ADVANTAGES OF STATIONARY ARMATURE OVER
ROTATING ARMATURE:
The various advantages of rotating field (i.e
field flux) are as follows:
1)A.c. is used everywhere, the generation
level of a.c. voltage may be higher as 11 KV to 33 KV or even more. This gets
induced in the armature. For stationary armature large space can be provided to
accommodate large number of conductors and the insulation's.
2) It is always better to protect high
voltage winding from the centrifugal forces caused due to the rotation. So high
voltage armature is generally kept stationary. This avoids the interaction of
mechanical and electrical stresses.
3) It is very easy to collect larger currents
at very high voltage if the armature winding is stationary so that any slip
rings and brushes can not come in to picture. The voltage required to be supplied
to the field is very low ( 230 V d.c.) and hence can be easily supplied with
the help of slip ring and brush assembly by keeping it rotating.
4) The problem of sparking at the slip rings
can be avoided by keeping field rotating which is low voltage circuit and high
voltage armature as stationary.
5) Due to low voltage level on the field side
(i.e., rotor side) the insulation required is less and hence field system has
very low inertia. Due to less winding heat liberated will be there and his can
be cooled quickly when compared to armature winding in rotor side.
6) If field is rotating, to excite it external d.c. supply two slip rings are
enough. Once each for positive and negative terminals. As against this, in
three phase rotating armature the minimum number of slip rings required are
three and can not be easily insulated due to high voltage levels.
7) The ventilation arrangement for high
voltage side can be improved if it is kept stationary.
Due to
all these reasons the most of the alternators in practice are using rotating
field type (stationary armature winding) of arrangement. For small voltage
rating alternators rotating armature arranged may be used.
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