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 micro controller, 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
1.1Â 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 dis connectors 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.
