TABLE OF CONTENTS With the increasing dependence on electricity supplies, in both developing and developed countries, the need to achieve an acceptable level of reliability, quality and safety at an economic price becomes even more important to customers. A further requirement is the safety of the electricity supply. A priority of any supply system is that it has been well designed and properly maintained in order to limit the number of faults that might occur.
Associated with the distribution networks themselves are a number of ancillary systems to assist in meeting the requirements for safety, reliability and quality of supply. The most important of these are the protection systems which are installed to clear faults and limit any damage to distribution equipment. Amongst the principal causes of faults are lightning discharges, the deterioration of insulation, vandalism, and tree branches and animals contacting the electricity circuits. The majority of faults are of a transient nature and can often be cleared with no loss of supply, or just the shortest of interruptions, whereas permanent faults can result in longer outages. In order to avoid damage, suitable and reliable protection should be installed on all circuits and electrical equipment. Protective relays initiate the isolation of faulted sections of the network in order to maintain supplies elsewhere on the system. This then leads to an improved electricity service with better continuity and quality of supply.
A properly co-ordinated protection system is vital to ensure that an electricity distribution network can operate within preset requirements for...
