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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.
Bronze is an alloy of (A) Copper and Tin. (B) Copper and Steel. (C) Copper and Mercury. (D) Copper and Aluminium. Ans: Bronze is an alloy of Cop
Explain the phenomenon of breakdown in dielectric materials. Breakdown in dielectric materials: This electric strength at breakdown is explained as the minimum electric stress
Distribution Loss Reduction and Efficiency Improvement You are well aware of the fact in which all energy supplied to a distribution utility does not reach the end consumers.
Q. Show a block diagram of a 4-bit, parallel-input shift-right register and brie?y explain its operation.
a 4 bit synchronous counter uses flip flops with propagation delay times of 15ns each. what will be the maximum possible time requires for change of state?
Consider the circuit shown in Figure (a) in which the switch S has been in position 1 for a long time. Let the switch be changed instantaneously to position 2 at t = 0. Obtain v(t)
By a simple time multiplexing of natural samples over a single line, a large radar site transmits 85 analog signals, each with 200-Hz bandwidth. If the sampling is done at twice th
distingish between maximum and minimum modes of operations of 8086 with timing diagrames
Switching Characteristics During Turn off The techniques used for turning off a thyristor is known as commutation techniques. A thyristor can be can be turn off by reducin
Gaussian derivatives Generate Gaussian kernels for a given scale "sigma", and display the kernel. The size of the kernel should be floor(3*sigm)+1; (i) Write an m-file "
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