Integrated metering and protective relay systems

The process of converting sampled analog signals to digital numbers using a low-cost microprocessor and an A/D converter for motor protection is considered. Distribution fault records, relay performance with extremely saturated low ratio current transformers, and advanced methods of protecting high-inertia drive motors are presented. The discussion also covers: digital filtering; range of operation of a digital overcurrent relay; the function of the anti-aliasing filter; advances in motor protection; rotor thermal model; and maintainable structured software