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The vibrating control regulator is a type of voltage regulator that is used in an excitation system to both supply and regulate the direct current in the rotor windings. Also, as the name suggests, it a type of regulator with vibrating contacts whose excitation current and pole field strength are automatically controlled using voltage regulating components. In this article we will learn how an alternator and its DC exciter with vibrating contacts work.
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The construction and working of the vibrating contact regulator is somewhat similar to that of the carbon pile type. The operating coil, which is arranged in the same way in both the regulator systems, is supplied with rectified current from the alternator output. An electromagnet is also used to attract an iron armature against a spring, which works as a voltage reference. The strength of the field generated by the electromagnet is controlled by the output voltage of the alternator, thus they are directly proportional to each other.
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Operation of the
The working of the operating coil, as is the arrangement for this system, is similar to that of carbon pile regulator i.e. electromagnetic coil. The current supplied to this electromagnet is passed through a transformer and rectifier circuit. Moreover, as the strength of electromagnet is related to the alternator output voltage, the increase in the value of the output voltage also increases the amount of field produced, resulting in more attraction of the plunger.
Similarly, as the value of output voltage decreases the amount of field produced also decreases which results in lesser attraction of the plunger. The movement of the plunger is resisted by a spring which acts as a voltage reference, as mentioned earlier. Now as the output voltage increases or decreases the control contact also moves up or down. The vibrating contact is continuously vibrated by a cam rotating at the rate of 120 times per second.
Now as the output voltage changes, the upper part of control contact moves up or down on the basis of voltage figure and the bottom part continuously keeps vibrating with the help of the rotating cam.The increase in the output voltage then increases the magnetic field which pulls the plunger up so that the upper control contact also moves up, lessening the contact between the two. In similar fashion, as the output voltage decreases, the lower magnetic field pulls down the plunger so that the upper control contact also moves down, increasing the space between the contacts.
It is this opening and closing of the contacts that work behind the regulator mechanism. The closing of these contacts has an effect of short circuiting the resistance in series, which results in the flow of current. This means that if the contact is small, the current passed is also small and thus the amount of flux produced is less, resulting in less exciter output and the output voltage.
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References and Image Credits
Marine Electrical Equipment and Practice by H.D McGeorge