CHAPTER ONE
INTRODUCTION
Industrial automation and control has contributed immensely to the high rate of the world’s technological growth. Power control and automation is a part of this field which is applied in virtually anywhere electrical power is used, generated or transmitted. Manual power change-over switches have been in existence and in different forms and shapes. 1959, the advent of microelectronics has paved way to modify the manually operated change-over switches. This project deals with the design and construction of automatic change-over switch with indicator. It eliminates the time and energy spent in operating the manual change – over and starting of Gen. Set. It is fully automated. It can be used in residential houses, offices and most importantly, in factories that required constant power supply. It has so many advantages over the existing ones/types.
1.1.  BACKGROUND OF THE STUDY
This project work is embarked upon to eliminate nearly every shortcomings associated with the manually operated type to ensuring that it is fully automated.
This system is realized in several functional blocks all combined to form one functional system. The first block is a 3-phase MAINS regulated dc power supply unit that powers the overall circuit and acts as the input. The output of thin block is fed into a priority encoder (74147) which selects the most prioritized phase at a time. The third block is a BCD – to – DECIMAL Decoder (7442) used to decode the prioritized phase.
The fourth is the driver stage which comprises of NPN transistor that energizes the electromagnetic relay which switches the phase in priority. The Gen set switching section is achieved using the least prioritized phase. This section switches ON the Gen set when all the NEPA phases are low, OFF or faulty. Once the Gen set phase is selected, a switching transistor fires an SCR which conducts large battering current to the ignition coil of the Gen set. Panel indicators are used to show the status of the system.