Work Transfer (Harder Examples)

Abstract

An electrical generator is used to measure the torque available from the output shaft of a prime mover. The stator of the generator is carried on trunnion bearings and is restricted from rotating under the interaction of rotor and stator magnetic fields by means of a torque arm (see figure 2.1). (The torque arm must be horizontal during use so that the torque is the product of the net restraining force and the torque arm radius.) For a particular trial a torque arm of 0.5 m carries a fixed load of 120 N. This downward force is greater than can be supported by the torque transmitted from rotor to stator and the force difference required to restrain the stator is provided by a spring balance registering 15 N. Calculate the shaft power for a rotational speed of 3000 rev/min.