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In all kinds of manufacturing, it is very common to haveequipment that has three phase motors for doing differentwork functions on the production lines. These motorfunctions can be extruders, fans, transport belts, mixers,pumps, air compressors, etc. Therefore, it is necessary tohave equipment for controlling the start and stop of themotors and in some cases for reversing them. Actually, oneof the most common solutions for performing this controlfunctions is by using three phase magnetic starters. Itconsists of a block with three main mechanical contactswhich provide the power to the three main terminals of themotor once its coil is energized. However, the magneticstarter has a lot of disadvantages and the most commonappear when they are driving high current levels that cancause arcing and sparks on their contacts each time they areactivated or de–activated. Because of these kind of effectsthe contacts of the magnetic starters get very significantlydamaged causing problems in their functionality. With timeit can cause bad and inefficient operation of the motors. Thisis why, thyristor should be considered as a low costalternative and indeed a powerful device for motor controlapplications. Thyristors can take many forms but they havecertain features in common. All of them are solid stateswitches that act as open circuits capable of withstanding therated voltage until triggered. When they are triggered,thyristors become low impedance current paths and remainin that condition (i.e. conduction) until the current eitherstops or drops below a minimum value called the holdinglevel. Once a thyristor has been triggered, the trigger currentcan be removed without turning off the device.
