A Practical Guide: Design and Protection Considerations for Developing Reliable Automatic Transfer Schemes (ATSs)

An automatic transfer scheme (ATS) is a widely used power system protection and control scheme to automatically transfer loads from one source to another during contingencies. Most modern ATS controllers and logic processors are also programmed with additional protection and operational functions that become sources of error when not applied properly in conjunction with the ATS. As a result, engineers face several challenges when dealing with such complex schemes. Therefore, this paper offers a step-by-step guide to developing reliable and secure ATSs, drawing from the authors’ field experiences and lessons learned while implementing such schemes. The paper explains various factors and steps to consider when developing an ATS, including (i) the location of the scheme and appropriate transfer initiate conditions, (ii) loads connected directly to the buses in the ATS and criticality of the loads, (iii) various functions and operations included in the ATS, (iv) ATS switchgear design considerations, (v) power system protection considerations, and (vi) testing and commissioning of the ATS.