Statistical methods applied to the control of loadings of h.v./m.v. transformers on a distribution network

At the present time the Area Boards are spending between £8 million and £20 million on capital work, mainly connected with the expansion of the supply network. The cost of equipment to transform from high to medium voltage, together with associated substation equipment and the connections to the high- and medium-voltage networks, represents in the Merseyside and North Wales Electricity Board (Manweb) area somewhere of the order of 30% of the total capital costs. Consequently, a small percentage saving in the number of substations required for the network can represent a considerable sum of money. This saving could result from a decrease in the number of transformers installed if an increase in the mean loading of the existing and future transformers could be considered acceptable. As this mean or average loading is increased, so also is the load on the most heavily loaded transformers, and this has to be limited, owing to the possibility of a certain number of these transformers exceeding the loading at which deterioration is excessive. The load on these transformers has to be considered under conditions of inclement weather and/or outage conditions, which could occur at any time. From a statistical survey of the network conditions in the Merseyside and North Wales Electricity Board area, it can be shown that, within a given probability, a higher mean loading can be considered acceptable, provided that the variation from this mean, i.e. the standard deviation of the individual loadings to the mean, is controlled. The form of this control is considered.