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DESIGN AND CONSTRUCTION OF A SINGLE PHASE AUTOMATIC CHANGE OVER SWITCH WITH PHASE SELECTOR

CHAPTER ONE

1.1     INTRODUCTION

Change over switch is a device used to switch off a power supply and subsequently switch on another power source. Basically it is aimed at switching on a more convenient power supply to the load. Since it switches on power to the load precaution has to be taken while choosing the type of change over switch. Also size, arcing control are put into consideration in the choice.

A good switch should be the one whose contact is made in such a way as to limit the arc formation by having no contact-bounce and by having contacts made of good conductive, corrosion resistance and wear resistance materials.

A good change over switch must have adequate insulation and must be so constructed and located as not to constitute a potential hazard.

A good change over switch should also have tight contacts so as to limit or eliminate the possibility of partial contacts at the contact point. The partial contact lead to over heating of the components and may lead to fire out break.

1.2     Aims and Objectives

Due to inconsistent supply of power, there is a growing need for an alternative source of power supply. This has led to heavy capital investment in a bid to curb power failure and ensure regular power supply for our industries, hospitals and homes. The problem of power failure can be checkmated with the use of standby generating set.

An Engineering author Tony Rudk Inn said in his book titled "Upgraded signal source with improved performance and reliability" that the cost and depreciation associated with breakdown vary from one application to the other, and in some cases, the user has little choice but to ensure that a stand-by unit is available to take over on event of failure of primary system.

If some of these big firms do not make provisions for stand-by power source, frustration could set in which may lead to the closure of business and thus throwing workers into unemployment. Also in the case of hospitals undergoing a surgical operation and the power supply suddenly goes off, the patient might loose his life due to power outage.

Furthermore, if the President of the country is making a nation wide broadcast and all of a sudden there is power failure in the transmitting station, it would be viewed as an attempt to sabotage the government ruling and some people must go for it.

Sequel to the rate at which more sophisticated electrical/electronics gadgets are being procured an installed in our homes, hospital and business premises, there is a justifiable need for a faster and more reliable change over system in an event of power outage.

In view of these considerations, this project is aimed at designing and constructing a workable automatic change-over switch with phase selector circuit which switches on the load from National Electric Power Authority (NEPA) to a generator when power comes back. Also when there is a phase failure in any of the NEPA phase carrying the load, the change-over switch will be changed to alternative phase.

1.3     SCOPE AND LIMITATION OF THE STUDY

The automatic change over switch is aimed to achieve the following automatic actions.

To start the generator

To change power to generator                                           

To change back to NEPA

To change the generator

To change to alternative phase in case of phase failure.

The automatic change over unit can be operated in single or three phase-system. The automatic change over switch has the following advantages.

i.  It minimizes damage to lives/equipment since it has its own monitoring system and its switching requires no human contact with the switch, thus eliminating human error.

ii.  It reduces its change-over timing to the minimum due to its fast response to power outage.

iii.  It maintains high quality of service through its fast and prompt response

iv.  It avoids and reduces fuel consumption since the generator is switch off immediately NEPA supply is restored.

Moreover the size and capacity of the Unit will depend upon the load for which it will be used. The Unit is also portable, easy, convenient and safe to install.