January 2012 Capital Investment - National Grid

Exhibit ___ (EIOP-19)Page 87 of 684Heavily Loaded Line TransformerThe distribution line transformer strategy endeavors to mitigate outage/failure risks dueto overloading of distribution service transformers. Transformer loading is reviewedannually via reports generated from the customer use information within theGeographical Information System (GIS). Transformers with calculated demandsexceeding load limits specified in the applicable Construction Standard are identified andinvestigated in the field.Heavily loaded units are to be systematically removed from the system over the nextfifteen years. Replacement levels may be adjusted based on changes to loading levels,the condition of the population and budget constraints.Drivers:There are approximately 250 transformer failures per year due to overloading whichaffect approximately 3,700 customers annually. Proactive management of equipmentloading through annual review has prevented overloaded transformers from becoming asignificant system performance problem.Customer Benefits:The main benefit of this strategy is that asset utilization will be maximized by maintainingunits in service until such point that replacement is required as identified throughrecurring loading reviews or visual and operational inspection, recognizing thattransformer life expectancy is predominantly affected by loading and environmentalfactors rather than age. Implementation of this strategy will ensure the sustainability ofthis asset class over time and maintain its relatively minor impact on overall systemreliability and customer satisfaction.2011 to 2012 Variance:The projected investment is shown in the table below.Table IV-7Heavily Loaded Line TransformerProgram Variance ($millions)CIP FY12 FY13 FY14 FY15 FY16 FY17 Total2011 3.7 3.0 3.2 3.6 3.7 - 17.12012 - 3.0 3.2 3.6 3.7 3.9 17.3IV-11 1188