The main aim of this paper is any electric power supply in world is to provide uninterrupted power supply at all times to all consumers. Like industries, colleges, public sector and private sector. Organization and even domestic user cannot permit the power outage because it pushes them in loss in business; interrupt in normal official work, obstruction in routine and domestic life. This paper we have to use of good interference in term of switching speed and smooth operation. By using this paper diesel generator set can start and stop automatically very nicely on main supply failure. In this case diesel generator set must have self start facility. At the time of power failure or abnormal condition main supply will be switch off and diesel generator set start automatically. When power supply is restored or voltage become normal diesel generator set will be stopped and power supply switch on automatically. This idea may be very use full for colleges, hotels, offices, etc. The result of its ability to perform the automatic power change over work is smoothly and no human effort.