INTRODUCTION A fault in electrical equipment is defined as a defect in its electrical circuit due to which the current is diverted from the intended path. Faults are generally caused by mechanical failure, accidents, excessive internal and external stresses etc. The fault impedance being low, the fault currents are relatively high. During the faults, the power flow is diverted towards the fault and the supply to the neighboring zone is affected. Voltages become unbalanced. It is necessary to detect the fault as early as possible that is why a kit is being made using microcontroller to make its process faster. It will detect following four major faults and will give trip signal to relay. The four faults detected by the model are: Overcurrent fault, undercurrent fault, Sparking and UV detection, Phase Failure faults. Purpose: The aim of this research is to develop a device used to detect faults in the line and isolate the connected system or instrument connected to it. Scope: This device involves the use of microcontroller for detection and isolation of the system of instrument with proper use of programming. The instrument devised is economical and effective compared to other protective devices available in market. After the patent of the product a large scale production is also possible for consumer use Design Approach: The design methodology involves the use of microcontroller in conjugation with the relay circuitry with display on a LCD screen. It is a totally new design in the market and it will be a substitute to ELCB’s, MCB’s and Relays in near future . Practical Implications: The circuit devised can be used in conjugation with the medical instrument, industrial instrument and even in the household application. It finds a lot of applications in factories and industries where costly instruments are to be saved from faults. Conclusion: The device thus developed is very economical and effective in the use of protection in household as well as industrial instrument protection. The added advantage of this circuit is that it shows the type of fault occurred on LCD and at the same time keeps the circuit in isolation until the fault is cleared WORKING: 1) The idea of the device designed is that it is used to detect the kind of fault that has occurred in a faulty line. 2) By using AVR microcontroller the fault is detected by the designed circuit and it also displays on the LCD screen. 3) Apart from that ,a relay circuit is also attached to it in order to save the system from being damaged by disconnecting the faulty circuit from the healthy one. 4) The AVR has an inbuilt ADC circuit which converts analog signal of the supply into digital signals. 5) According to the digital signal fed to the microprocessor it detects the normal or abnormal conditions. 6) Thus we finally obtain the tripping as well as display of the fault at same time. Components STEPDOWN TRANSFORMERS (230V/11V) RESISTORS CAPACITORS DIODES TRANSISTORS MICROCONTROLLER(AVR) SEVEN SEGMENT DISPLAY LED VOLTAGE REGULATOR (IC-7805) 1. Phase Failure Fault: 1)In case of any abnormality the phase voltage is seen to be affected first. The value of phase voltage decreases which leads to abnormal and faulty operation. 2) In case if any of the 3 phase’s viz. R, Y, B fails then such kind of phase failure fault is detected and is displayed on the LCD screen. 3) If the fault persists for a longer time, LCD keeps displaying the type of fault and it also displays the respective faulty phase. 4) Also the following display is seen on the LCD screen 5) In case if any of the phase is detected to be faulty then that phase initial is not seen in the ok section. 2. SPARK DETECTION:- Normally, the protective devices are not capable of detecting the faults that occurs due to sparking or heating during normal working conditions. Such abnormal heating leads to faulty currents and heat loss which can also result in damage of the circuit sometimes. On passage of time if such kind of a fault is not detected the heat rises to an uncontrollable value leading to damage or fire. A UV detector (sensor) is used in the device to sense the sparking or heat produced in the surrounding Over current A threshold value of min. and max. current is preset in the microcontroller and if the value of current increases over the set value, it trips the relay. This is done by a voltage divider circuit connected for each phase. Potentiometer is used to manually vary the threshold value. Under current fault A threshold value of min. and max. current is preset in the microcontroller and if the value of current decreases over the set value, it trips the relay. This is done by a voltage divider circuit connected for each phase. Potentiometer is used to manually vary the threshold value. Summary With the help of this model one can know what kind of fault has occurred in which phase and also one knows the exact working of microcontroller and LCD circuit in detail. The main advantage of this circuit is that any lay man can use this circuit and can know the type of fault. Henceforth it finds its application at various medical hospitals, industries and places where high protection is needed for saving the costly equipments connected to the main line. By studying the working of transformers and relay one can easily device new circuitry with some research work. It gives a detailed and wide application along with knowledge of each and every element attached in the circuit. By some variations in the circuit one can devise a new protective system for each individual phase too! By using the microcontroller circuitry the project is compact and easy to use.