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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.
What are plastics? Plastics are materials (containing carbon as common element) that have organic substances of high molecular weight and are able of being formed in required
Explain the significance of the loss tangent of a dielectric material. The loss tangent contains a very small value for free space. For solid materials there tan δ = 0.003, tha
Q. Consider an elementary three-phase, four-pole alternator with a wye-connected armature winding, consisting of full-pitch concentrated coils. Each phase coil has three turns,
The maximum clock frequency for 8085 is 3 MHz
Q. For the circuit shown in Figure, develop and execute a PSpice program to obtain the node voltages and the current through each element.
Q. The current sources in Figure are given to be I A = 30 A and I B = 50 A. For the values of R 1 = 20 ,R2 = 40 , and R3 = 80 , find: (a) The voltage V. (b) The current
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Consider the point-to-point radio link introduced in problem 9. By how much must transmit power be increased to maintain the maximum BER of 10-5 if the channel is flat Rayleigh-fad
what is the method to do this project and what material used for?
Among copper and mercury which is better conductor of electricity?
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