Influence of instrument transformers and anti-aliasing filters on the performance of fault locators

Anti-aliasing filters are used in cascade with instrument transformers (IT) as part of protective relay data acquisition systems for providing input signals to fault locators. Due to IT and anti-aliasing filters transient responses, the fault locators input data may not be replicas of the power network voltage and current waveforms, and incorrect information may be transferred to protection devices. In this paper, the performance of traveling wave-based and impedance-based fault location techniques are evaluated by extensive short-circuit simulations considering different IT topologies and anti-aliasing filters. The total amount of fault location estimated errors were combined to generate an error function and an original study about a thorough statistical analysis was performed. From the obtained results, the errors can be approximated by a function with normal probability distribution, and the fault location performances are directly affected by the fault-induced amplification and attenuation of the highest frequencies at the IT spectrum and the oscillations presented in the anti-aliasing filters bandpass.