Protection and control aspects of improved utilisation of existing overhead lines

High continuous thermal ratings of protection equipments are needed to match primary circuit loading. On the NGC 400 kV system the highest conductor rating is the post fault, 75°C winter rating for L6 lines at 3420 MVA. With 2000/1 current transformers this represents a continuous secondary current of just over 2.4 A. Modern protection equipment is able to closely match this requirement, however older protection designs often have lower continuous ratings and may have to be considered for replacement if the full circuit rating potential is to be realised. The authors outline how new developments in the area of protection and control in order to work the system harder are actively being encouraged within NGC. They currently sponsor and promote research and development in a number of areas that will provide important indicators as to the suitability of for example adaptive relaying, better protection of three ended circuits and new protection designs not requiring the use of dedicated communication circuits