DESIGN AND CONSTRUCTION OF AN AUTOMATIC SINGLE PHASE CHANGE OVER SWITCH

ABSTRACT
Considering the epileptic power supply in Nigeria and other developing countries today, a high demand of an alternative service is required. A single phase automatic change over switch from the public mains supply to the auxiliary supplies (single phase ac generator) and vice-versa has been developed. The design was realized using major components like a step down transformer (220V-12V dc), atmega8 microcontroller, rectifiers, voltage regulators, 555 timers, relays, circuit breaker and others like resistors, diodes, and capacitors. The device automatically switches from public mains to an auxiliary whenever there is an outage in the public mains. This device also detects the public main power supply when available and switches from auxiliary power supply to the mains with a delay period of 4 seconds in starting and switching off the generator. The device has been constructed successfully, and it demonstrated a tendency to automatically switch from mains to the auxiliary source and vice-versa without human interception.

CHAPTER ONE
INTRODUCTION
1.1 Background of study
The need for continuous power supply and its reliability has increased rapidly over the years, especially in all those areas where uninterrupted power supply is a must. Modern systems are power dependent. Their complexity has increased as continuous information and communications are needed to control automated process, be in industries, commercial complexes, hospitals, hotels or even modern residences. The need, as such, for independent standby power system has therefore increased manifold. The power distribution, control, monitoring and protection of standby power systems need to be integrated. Standby generator systems, for example are required to serve:-

Sensitive Loads- are supplied by UPS systems. The period of non-availability of power, before the standby supply takes over, is bridged by battery banks. Typical loads are computers, hospital equipment, microprocessor controlled industrial machines etc.

Critical Loads- thesemostly involve standby generator systems which supply power to lighting systems, air conditioning, elevators etc in Airports, Hotels and commercial complexes.

Essential Loads- thesealso use standby generator systems mostly in process industries as they relate to high restarting times or high down times. Automatic transfer from mains supply to standby supply is vital for all the above kinds of loads.

In the event of power failure, the standby power is usually expected to take over automatically. Electrical starting equipment, battery bank and diesel generator are required for the automatic operation. The automatic transfer is achieved mostly by automatic mains failure systems. The process of on-load transfer has to be monitored and controlled for a smooth Changeover and within safety limits of all elements of the system. This is achieved by an Automatic Changeover Switch.

Changeover switches find a wide application wherever the reliability of electrical supply from the utilities is low and they are used in lighting/motor circuits wherever continuity of supply is necessary, for switching to an alternative source from mains supply and vice versa. They are switch disconnectors with independent manual operation capable of making, carrying and breaking currents under normal circuit conditions which may include operating overload conditions and also carrying currents under specified abnormal circuit conditions such as those of short circuit for a specified time.

Automatic changeover switch (also known as automatic transfer switch ATS) is an integral part of a power generation process, allowing smooth and immediate transfer of electric current between multiple sources and load. When the generator is in operation, the transfer switch prevents any feedback current to the load. It also ensures that the different power sources are synchronized before the load is transferred to them. The transfer switch senses when there is interruption if the mains supply remains absent. Fluctuations and voltage drop below a particular level within a specified time in the mains supply will also cause the automatic transfer switch to transfer the load to the generator. The starting of the generator is done by a relay which switches the battery voltage to the ignition coil of the generator. In about a few seconds when the generator is producing full power, the transfer switch disconnects the load from the mains supply and connects it to the generator supply, restoring electricity to the load. The transfer switch continues to monitor the mains supply and when it is restored, it switches the load from the generator back to the mains supply. Once the generator is disconnected, it goes through a cool down routine and shuts down automatically.

Power outage in general does not promote development to public and private sector. The investors do not feel secure to come into a country with constant or frequent power outage. 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, bank transactions and lots more. An automatic change over switch can be entertained to allow smooth and fairly uninterrupted supply of electricity for operation and services that require no discontinuity in electricity supply.This is achieved by the use of integrated circuits that have timing abilities and relays to effect switching.

Power supply instability in developing countries creates a need for automation of electrical power generation or alternative sources to back up the utility supply. This automation becomes predominantly high. Most industries and commercial processes are partly dependent on generators and public power supply. The public mains supply remains epileptic especially in tropical African countries where Nigeria forms a part. Therefore, if the processes of power changeover between these two power supplying sources are manual, human error during change over connections may occur; leading to machine damage, electric shock electrocution as well as increased down time consequently introducing massive losses.

1.2 Statement of Problem
Electricity plays a major role in economic development of a nation, and this forms the basis of this study, with interests in human, infrastructural and economic development. In most developing and undeveloped 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 of power supply to meet up with the energy demands.

Of all the existing types of changeover switch, the most populous changeover is the manual change over which consists of a manual change over switch box, switch gear and cut-out fuse or the connector fuse. Ahmed et. al., 2006 stipulates that, this change over switch box separates the source between the generator and public supply, as the contact is manually switched from mains terminal to the generator terminal and vice versa. Many challenges are experienced in this manual changeover as it requires lots of human activities in its operation. Electric shock can occur during the switching due to electric wire contact with the device metal casing as a result of crack in the ceramic insulator in the switch. This has led to several deaths and damage to electrical appliances.Nwaforet. al., 2012 also stipulates one of the disadvantages as wear and tear of some mechanical parts due to frequent movement from one source to the other.

Electrical changeover switch is another type of changeover switch, which involves the use of electrochemical type relays, contactors, voltage monitoring relays and delay timer relays as main components of the device. The device is cheap and the construction is easy, but associated with noise in switching of relays, leading to wear and tear, loss of reliability, and thereby making the device to be prone to failures.

The electronic change over switch has proven to be a better device compared to both the manual and electrical changeover switch as it gives no noise, eliminates wear and tear, reduces damages to lives, and maintains high quality of service as it provide quick response for the interchanging of power to the load automatically from the main supply to the generator and vice versa. The electronic changeover device employed in this research work changes over immediately when the public mains is out. However, the generator starter/off has a periodic delay to start/off the generator. This requires the generator to have a kick starter and off facility, and a battery in good condition. This paper presents the construction of a single phase power changeover switch that switches power supply from public mains supply to an auxiliary source (ac generator) and vice versa.

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Item Type: Project Material  |  Attribute: 67 pages  |  Chapters: 1-5
Format: MS Word  |  Price: N3,000  |  Delivery: Within 30Mins.
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