Alternative paths & reserve capacity
The main task of every electric power system is to provide its customers with a reliable and economically feasible supply of electricity. In order to provide a reliable supply of electricity, there is a built in reserve capacity within the grid to cope with contingencies, increased demand and scheduled maintenance.
This reserve capacity must be designed and constructed in the most economically and technically optimal way in order to ensure reliable power transmission as well as the lowest possible cost.
Reliability is defined by the International Electrotechnical Commission (IEC) as: “the ability to perform a required function under given conditions for a given time interval“. Reliability of the electric power system can be increased by either shortening the duration of the interruptions of the power supply or by lowering the frequency by which interruptions occur.
The probability that a component in the system will fail is generally increased when the number of components rises.
By calculating the impact of using reserve capacity and its impact on SAIDI, it is easier to determine if the risk taken is acceptable. Risk is defined as the “effect of uncertainty on objectives” which implies that risk can both have positive and negative implications.
Reserve alternatives to loop configurations
This thesis is focused on analysing reserve alternatives to loop configurations and their impact on SAIDI in the electrical distribution system (EDS). The results are used to propose dimension criteria that can be used by the DSO in the general case of the medium voltage distribution system in Gothenburg.
The medium voltage distribution system in Gothenburg is composed mostly of 11 kV underground cables and it is the different configurations of the underground cables that has been analysed.
Provided statistics from GENAB are used as input in the models to provide a high correlation between the models and reality. One part in maximising the reliability and utilising the reserve in an efficient manner is to use probabilistic methods to analyse the probabilities of potential faults and contingencies.
By performing simulations and creating simplified models of the system it is possible to acquire the data needed to make motivated and analysed decisions on utilisation and future investment of the reserve capacity.
The dimension criteria include the maximum amount of 11/0.4 kV secondary substations per loop that can use the same reserve as well as including the eventual implications on SAIDI and reliability associated with the utilisation. These criteria are presented for different cases that are applicable in the Gothenburg region.
The criteria should also take current carrying capacity of the underground cables and the resulting voltage drop into consideration. By using appropriate models of the power system to portray the different cases, the impact on SAIDI (System Average Interruption Duration Index) could be calculated.
|Title:||Reliability of the Electric Power Distribution System for Alternative Reserve Configurations; Master’s Thesis in Electric Power Engineering – Aron Von Scheele at Department of Energy and Environment, Electric Power Engineering, Chalmers University of Technology|
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