Electrical System Design of Local Generator Applications Involving Adjustable-Speed Drives

The term local generator as used in this paper is intended to describe a generator supply dedicated to a specific facility which would have a more limited and specific capacity and loading than a broader and higher capacity utility supply. These systems, particularly when there is a large nonlinear component, require additional coordination and design considerations as a result. Generator suppliers obviously understand their equipment in great detail and have well-defined application guidelines for the more typical linear loads which they are expecting to supply. Adjustable-speed drives (ASDs) and other nonlinear loads bring additional factors into play such as harmonics, possible requirement for harmonic filters, and the specifics of their topology design such as the inherent capacitance involved in all drive designs. The intent of this paper is to address the necessary application considerations when applying nonlinear loads on local generation starting at the basics of sizing and progressing through topics such as alternator sizing, voltage and speed regulation, etc. Specific focus will be with respect to an application issue which arose for a recent offshore application involving a high component of nonlinear ASD loading on their offshore distribution system per the author's experience.