Occurrence of single line to ground fault causes very low fault current, which in turn causes difficulty in identifying the faulted line in an ungrounded system. Due to the complexity of distribution network, there is every necessity to clear the fault in a very short span of time, otherwise the complete system will be affected. In order to overcome this difficulty, an ungrounded system is temporarily converted as a grounded system using thyristor-based grounding. Due to this, the magnitude of fault current will be increased, which helps in identifying the faulted line in distribution system. In this paper, the methodology of identification of faulted line is presented using thyristor grounding method. The effectiveness of this method is verified by theoretical analysis and simulation results. This method is also applicable for resonant grounded and high resistance grounded systems.

Ungrounded, high-resistance grounded and resonant grounded neutrals are commonly practiced in power distribution systems of some European and Asian countries and in several types of industrial systems in North America. When a single-phase-to-ground fault occurs, such configurations allow the system to continue to operate without tripping immediately. After the fault is detected, it can be cleared at a convenient time, resulting in minimized losses. Typically, the faulted line must be identified and cleared within a required time frame of 30 min to 2 h. Identifying the faulted line among a number of distribution lines connected to the same distribution bus is a significant challenge due to the small ground fault currents produced in the systems.

The identification of faulted distribution line has motivated a great deal of research work since the 1980s. One series of the developed methods identifies the faulted distribution line according to the steady-state zero-sequence fault current on each distribution line. These methods have problems in accuracy since the steady-state fault currents in ungrounded systems are weak signals. Another series of methods uses the transient currents caused by single-phase-to-ground faults for identification. Although the transient fault currents are stronger than the steady-state fault currents, they are highly random and not repeatable, reducing the reliability of the identification of the faulted distribution line. In the present days, new series of methods work by injecting special current signals between the neutral and the ground. Strong current signals flow through the faulted distribution line and are used for identification of fault. In some heavily polluted industrial systems, the faulted distribution lines are still identified by switching off the distribution lines one by one.

Electrical and Electronics Engineering Journal, Distribution system, Ungrounded system, Power system faults, Grounding methods.