Practical fault detection schemes for resonant grounded power distribution networks in bushfire prone areas

Pirmani, Susheel Kumar (2024) Practical fault detection schemes for resonant grounded power distribution networks in bushfire prone areas. Doctoral thesis, Northumbria University.

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Abstract

Electric faults (especially, single line-to-ground) have been the reason for the most severe powerline bushfires around the world as the fault current is too high to ignite fires. A special grounding technique, called the resonant grounding, is utilized to significantly reduce to the fault current (e.g., around 0.5 A). As a result, the resonant grounded distribution network exhibits the behaviors of high impedance faults making the traditional protection devices obsolete to detect faults causing powerline bushfires. This thesis aimed to detect single line-to-ground faults in resonant grounded distribution networks to mitigate powerline bushfires.

The first contribution of this thesis is to rigorously analyze the fault current in resonant grounded distribution networks. The fundamental circuit theory is employed to determine the fault current and carry out the analysis by considering practical operational characteristics. The rigorous analysis of the fault current is used to develop fault detection algorithms.The second key contribution of this thesis is the identification of faulty feeders using the zero-sequence current ratio by considering a range of fault impedance scenarios. In this approach, the zero sequence current ratio is computed using the zero-sequence current of the individual feeder and the total zero-sequence current of the system. Finally, the trait of the zero-sequence current ratio determines the faulty feeders.

Since the zero-sequence current ratio is not capable to detect faulty phases and sections, a modified charge similarity approach is used where a charge similarity factor is computed based on the double integration of the current. The changes in the charge ratio are then used to detect faulty feeders, phases, and sections. Another major contribution of the thesis is developing an approach based on the energy and current ratios to detect faulty feeders and phases without requiring measurements from phasor measurement units as in the charge similarity approach. This approach is also used for the cross-country fault detections. Finally, a fault sensing approach is developed using the quantum energy strategy where the traits of the quantum energy is utilized for sensing faults.

The fault detection and sensing approaches developed in this thesis are practically implementable as these can operate irrespective of sampling frequency of field devices and fault impedances.

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