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CHAPTER ONE

INTRODUCTION

1.1.  BACKGROUND OF THE STUDY

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.

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.

1.2. OBJECTIVES OF THE STUDY

The aims and objectives of this project is to:

1.  Design and construct an automatic change-over switch with indicator that will switch load from the mains power supply (PHCN) power supply (Generator) with simplicity.

2.  To introduce a circuitry that will sense power outage and at the same time sense fluctuation in the power supplied to the load at any point time.

1.3.  SIGNIFICANCE OF THE STUDY

  This project eliminates the stress, time delay and other drawbacks in manually operated types. The project is modified to display the phase in use at a particular time using a single seven segment Display and its appropriate circuitry.

1.4.  SCOPE OF THE STUDY

This project work was carried out primarily with the aim of solving the problem of manual change-over switch when there is need for changing to generator due to power failure from public power supply.

Also, the essence of this project work is to design and construct a 90A, 220V, 50Hz automatic change-over switch which will serve as a standby switch to generator when there is power outage.

1.5.     LIMITATIONS OF THE STUDY

Due to the principal operation of the device, it cannot switch two voltage supply once, during operation. So the power switching of the supplies depends on the state in which the device is, that means it can only be in an on or off state, so as to avoid voltage clashing which will lead to fire outbreak.