Design And Construction Of An Automatic Changeover Switch With Phase Monitoring Device

ABSTRACT

This project work is on the design and construction of automatic changeover switch. It provides a means of switching from one phase of AC mains to another in the case of failure in the existing phase; it also changeover to generator if there is failure in all the three phases of the AC mains. The circuit also senses the restoration of any or all the three phases of the mains and changeover without any notice of power outage. This project has been improved on the existing types of electromechanical device that has being in use over the years.

The aim of this work is to introduce an automatic solution to overcome power fluctuation/phase interruption by selecting next most healthy available phase to feed the equipment without any notice of power outage which is achieved by the use of operational amplifier, timing circuit and high current relay switches and it is powered by 12V dc power supply Hence this has been achieved by the use of operational amplifier, timing circuit and high current relay switches and it is powered by 12V dc power supply.

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                         BACKGROUND OF THE PROJECT

The main aim of any electric power supply in the world is to provide uninterrupted power supply at all times to all its consumers. Although, in developing countries, the electric power generated to meet the demands of the growing consumers of electricity is insufficient, hence power instability and outage.

Power instability or outage in general does not promote development in the public and private sector. The investors do not feel secure to come into a country with constant or frequent power failure. These limit the development of industries. In addition, there are processes that cannot be interrupted because of their importance for instance, surgery operation in hospitals, transfer of money between banks and lots more. Power instability and outage in developing countries (Nigeria) creates a need for alternative sources of power to backup the mains supply.

Automatic changeover switches find a wide application scope wherever the reliability of electrical supply from the utilities is low and it is used in lighting/motor circuits wherever continuity of supply is necessary, for switching to an alternative source from main supply and vice versa.

The Change Over Switch is a device used to switch off a power supply and subsequently switch on another power supply. Basically it is aimed at switching on a more convenient power supply to the load. Since it switches on power to the load, precautions has to be taken while choosing the type of Change Over Switch, while selecting the appropriate size, the control of arcing has to be put into consideration.

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 contact points so as to limit or eliminate the possibility of partial contact at the contact point. The partial contact leads to over-heating of the components and may lead to fire outbreak in the entire room.

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 lead to heavy capital investment in a bid to suppress power failure and ensure regular power supply for the industry, hospitals, schools and homes. The problem of power failure can be checkmated with the use of stand-by generating set.

An Engineering Author, “Tony Rudkin” said in his book titled “Upgraded Signal Source with Improved Performance and Reliability” that the cost and depredation 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 firm 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 hospital, undergoing a surgical operation and power supply suddenly go off, the patient might loose his or her life due to the power outage.

Furthermore, if the president of the country is making nationwide broadcast and all of a sudden power went off in the transmitting station, it would be viewed as an attempt to sabotage the government ruling and some people must pay for it.

In his book, Tony Rudkin also said that the depredation caused by such reduce efficiency of the organization and leads to a great deal of frustration.

Sequel to the rate at which more sophisticated electrical/electronics gadgets are being procured and installed in our homes, hospitals 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 a phase failure detecting circuit also known as “Automatic Mains Failure” which switches on the head from power Holding Company (PHC) to a generator when power fails and from generator to PHC when power comes back.

1.3                                         SIGNIFICANCE OF THE PROJECT

The automatic change over switch, the switch aimed at achieving the following automatic actions;

• To change power over to generator
• To change back to PHC
• To change the generator.

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

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

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

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

Moreover, the size and captivity 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.

1.5                                     STATEMENT OF THE PROBLEMS

In every home, office or industries, automatic power changeover  plays a vital role, that is, It provides a means of switching from utility AC mains to generator in the case of power failure; This project has been improved on the existing types of electromechanical device that has being in use over the years.

In the course of designing this project, different kinds of problem was notice such as:

• Difficulty in troubleshooting with circuit without the circuit diagram
• Difficulty in connecting the output without short-circuiting, until a multiplexing circuit was gotten.
• Difficult in wiring because of the strong wiring the project required..

1.6                              SCOPE AND LIMITATION OF THE STUDY

This work covers only a three phase automatic changeover which can only be used for providing a means of switching from one phase of AC mains to another in the case of failure in public utility, which can also be used to switch from public utility to generator when there is total failure in the three phase of public utility.