Microprocessor-implemented digital filters for inrush current detection

Abstract A digital inrush-current detection algorithm is described, which is based on a least-squares curve fitting of the sampled differential current by a decaying DC and five harmonic components. The digital filters developed on the basis of this theory are implemented by means of a microprocessor. Laboratory tests demonstrate that the microprocessor is capable of handling the rather complicated digital filtering. To carry out these tests, the digital filters are incorporated in a protection scheme. The resulting digital protection is tested online. Some typical programming features, necessary for microprocessor implementation, are discussed.