January 2012 Capital Investment - National Grid

Exhibit ___ (EIOP-19)Page 76 of 684Pilot WireVarious projects call for the replacement of metallic pilot wire schemes used to protectsub-transmission underground cables. Due to the complexity of these networks,communication aided protection schemes are required.Drivers:There have been several pilot wire failures over the last several years which havecaused protection mis-operation and increased the risk of customer interruptions due toloss of supply to distribution substations. Typically, when a pilot wire scheme is not ableto operate as designed, the line protection reverts to a non-directional over-currentscheme. On a networked system, this may be lead to “over-tripping”, i.e. more elementsof the system are de-energized than necessary to isolate a fault, possibly resulting inelectrically isolating a distribution system resulting in customer interruptions.Customer Benefits:Engineering and construction costs should be reduced for planned work instead of adamage/failure replacement. In addition, replacement of the pilot wire schemes withmodern protective relays will minimize the risk of relay mis-operations causing customerinterruptions.2011 to 2012 Variance:The projected investment is shown in the table below and is based on specific projectestimates.Table III-13Pilot WireProgram Variance ($millions)CIP FY12 FY13 FY14 FY15 FY16 FY17 Total2011 0.9 1.8 1.8 1.8 1.8 - 8.02012 - 0.3 1.1 0.9 - - 2.3III-18 1877