31-07-2014, 04:27 PM
THE TECHNICAL UNIVERSITY OF MOMBASA
ABSRTACT
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 (Kenya inclusive) 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 and motor circuits wherever continuity of supply is necessary, for switching to an alternative source from main supply and vice versa.
This project is a design of an automatic changeover panel. This means that when there are any mains black out, the automatic changeover panel will change to an alternative power supply (Generator), and back to the main supply when it is restored.
The purpose of this project is to maintain constant supply to the main circuit that is being supplied by making-up for the time lapse or delay that usually accompanies the manual switching from one source to another.
The design comprises of the power connection circuit and control connection circuit. The main components to be used include; contactors, relay and timers.
Introduction
A changeover panel can generally be described as a system that allows the connection from one source of power or state to another (example from mains supply - in Kenya it’s from Kenya power and lighting company - or supply from a stand-by generator).
The purpose of this project is to design and construct this unique system that provides a solution to the erratic power supply problem we are facing in Kenya and the other developing counties as a whole. The automatic changeover panel can be described as a unique switching system, which can be used to change from one power supply to another as well as maintaining constancy in the supply to a particular network or load. The electrical equipment to be designed and constructed in this project will interface between two different electrical power sources (that is the mains supply and the generator.)
The uniqueness of this system lies in its ability to maintain constant supply to the load circuit that is being supplied by making-up for the time lapse or delay that usually accompanies the manual switching from one source to another.
Changeover panels find a wide application wherever the reliability of electrical supply from the supply authority is low and they are used in lighting or even 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 panel (also known as automatic transfer panel) 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 panel 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 panel senses when there is interruption and in case 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 panel to transfer the load to the generator. The change over panel 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.
Problem statement
From various surveys, it was generally noticed that industries are vulnerable to long and short interruptions (that are considered as ‘reliability issues’ in the power system analysis). The automatic changeover switch to be designed is a complete system with various sub- systems and components arranged and linked to function primarily as a means of manipulating the supply of electrical power to any desired load.
In Kenya and Africa in general we have been faced with erratic power failures or outages which do not promote development in both private and public sector. Investors do not feel secure to come into a country with constant or frequent power failure. In addition there are processes that cannot be interrupted because of their importance, for instance; surgery operation in hospitals, commercial complexes transfer of money between banks, elevators, airport and lots more. Furthermore the switching obtainable from the changeover switch is usually manual, that is, the user has to move a lever to change from one source to another. This is usually associated with time wasting as well as some health hazards, like electric shock are concerned especially if done by a layman.
In other to eliminate this human intervention as well as introduce some speed and precision in the operation, there is the need for an automatic changeover switch especially if done by a layman (a person without professional or specialised knowledge).
LITERATURE REVIEW
Emergency power systems were used as early as World War II on naval ships. In combat, a ship may lose the function of its steam engines, which powers the steam driven turbines for the generator. In such a case one or more diesel engines are used to drive back-up generators Early transfer switches relied on manual operation; two switches would be placed horizontally, in line and the “ON” position facing each other, a rod is placed in between. In order to operate the switch one source must be turned off, the rod moved to the other side and the other turned on. [5]
Switches therefore allow switching from a primary power source to a secondary or tertiary power source and are employed in some electrical power distribution systems; most often transfer switches can be seen where emergency power generators are used to back up from the utility source. The transfer switching allows safely switching from utility power to emergency generator power while maintaining isolation of each source from the other. The switch may be a manual switch, an automatic switch or a combination of manual and automatic. In a home, for example, during power outages, the power transfer switch allows isolation of the owners critical circuits (e.g. cooling, refrigerator, lighting) from the utility service, hence allowing for operation of the generator without back feeding to the utility which can damage utility equipment.
Automatic transfer switches continually monitor the incoming utility power. Any anomalies such as voltage drops, brownouts spikes, or surges will cause the internal circuitry to command a generator to start. This will then transfer to the generator when additional switch circuitry determines that the generator has the proper voltage and frequency. When utility power returns or no anomalies occur for a certain time, then transfer switch will then facilitate the load shedding or prioritization of optional circuits such as heating and cooling equipment
METHODOLOGY
The aim of this section/chapter is to transform the theory of the design problem as well as the block diagram of the automatic change-over switch into a realistic unit. The two sections that make up the unit will be realized electrically as much as possible using the available components and devices.
Control section
This is actually the heartbeat of the unit; it controls everything on the panel. Here contactors and timers are used and are configured to achieve the required isolation and preference for the power source such that only one will supply the load at any given time. And also offer the required delay for each type of supply to start supplying the load after the other is not available or intentionally eliminated
Light- Bulbs
An electric light bulb is a device that produces light by the flow of electric current. It is the most common form of artificial lighting and is essential to modern society, providing interior lighting for buildings and exterior light for evening and night time activities. Most electric lighting is powered by centrally generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems. Battery-powered lights, usually called "flashlights" or "torches", are used for portability and as backups when the main lights fail. The two main families of electric light are incandescent lamps, which produce light by a filament heated white-hot by electric current, and gas-discharge lamps, which produce light by an electric arc through a gas. The energy efficiency of electric lighting has increased radically since the first demonstration of arc lamps and the incandescent light bulb of the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to a myriad of applications.
Operation of the control circuit
This is the circuit that does the actual switching of the load from the mains to the generator and vice-versa. It consists of a relay which is energized or de-energized depending on the signal it receives from the control circuit. The relay is connected in such a way that when its contact is in the normally opened position, the load is connected to the mains supply and at normally closed position the load is connected to the generator. Upon energizing the relay, which is an indication that there is need for power supply change, its contacts move from their normally closed position to the normally opened position. When the mains supply is restored the control circuit again sends a signal to the relay to de-energize it causing it to move its contacts back to the normally closed position
Conclusions
In conclusion the project was a great success as it has managed to function as proposed. That is it changed safely from mains supply to generator supply and within the given time.
This resulted from extensive research and desire to attain the set objectives which resulted to tireless consultation and study of wide range of books. On addition the supervisor spent his time to advice the student and when possible directs him on the relevant material.
The automatic transfer panel has immense advantage in every area where power is required. It is a fact that there is hardly any aspect of human life where electrical power is not required, at homes, offices, hospitals and other such places.
It finds a wide application scope wherever the reliability of electrical supply from the utilities is low and is used wherever continuity of supply is necessary, for switching to an alternative source from main supply and vice versa