The location of protection devices on electrical tree networks: a heuristic approach
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The location of protection devices on electrical tree networks: a heuristic approach JC James and S Salhi* University of Birmingham The problem of determining the number of protection devices and their locations on an electrical tree network with subtrees dependency is investigated. The aim is to reduce the amount of inconvenience caused to customers that are affected by any given fault on the network. A constructive heuristic and an appropriate implementation of tabu search are proposed and compared against a method currently used by the electrical supply companies. Computational tests are performed on randomly generated electrical tree networks varying in size and branch complexity. Both the proposed methods outperformed the one used in practice. In particular our tabu search implementation was found to produce the best results without taking an excessive amount of computational time. Keywords: heuristic; tabu search; electrical trees; location
Introduction The electrical supply network in the UK consists of several electricity generators, for example, a power station, supply network and customers. Electricity is transmitted via electrical cables at various voltages along the supply network. High voltages are used in order to maximise the transmission ef®ciency, however low voltages are used on the network in proximity to the customers for safety reasons. The voltages used are 132 kV, 66 kV, 33 kV, 11 kV and ®nally the 24 V which enters the customer' homes or factories. The network which transmits the electricity at the higher voltages uses sturdier pylons and cables resulting in it being less prone to faults and is therefore not worthwhile considering in this work. This study is concerned with the 11 kV network, where there is a high number of faults in transmission due to the weather, third party interference, the result of falling branches or trees, etc. For instance in the Midlands area of the UK, the 11 kV network is responsible for approximately 83% of all faults on the network.1 According to the report1 faults can either be transient, that is, sudden and minor, or permanent. Of the faults that occur in the 11 kV network approximately 76% are of the permanent type and cause annual losses of around 56.5 min=customer in the Midlands area alone. Transient faults cause the remaining 24% of the losses which is around 18 min=customer. At the moment several devices exist to minimise the damage done and the outage times when a fault does occur.
*Correspondence: Dr S Salhi, The University of Birmingham, School of Mathematics and Statistics, Edgbaston, Birmingham B15 2TT, UK.
This costs approximately £10 K including ®tting. These devices are mainly based around the fuse concept. When an extraordinarily high voltage or current surge is experienced by the device, it will `trip', disconnecting the damaged section of the network from the rest of the network before the device, and so reduce the damage caused.
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