CYCLIC DURATION FACTOR
Cyclic duration Factor ( CDF ) is defined as follows.

Generally the values for the cyclic duration factor used 25%, 40%, 60% and 100%.

STARTING OF WOUND ROTORS
STARTING BY ADDING EXTERNAL RESISTANCE

The slipring motors are generally started by means of variable resistance in the rotor circuit to get required starting torque. The value of external starting resistance can be calculated as under

Rrt is generally small compared to Rext and may be neglected. However if required, can be calculated approximately by following formula.

The starting torque can be increased upto the value of maximum torque available for that particular design. Usually starting torque as high as 2.5 times the normal torque can be obtained. The typical examples of curve showing, the increase in starting torque with addition of different rotor resistance & corresponding change in current with respect to speed are given in the figure.