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Feb 24, 2012 · 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. If the current reversal isn’t completed during the short circuit time, sparking occurs at the brush contacts, causing overheating and damage to the commutator surface.
This is known as under commutation or delayed commutation. The curve of current against time in such a case is shown in figure E by the curve A. In ideal commutation curve B, the current of the commutating coils changes linearly from +I to –I during the commutation period. In actual practice, the current in the short-circuited coil after the ...
Commutation in DC Generator. The voltage induced in a single coil of a DC generator is alternating. A commutator is therefore necessary to ensure that the current in the external circuit always flows in the one direction. During the brief interval when a coil is short-circuited by a brush, the current in the coil must reverse its direction.
Dec 17, 2020 · The short-circuited period of the coil with the brush is very short order of 0.0005 to 0.002 sec, it is termed as 'Commutation Period'. For the study of commutation, let us consider that the machine has a ring winding, a part of which is shown concentrate on coil B. In the figure below the coil, B is about to short-circuit because the brush is ...
- Resistance Commutation
- E.M.F. Commutation
- Interpoles Or Compoles
The reversal of current in a coil (i.e., commutation) takes place while the coil is short-circuited by the brush. Therefore, there are two parallel paths for the current as long as the short circuit exists. If the contact resistance between the brush and the commutator is made large, then current would divide in the inverse ratio of contact resista...
In this method, an arrangement is made to neutralise the reactance voltage by producing a reversing voltage in the coil undergoing commutation. The reversing voltage acts in opposition to the reactance voltage and neutralizes it to some extent. If the reversing voltage is equal to the reactance voltage, the effect of the latter is completely wiped ...
The best way to produce reversing voltage to neutralize the reactance voltage is by using interpoles or compoles. These are small poles fixed to the yoke and spaced mid-way between the main poles (See Fig. 2.13). They are wound with comparatively few turns and connected in series with the armature so that they carry armature current. Their polarity...
During the period of Commutation in DC Machine as the coil passes from right to the left of the brush, the coil current must reverse. During this period the brush short-circuits the coil via segments x and y as shown in Fig. 7.14(b).
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May 23, 2015 · The brief period during which coil remains short-circuited is known as commutation period Tc. If the current reversal i.e. the change from + I to zero and then to – I is completed by the end of short circuit or commutation period, then the commutation is ideal. If cur- rent reversal is not complete by that time, then sparking is produced ...
