Modeling Secondary Services in Engineering and Mapping

With the exponential growth in computer hardware power and computer software functionality, it is now possible to include distribution transformers and secondary systems in our engineering models. With the ever growing demands and expectations associated with “Smart Grid,” it is further becoming a requirement that we model secondary. The traditional engineering model has ended at the high side of the distribution transformer and did not necessarily include every foot of distribution line. Secondary and distribution transformers add directly to the size and complexity of the engineering database required to model each transformer and all secondary to each meter. They also add to the size and complexity of the primary system because almost all, if not all, of the primary must be modeled in order to provide connection points for transformers. This paper will discuss the reasons for modeling secondary, define the modeling requirements of center-tapped transformers, define the modeling requirements of secondary and services, explore the sensitivity of data accuracy when modeling secondary systems, explain the derivations of X/R for center-tapped transformers, illustrate transformer X/R calculations when supplied with transformer loss data, and summarize the algorithm theory required to accurately model center-tapped transformers and secondary triplex systems.