Hassan Abniki - Deputy Director General of the Office of Research and Technology Development, Tavanir Co., Tehran, Iran
Mostafa Hajati Samsi - Qazvin Islamic Azad University, Qazvin, Iran.
Behrooz Taheri - Young Researchers and Elite Club, Qazvin Branch, Islamic Azad University, Qazvin, Iran.
Seyed Amir Hosseini - Isfahan University of Technology

Power transmission lines are vital components of today's power systems. These power lines transmit the electricity produced in power plants in high volume and with very low losses to distant areas so that it can be reached to consumer through distribution networks. In fact, these lines are the intermediary between major energy producers and distribution networks. Accordingly, these transmission lines are of a great importance and must be protected appropriately with a suitable protection system. Distance relays are widely used to protect these lines due to their convenient coordination characteristics and simplicity. High impedance fault (HIF) can be a critical challenge for distance relays due to their low current amplitude and similarity to conventional events in power systems such as capacitive bank switching. For this reason, in this paper a new approach is presented based on the instantaneous frequency variations obtained from the current RMS in order to detect the high impedance fault. This method detects high impedance faults via calculating a Detection index (DI) and considering a threshold value. The proposed method has been tested using DIgSILENT and MATLAB software in an IEEE standard ۳۹-bus network. The presented results evidently demonstrate that the proposed method is suitable for detecting HIF and Low impedance fault (LIF). In addition, this method has a proper performance during capacitor bank switching and can well distinguish between HIF and capacitive bank switching. Moreover, the presented method is resistant to noise and also is capable to detect the faulty phase.

High Impedance Fault (HIF), Power system protection, Power Transmission Lines, Hilbert Transform (HT)