DC Generators Objectives Part 05
81 . The polarity of a dc generator can be reversed by reversing the field current.
82 . In a dc generator sparking between brushes and commutator surface may be due to a over commutation, under commutation or too rapid reversal of current.
83 . In a dc generator rapid brush wear may be due to rough commutator surface, severe sparking or imperfect contact with commutator.
84 . A dc shunt generator has full-load voltage regulation of 5% at rated speed of 400 rpm. The generator is new driven at 500 rpm. Its voltage regulation now will be more than 5 percent.
85 . 1 ohm is closest to the armature circuit resistance of a dc generator.
86 . The voltage at the terminals of a dc series generator running at a rated rpm and no load will be a very small voltage.
87 . A cumulatively compounded dc generator is supplying 20A at 200 V. now if the series field winding is short circuited, the terminal voltage will shoot upto a very high value.
88 . DC machines are generally designed for maximum efficiency around full load.
89 . A dc machines is fitted with both interpole winding and a compensating winding. These two windings with respect to the armature circuit will be in series.
90 . Over and under compounded of dc generator is obtained by shunting more or less current from the series field.
91 . The magnetic field which initially induces armature current in a self-excited generator is caused by residual magnetism.
92 . Equalizer connections are required when paralleling two compound generators.
93 . In order to ascertain whether a generator is lap or wave wound, on the basis of visual observation of the armature, one should observe the direction of the end connections.
94 . When the shunt field of a compound generator is connected across both the series field and the armature. Such a connection is known as a long shunt.
95 . A self-excited shunt generator fails to excite because the residual magnetism has destroyed. In order to revive the machine, one should excite the field for a few minutes with a battery.
96 . Two generator having series excitation are connected in parallel. If equalizer bar is not used one of the generators may start reversed.
97 . If two compound interpole dc generators are worked in parallel the equalizing bar must be connected to function of series and interpole fields.
98 . A dc over-compound generator is supplying power to an infinite bus. If the prime mover is accidentally cut off, the dc machine will stop running.
99 . The type of dc generator used for arc welding purposes is a differentially compound generator.