Commutation In Dc Machine Pdf
Commutator consists of number of segments or bars insulated from each other and are combined together tightly to form a cylinder as shown in figure, and fitted on the insulated Shaft of the armature. It is now necessary for the current I reaching the brush from the right-hand side in the anticlockwise direction. Let the commutator is moving from left to right. Your email address will not be published.
At the fifth instant, when brush occupies the complete area of bar B, now the coil A is open circuited and therefore carries current from right to left as shown in below figure. The commutation is called ideal if the commutation process or the reversal of current is completed by the end of the short circuit time or the commutation period. For understanding the physical concept behind the process of communication, let us consider, five instants of commutator working with respect to brushes. When the brush span has two commutator segments, the winding element connected to those segments is short-circuited. This is known as under commutation or delayed commutation.
Thus, the cause of sparking at the commutator is the failure of the current in the short-circuited elements to reach the full value in the reverse direction by the end of the short circuit. The insulating mica sheet is usually M or V shaped so as to prevent the segments from flying out due to centrifugal forces.
Then the brush will move from right to left. When the armature starts to move right, then the brush comes to contact of bar a.
This phenomena of the reversal of current is termed as commutation process. Then the direction is reversed which is in the away from the commutator segments. The time of the short circuit is called the period of commutation. The reversal of current in the armature winding by means of commutator bar and brushes is known as commutation process.
This is known as commutator. What is the function of a commutator? The sparking of the commutator is much harmful, and it will damage both commutator surface and brushes.
Commutation in DC Machine or Commutation in DC Generator or Motor
In figure two segments E and F are shown. Area of contact between brush and bar decreases thus decreasing the current in bar A to ie. It is called commutation period.
Let us understand Commutation more clearly by considering a simple ring windings shown below in Figure A. Such a commutation is called Ideal Commutation or Straight-line Commutation. The change from a generated alternating current to the direct current applied involves the process of Commutation. The large voltage appearing between commutator segments to which the coil is connected causes sparking at the brushes of the machine. Its effect is cumulative which may lead to a short circuit of the machine with an arc round the commutator from brush to brush.
The position of the brushes is generally based on the winding. Electronic Instrumentation. It is called a mechanical, rectifier in generator and an inverter in motor. As the voltage build up in the armature conductors is A. In the figure D shown below, the bar b has just left the brush, second chance romance sophie monroe pdf and the short circuit of coil one has ended.
As the conductor passes through the influence of the north pole and enters the south pole, the current in them is reversed. The curve of current against time in such a case is shown in figure E by the curve A. It facilitates the collection of current from armature.
When the conductors of the armature are under the north pole, the current which is induced flows in one direction The current flows in the opposite direction when they are under south pole. The direction of current flow is from point A to B. Let us also consider that the width of the commutator bar is equal to the width of the brush and current flowing through the conductor is I C.
In this process the reversal of current or the process of commutation is done. Poor mechanical conditions like uneven surface of commutators, vibrations of brushes etc.
It keeps rotor or armature M. In actual practice, the current in the short-circuited coil after commutation period does not reach its full value.
Commutation In DC Machine Generator or Motor
Now consider the other figure B shown below. The current is still I from the left-hand side and I from the right-hand side. The armature of the considered D. As the contact area of the bar a with the brush increases and the contact area of the bar b decreases, the current flow through the bars increases and decreases simultaneously.
After this short-circuit time the armature coils rotates under S pole and rotates between a negative brush and its succeeding positive brush. Leave a Reply Cancel reply Your email address will not be published.
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