Test for Insulating Liquids”, IEEE Transaction on Dielectrics and Electrical Insulaton, Vol. 22, N. 5, 2015;
  2. M. Pompili, R. Bartnikas, “Gas Formation in Transient Cavities Undergoing PD Pulse Burst Discharges in Transformer Oils” IEEE Transaction on Plasma Science, Vol. 42, June 2014; 
  3. M. Pompili, M. Baur, “Pre-Energizing Effect on Breakdown Voltage Test for Insulating Liquids”, IEEE 2014 ICDL, Bled (Slovenia) July 2014;
  4. M. Baur, M. Pompili, R. Bartnikas, “A Comment on the Test Methods for the Breakdown Voltage of Dielectric Liquids, IEEE Transaction on Dielectrics and Electrical Insulation, October 2012; 
  5. M. Pompili, R. Bartnikas, “On Partial Discharge Measurement in Dielectric Liquids”, IEEE Transaction on Dielectrics and Electrical Insulation, October 2012;
  6. M. Pompili, C. Mazzetti, R. Bartnikas, “Comparative PD pulse burst characteristics of transformer type natural and synthetic ester fluids and mineral oils”, IEEE Transaction on Dielectrics and Electrical Insulaton, Vol. 16, N. 6, pp. 1511-1518, 2009;
  7. M. Pompili, “Partial discharge development and detection in dielectric liquids”, IEEE Transaction on Dielectrics and Electrical Insulaton, Vol. 16, 2009;
  8. M. Pompili, C. Mazzetti, R. Bartnikas, “PD pulse burst characteristics of transformer oils”, IEEE Transaction on Dielectrics and Electrical Insulaton, Vol. 13, 2006.

  Corrosive sulfur in insulating oils: its detection and correlated power apparatus failures

This research topic was set up in 2005 to deal with the problem of formation of copper sulphide in transformer insulation. The phenomenon has caused numerous failures in transformers and reactors. Even though it has relatively recently been recognized as a serious problem, the re-examination of old failure cases indicate that the problem is not really new. However, there is little doubt it has been increasing in recent years. The view has been expressed that the growth of copper sulphide with subsequent failures is only part of a more general problem, characterized by the contamination of transformer insulation by conductive oil degradation products. Some progress has now been made, especially in the fields of test methods and the decontamination processes.

 References

  1. F. Scatiggio, M. Pompili, R. Bartnikas, “Effects of metal deactivator concentration upon the gassing characteristics of transformer oils”, IEEE Transaction on DEI, Vol. 18, 2011;
  2. R. Maina, V. Tumiatti, M. Pompili, R. Barnikas, “Transformers surveillance following corrosive sulfur remedial procedures, IEEE Transaction on Power Delivery, Vol. 26, 2011;
  3. R. Maina, M. Pompili, R. Bartnikas, “Dielectric loss characteristics of copper-contaminated transformer oils”, IEEE Transaction on Power Delivery, Vol. 25, p. 1673-1677, 2010;
  4. R. Maina, V. Tumiatti, M. Pompili, R. Bartnikas, “Corrosive sulfur effects in transformer oils and remedial procedures”, IEEE Transaction on DEI vol. 16, p. 1655-1663, 2009;
  5. F. Scatiggio, V. Tumiatti, R. Maina, M. Pompili, R. Bartnikas, “Corrosive sulfur induced failures in oil-filled electrical power transformers and shunt reactors, IEEE Transaction on Power Delivery, vol. 24, p. 1240-1248, 2008;
  6. F. Scattiggio, V. Tumiatti, M. Pompili, R. Bartnikas, “Corrosive sulfur in insulating oils: its detection and correlated power apparatus failures”, IEEE Transaction on Power Delivery, vol. 23, p. 508-510, 2007.

 

 Analysis and estimation of risk due to lightning for the selection and coordination of surge protection measures

Aim of the investigation:

  • to give criteria for selection of discharge currents and protection levels of upstream and downstream surge protection devices (SPD) in case of flashes to and near the structure, to and near the connected lines; 
  • a proper installation and coordination of SPDs, namely switching and limiting SPD, for the protection of electrical and electronic systems within a structure. 

References

  1. Kisielewicz T., Mazzetti C., Lo Piparo G.B., Kuca B., Flisowski Z., “Electronic apparatus protection against LEMP: Surge threat for the SPD”, Proc. International Symposium on Electromagnetic Compatibility 2012;
  2. Kisielewicz T., Fiamingo F., Flisowski Z., Kuca B., Lo Piparo G.B., Mazzetti C., “Factors influencing the selection and installation of surge protective devices for low voltage systems”, Proc. International Conference on Lightning Protection, 2012;
  3. R. Tommasini, M. Pompili, C. Mazzetti, Z. Flisowski (2009). Avalicao de risco em structuras com perigo de explosao. ELETRICIDADE MODERNA, vol. 427, p. 62-71, ISSN: 0100-2104 (Brazil - in Portuguese)

 Innovative Electrodes for HVDC Submarine Cables

The number of HVDC submarine cable connections are increasing around the world. In these applications, electrodes design is paramount for technical and economic feasibility. Cathode’s design is kept as simple as possible, if bidirectional operation is not required, since reduction reactions do not produce corrosion of the material. The situation is completed reversed for the anodes submersed in seawater: in this case, the corrosion mechanism could provoke removal of surface material.

For this reason, in order to ensure a sufficiently high life span, the anode is usually made of different and more expensive materials, like titanium rods, coated with layers of a noble metal oxide, such as platinum, or a mixture of several of them. Sometime the seawater anodes are also immersed in materials based on transition elements such as rare earths.

In the present research, innovative prototypes design for seawater anodes, based on steel reinforced concrete, are presented. Experimental comparison between steel, titanium, MMO titanium and concrete-steel seawater anodes showing important reduction of the corrosion phenomena is also considered.

References

  1. M. Pompili, B. A. Cauzillo, “Innovative Electrodes for HVDC Submarine Cables”, Transaction on Power Delivery, accepted for publication, 2015
  2. M. Pompili, B. A. Cauzillo, “An innovative steel reinforced concrete anode for HVDC submarine cables connections”, SC D1 Colloquium 2015 in Rio - Cigré Rio de Janeiro, Brazil, September 2015


Maintenance and recovery of high voltage electricity transport systems by the use of space telecommunication assets (NEW SUBJECT)

This proposal regards the use of current space Telecommunication, Navigation and EO assets to develop an integrated solution and associated services that meet the needs and conditions of entities operating high voltage (132 kV up) electricity transmission and distribution systems with the objective to reduce the probability of occurrence and duration of electricity breakdowns.

The proposed solution aims at offering to the user an innovative platform able to collect data on integrity status of user infrastructures and to provide the user itself with reports/data/ evaluation (following the user requests) which support the user in scheduling maintenance intervention, in order to guarantee the safety and the efficiency of the targeted infrastructures, and to shorten recovery actions: the information gathered would allow, in fact, the elaboration of an “educated recovery plan”, swiftly putting into action corrective actions.

The key point of the proposed solution is the utilization of existing space assets in conjunction with a terrestrial system in order to propose an improved service with innovative capabilities: the terrestrial system will be based on local sensor networks, which communicate in remote way through a control centre by means of satellite/terrestrial data links.

Satellite telecom assets will be used as a link between a Sensor Network (SN) installed on the Asset Under Monitoring (AUM) and a remote control centre located elsewhere.

Weather forecasts services will be used to collect and analyze weather data in order to:

  • Optimize the monitoring effectiveness;
  • Evaluate the actual climatic condition in which infrastructures operates.

The possibility of using GNSS to perform centimeter measurements will be evaluated.

The SM components, integrated with space assets, will enable to offer to target organizations a new class of monitoring services aimed at supporting all aspects of Operation & Maintenance activities of critical structures, according to all enforceable safety rules. Special effort will be paid to empathize monitoring services capability to support the user in catastrophic failures prevention as well as to assess post-event damages. Such monitoring services will be designed to answer the demand of specific users needs.