Severe Contingencies Analysis in Portuguese Transmission System

Abstract

Nowadays when utilities are faced with increasing requirements regarding Quality of Service, it is important to be aware that severe contingencies can happen, in an unpredictable way which far exceeds all the security principles used for planning and system operation. In any electricity transmission system, a security condition must be assuredeither in steady or in transient state -otherwise the essential service provided to costumers could be severely jeopardized. Present day Quality of Service requirements that are imposed on the electrical utility companies force them to develop efficient processes to analyze and react to incidents that can happen in an unpredictable way and far exceed all the security principles used. The simulation and analysis of these scenarios allow us to minimize the risk of system unbalance and voltage collapse. The steady state simulations of the Portuguese Transmission System were made in PSS/E software from Siemens Power Transmission Distribution, Inc., using savecases that represent pictures of the real system. The simulation results presented focus on aspects like energy not supplied, generation lost and topological changes resulting from an incident, which will affect mainly the power flow distribution within the grid elements that will remain in service (connected) and the voltage level in the system bus-bars. These results allow us to be better prepared to face these severe disturbances, defining procedures for emergency situation and training the control room operators.

Integration of common cause faults in the operational probabilistic approach

“…The most common situation is faults caused by lightning that affect simultaneously OHLs that share the same towers during the whole or part of their path. Another possible origin of common cause faults is forest fires affecting a corridor composed by several OHLs [9].…”

“…-List C -Loss of overhead line corridors (which were selected using a proximity specific criterion, due to the risk of all lines in the corridor being affected by a forest fire). The OHL corridor definition can be found in [9]. -List D -Distribution failures (includes closed rings through the distribution 60 kV network and the EHV/60kV transformers, excluding single feeders).…”

Graphical Ways to Visualize Operational Risk Results for Transmission System Contingencies

“…Failure rate and repair rate are the main constituents of component unavailability Q(t) given by (1), where it is assumed that the component is known to be available at time zero.…”

“…The use of this criterion poses unnecessary limitations during periods with low component failure rates; on the other hand, it leads to an underestimation of the risk during periods when components have a high failure rate. Moreover, the N-1 deterministic method does not consider local conditions, e.g., adverse environment and geographical locations in the contingency list [1,2]. The limitations of the existing methods for maintaining operational security were also the base for the development of alternative methods in the GARPUR project [3][4][5][6], in which a number of European transmission system operators (TSOs) played a major role.…”

Impact of external elements on the responsibility area of a Transmission System Operator using the influence factor method

“…The new paradigms associated with the restructuring of the electric power industry has introduced a much more competitive environment, new economic and social constraints, that forced the electric utilities to operate their power networks closer to their physical and security limits [4]. Under such increasingly complex conditions, the maintenance of power systems security has become a very important issue [5].…”