An automatic tripping mechanism for the threephase transmission system. In the event of a temporary fault, the output of the project resets while it acquires permanent trip condition in case of a permanent fault. There can occur several failures in a three-phase supply system that provides power to industrial and domestic consumers. These failures are results of some faults which may be temporary or permanent in nature. Due to these faults, the power system may suffer considerable damage. This can lead to disturbance in power supply and may cause a standstill to various industries linked to the system. In a threephase power system, these faults are classified as LG (Line to Ground), LL (Line to Line), overload. This system can overcome such problem which by sensing the fault automatically and disconnects the system from the supply so that large scale damage to the system equipment can be avoided. The system automatically differentiates between a temporary disturbance and a permanent fault and A. appropriately cuts the supply for a short duration or long respectively.