Control of tap change under load transformers through the use of programmable logic controllers

This paper describes a method developed by Pennsylvania Power and Light Company (PP&L) for applying programmable logic controllers to control tap change under load (TCUL) power transformers. Equipment was identified, and a set of software programs developed, to completely replace the existing analog-based TCUL control systems. There is a significant cost savings from this approach, and PP&L expects an increase in the reliability of the TCUL controls from this design, as well as fewer operations of the TCUL equipment. Several additional functions and alarms were implemented in the new design which will enhance the operation of these transformers