Question 161Electricity & Electronics - 1st Asst/Chief

The correct answer is A) A short-circuited DC motor field control rheostat. In a Ward-Leonard drive system, the speed of the DC winch motor is controlled by varying the strength of the motor's field winding. If the DC motor field control rheostat is short-circuited, it would prevent the field strength from being adjusted above the base speed, resulting in the observed speed behavior where the speed cannot be elevated above the base speed. The other options are incorrect because: B) An open-circuited DC generator field winding would prevent any speed control, not just the inability to exceed base speed. C) An open-circuited DC winch motor field winding would result in the motor not operating at all, not just a limited speed range. D) A failure of the DC static power supply would prevent the system from functioning altogether, not just limit the speed range.