Recovering Lost Technology- The Magnetic Amplifier

Ang, Lay Eng (2016) Recovering Lost Technology- The Magnetic Amplifier. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

The conventional method used to control power delivered to a load is by using the thyristor, triac, power transistor, MOSFET and IGBT with some limitations. The limitations are the silicon transistors can age and fail and would not tolerate overload. The thyristor and triac are solid state switches; they cannot produce an output proportional to the input. The high-power, high-frequency operation, such as that used in over-the-air television broadcasting, is better achieved with vacuum tubes due to improved electron mobility in a vacuum. A vacuum tube momentarily gets overloaded will just get a little hotter; solid state devices have less mass to absorb the heat due to overload, in proportion to their rating. Lastly, solid state devices are sensitive and venerable to radiation and cosmic rays. Vacuum tubes create a higher distortion than solid state devices and they (vacuum tubes) need an additional power supply for the filaments before they can function. Many a time, the magnetic amplifier, which can tolerate overload, radiation and aging, is a better choice than solid state devices and vacuum tubes as far as applications that require high power output are concerned. Basically, the magnetic amplifier consists of a DC winding and a gate AC winding wound on a transformer core. The DC winding accepts a small DC current and produces a big change in AC current in the gate AC winding. The magnetic amplifier works by using a small DC current to saturate the transformer core so that the inductive reactance in the gate AC winding falls allowing a large AC current to flow through the AC winding. Hence, the AC current in the gate AC winding can be made to vary by changing the amount of DC current fed to the DC winding. Thus in this case, unlike the thyristor or the triac which can only perform on and off switching action, we have a power control device whose AC output varies with the DC input. In this project, a magnetic amplifier is built by using two transformers of type 110V/240V. The 110V side is the gate AC winding and the 240V side is the DC winding. The magnetic amplified built can be used to control the light intensity of a light bulb and the speed of a 240V AC electric fan. Besides that, some electronic circuits with output current varies with temperature or sunlight are fed to the DC winding of the magnetic amplifier allowing the AC current output in the gate AC winding to vary with temperature or sunlight. The AC current in the gate AC winding is then used to drive light bulbs, electric fans, heating elements etc. In conclusion, this project has been successful in producing useful magnetic amplifier prototypes which can be used for industrial power control and intelligent power automation.