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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.
Explain piezoelectricity. Piezoelectricity: It gives us a means of converting electrical energy to mechanical energy and vice versa. While an electric field is applied to
Q. For the circuits shown in Figure, sketch the frequency response (magnitude and phase) of ¯V out / ¯V in .
Hall Effect is associated with (A) Conductors. (B) Semiconductors. (C) Thermistors. (D)Solders. Ans: Hall Effect is associated with semiconductors.
The far-field pattern of an antenna can be modeled as the two dimensional Fourier Transform of the aperture. 1. Determine the 2D Fourier Transform for the function
define propagation characteristic in transformer
With respect to serial communication define the parity. Besides the synchronization given by the use of start and stop bits, an additional bit termed as a parity bit may opt
Q.9 What are the main differences between VGA and CGA graphics adapters? Ans: Colour Graphics Adapter (CGA), initially also known as Colour/Graphics Adapter or IBM Colo
Calculations of sending line voltage
Q. What are the benefits of ccs over in-channel signalling? The benefits of CCS over in-channel signalling are listed below: a. Information can be exchange between processor
For the 3 bus system shown below all values are given in pu on a 100MVA base (a) Use Matlab functions lfgauss and lfnewton to find power flow solution for the system, accurate
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