Correct option is D
· A field test is performed on a DC series motor:
· A field test is a method for calculating the efficiency of a DC series motor or generator at any load.
· The test involves coupling two similar DC series motors together. One motor runs as a motor and drives the generator, while the generator's output is wasted in a variable load. The series field winding of the generator is joined in the motor armature circuit to make the iron and friction losses of both machines equal. The motors are then run at equal speed.
· DC series motors are used for traction work, such as electric locomotives and electric trams, as well as for other applications that require high torque at low speeds, such as hoists and cranes.
