Adaptive filtering for noise reduction in the input circuits of protection relay systems

This paper describes an adaptive filtering to reduce noise in the analog input circuits of microprocessor-based protection relay (digital relay) systems. Considering that digital relays tend to have multiple functions, it is important to raise signal to noise ratios (SNR) in analog input circuits to a level that will satisfy the requirements of these functions. We have realized a noise reduction method employing an adaptive filter which can be generally applied; not only within digital relays but also for IEDs in substations and independent of protection schemes. This paper presents the concept of this method and illustrates this effectiveness using a number of examples and experimental results.