A 30kw , 500 volt shunt generator has its driving machine uncoupled after it has reached normal operating temperature. It is then run as motor drawing an armature current of 4A from a 500 volt supply. The machine has an armature and shunt field resistance of 0,4 ohms and 100 ohms respectively. Calculate:

Question

A 30kw , 500 volt shunt generator has its driving machine uncoupled after it has reached normal operating temperature. It is then run as motor drawing an armature current of 4A from a 500 volt supply. The machine has an armature and shunt field resistance of 0,4 ohms and 100 ohms respectively. Calculate:
a.The full load efficiency as a generator, and 
b. The efficiency of the machine when running as a motor supplying a load and drawing a current  of 65A from the constant voltage busbars.