CONSTRUCTION AND DESIGN OF AUTOMATIC CHANGEOVER SWITCH

INTRODUCTION

1.1             BACKGROUND OF STUDY

The project is designed for power supply applications. It involves automatic changeover between the main power supply and an auxiliary power supply, such as a generator. The circuit of the project consists of logical control unit and relay switches. The basic operation of the project is to switch ON an auxiliary power supply (like a generator). This operation connects the power supply from the generator to the load after a predetermined time interval. Switching is possible through the use of the relays. The system was designed to automatically change power supply back to the main supply moments after the A.C. mains are restored and to switch OFF the generator. The device removes the stress of manually switching ON the generator when power failure occurs. The operation allows electric current to flow through the motor/starter. It is noted that one of the motors terminals is already connected to 12V+ terminals. The switching of the relay allows the other terminal to be grounded thereby completing the circuit of the electric motor.(Hammed and Mohammed, 2006).

Power supply instability in developing countries creates a need for automation of electrical power generation or alternative sources of power to back up the utility supply. This automation becomes necessary as the rate of power outage becomes predominantly high. Most industries and commercial processes are partly dependent on generators and public power supply which is epileptic especially in tropical Africould countries where Nigeria forms a part.
However, if the starting of the generator is automatically done by a relay which switches the battery voltage to ignition coil of the generator while the main power relay switches the load to either public supply or generator, the down time would greatly be reduce thereby maintaining the tempo of production in such industries. The approach used in this work is the modular approach where the overall design is first broken into functional blocks. Each of these blocks carries out a specific function in the entire system by the interconnections between the block (Kolo, 2007).

Electricity (energy), which plays a major role in economic development of a nation, forms the basis of this study, with interests in human, infrastructural and economic development. In most developing and underdeveloped parts of the world, the supply of electricity for industrial, commercial and domestic use is highly unstable. This gives rise to the frequent use of alternative sources of power supply to meet up with the energy demands. The introduction of these alternative sources of supply brings forth the challenge of switching smoothly and timely between the mains supply and the alternative sources whenever there is a failure on the mains source. There is also the need to reduce drudgery from switching between the two sources on the human side. Solving these challenges forms the focus of this work. The Automatic Change-over switch, automatically switches over to the alternative source of power supply (generator) when there is a power outage. It equally switches over to the mains supply when power is restored and turns off the generator automatically. Therefore automatic power change-over switch is a device that links the load and mains supply or the alternative supply together. This enables the use of either the mains supply or an alternative source when there is outage on the mains source. This could either come in with three phase or single phase. This device maintains constant power supply
to the load by automatically activating the generator when there is need. (Boylestad and Nashelsky, 2012).

1.2             AIMS AND OBJECTIVES

Due to inconsistent supply of power, there is a growing need for an alternative source of power supply. The analysis of this project cannot go without enumerating the goals meant to be achieved in the pursuit of this work. This include:

1. To develop a simple low-cost device aimed at easing constant power outage faced by industry, hospitals, schools and homes.

 2. To minimize power interruption.

            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.

            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 (PHCN) to a generator when power fails and from generator to PHCN when power comes back.

1.3              SCOPE AND LIMITATION

The automatic changeover switch, the switch aimed at achieving the following automatic actions;

a)                  To change power over to generator

b)                  To change back to PHCN

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

a)                  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.          

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

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

Moreover, the size and captivity of the unit would depend upon the load for which it would be used. The unit is also portable, easy, convenient and safe to install. Figure 1.0 shows the working principle of automatic changeover switch

Figure 1.0: Block diagram showing the working principle of automatic changeover switch