Download Action of the Commutator

Action of the Commutator
Action of the Commutator
We have seen that the e.m.f. induced in the simple
coil rotating in a magnetic field is an alternating e.m.f.
Hence if the two ends of the coil are connected to
insulated slip rings mounted on the shaft, and the
external circuit is connected to brushes which press on
these slip rings, the electrical polarity of each ring will
alternate as the coil rotates, so that the current set up
will also be alternating. In order that the current may be
unidirectional, it is necessary for one brush always to be
positive and the other always negative. In other words,
the negative parts of the induced voltage wave must be
rectified. This is done by using one ring which is split
into two halves, the halves insulated from one another,
and each connected to one end of the coil. In this way
the positive end of the coil is always under the same
brush, because, as the polarity of one end is about to
reverse that end passes to the next brush. Similarly, the
negative end of the Coil is always under the other brush.
The voltage across the brushes therefore always acts in
the same direction, and the current produced in the
external circuit always flows in one direction. This current
will obviously pulsate with the variations in magnitude
of the rectified voltage curve, so that, although it will be
unidirectional, it can hardly be termed a continuous
current. It must be remembered that this rectification of
the current and voltage takes place in the external circuit
only. The current and voltage in the rotating coil remain
alternating
We have seen that the e.m.f. induced in the simple
coil rotating in a magnetic field is an alternating e.m.f.
Hence if the two ends of the coil are connected to
insulated slip rings mounted on the shaft, and the
external circuit is connected to brushes which press on
these slip rings, the electrical polarity of each ring will
alternate as the coil rotates, so that the current set up
will also be alternating. In order that the current may be
unidirectional, it is necessary for one brush always to be
positive and the other always negative. In other words,
the negative parts of the induced voltage wave must be
rectified. This is done by using one ring which is split
into two halves, the halves insulated from one another,
and each connected to one end of the coil. In this way
the positive end of the coil is always under the same
brush, because, as the polarity of one end is about to
reverse that end passes to the next brush. Similarly, the
negative end of the Coil is always under the other brush.
The voltage across the brushes therefore always acts in
the same direction, and the current produced in the
external circuit always flows in one direction. This current
will obviously pulsate with the variations in magnitude
of the rectified voltage curve, so that, although it will be
unidirectional, it can hardly be termed a continuous
current. It must be remembered that this rectification of
the current and voltage takes place in the external circuit
only. The current and voltage in the rotating coil remain
alternating
М.А. Беляева и др. «Сборник технических текстов на англ. языке»
М.А. Беляева и др. «Сборник технических текстов на англ. языке»