A Simplified Lumped Parameter Model for Finding Distribution Transformer and Secondary System Responses to Lightning

The results of other investigations on distribution transformer and system response to lightning strokes to the primary terminal of the transformer are briefly reviewed, from the standpoint of system and transformer currents, and service entrance phase-to-neutral voltage. These investigations were conducted with either full size transformers and scaled primary and secondary lines [1], or by modeling with digital computer programs [2], [3]. With the computer programs employed in [2] and [3], most all known models for the distribution transformer, surge arrester, service drop, load, and primary lines can be handled, thereby enabling simulations whose accuracy is limited primarily by the accuracy of the component models. To examine the effects of changing values of model parameters, different cases are run with the digital programs. A limitation of the digital simulations is the large number of cases which frequency must be run before the effects of varying a single parameter, over a wide range, can be seen. This paper presents and analyzes a simplified lumped parameter model for the distribution transformer and connected system of Fig. 1 with a lightning stroke to the H1 terminal of the transformer. The model is described, and equations are presented for the current entering transformer terminal X2 and the service entrance phase-to-neutral voltage. These equations give significant insight on how these responses are affected by certain transformer and system parameters, without resorting to use of digital computers.