Design and construction of a three-way single phase Automatic transfer switch.
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In any operation where continuous electrical power is required, an interruption in the flow of power could result in significant losses unless backup power comes online quickly. A prolonged power outage could disastrously effect numerous aspects of the operation, from data center critical loads to emergency systems, including life safety. The automatic transfer switch quickly and automatically transfers power to a generator or other power source, eliminating the need to manually switch from utility service to backup. When power is restored, the ATS automatically transfers back to the utility service or normal power source, after an adjustable time delay to allow for utility stabilization. This transfer and retransfer of the load are the two most basic functions of a transfer switch. For automatic transfer switches to work automatically, quickly, and dependably, they must be properly selected, sized and installed and, of course, properly maintained. An automatic transfer switch (ATS) typically controls the engine start and transfers a load automatically to an alternate source of power, in case of normal power failure. The ATS is one of the basic building blocks of a backup power system, and performs a key role in power reliability. Although a standby generator typically includes internal engine starting and operating controls, the actual control of timing of engine starting, load transfer, and shut down is typically external to the generator and is located in one or more ATSs or in separate generator control switchgear. The existing three-way automatic change over switches use either electromagnetic relays or solid state relays to switch between three power sources. They also have a slow switching speed, experience switching arcs and over-heating, have an inflexible switching operation and are strongly affected by switching transients. These problems cause damage to the switching devices and load, waste resources, and lead to discomfort among power users. The project started with defining the problem statement and thus the objectives of the project. We then proceeded to designing the hardware and software needed to achieve the objectives of the project. The hardware requirements were divided into switching units, voltage transducer units, control unit, and display unit. The switching units consist of the SRD-05VDC-SL-C electromagnetic relays and triacs (BTAL2-600B). The HI-Link HLK-PM01 AC-DC 220V to 5V Step-Down Power Supply Module is the voltage sensing unit for all three power sources. The control unit is made up of the ATMega328p microcontroller on the Arduino Uno. The display unit is made up of blue, yellow, and green light-emitting diodes. The Proteus software version 8.8 was employed to run the simulation, and Arduino IDE software to help in compiling the code. After simulating with Proteus software, we built the prototype of the switch and integrated the hardware and software algorithm. The constructed prototype was tested using a 7 W LED bulb as the load and AC power sources with voltages that lie in the scope. The prototype has a very quick switching response of 20ms, prioritizes grid electricity with the alternative energy source as the second option, and the diesel generator as the last option. It also eliminates any possibility of arcs. Some challenges were however encountered along the way for example the current flow from the load side to power sources not prioritized which was solved by use of silicon diodes which allow current to flow in one direction thus blocking current from flowing in the unwanted paths, crashing of Proteus software while running the simulations and delay in getting the electronic components due to the corona virus pandemic which led to closure of transportation means. I recommend that a more advanced switching design capable of handling a bigger load is made with even an option of switching between more than three power sources.