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In the conventional dc machine (with a closed continuous commutator winding on its armature), for example, full-wave rectification of the alternating voltage induced in individual armature coils is achieved by means of a commutator, which makes a unidirectional voltage available to the external circuit through the stationary carbon brushes held against the commutator surface.The armaturewindings of dcmachines are located on the rotor because of this necessity for commutation and are of the closed continuous type, known as lap and wavewindings. The simplex lap winding has as many parallel paths as there are poles, whereas the simplex wave winding always has two parallel paths. The winding connected to the commutator, called the commutator winding, can be viewed as a pseudostationary winding because it produces a stationary flux when carrying a direct current, as a stationarywindingwould. The direction of the flux axis is determined by the position of the brushes. In a conventional dc machine, in fact, the flux axis corresponds to the brush axis (the line joining the two brushes). The brushes are located so that commutation (i.e., reversal of current in the commutated coil) occurs when the coil sides are in the neutral zone, midway between the field poles. The axis of the armature mmf is then in the quadrature axis, whereas the stator mmf acts in the field (or direct) axis. Figure shows schematic representations of a dc machine. The commutator is thus a device for changing the connections between a rotating closed winding and an external circuit at the instants when the individual coil-generated voltages reverse. In a dc machine, then, this arrangement enables a constant and unidirectional output voltage. The armature mmf axis is fixed in space because of the switching action of the commutator (even though the closed armature winding on the rotor is rotating), so the commutator winding becomes pseudostationary.
Q. With the help of the structures explain LCD. A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in fro
Properties of a good heat sink For maximum efficiency, a heat sink should be 1)Be in good thermal contact with the transistor case 2)Have the largest surface area 3)Be
how does the kb come across the sheet charge in the amperian sheet?
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A quantizer has 130 quantum levels that exactly span the extremes of a symmetrically ?uctuating message with step size δv = 0.04 V. Determine the following: (a) |f(t)|max.
disadvantages of shunt&series clippers
An industrial plant consumes 500 kWat a lagging power factor of 0.6. (a) Find the required kVA rating of a synchronous capacitor to improve the power factor to 0.9. (b) If a
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Based on Figure, using star-delta transformation, calculate the current flow and voltage drops at 6kΩ resistor.
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