34621 - Power systems M

Course contents

Power transmission lines. Technical characteristics of overhead transmission lines: bundle conductors; towers; grounding wires. Primary and secondary constants per unit of length: resistance, positive sequence inductance, positive-sequence capacitance, conductance. Cable transmission lines: description of the most common cable types. Steady state of transmission lines; characteristic and surge impedances; propagation, attenuation and phase constants; propagation speed; wavelength; characteristic and natural load. Electrical design of transmission lines. Transmission line as equivalent two-port circuit; Perrine-Baum diagram; phasors power diagrams.

 

Study of power systems load flow. Formulation of the problem for the calculation of the load flow in power networks. Solution of the problem: Gauss-Seidel and Newton-Raphson methods. Approximations of the solution methods: DC approximation, Carpentier and Stott methods. Capability curves of three-phase linear and isotropous synchronous generators. Base aspects of the economic dispatch and unit committment.

 

Power system stability. Stability of synchronous generator connected to a synchronous motor and to an ideal network. Concept of ‘static' and transient stability. Dynamic equations. Equal area criterion. Application of the equal area criterion to some typical cases (three-phase fault followed by a permanent breaker opening, ...). Calculation of the rotor shift angle of synchronous machines. Calculation and analysis of small oscillations of a synchronous machine connected to an ideal network. Concept of dynamic stability.

 

Calculation of short circuit currents. The short circuit and its consequences in power networks. Short circuit transients. Symmetrical components. Impedances of typical elements of power systems (synchronous machines, power transformers, transmission lines). Calculation methods of short circuit currents in complex networks relevant to different short circuit types (three-phase, single phase grounded, …). Solution methods for multi-node networks. Impedance matrix.

 

Protection of transmission lines and transformers. Requirements of a protection system. Classification of power system relays. Protection of transmission lines: distance protections; directional relays. Protection of power transformers: differential current relay; Bucholz relay; earth protection; protection against external faults. Bus-bar protection. Protection against overloads (base aspects).

 

Voltage control. Voltage control in transmission and distribution networks. Reactive power flow controls. Transformers with on-load tap-changers. Voltage collapse.

 

Frequency control. Typical behaviour of speed controls of thermo-electrical power plant units. Primary frequency control in presence of a single generation unit with loads. Frequency control in a system with multiple generation units; distribution of the active power load among the generation units of the network. Power-frequency control for interconnected networks.

 

Insulation coordination. Probabilistic approach. Lightning overvoltages. Base aspects of the lightning phenomenology. Lightning location systems. Protection of overhead transmission lines against direct lightning (‘shielding failure' and ‘back-flashover'); protection of distribution overhead distribution lines against indirect lightning. Typical structure and operation characteristics of surge arresters; shielding wires and their role in the protection of overhead lines.

 

Electromagnetic transients in power systems. Summary of theory on travelling waves in loss-less transmission lines; reflection transmission coefficients. Transient behaviour of transmission lines with general termination loads including non-linear components; equivalent generator method; lattice diagram. Travelling waves in presence of losses; ground impedance; Carson formula. Bergeron method. The ElectroMagnetic Transient Program (EMTP). EMTP-application for the design of transmission line protection system against lightning.

 

DC current applications. Typical cases of DC technology application relevant to: long distance transmission lines; submarine links and back-to-back connection between different networks (e.g. link between east and west Europe power networks).

Readings/Bibliography

J. Grainger, W. Stevenson, Power Systems Analysis, McGraw Hill, 1994 

R. Marconato, Electric Power Systems, CEI, Milan, 2004. 

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R. Marin, M. Valtorta, Trasmissione ed interconnessione, V Ed., Cedam, Padova, 1973.

D. Zanobetti, M. Pezzi, Lezioni di impianti elettrici, CLUEB, Bologna, 1981.

F. Iliceto, Impianti elettrici, Pàtron, 1981, o edizioni seguenti.

R. Marconato, Sistemi elettrici di potenza, 2 voll. CLUP, Milano, 1985, o edizioni seguenti.

A. Paolucci, Lezioni di trasmissione dell'energia elettrica, Cleup, Padova, 1990 o edizioni seguenti.

G. Malaman, A Giorgi, M. Calzati, Teletrasmissioni al servizio delle reti elettriche di energia, Pitagora editrice, Bologna, 1988.

A. Silvestri, “Sistemi elettrici per l'energia” nel Nuovo Colombo - Manuale dell'Ingegnere, Hoepli, 2000.

Teaching methods

In addition to classical blackboard and/or videobeam slides, the Course includes laboratory exercises (load flow and short circuit calculation, calculation of transmission stability) and computer sessions (calculation of power flow in high voltage transmission networks, calculation electromagnetic transients in transmission lines). Additionally, a visit to a large TSO substation, whose structure will be illustrated in detail before the visit, is scheduled.

Assessment methods

The exam consists in a written exercise that allows, after a positive evaluation, to proceed with the oral exam.

Teaching tools

Lecture notes (in Italian) prepared by the docent, available at http://campus.cib.unibo.it

Office hours

See the website of Carlo Alberto Nucci