In a series motor the flux depends upon the current in the series field, which is the same current that flows through the armature. At light loads the armature current is small; therefore, the flux and torque are small. An increase in the load increases both the armature current and the flux, producing a much greater increase in the torque. With no load connection to the motor, the value of Ia is very small. So, the speed of the motor will be extremely large. For this reason that series motors are never used unless they are directly connected to the load.
This is the principle
characteristics of a series motor.
What
are its uses?
Uses: It is used in trains and cranes.
Back e.m.f.:
If a conductor is
rotated inside a magnetic field a voltage will be induced in. This induced
voltage is opposite to the applied voltage and therefore, it called back e.m.f.
What causes the extraordinarily
fast voltage drop with increasing load on a differentially compound dc
generator?
The greater the load the greater the voltage drop in the
line because not only the terminal voltage of the generator drop as load
increases but there is also a voltage drop in the line .The combined effect of
the reduction in generator voltage plus the line drop makes the differential
compound generator makes unsatisfactory for the transmission of power.
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