Optimal Sampling Requirements for Robust and Fast Vegetation High Impedance Fault Detection

Abstract

Low fault currents, associated with Vegetation High Impedance Fault (VeHIF) events, are often challenging to clear by relying on traditional overcurrent based protection schemes. Low Frequency (LF) harmonics have readily been used in the literature as potential fault detection features. High Frequency (HF) signatures are also generated during VeHIFs events. These have generally been underrepresented, potentially for reducing the computational burden and the cost of proposed solutions. This work presents the temporal magnitude growth comparison of the LF and HF fault current spectrums using a dataset of 125 phase-to-earth (ph-to-e) tests. The key focus is on comparing the protection-speed efficacy of the LF and HF fault signatures. For the analysed dataset, the temporal growth in the HF spectral components was determined to be faster in a larger number of tests and with higher average lead-time margins. Conversely, growth in the LF spectral components was faster in fewer tests and with a smaller average lead-time margin. The HF spectrum was the lead indicator in 68.2 % of the 125 ph-to-e test recordings with an average lead-time of 26.95 s. For the same dataset, the LF spectrum was the leading indicator in only 25.6 % of the tests with an average lead-time of 7.85 s. Analysis has also revealed that a sampling frequency, as large as 1.8 MHz, may be required when designing protection applications, where the speed of protection is as critical as robustness.

Keywords

• Current signals
• high frequency sampling
• high frequency signatures
• high impedance faults
• vegetation faults
• speed of detection