Global Journal of Energy Technology Research Updates, 2015, 2, 01-05 1 E-ISSN: 2409-5818/14 © 2014 Avanti Publishers Construction and Operation of an Electronic Automatic Transfer Switch (Ats) J.O. Olowoleni, A.U. Adoghe * , A. Ademola, A.O. Omadoye, A.F. Agbetuyi, H.E. Orovwode and C.O. Awosope Department of Electrical and Info Engineering, School of Engineering, Covenant University, Ota, Nigeria Abstract: The inconsistency of power supply in Nigeria has been a major stumbling block to the advancement of her economy and as such it is an issue that requires immediate attention. Uninterrupted power supply is critical in so many applications especially in cases like hospital operations or financial transactions. This work was born out of the need to provide a cost effective and locally available way to automate the switching between various power sources. This issue can be addressed by implementing an Automatic transfer switch which automatically switches on a backup generator in the absence of the utility supply and transfers the load to the generator. The automatic transfer switch also switches off the backup generator and connects back to the utility supply when the power comes back. The circuitry consists of time delay integrated circuits and switching relays. The present effort is a prototype design to create an automatic transfer switch that can be used in an average Nigerian household because of its affordability and simplicity of operation. Keywords: Generator, switching, relays, automatic-transfer, load transfer. 1. INTRODUCTION A transfer switch is an electrical device that continuously monitors electric power utility and connects the load to a backup source of power if the utility power goes off [1]. This is designed to automatically switch the power supply to loads from a utility source to a backup source (such as a generator) and vice versa depending on the availability of the utility power source. The automatic transfer switch (ATS) also automatically switches OFF and ON the backup generator. The main components of this design are relays and a control unit based on a 4060B oscillator timer [2]. Basically, the way the automatic transfer switch works is that it senses the availability of the utility power supply and when the utility source is not available it switches ON the backup generator and transfers the load to the generator. This transfer of the load to generator is done after a predetermined time interval in order to allow for generator current to normalize [3]. The ATS also switches OFF the generator and reconnects the load back to the mains when the utility power is restored. This eliminates the stress and error of manually switching ON and OFF the generator [3]. 2. METHODOLOGY The automatic transfer switch’s operation is based on a logical control unit which has a 4060B control *Address correspondence to this author at the Department of Electrical and Info Engineering, School of Engineering, Covenant University, Ota; Tel: 08039404608; E-mail: anthony.adoghe@covenantuniversity.edu.ng oscillator as its main control component. This design consists of two distinct parts: The power sensing unit, and Logic control unit. Power sensing unit consists of the bridge rectifier circuit and Relay1 CRL1 as shown in Figure 1. The AC mains is connected to a step-down transformer, the output of this transformer is then rectified by a full- wave rectifier circuit. The bridge rectifier converts the AC output of the transformer to pulsating DC. The capacitor is used to filter out the DC and the zener diode is used to limit and stabilize the voltage to 12V. The diode D4 is used to protect RL1 from voltage spikes. When the utility power is ON i.e. the AC mains supply is ON, the rectifier circuit supplies 12VDC to RL1 and the normally open (NO) contact of the relay becomes normally closed (NC). The normally open contact of the relay is left unconnected while the normally closed contact of the relay is connected to Vcc of the control oscillator in the logic unit of the circuit. The common terminal of the relay is then connected to the positive terminal of the 12-V battery, while the negative terminal of the battery is connected to ground. When electric power is available from the mains supply, it energizes relay3 CRL3 and terminals C3 and B3 of the relay are connected, when this happens there is no longer any supply to the 4060B control oscillator. And this triggers a series of events in the control unit that leads to the load being connected to the mains power supply. When there is no power being supplied from the utility source, RL3 is de-energized and terminals C3