6.2.1. Power generation (direct current motor)
Initially (Cp. 4.1.1.) an alternating voltage is generated in the rotor windings of every generator. This alternating voltage can, however, be rectified so that current always passes through the external circuit in the same direction (Cp. Figure 30). Rectification of the generated alternating voltages takes place in the following manner: Instead of the two slip rings isolated from one another in Figure 30, only one slip ring appears in Figure 83. This latter slip ring has, however, been divided into two halves insulated from each other (lamella) and is known as a commutator.
The beginning and end of the conductor loop (winding) have been connected to the lamella. The two brushes face each other. They always run from one lamella to another as the conductor loop passes through the neutral zone. The induced voltage in the conductor loop is just zero at this moment and changing its direction. Figure 84 shows the principle of mechanical rectification.
1, 2 Conductor loop, 3 Rotational direction, 4 Neutral zone
The commutator ensures that polarity of the carbon brushes remains constant at all times. The course of the rectified voltage is shown in Figure 85. We can perceive that the generated voltage still ranges between zero and a top value whilst always evidencing the same direction.
Where a less pulsating voltage is required it is necessary to increase the number of conductor loops whereby they should be spatially positioned. The number of lamella must be increased for every additional conductor loop. Figure 86 sets out the basic drawing of a direct current generator with two conductor loops.
The commutator comprises four lamella. The generated voltage is shown in Figure 87.
1, 2 Conductor loop; 3, 4 Conductor loop
1 Voltage in the conductor loop ½, 2 Voltage in the conductor loop ¾, 3 Terminal voltage, 4 Voltage in volt
The resultant voltage no longer varies as much however it has the disadvantage that the carbon brushes only tap off a voltage from the conductor loops when they generate a peak voltage. The conductor loops are ineffective at all other times. However, the two conductor loops add together their voltages once they are series connected.
The voltage presented in Figure 89 also features an increased voltage alongside an even one. Moreover, the direct voltage can be improved still further by increasing the number of conductor loops. In practise coils with several windings are employed instead of conductor loops. Operating current IA flows when a consumer connects to the carbon brush terminals.
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