A 3rd Harmonic Power Based Open Conductor Detection Scheme

Detection of open conductor condition in a system with unloaded ${{{\bf Y}}_{{\bf g}}}$ connected primary transformers has been a challenging task. This is due to the lack of detectable abnormal voltage and current responses when a conductor opens. This paper recognizes that the above situation is related to the positive sequence nature of the supply voltage. If the supply voltage were in zero-sequence, an open conductor would result in distinct voltage and current responses. Based on this understanding, a relaying scheme that uses the 3rd harmonic power is proposed to solve the open conductor detection problem. The 3rd harmonic is known to be dominant in zero-sequence and it exists in various parts of a power system. Performances of the proposed method have been evaluated using simulation and experimental studies. The proposed scheme can be easily implemented using a relay similar to the zero-sequence power relay. Extensive study results show that the proposed method is a promising technique to solve the open conductor detection problem.