Analysis of the Harmonic Distortion and Unbalanced Conditions in the Operation of Electro-Mechanical and Digital Protection Relays

摘要

It is well known and documented on specialized literature about protection systems that the power system need to be protected against different abnormal operation conditions. Two special cases of abnormal operation conditions are the presence of harmonic distortion and the unbalance. The presence of harmonic distortion on voltage and current waveforms adversely affects the behaviour of electric devices including protection systems, resulting in their miss-operation or wrong operation. Specialized literature about protection systems and power quality normally presents studies realized on electro-mechanical relays but there is not much information about static and digital protection systems behaviour under distorted waveforms conditions. For the case of power system operation under unbalanced conditions, literature documents among different protection schemes the use of the negative sequence component, however, detailed studies are rarely presented about the use of sequence protection functions, in contrast with phase protection functions; there is no information about the impact of harmonic distortion on sequence protection functions. This contribution details the results of harmonic tests conducted with three different relay generations, in order to know if established knowledge still apply to new protection system technologies. A comparison of sensibility of response between phase and sequence protection functions under unbalanced conditions in the presence of harmonic distortion is in addition presented.